Unit 6 Tutorials: Genetics and
Biotechnology
INSIDE UNIT 6
Genetics and DNA
Structure of DNA and Chromosomes
Mitosis
Meiosis and Genetic Variability
DNA Replication
Protein Synthesis, Part 1: Transcription
Protein Synthesis, Part 2: Translation
DNA Sequencing
DNA Technology and Research
Genetics and Inheritance
Heredity
Punnett Squares
Codominance
Polygenic Traits and Pleiotropy
Pedigrees
Chromosome Structure Changes
Chromosome Count Changes
Autosomal Recessive Traits and Disorders
Autosomal Dominant Traits and Disorders
X-Linked Traits
Structure of DNA and Chromosomes
by Sophia Tutorial

WHAT'S COVERED
This lesson will discuss the structure of chromosomes by looking at:
1. Chromosome Structure & Function
2. Chromosome Number & Location
3. DNA Structure
a. Nitrogenous Bases
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b. Base Pairs
c. Nucleotide Sequence
1. Chromosomes
When a cell is getting ready to divide, genetic information in the form of DNA will condense into structures
called chromosomes. This is how genetic information is passed from parent to offspring.
Homologous chromosomes are chromosomes that contain the same set of genes and are the same length
and shape. One is from the mother of the offspring, and other is from the father.
There are two types of chromosomes within our body:
Sex chromosomes: Chromosomes associated with sex and gender
Autosomes: All the chromosomes in our body except for the sex chromosomes

TERMS TO KNOW
Chromosome
A condensed DNA structure.
Homologous Chromosomes
Chromosomes paired together that are the same length and shape and contain the same sets of genes;
typically, one of the homologous pair is contributed by each parent.
Sex Chromosomes
Chromosomes associated with sex and gender.
Autosomes
All of the chromosomes in the body except for sex chromosomes.
2. Chromosome Number and Location
The chromosome number is the number of chromosomes in a species' cells. Each species has its own
number of chromosomes.
 EXAMPLE For humans, the chromosome number is 46. This means that we have 46 chromosomes, or
23 pairs of homologous chromosomes, in our cells. Of those 46 chromosomes, most of them are
autosomes. Only two of those chromosomes are sex chromosomes. A mouse has a total of 40
chromosomes.
Chromosomes are only visible in this form when the cell is preparing to divide. The rest of the time, our
genetic information can be found in the form of chromatin, which has a balled-up thread-like form and is found
within the cell's nucleus.
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This makes sense; when the cell isn't dividing, the DNA is more stretched out so its information is physically
accessible. When the cell is dividing, The DNA has to move all the way across the cell. It's not being accessed
for much information, so it's better to be wound up tight with a bunch of protective proteins. It's like packing a
suitcase: It's easier to take everything you need if all the clothes are rolled up tightly (just as the DNA is
condensed into visible chromosomes) than if you just throw clothes in a pile in your suitcase (like when the
DNA is stretched out).
3. DNA Structure
DNA is said to be in the structure of a double helix, or a "twisting ladder". The outside parts of the ladder (the
"side rails") are made up of a phosphate-sugar backbone--that is, phosphate and deoxyribose sugar
molecules. In DNA, the sugar within its nucleotides is called deoxyribose; in RNA, the sugar within its
nucleotides is called ribose.
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3a. Nitrogenous Bases
The "rungs" of the ladder are made up of four nitrogenous bases:
Adenine
Thymine
Cytosine
Guanine
These nitrogenous bases compose two base pairs. Adenine always pairs with thymine, and cytosine always
pairs with guanine.

TERMS TO KNOW
Double Helix
The shape of the DNA molecule; often is referred to as the “twisted ladder” and is the title to the book about
Watson & Crick's discovery of DNA's structure.
Adenine (A)
A nucleotide building block of DNA and RNA, adenine is classified as a purine and complements thymine (T) in
DNA and uracil (U) in RNA.
Thymine (T)
A nucleotide building block of DNA, thymine is classified as pyrimidine and complements adenine (A) in DNA;
thymine is not found in RNA.
Guanine (G)
A nucleotide building block of DNA and RNA, guanine is classified as a purine and complements cytosine (C)
in DNA and RNA.
Cytosine (C)
A nucleotide building block of DNA and RNA, it is classified as pyrimidine and complements guanine (G) in
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DNA and RNA.
3b. Base Pairs
The phosphate, the sugar, and the nitrogenous base together make anucleotide, and each "rung" of the
double helix (and the rung's small portion of "side rail") is made of two nucleotides facing each other. In DNA,
the two nucleotides that make up a particular rung of the twisted ladder are called a base pair. Adenine
always pairs with thymine, and cytosine always pairs with guanine.

TERMS TO KNOW
Nucleotide
Organic molecules that consist of a five-carbon sugar (ribose in the case of RNA and deoxyribose in the case
of DNA), a phosphate group and a nitrogenous base; nucleotides are the building blocks of nucleic acids
(DNA & RNA).
Base Pair
The way that nucleotides interact with one another, A bonds with T and C bonds with G in DNA, while C
bonds with G and A bonds with U (uracil) in RNA; the sequence of base pairs creates the genetic code that is
transcribed and translated into proteins.
3c. Nucleotide Sequence
If you follow one of the "rails" of the DNA's "twisting ladder", you will see the nucleotides' order (A, T, C, etc.).
This is called a nucleotide sequence. The order of letters (nucleotides) in the nucleotide sequence is very
important because the sequence contains instructions or "recipes" for all our thousands of proteins. These
"recipes" for our proteins are called genes. Any change in the nucleotide sequence is amutation, and can
have a negative impact on a protein's structure or production.
For example, one of the genes for making hemoglobin is 1,605 nucleotides long. Within that stretch of DNA,
there is a sequence of three nucleotides that reads "GAG", but in some people, the nucleotide sequence at
that location reads "GTG". It's like a typo; instead of saying "Shall I compare thee to a summer's day" the gene
says "Shawl I compare thee to a summer's day".
Hemoglobin produced from this mutated gene is more likely to clump. If only one the two copies of
chromosome 11 (one of its two homologous pairs) has this mutation, it means only half of the hemoglobin the
person produces is clumpy, and the person is less vulnerable to malaria. But if both of the homologous
chromosomes have the mutated genes, all of the hemoglobin produced is clumpy, and the person will suffer
from sickle cell anemia.

TERMS TO KNOW
Nucleotide Sequence
The arrangement of nucleotides (the order of A's, C's, G's and T's) that form genes in strands of DNA.
Gene
A segment of DNA that codes for a specific protein, genes are a sequence of nucleotides.
Mutation
A change in the nucleotide sequence.

SUMMARY
Chromosomes are the form DNA takes when a cell is getting ready to divide, and are only visible
during this time. Homologous chromosomes are chromosomes that contain the same set of genes.
There are two types of chromosomes within our body: Autosomes and sex chromosomes. The
chromosome number is the number of chromosomes a species has in its cells.DNA, the genetic
information that makes up chromosomes, come in the form of a double helix. It is made up of
phosphate and deoxyribose sugar molecules as the backbone of the structure with adenine/thymine
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or cytosine/guanine base pairs in between. Keep up the learning and have a great day!
Source: SOURCE: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND

ATTRIBUTIONS
Chromosomes | Author: Wikipeda | License: Creative Commons
Cell Nucleus and Chromosomes | Author: Wikipeda | License: Creative Commons
Double Helix | Author: Wikipeda | License: Creative Commons

TERMS TO KNOW
Adenine (A)
A nucleotide building block of DNA and RNA, adenine is classified as a purine and complements
thymine (T) in DNA and uracil (U) in RNA.
Autosomes
All of the chromosomes in the body except for sex chromosomes.
Base Pair
The way that nucleotides interact with one another. In DNA, A bonds with T, and C bonds with G. In
RNA, C bonds with G, and A bonds with U (uracil). The sequence of base pairs creates the genetic
code that is transcribed and translated into proteins.
Chromosome
A condensed DNA structure.
Cytosine (C)
A nucleotide building block of DNA and RNA, cytosine is classified as pyrimidine and complements
guanine (G) in DNA and RNA.
Double Helix
The shape of the DNA molecule; often is referred to as the “twisted ladder” ("Double Helix" is the title
to the book about Watson & Crick's discovery of DNA's structure).
Gene
A segment of DNA that codes for a specific protein, genes are a sequence of nucleotides.
Guanine (G)
A nucleotide building block of DNA and RNA, guanine is classified as a purine and complements
cytosine (C) in DNA and RNA.
Homologous Chromosomes
Chromosomes that are paired together that are the same length and shape and contain the same
sets of genes. Typically, one of the homologous pair is contributed by each parent.
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Mutation
A change in the nucleotide sequence.
Nucleotide
Organic molecules that consist of a 5 carbon sugar (ribose in the case of RNA, and deoxyribose in the
case of DNA), a phosphate group and a nitrogenous base; nucleotides are the building blocks of
nucleic acids (DNA & RNA).
Nucleotide Sequence
The arrangement of nucleotides that form genes in strands of DNA.
Sex Chromosomes
Chromosomes associated with sex and gender.
Thymine (T)
A nucleotide building block of DNA, thymine is classified as pyrimidine and complements adenine (A)
in DNA; thymine is not found in RNA.
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Mitosis
by Sophia Tutorial

WHAT'S COVERED
This lesson will cover the role of Mitosis in the cell cycle by looking at:
1. The Cell Cycle
2. Interphase
3. Mitosis Phases
4. Cytokinesis
1.The Cell Cycle
Mitosis is a part of the cell cycle . The cell cycle describes events that happen from the time a cell is formed
until it divides. Mitosis is a type of cell division that happens in somatic cells (all the cells in your body except
for gametes). This process produces new cells. Cells are constantly going through the cell cycle and
producing new cells. As cells grow old and die, they need to be replaced by new ones.

TERM TO KNOW
Cell Cycle
Describes the events that occur from the time a cell is formed until it divides.
2. Interphase
Interphase is the first part of the cell cycle, but it's not considered to be a part of mitosis. Interphase is the part
of the cycle where the cell is getting ready to divide but is not dividing yet. It is the longest phase of the cell
cycle and is where the cell spends most of its life.
There are three sub-phases to interphase:
G1 Phase: Part of interphase is when the cell will start to increase in size and grow in preparation for cell
division.
S Phase: During this part, DNA is copied (DNA synthesis), and chromosomes are duplicated
G2 Phase: Cell grows, making its final preparations in order to get ready to divide
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Typically in interphase, chromosomes are not visible. Genetic information, or DNA, is found in the form of
chromatin, which is like a thread-like ball of yarn that's found within the nucleus. As a cell is preparing to
divide, that DNA will then condense into chromosomes which will be copied in preparation for division.
Chromosomes are made of sister chromatids attached in the middle at a point called thecentromere.

TERMS TO KNOW
Interphase
A phase of the cell cycle in which a cell carries out its normal functions; includes all parts of a cell’s life except
for when the cell is dividing.
G1 Phase
The portion of interphase in which a cell grows in size.
S Phase
The portion of interphase in which a cell’s DNA is copied.
G2 Phase
The portion of interphase in which a cell makes final preparations for cell division.
Sister Chromatid
A duplicate of an original chromosome produced during mitosis.
Centromere
The point at which sister chromatids are attached to one another.
3. Mitosis Phases
Mitosis actually includes four phases:
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Prophase. During this phase, the nuclear envelope that normally surrounds the genetic information will
start to break down. Poles will form on opposite ends of cells; they become the attachment points to each
sister chromatid's centromere so that each new cell gets exactly one of the two sister chromatids for
each chromosome.
Metaphase. Chromosomes will line up on the metaphase plate, which is an invisible line in the middle of
the cell. Spindle fibers are attached to the centromeres of the chromosomes to prepare these
chromosomes to be pulled apart to separate ends of the cell.
Anaphase. Sister chromatids are separated and moved to opposite ends of the cell.
Telophase. The nuclear envelope will begin to reform around the chromosomes, and the plasma
membrane will start to pinch off. This area where it's pinching off is called the cleavage furrow.

TERM TO KNOW
Prophase
The first phase of mitosis in which chromosomes are condensed, the nuclear membrane breaks down, and
poles at opposite ends of the cell begin to form.
Metaphase
The second phase of mitosis in which chromosomes line up on the metaphase plate and are attached at the
centromere to spindle fibers.
Anaphase
The third phase of mitosis in which sister chromatids are separated and pulled by spindle fibers toward
opposite poles of the cell.
Telophase
The final phase of mitosis in which the plasma membrane begins to pinch off and the nuclear membrane
begins to reform; chromosomes begin to return to their thread-like state.
Cleavage Furrow
The pinching off of the plasma membrane to produce two new cells.
3. Cytokinesis
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Cytokinesis follows mitosis. Cytokinesis is were two completely new individual cells exist. These two separate
cells are diploid daughter cells. They are called diploid because they each contain 46 chromosomes (23
chromosomes from each of the two parents), the same number as the original cell. These diploid cells are also
identical to the original cell. At this point, the nuclear envelope has completely reformed, and the DNA will
return to its thread-like form.

TERMS TO KNOW
Cytokinesis
The end result of mitosis in which two diploid daughter cells are produced which are identical to the parent
cell.
Daughter Cells
The name for cells produced by the process of mitosis.
Diploid
Cells that contain two copies of each chromosome (one copy from our mother, and one copy from other
father).

SUMMARY
Mitosis the part of the cell cycle where a cell divides to reproduce. Interphase is the part of the cycle
where a cell spends most of its life and is preparing for mitosis. There are three phases to interphase.
G1 is the phase where the cell is growing, S phase is where DNA is copied, and G2 is where the cell
makes final preparations for mitosis. During interphase, chromosomes are normally not visible, but as
the cell prepares to divide it will condense and become visible. Once duplicated sister chromatid are
held together by a centromere.
There are four phases of mitosis. Prophase is when the nuclear envelope breaks down, and poles are
formed at opposite ends of the cell. Metaphase is when the chromosomes start to line up in the
middle of the cell, and spindle fibers attach to the centromeres of the chromosomes. During
anaphase, sister chromatids are separated and move to the poles. Finally, in telophase, the nuclear
envelope will begin to reform around the chromosomes, and the plasma membrane will pinch off.
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Cytokinesis follows mitosis and is where two completely new daughter cells exist. Keep up the
learning and have a great day!
Source: SOURCE: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND

ATTRIBUTIONS
Sister Chromatids | Author: Wikipeda | License: Creative Commons
Mitosis | Author: Wikipeda | License: Creative Commons

TERMS TO KNOW
Anaphase
The third phase of mitosis in which sister chromatids are separated and pulled by spindle fibers
toward opposite poles of the cell.
Cell Cycle
Describes the events that occur from the time a cell is formed until it divides.
Centromere
The location at which sister chromatids are attached to one another.
Cleavage Furrow
The pinching off of the plasma membrane to produce two new cells.
Cytokinesis
The end result of mitosis in which two diploid daughter cells are produced which are identical to the
parent cell.
Daughter Cells
The name for cells produced by the process of mitosis.
Diploid
Cells that contain two copies of each chromosome.
G1 Phase
The portion of interphase in which a cell grows in size.
G2 Phase
The portion of interphase in which a cell makes final preparations for cell division.
Interphase
A phase of the cell cycle in which a cell carries out its normal functions; includes all parts of a cell’s life
except for when the cell is dividing.
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Metaphase
The second phase of mitosis in which chromosomes line up on the metaphase plate and are attached
at the centromere to spindle fibers.
Prophase
The first phase of mitosis in which chromosomes are condensed, the nuclear membrane breaks
down and poles at opposite ends of the cell begin to form.
S Phase
The portion of interphase in which a cell’s DNA is copied.
Sister Chromatid
A duplicate of an original chromosome produced during mitosis.
Telophase
The final phase of mitosis in which the plasma membrane begins to pinch off and the nuclear
membrane begins to reform. Chromosomes begin to return to their thread-like state.
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Meiosis and Genetic Variability
by Sophia Tutorial

WHAT'S COVERED
This lesson is going to cover the process of Meiosis by looking at:
1. Meiosis Overview
2. Meiosis I
a. Phases of Meiosis I
b. Difference Between Mitosis
3. Meiosis II
1. Meiosis Overview
Meiosis is a type of cell division that is specific to germ cells, or cells that give rise to gametes. In this type of
cell division, germ cells are going through a division to form gametes. Gametes are the sperm cells in men
and the oocytes in women. The result of meiosis is haploid daughter cells, and haploid cells contain half as
many chromosomes as the original germ cell.
 EXAMPLE In humans, meiosis starts out with a germ cell of 46 chromosomes and ends up with
haploid daughter cells that each have 23 chromosomes.
Each round of meiosis is similar to mitosis. There are two types of meiosis, depending on if it is creating a
sperm or an egg gamete:
Spermatogenesis is meiosis in sperm cells and leads to four sperm cells.
Oogenesis is the formation of egg cells and leads to one oocyte. While four cells are generated in
oogenesis (just as in spermatogenesis), only one becomes an oocyte; the others disintegrate.
Whether it's spermatogenesis in men or oogenesis in women, meiosis involves two rounds of cellular division:
Meiosis I and meiosis II.

TERMS TO KNOW
Meiosis
A type of cell division that occurs in germ cells to produce haploid gametes.
Germ Cell
A cell that gives rise to gametes.
Gamete
A cell which contains a haploid number of chromosomes (male gametes are sperm; female gametes are
oocytes).
Haploid
The number of chromosomes in the gametes of an organism which is equal to half of the number of
chromosomes of somatic (all non-gamete) cells.
Spermatogenesis
The process that forms four haploid sperm cells.
Oogenesis
The process that forms a haploid egg cell.
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2. Meiosis I
Meiosis I is the first round of meiosis. The process of meiosis is similar to mitosis. Before meiosis begins, the
germ cell has undergone interphase: There was growth (G1), synthesis (S) of DNA to make two copies of every
chromosome, and more growth (G2). As a result of DNA synthesis, the germ cell looks a lot like a somatic cell
that's about to divide: Its 23 pairs of homologous chromosomes (46 total) now each have two sister
chromatids (92 chromatids total).
2a. Phases of Meiosis I
Prophase I : The germ cell begins in prophase I. In this phase, similar to prophase of mitosis, homologous
chromosomes (each with two identical sister chromatids) will condense. Also during this stage, the
nuclear envelope will break down, and spindle microtubules will attach to the centromeres.
Metaphase I : Chromosomes will line up in pairs of homologs (each member of a pair of homologous
chromosomes is called a homolog). Remember that for each chromosome, one homolog was inherited
from your mother, and one homolog was inherited from your father. Both have the same set of genes
(e.g., both copies of your 11th chromosome have a gene for hemoglobin), but the homolog from your
mother will have a slightly different nucleotide sequence than the homolog from your father (e.g.,
somewhere in the hemoglobin gene from your father's homolog is a GTG instead of a GAG). Sometimes, a
gene that started on your mother's homolog will get swapped with the gene on your father's homology,
creating more genetic variation between your kids and your siblings' kids, for example. This process of
swapping genetic material between homologous chromosomes is called crossing over.
Anaphase I : This is where anaphase in meiosis looks very different from mitosis: It's in the process of
disjunction, which is how the chromosomes separate. In mitosis, the sister chromatids from each homolog
split and move toward opposite poles, so that each cell gets one chromatid from your maternal homolog
and one chromatid from your paternal homolog (just like the original cell had). In anaphase of meiosis I,
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both sister chromatids of one homolog go to one pole, and both sister chromatids from the other
homology go to the other pole. That means that Daughter Cell A might get Chromosome 1, 3, and 10-23
from your dad and Chromosome 2 and 5-9 from your mom. Daughter Cell B will, therefore, get the
opposite: Chromosome 1, 3 and 10-23 from your mom and Chromosome 2 and 5-9 from your dad. It's
completely random which parent's homolog will end up in which daughter cell. This means that the odds
of you producing the exact same gamete twice are 1 in 223, or roughly 1 in 8 billion! This creates genetic
diversity even among siblings.
Telophase I : The nuclear envelope then starts to reform, and we end up with one homolog of each
chromosome instead of two, but each homolog has two sister chromatids. The cells still need to go
through another round of cell division to ensure they end up with only 23 chromosomes in each cell.

TERMS TO KNOW
Meiosis I
The first round of cell division in meiosis.
Homolog
One of the members of a pair of homologous chromosomes; with homologous chromosomes, one homolog is
inherited from your father, and one homolog is inherited from your mother.
Crossing Over
A process in which homologous chromosomes will exchange genetic material with one another, resulting in
genetic variation.
Disjunction
The process of separating chromosomes; it occurs in meiosis I when homologous chromosomes are
separated, and in meiosis II when sister chromatids are separated.
2b. Difference Between Mitosis
You can illustrate the difference between mitosis and meiosis I on your fingers. Hold up your index finger on
each hand, and pretend that your index fingers are homologous chromosomes. Your right finger is the
homolog you inherited from your mom, and your left finger is the homolog you inherited from your dad. Now,
pretend your chromosomes are undergoing S-phase, so they both get synthesized. To represent this, both
hands should now be holding up your index and middle finger on each hand, close together. This represents
both homologs having two sister chromatids.
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In mitosis, one sister chromatid from each of your parents would go into each new daughter cell (just like the
original). You can represent this by facing your palms toward each other, having both hands form "peace"
signs. Thus, your index fingers are going in one direction (the right index finger is the homolog from mom, and
the left index finger is the homolog from dad), into Daughter Cell A. Similarly, your middle fingers split off in
the same direction (the right finger from mom, the left finger from dad), into Daughter Cell B.
Here's how meiosis I is different: Start at S-phase, with two "sister chromatids" on each hand. The pair of sister
chromatids from mom will head over to Daughter Cell A, while dad's pair of sister chromatids head over to
Daughter Cell B.
3. Meiosis II
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After telophase I is done, the cells begin meiosis II.
Prophase II: Spindle microtubules will attach to the sister chromatids, and the nuclear envelope will start
to break down.
Metaphase II: In metaphase II, the chromosomes well then again line up at the middle of the cell.
Anaphase II: Anaphase II looks like mitosis: Sister chromatids separate, and start moving towards
opposite poles.
Telophase II: Again, in Telophase II the nuclear envelope will reform. This time the end will result in four
haploid nuclei, all that have 23 chromosomes. The reason sex cells are haploid is that when the sperm
fertilizes the oocyte, the nuclei combine with to form a diploid cell.
 EXAMPLE In humans, both the sperm cell and the egg contain 23 chromosomes which combine to
give a total of 46. In you, half of these came from your mother and half from your father.

TERM TO KNOW
Meiosis II
The second round of cell division in meiosis.
Diploid
Cells that contains two sets of each chromosome.

SUMMARY
Meiosis is the process of cell division that creates gametes. There are two phases of Meiosis. In
Meiosis I the cell goes through prophase I, like in mitosis, homologous chromosomes will condense
and pair up. Unlike mitosis, they will also swap segments of themselves to create genetic variability.
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The cell will move through metaphase I and anaphase I, ending in telophase I with two haploid cells.
Meiosis II is similar, but result in four haploid cells. Keep up the learning and have a great day!
Source: SOURCE: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND

ATTRIBUTIONS
Meiosis | Author: Wikipeda | License: Creative Commons

TERMS TO KNOW
Crossing Over
A process in which homologous chromosomes will exchange genetic material with one another,
resulting in genetic variation.
Diploid
Cells that contains two sets of each chromosome.
Disjunction
The process of separating chromosomes. It occurs in meiosis I, when homologous chromosomes are
separated, and in meiosis II, when sister chromatids are separated.
Gamete
A cell which contains a haploid number of chromosomes (male gametes are sperm; female gametes
are oocytes).
Germ Cell
A cell that gives rise to gametes.
Haploid
The number of chromosomes in the gametes of an organism which is equal to half of the number of
chromosomes of somatic (all non-gamete) cells.
Homolog
One of the members of a pair of homologous chromosomes. With homologous chromosomes, one
homolog is inherited from your father, and one homolog is inherited from your mother.
Meiosis
A type of cell division that occurs in sex cells to produce haploid gametes.
Meiosis I
The first round of cell division in meiosis.
Meiosis II
The second round of cell division in meiosis.
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Oogenesis
The process that forms a haploid egg cell.
Spermatogenesis
The process that forms 4 haploid sperm cells.
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DNA Replication
by Sophia Tutorial

WHAT'S COVERED
This lesson will cover the role of DNA polymerase in:
1. DNA Replication
2. DNA Repair
1. DNA Replication
Recall that before a cell divides (via mitosis or meiosis I), the cell undergoes interphase, in which it prepares
for division. Part of the preparation of interphase is Synthesis (S phase), where the DNA copies itself. This
makes it possible for both daughter cells to receive all the necessary genetic information. This process of
copying DNA is called DNA replication.
DNA molecules are copied so that traits can be passed from parents to offspring.DNA polymerase is an
enzyme that assists in DNA replication. This enzyme unwinds a DNA molecule and then separates the DNA so
that new DNA molecules can be produced using the old DNA molecules as a template.
Recall that DNA is in the shape of a "twisting ladder", where each "side rail" is a strand of DNA (hence, DNA is
double-stranded), and each "rung" of the ladder is made up of one nucleotide from each strand (either an A
matched to a T, or a C matched to a G).
During DNA replication, DNA polymerase will unwind and separate those DNA strands. Then the old strands
of DNA are used as a template in order to build new strands of DNA.
The new bases pair up using the rules of base pairing (A to T, C to G) to create a molecule that is half old and
half new. These two strands will be identical to the original strand and each other. This is called
semiconservative replication, and this is how DNA is replicated so that the traits can be passed from parents
to offspring.

TERMS TO KNOW
DNA Replication
The process of copying (replicating) DNA.
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DNA Polymerases
An enzyme that assists in the process of DNA replication.
Semiconservative Replication
When a stretch of double-stranded DNA is replicated into two copies, each copy contains one strand from the
original copy and one strand that is new; the new strands used the original strands as templates.
2. DNA Repair
DNA polymerase, in addition to playing a role in DNA replication, also helps with DNA repair. Sometimes
during the process of DNA replication, DNA can change in a way that will change a gene, so a gene mutation
can occur.
A mutation is a change to a nucleotide sequence. There are various types of mutations, but one type is a
base-pair substitution. A base-pair substitution is when the wrong nucleotide pairs with a base during
replication. These mutations can occur and affect how a gene is produced or functions.
 EXAMPLE If thymine paired with guanine instead of adenine.
All DNA polymerases have some ability to proofread; if they create a base-pair substitution, they can back up
(removing a couple of nucleotides), and try again.
How do DNA repair enzymes know which strand is the "old", correct strand and which strand is the "new",
erroneous one? Before DNA replication, both strands of the DNA are methylated--marked as the original
strands. Thus, when they are copied, the strand that isn't methylated is recognized by DNA repair enzymes as
the new strand. It is the new strand that is more likely to have the mistake, and that is the strand that is edited
if there's a base-pair substitution, for example.}}
Beyond base-pair substitution, there are many kinds of DNA damage, and specific enzymes to deal with each
kind of damage. This is important for cancer therapies, for example. The mutations that make cancer cells
able to ignore signals to stop dividing uncontrollably also make cancer cells struggle to repair DNA damage.
Radiation therapy deliberately introduces double-strand breaks (breaks that cut all the way through both
strands of the "twisting ladder") to the site of the tumor. Healthy cells will be able to repair these breaks within
24 hours, but cancerous cells won't be to fix the breaks so quickly. Often radiation therapy involves treatments
over several days, so healthy cells have time to repair, but cancer cells don't. Eventually, the cancer cells have
so much DNA damage they cannot function, and they die.

TERMS TO KNOW
Gene Mutation
A change in the sequence of nucleotides in a gene.
Base-Pair substitution
A type of gene mutation in which the wrong nucleotide is paired with a base during the process of DNA
replication; the effects can range from none at all to life-threatening.

SUMMARY
DNA polymerase plays an important role in DNA Replication. It is the signal for DNA to unwind and
separate. This allows new bases to come in a pair with the unwound strands. This is semiconservative
replication because the new copies each contain one original strand and one new strand. Two copies
of the DNA are created that are identical to the original. DNA polymerase also plays a role in DNA
repair when mutations like base pair substitutions occur.
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Page 22
Source: This work is adapted from Sophia Author Amanda Soderlind

ATTRIBUTIONS
DNA Replication | Author: Wikipeda | License: Creative Commons

TERMS TO KNOW
Base-Pair substitution
A type of mutation in which the wrong nucleotide is paired with a base during the process of DNA
replication. The effects can range from none at all to life threatening.
DNA Polymerases
An enzyme that assists in the process of DNA replication.
DNA Replication
The process of copying (replicating) DNA.
Gene Mutation
A change in the sequence of nucleotides in a gene.
Semiconservative Replication
When a stretch of double-stranded DNA is replicated into two copies, each copy contains one strand
from the original copy, and one strand that is new. The new strands used the original strands as
templates.
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Protein Synthesis, Part 1: Transcription
by Sophia Tutorial

WHAT'S COVERED
This lesson will cover the process of transcription and its role in protein synthesis by looking at:
1. Transcription
2. RNA polymerase
3. Introns and Exons
1. Transcription
The path from genes to proteins involves two steps:
Transcription
Translation
Transcription is the first step in protein synthesis. In transcription, a single strand of RNA is assembled using
the DNA as a template. You can think of your DNA as the reference section of a library: It has all the "recipes"
for making every component your cell needs, so it's really important. It needs to be protected, so it never
leaves the nucleus (just as reference books can't be checked out of the library).

TERMS TO KNOW
Transcription
The process of converting DNA into RNA.
Protein Synthesis
The formation of proteins by using information stored in DNA to form proteins.
2. RNA polymerase
If DNA can't leave the nucleus, how is the information accessed by the ribosomes so that the information can
be used to make the necessary cellular components?
If you want to take information from a reference from the library, you make a copy. Similarly, if your cell needs
to make a protein, it makes a copy of that protein's "recipe" via RNA polymerase, which is a lot like DNA
polymerase.
You can think of DNA and mRNA, also known as messenger RNA, as being in the same chemical "language".
They are both nucleic acids, and the "copy" mRNA makes of a gene's nucleotide sequence is complementary
to the DNA the way the DNA's other strand is complementary. So you make a copy (an RNA message) of a
gene (a DNA "recipe") within the nucleus, then the mRNA moves from the nucleus to the endoplasmic
reticulum.
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Using mRNA as the go-between for DNA and ribosomes has a lot of advantages. For example, if you only
need to make one "recipe" (one protein), it would be silly to lug the entire "recipe book" (your genetic code--all
of your DNA's gene "recipes") out of the "library" (the nucleus). You don't need to make every single recipe in
the recipe book all the time; mRNA allows you to copy only those proteins you need at any given moment.
Because mRNA is single-stranded (only one strand of the DNA codes for a particular gene, so you only need
to copy one strand) and mRNA made of ribose sugar instead of deoxyribose (as DNA is), mRNA much more
unstable. This means that it will degrade quickly, so once you have enough protein, the mRNA message won't
linger and force you to keep making a protein you don't need anymore.

TERMS TO KNOW
RNA Polymerases
An enzyme used to form a single strand of RNA from a DNA strand.
mRNA
Messenger RNA that is used to make a copy of a gene that can leave the protection of the nucleus and give
instructions for converting that nucleic information into functional protein.
Genetic Code
Information stored in the nucleotide sequence of DNA that forms our genes.
3. Introns and Exons
At this point, you may be wondering, "If there's DNA that contains my genetic code, what else does it
contain?" Quite a lot, actually. Indeed, about 98% of your DNA doesn't code for protein directly; rather, it
performs subtler functions. For example, within a gene, you will have stretches of sequence that get
translated into protein, called exons. Between them, you will have introns; instead of getting translated into
protein, introns are nucleotide sequences that recruit regulator proteins. Regulatory proteins modulate the
timing and amount of a gene's expression into protein. They can even alter the protein into different versions
that perform similar but subtly different functions.
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
TERMS TO KNOW
Exons
Sections of RNA that code for proteins.
Regulatory Proteins
Proteins that can stop or speed up transcription.

SUMMARY
Transcription is the first step in the process of using genes to build proteins. DNA is used as a
template for RNA to be built, which is involved with RNA polymerases. The RNA that plays a role in
transcription is mRNA. Depending on the nucleotides that line up in this mRNA, it forms which then
code for specific amino acids. Also, within a gene, you will have stretches of sequence that get
translated into protein, called exon and introns. Keep up the learning and have a great day!
Source: This work is adapted from Sophia Author Amanda Soderlind

ATTRIBUTIONS
Transcription | Author: Wikipeda | License: Creative Commons
Introns and Exons | Author: Wikipeda | License: Creative Commons

TERMS TO KNOW
Exons
Sections of RNA that code for proteins.
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Genetic Code
Information stored in the nucleotide sequence of DNA that forms our genes.
Protein Synthesis
The formation of proteins by using information stored in DNA.
RNA Polymerases
Enzymes used to form a single strand of RNA from a DNA strand.
Regulatory Proteins
Molecules that can modulate the production of certain target proteins.
Transcription
The process of converting DNA into RNA.
mRNA
Messenger RNA that is used to make a copy of a gene that can leave the protection of the nucleus
and give instructions for converting that nucleic information into functional protein.
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Protein Synthesis, Part 2: Translation
by Sophia Tutorial

WHAT'S COVERED
This lesson goes into greater depth on the translation portion of protein synthesis. Specifically, you'll
learn about:
1. Translation Overview
2. Codons
3. Stages of Translation
a. Initiation
b. Elongation & Termination
1. Translation Overview
Translation is the second step in protein synthesis, following transcription. Once mRNA leaves the nucleus, it
enters the rough endoplasmic reticulum (rough ER) in the cell's cytoplasm. It's rough in appearance because it
has a lot of ribosomes. As soon as mRNA leaves the nucleus for the ER, it's going to encounter a ribosome
that can convert its nucleic acid message into functional protein.
Remember that mRNA is a nucleic acid, and protein is a sequence of amino acids. This means that converting
the information coded in a gene into a protein means translating that information into a different chemical
"language". That translator is rRNA--the RNA enzyme (called a "ribozyme") within ribosomes that reads the
information contained within the mRNA's nucleotides to the amino acids of a protein.
To do this, rRNA uses "decoders" called tRNA . These are short pieces of RNA that have a unique codon (a
sequence of three RNA nucleotides) on one end, and the corresponding amino acid on the other end. Recall
that there are four different nucleotides in RNA: A, C, G and T. This means that there are 4x4x4=64 unique
three-nucleotide codon combinations. This more than covers the 20 different amino acids we use to make our
proteins. Each tRNA ("transfer RNA") has a unique three-nucleotide codon, and a corresponding amino acid
attached to it.
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Page 28

TERMS TO KNOW
Translation
The process of “reading” a strand of mRNA and translating its message into a protein; this occurs in
ribosomes and consists of mRNA and tRNA interacting with one another.
rRNA
Ribosomal RNA is used to produce the structure of ribosomes.
tRNA
Transfer RNA that is used to bind ribosomes to the start codon of a nucleotide chain in order for translation to
occur.
Codons
Sections of three nucleotides that code for an amino acid.
2. Codons
If only 20 codons are needed to cover all the amino acids, and there are 64 possible codons, what do we do
with the excess? One of the amino acid-coding codons (methionine) is the start codon. The start codon marks
the first amino acid of a polypeptide chain.
 EXAMPLE AUG is the start code. This is adenine, uracil, guanine together in this chunk of three
nucleotides. It signals the start of a polypeptide chain.
Three of the excess codons are stop codons. A stop codon marks the end of a polypeptide chain. Stop
codons are UAA, UAG and UGA. It marks the end of a polypeptide chain, and when that polypeptide chain
would be finished being made.
The other 41 excess codons are duplicates. This is part of the reason why most gene mutations don't have
any effect: Most mutations in any given codon result in another codon for the same amino acid.

TERMS TO KNOW
Start Codon
A codon used to signal the start of an amino acid sequence on a strand of mRNA.
Stop Codon
A codon used to signal the stop of an amino acid sequence on a strand of mRNA.
3. Stages of Translation
In translation, instructions from a single-stranded mRNA, which was formed from transcription, are translated
into proteins. This occurs in the rough endoplasmic reticulum of the cell's cytoplasm. There are three stages to
translation:
Initiation
Elongation
Termination
3a. Initiation
The first step is initiation. During initiation, the small and large ribosomal subunits will join together, and then
initiator tRNA will arrive at the start codon (UAG) on mRNA. The start codon marks the beginning of a new
polypeptide chain, and codons are groups of three nucleotides that code for amino acids. After this first amino
acid (start codon = the amino acid methionine), more amino acids can be added.
The tRNA carries an anticodon, and these will match up with the strand of mRNA using the base pair rules.
The tRNA also carries an amino acid.
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The same thing will happen with this next codon or group of three nucleotides. The next codon and anticodon
will match, which signal for a certain amino acid. These amino acids will start building up in this chain called a
polypeptide chain.

TERM TO KNOW
Initiation
The beginning of translation, initiation occurs by the assembly of the ribosomal subunits and when tRNA
interacts with the start codon on mRNA.
Polypeptide Chain
The primary structure of a protein, a polypeptide chain is a linear chain of amino acids that are covalently
bound by peptide bonds.
3b. Elongation
The newly formed polypeptide chains compose proteins. These amino acids are held together by a peptide
bond. This stage is where those amino acids are being built into a growing polypeptide chain through a
process called elongation.

TERM TO KNOW
Elongation
When the appropriate anticodon of tRNA interacts with its codon counterpart on mRNA during translation.
Elongation is the second step of translation and will continue until the stop codon is reached.
3c. Termination
Being the last stage of translation, termination is when the stop codon of mRNA signals the end of translation.
With that, the polypeptide chain is complete.

TERM TO KNOW
Termination
When the stop codon is reached during translation, translation ends, and the polypeptide chain is released.

SUMMARY
Initiation is the first stage in translation. Here the ribosomal units come together, and then tRNA will
arrive at the start codon of mRNA. The anticodons on the tRNA will match up with the codons on the
mRNA. They will signal for certain amino acids, which then begin to build up and form a polypeptide
chain. Elongation occurs as the chain gets longer, and termination occurs when stop codon of the
mRNA signals the end of translation.
Source: This work is adapted from Sophia Author Amanda Soderlind

ATTRIBUTIONS
Types of RNA | Author: Wikipeda | License: Creative Commons

TERMS TO KNOW
Codons
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Page 30
Sections of 3 nucleotides that code for an amino acid.
Elongation
When the appropriate anticodon of tRNA interacts with its codon counterpart on mRNA during
translation. Elongation is the second step of translation and will continue until the stop codon is
reached.
Initiation
The beginning of translation, initiation occurs by the assembly of the ribosomal subunits and when
tRNA interacts with the start codon on mRNA.
Polypeptide Chain
The primary structure of a protein, a polypeptide chain is a linear chain of amino acids that are
covalently bound by peptide bonds.
Start Codon
A codon used to signal the start of an amino acid sequence on a strand of mRNA.
Stop Codon
A codon used to signal the stop of an amino acid sequence on a strand of mRNA.
Termination
When the stop codon is reached during translation, translation ends and the polypeptide chain is
released.
Translation
The process of “reading” a strand of mRNA and translating its message into a protein. This occurs in
ribosomes and consists of mRNA and tRNA interacting with one another.
rRNA
Ribosomal RNA is used to produce the structure of ribosomes.
tRNA
Transfer RNA that is used to bind ribosomes to the start codon of a nucleotide chain in order for
translation to occur.
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DNA Sequencing
by Sophia Tutorial

WHAT'S COVERED
This lesson is going to cover DNA sequencing by looking at :
1. DNA Sequencing
2. The Human Genome Project
1. DNA Sequencing
DNA sequencing provides a lot of information about genes, like where a gene is located on a chromosome. It
can tell us about the order of nucleotides involved in a gene, how a gene functions, about mutations of a
gene, and how genes interact with other genes. This can be really beneficial in the medical world because, if
the way genes work is understood, information about certain types of genetic disorders can be gained.
It's also useful in the study of genomics. A genome is all of the DNA in a species' entire set of chromosomes.
A variable number tandem repeat is a region of DNA that varies from person to person.
 EXAMPLE Within a species, a certain percentage of their DNA will be the same. More than 99% of all
human DNA is the same. It is the less than 1% that is the variable number tandem repeat.
Of all the variable number tandem repeats, you have a unique combo of repeats. This unique combination of
repeats of nucleotides is like your genetic fingerprint. This is what is used in forensics if people are doing
blood tests or DNA tests.

TERMS TO KNOW
DNA Sequencing
A genetic technology that allows us to characterize and leverage genes.
Genomics
The study of genomes.
Genome
All of the DNA in an individual's complete set of chromosomes.
Variable Number Tandem Repeats
The portion of DNA (about 1%) that is unique to each individual.
2. The Human Genome Project
The Human Genome Project was a project that mapped the complete human genome using DNA sequencing.
This was a huge project because there are over three billion nucleotide bases in a total of about 21,500
genes. The knowledge of this information is very helpful in the research of genetic disorders and medicine.
The 21,500 genes mentioned above code for all the proteins we make. However, if you add all the
nucleotides from all those gene sequences together, nucleotides that code for genes only make up 2% of all
the nucleotides in our genome. The rest of the DNA is noncoding DNA. Historically, the noncoding DNA has
been referred to as "junk DNA" because it doesn't code for proteins. However, we are beginning to discover
that it has subtler functions, such as modulating the timing and location of protein expression. Biologists are
working on trying to figure out what the purpose of this junk DNA is.
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
TERM TO KNOW
Human Genome Project
A complete map of the entire human genome completed with DNA sequencing.

SUMMARY
DNA sequencing has been very useful in the medical field, and it has provided us with a lot of
information about how genes function, where they're located, and how they interact with other genes.
The Human Genome Project mapped the complete human genome using DNA sequencing.
Source: This work is adapted from Sophia Author Amanda Soderlind

TERMS TO KNOW
DNA Sequencing
A genetic technology that allows us to characterize and leverage genes.
Genome
All of the DNA in an individual's complete set of chromosomes.
Genomics
The study of genomes.
Human Genome Project
A map of the entire human genome completed with DNA sequencing.
Variable Number Tandem Repeats
The portion of DNA (about 1%) that is unique to each individual.
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DNA Technology and Research
by Sophia Tutorial

WHAT'S COVERED
This lesson will cover the role of recombinant DNA technology in genetic engineering by looking at:
1. Recombinant DNA Technology
2. Genetic Engineering Applications
3. Gene Therapy
4. Cloning
1. Recombinant DNA Technology
Genetic engineering is a process which involves the alteration of the genes of an organism. Recombinant
DNA is a tool used in genetic engineering; a short segment of DNA from one organism is "recombined" with
the DNA of another organism.
One of the first attempts to create recombinant DNA was to help people with diabetes. At the time, the only
way to prevent someone with diabetes from starving to death (remember, type I diabetics can't produce
insulin, and therefore can't move sugar from their blood to their hungry cells) was to give them cow's insulin.
Cow's insulin was expensive, difficult to come by and didn't work well; people with diabetes had very
foreshortening, poor-quality lives.
Scientists used genetic engineering to rapidly produce human insulin, which is far more effective than cow's
insulin. They used restriction enzymes to introduce cuts into DNA extracted from cells swabbed from the
inside of your cheek, for example. These cuts reduced the human genome to smaller-sized pieces that are
easier to manage. They then took these pieces and inserted them into small circles of DNA called plasmid
DNA. In the diagram below the dark strand is the human DNA, while the yellow is the plasmid. These plasmids
are relatively easy to insert into transformation (briefly opening holes in a cell's plasma membrane so DNA
outside the cell can be taken in and expressed). The plasmids also contain instructions for how to get rid of
cells that didn't take up the correct DNA, as well as instructions for producing the protein encoded in the
recombinant DNA.
This technology was used to introduce
the gene for human insulin into E. coli, which grows rapidly and can produce this effective treatment for
diabetes very cheaply. Thanks to this transgenic organism (an organism that contains genes from another
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Page 34
organism), people with diabetes can live long, healthy lives.

TERMS TO KNOW
Genetic Engineering
Manipulating an organism’s DNA to create a genetically modified organism (mice, crops).
Recombinant DNA
A DNA molecule that contains DNA from multiple species, often used with bacteria (example: Using
recombinant DNA to stimulate E. coli to produce human insulin).
Restriction Enzyme
Enzymes that cut apart specific segments of DNA.
Plasmid DNA
DNA that is separate from a chromosome but can code for a protein, are often circular, double-stranded and
common in bacteria.
Transformation
A method of introducing new genes into cells (often bacterial cells).
Transgenic Organism
Organisms that contain genes from another organism.
2. Genetic Engineering Applications
Since the use of genetic engineering to create a therapy for diabetics, the technology has continued to
improve, and the number of applications has increased.
For example, instead of isolating a whole bunch of DNA, cutting it up with restriction enzymes and hoping the
correct gene gets inserted into one of your billions of plasmids, we can use polymerase chain reaction (PCR)
to copy the precise gene in a couple of hours.
Besides creating medicinal proteins and molecules, genetically modified organisms (GMOs) can be used to
make our environment cleaner and safer. For example, bacteria can be genetically modified to have genes
that allow them to eat oil. These GMOs have been deployed at oil spills. This genetic engineering application
is called bioremediation.
Genetic engineering has also been used to make food more affordable and more nutritious. Plants are being
used in genetic engineering, and they can produce genetically modified foods. These genetically modified
foods can be pest resistant and more resilient. They also can be genetically modified to do things like provide
more vitamins.
In a way, this technology isn't new; people have been selectively breeding animals and hybridizing plants for
thousands of years. Everything we eat has been "genetically modified" over generations. The benefit of
genetic engineering technology is that it is more precise, so it introduces less risk of including harmful DNA
along with the beneficial DNA. It's also faster and cheaper; reverting back to old insulin technology, for
example, would be a death sentence to a lot of diabetics.

TERMS TO KNOW
Polymerase Chain Reaction (PCR)
Genetic technology that allows scientists to copy DNA quickly.
Genetically Modified Organism (GMO)
An organism that contains foreign DNA produced by genetic engineering.
Bioremediation
Using genetically modified organisms to clean pollutants.
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3. Gene Therapy
Gene therapy is a process that's used to help fix genetic diseases. As of right now, its use is not widely spread
because it's still very experimental and costly. There are several ways gene therapy can be used. It is hoped
that gene therapy can be used to replace or edit mutated genes.
 EXAMPLE You may have heard about the pregnant mother who has HIV. There was a very good
chance her unborn children were going to contract the virus. CRISPR technology was used to alter the
CCR5 receptors in the babies' T cells. This is a mutation that already exists in many people; people who
are homozygous for this mutation are immune to HIV. Genetic engineering was used to give these babies
a mutation that already exists, and make them immune to their mother's HIV.
There are a couple of different ways in which genes can be inserted into a person in the process of gene
therapy:
Transformation: Briefly opening holes in a cell's plasma membrane so DNA outside the cell (such as
recombinant plasmids) can be taken in and expressed.
Transfection: A way in which genes can be inserted into a cell using a virus. A gene is inserted into a
virus, and then the virus will be inserted into the person. It will transfer that gene to a target cell, and
integrate the DNA with the host's DNA.
There have been some different trials with gene therapy. One is with a disease called Severe Combined
Immune Deficiency. Severe Combined Immune Deficiency is a type of disorder in which a person's immune
system doesn't work; they have to live in a bubble. Children with this disorder are often referred to as "bubble
kids" because they literally have to live in a bubble and can't be exposed to any germs, due to their deficient
immune system. Gene therapy has actually come a long way with this type of disease and helping to allow
those children to lead a more normal life.
Cystic fibrosis is another example of a disease that has had some trials with gene therapy. With this disorder,
scientists have used a virus to deliver normal copies of a gene to the respiratory system. With cystic fibrosis,
you get a buildup of mucus in the respiratory system. By using this virus, they can deliver normal copies of the
gene to the respiratory system to help with this condition.
The most common use of gene therapy thus far has been with cancer. It's had the biggest success thus far
with gene therapy of any of the other diseases that they've done trials with.

TERMS TO KNOW
Gene Therapy
The process of replacing mutated genes with normally functioning genes; gene therapy can be done directly
or with vectors (virus).
Transfection
A gene is inserted into a vector (virus) and injected into a person; the virus will deliver the gene into the host
cells.
4. Cloning
Cloning is the process of producing a genetic copy of a cell or an organism. So far, scientists have cloned
bacteria in recombinant DNA technology and embryos for stem cell use. They've also cloned animals, one of
the most famous examples being Dolly the sheep.
There are two different types of cloning that can be used:
Therapeutic cloning: A type of cloning in which an embryo is cloned as a source of embryonic stem cells.
These embryonic stem cells have undergone very little differentiation, so they are capable of becoming a
wider variety of tissues (for organ transplants, for example). However, embryonic stem cells are difficult to
come by, and there are ethical concerns. Research is ongoing to coax adult stem cells (such as those
found in fat tissue) to differentiate into a wider variety of tissues.
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Reproductive Cloning: A type of cloning technology in which a cloned embryo is created. That cloned
embryo is then transferred into a woman's uterus, where it can develop into a baby. The parents who are
carriers of a genetic disorder such as cystic fibrosis would be able to ensure that their children (and all
future generations) didn't carry genes that could make them or future generations sick. This is just one of
the different ways that reproductive cloning is developing and being used.
Both therapeutic and reproductive cloning are in the very early stages of development. For example, often
cloned organisms have health problems. Scientists have noticed this with some of the cloned animals that
they've produced—these animals tend to have a lot of health issues, and they will age faster than average.
Additionally, there has been an ethical debate about altering the genetic makeup of an embryo before it's
implanted. Many people consider this to be unnatural because rather than letting nature take its course, this
process involves messing with aspects of biology that are typically out of people's hands. However, cloning
can certainly be a useful tool.

TERMS TO KNOW
Cloning
The production of a genetic replica of a cell or organism.
Therapeutic Cloning
A type of cloning in which embryonic stem cells are used to produce organs or tissues.
Embryonic Stem Cells
Cells from an embryo that have not yet specialized and therefore can be coaxed to produce various types of
organs and tissues.
Reproductive Cloning
A type of cloning in which a cloned embryo is implanted into a mother's uterus and allowed to develop into a
baby.

SUMMARY
Recombinant DNA technology is used in genetic engineering. It often contains the DNA of more than
one species. It often involves using restriction enzymes to cut sections out of DNA. This DNA is
combined with plasmid DNA with the help of modification enzymes. From there it is placed (via
transformation or transfection) in another organism (such as a bacterial cell) to replicate. Polymerase
chain reaction (PCR) is an even faster, more precise way to isolate a useful gene and create a
genetically modified organism (GMO); GMOs can be used in bioremediation, medical therapeutics,
and agriculture. Genetic engineering can also be used in gene therapy to try and directly fix mutated
genes (such as those found in cancer cells). Future technologies may be able to use cloning to create
replacement organs, or help parents with a genetic disorder have healthy babies. Keep up the
learning and have a great day!
Source: This work is adapted from Sophia Author Amanda Soderlind

ATTRIBUTIONS
Recombinant DNA | Author: Wikipeda | License: Public Domain

TERMS TO KNOW
Bioremediation
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Page 37
Using genetically modified organisms to clean pollutants.
Cloning
The production of a genetic replica of a cell or organism.
Embryonic Stem Cells
Cells from an embryo that have not yet specialized and therefore can be coaxed to produce various
types of organs and tissues.
Gene Therapy
The process of replacing mutated genes with normally functioning genes. Gene therapy can be done
directly or with vectors (virus).
Genetic Engineering
Manipulating an organism’s DNA to create a genetically modified organism (GMOs).
Genetically Modified Organism (GMO)
An organism that contains DNA produced by genetic engineering (such as DNA from more than one
species).
Plasmid DNA
DNA that is separate from a chromosome but can code for a protein. Plasmids are often circular,
double-stranded and common in bacteria.
Polymerase Chain Reaction (PCR)
Genetic technology that allows scientists to copy DNA quickly.
Recombinant DNA
A DNA molecule that contains DNA from multiple species, often used with bacteria (example: using
recombinant DNA to stimulate E. coli to produce human insulin).
Reproductive Cloning
A type of cloning in which a cloned embryo is implanted into a mother's uterus and allowed to
develop into a baby.
Restriction Enzyme
Enzymes that cut apart specific segments of DNA.
Therapeutic Cloning
A type of cloning in which embryonic stem cells are used to produce organs or tissues.
Transfection
A gene is inserted into a vector (virus) and injected into a person; the virus will deliver the gene into
the host cells.
Transformation
A method of introducing new genes into cells (often bacterial cells).
Transgenic Organisms
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Organisms that contain genes from another organism.
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Heredity
by Sophia Tutorial

WHAT'S COVERED
This lesson will cover the basics of heredity by looking at:
1. Heredity
2. Dominant & Recessive Traits
1. Heredity
Heredity is the passing of traits from parents to offspring. Gregor Mendel is considered the father of genetics
because of his work with heredity. He examined how information is passed through generations from parent
to offspring. To this day, research is still ongoing as to what traits are inherited and what traits are the result of
environmental factors.
 EXAMPLE It appears that certain nucleotide sequences (which are inherited) make a person more
likely to contract Type I diabetes, but whether they develop diabetes is also influenced by what pathogens
they encounter.
Mendelian inheritance is a term that was coined due to Mendel's research on pea plants. His first discovery
was that traits aren't infinitely mixable. For instance, if you breed a yellow pea plant with a green pea plant,
you don't get a chartreuse pea: You get a yellow pea. This led to the discovery of genes: Indivisible, heritable
units. Genes are found on chromosomes and are passed from parents to offspring. They contain information
about specific traits. Some different types of inheritance include:
Autosomal dominant
Autosomal recessive
X-linked inheritance
X-linked dominant
Homologous chromosomes are pairs of chromosomes found within your cells that contain variations of the
same information and are the same size and shape. A person inherits one homolog of each chromosome from
their mother and one homolog from their father. A human has 46 total chromosomes in their body, 23 from
each parent. Each chromosome is a long stretch of DNA with hundreds of genes coded along its length. A
locus is the physical location of a gene along the chromosome's length. For instance, one of the genes for
hemoglobin is located along the middle of chromosome 11.
Alleles are different versions of a gene; you have two alleles for each trait, one on each homologous
chromosome. The combination of alleles that you inherit will determine the outcome of that trait.
 EXAMPLE A trait a person’s genes decides is their hairline. A person can have a straight hairline, or
they can have a widow's peak. This person has a pair of alleles at a specific locus, and each allele (straight
or widow's peak) is a version of the gene for hairline.

TERMS TO KNOW
Heredity
The passing of traits from parents to offspring.
Gregor Mendel
Dubbed the "father of modern genetics" and arguably modern biology, Mendel was an Austrian monk who
studied heredity and inheritance in plants.
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Inheritance
Receiving genetic characteristics from parents, the manner in which genes are passed down to offspring.
Gene
A genetic unit of heredity; a specific section of DNA that codes for a specific protein.
Allele
Variation in a gene, an example would be eye color; there is a gene for eye color, but there are different
versions of genes that allow for different eye colors (blue, green, hazel, brown).
Locus
The term used to describe the specific location of a gene/DNA sequence on a chromosome; variations of
these genes are referred to as alleles.
2. Dominant and Recessive Traits
Traits can be either dominant or recessive. Recessive traits are only expressed when adominant allele is not
present. If a recessive allele is in the presence of a dominant allele, the dominant allele will always rule. There
are three ways the mix of dominant and recessive alleles can present:
Homozygous dominant: When there are two dominant alleles together
Homozygous recessive: When there are two recessive alleles together
Heterozygous: When a recessive and dominant allele are together

DID YOU KNOW
The prefix ‘homo’ means ‘“the same” and the prefix 'hetero' means “different”
In genetics, letters are used to represent the combinations of alleles. A capital letter is used to represent an
allele that is dominant, and a lowercase letter to represent a recessive allele.
IN CONTEXT
The gene for having a widow’s peak is dominant. Suppose there are two parents that both have
heterozygous alleles for a widow’s peak. This means that each parent has one dominant allele (W)
and one recessive allele (w) to make a heterozygous allele (Ww).
What are the possible phenotypes, or the physical manifestation of the genes you inherit, for each
genotype going to be?
If you have two parents that are both heterozygous, they could have children that are homozygous
dominant, heterozygous or homozygous recessive.

TERMS TO KNOW
Dominant Alleles
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When one allele masks the expression of another on the same locus; this is seen at the phenotype level.
Recessive Allele
An allele that is masked by a dominant allele, recessive alleles are only expressed when they are found in
homozygous pairs.
Homozygous
An organism with two identical alleles of a gene.
Heterozygous
An organism with two different alleles of a gene.
Genotype
A trait or characteristic expressed at the genetic level, that is, the genetic makeup of an organism.
Phenotype
An observable characteristic of someone’s genotype, examples: Eye color, skin color, height, gender, etc.

SUMMARY
Heredity is the passing of traits from parents to offspring. Genes are the genetic information on
chromosomes that pass from parent to child, and alleles are the different versions of a gene. You
inherited one allele of each gene from your mom, and one from your dad. Alleles can cause either
dominant or recessive traits to be expressed. A dominant trait will always show if a person has the
dominant allele. If a person is homozygous recessive, then the recessive trait will determine a
person’s phenotype. Keep up the learning and have a great day!
Source: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND

ATTRIBUTIONS
Face | Author: Wikipeda | License: Public Domain

TERMS TO KNOW
Allele
Variation in a gene. An example would be eye color; there is a gene for eye color, but there are
different versions of genes that allow for different eye colors.
Dominant Alleles
When one allele masks the expression of another allele of the same gene. This is seen at the
phenotype level.
Gene
A genetic unit of heredity; a specific section of DNA that codes for a specific protein.
Genotype
A trait or characteristic expressed at the genetic level, that is, the genetic makeup of an organism.
Gregor Mendel
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Page 42
Dubbed the "father of modern genetics" and arguably modern biology, Mendel was an Austrian monk
who studied heredity and inheritance in plants.
Heredity
The passing of traits from parents to offspring.
Heterozygous
An organism with two different alleles of a gene.
Homozygous
An organism with two identical alleles of a gene.
Inheritance
Receiving genetic characteristics from parents, the manner in which genes are passed down to
offspring.
Locus
The term used to describe the specific location of a gene/DNA sequence on a chromosome;
variations of these genes are referred to as alleles.
Phenotype
An observable characteristic of someone’s traits, examples: eye color, skin color, height, gender etc.
Recessive Allele
An allele that is masked by a dominant allele, recessive alleles are only expressed when they are
found in homozygous pairs.
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Punnett Squares
by Sophia Tutorial

WHAT'S COVERED
This lesson is going to cover Punnett squares and their use by looking at:
1. Punnett Squares
a. Sex Chromosome Example
b. Hairline Example
2. Independent Assortment
1. Punnett Squares
Punnett squares are tools that are used to determine the probability or the chance that a trait will show up in
an offspring. Genetic traits are characteristics of an organism that are determined by their genes and are
inherited.
 EXAMPLE An example of a trait could be eye color, height, hair color or certain genetic disorders.

TERMS TO KNOW
Punnett Square
A tool used to determine the probability of offspring inheriting a trait based on the genotypes of both parents.
Probability
A measure of the chance of an outcome.
Genetic Trait
A characteristic of an organism such as eye color, skin color, hair color, gender, body type, etc.
1a. Sex Chromosome Example'
A Punnett square helps determine the odds of an offspring’sgenotype given the parent’s genotype.
Ultimately, genotype will determine the phenotype.
To see how Punnett squares are used, look at this square crossing male and female sex chromosomes:
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The Punnett square crosses the sex alleles of a male and a female. A female will have two X chromosome,
and a male will have an X and a Y chromosome. The mother’s alleles are listed on top, and the fathers are
listed on the side.

THINK ABOUT IT
Using the square above, what are the odds an offspring will be female?
We can see that there is a 50% chance that any offspring would have two XX chromosomes, making the child
female.

TERMS TO KNOW
Phenotype
The physical manifestation of the expression of an organism's genes.
Genotype
The genes inherited by an organism which represent a trait.
1b. Hairline Example
Below is a Punnett square related to hairline showing whether a person is going to have a straight hairline or a
widow's peak. A widow's peak is a dominant trait; if a person has at least one dominant allele (W), they will
have the widow's peak.
The mom in this example is homozygous dominant for widow's peak. This means that she has the same
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Page 45
alleles (W and W), and both are dominant. Her phenotype would be the dominant trait, which is this case
means she has a widow’s peak.
The father is heterozygous for the trait, meaning that he has one dominant allele (W) and one recessive allele
(w). Since he has at least one dominant allele, it masks that recessive allele. The dad will also have a widow's
peak as his phenotype.

THINK ABOUT IT
How many of the offspring from this example are going to have a widow’s peak?
We can see that because each box has at least one big W, or dominant allele, 100% of their offspring will have
a widow's peak.
2. Independent Assortment
Recall how gametes are made: In meiosis I, both sister chromatids of one homolog goes to daughter cell A,
and both sister chromatids of the other homolog goes to daughter cell B. For each of the 23 homologous
pairs of chromosomes, it's random which homolog goes where. That means that genes on separate
chromosomes may or may not be inherited together.
 EXAMPLE If you inherited an allele for green eyes and an allele for sickle cell anemia your father, and
the allele for brown eyes and the allele for normal hemoglobin from your mother. each of your children
might have green eyes and sickle cell anemia, or brown eyes and sickle cell anemia, or green eyes and
normal hemoglobin, or brown eyes and normal hemoglobin.
The law of independent assortment is a law that states that the vast majority of traits are inherited
independently of one another. This means that the inheritance of one trait is not influenced by the inheritance
of another trait.
 EXAMPLE The inheritance of a Y chromosome does not influence, or is not dependent on, the
inheritance of a widow's peak, for example. So traits are inherited independently of one another.

TERM TO KNOW
Independent Assortment
A law that states genes on different chromosomes are inherited independently of one another; the
inheritance of one trait does not influence the inheritance of another trait.

SUMMARY
Punnett squares are used to determine the probability of inheriting a trait based on the parent’s
genotype. The dominant trait will always determine the phenotype of the offspring. The law of
Independent Assortment says that traits on separate chromosomes are inherited independently of
one another. Keep up the learning and have a great day!
Source: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND

TERMS TO KNOW
Genetic Trait
A characteristic of an organism such as eye color, skin color, hair color, gender, body type, etc.
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Genotype
The genes inherited by an organism which represent a trait.
Independent Assortment
A law that states genes on different chromosomes are inherited independently of one another. The
inheritance of one trait does not influence the inheritance of another trait.
Phenotype
The physical manifestation of the expression of an organism's genes.
Probability
A measure of the chance of an outcome.
Punnett Square
A tool used to determine the probability of offspring inheriting a trait based on the genotypes of both
parents.
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Codominance
by Sophia Tutorial

WHAT'S COVERED
This lesson is going to look at codominance by covering:
1. Codominance
2. Alleles for Blood Type
1. Codominance
Codominance is when both alleles for a trait can be expressed together. Normally, if a trait is dominant, that
trait will be expressed in the phenotype of the offspring and a recessive trait will be masked. In cases of
codominance, however, both traits will be expressed together rather than one dominating over another.
A common example of codominance is blood type. There are three alleles for blood type: A, B, and O. Many
traits only have two alleles for the trait, but sometimes there can be three or more alleles that can represent a
trait. When a gene has three or more alleles, it is called a multiple allele system. With blood type, A and B are
considered dominant. This means that both antigens are expressed on the surface of red blood cells; O is
considered a recessive gene because no antigen is expressed.

TERMS TO KNOW
Codominance
When two alleles express themselves vs. one dominating the other; an example would be A and B blood
types.
Multiple Allele System
A gene that has three or more alleles or alternative sets of genes, again an example would be the A.B.O.
blood group.
2. Alleles for Blood Type
Let's say a person has a genotype of AA or AO. Remember, for each trait, there will always be two alleles, one
inherited from the mother and one from the father. Even though there are three possible alleles for blood
type, there is only going to be two present in a person’s genotype. If a person has AA or AO, then their blood
will be type A.
Keep in mind the recessive gene is masked when combined with a dominant gene. In this case, A is dominant
over O, meaning the O allele does not influence the phenotype.
Let's say a person’s genotype is BB or BO. Again, O is recessive so it will be masked by the B allele. This
person will end up with a phenotype of type B blood as a result of these genotypes.
Now imagine a person inherits an A allele from their mother and a B allele from their father. As mentioned
earlier, these two alleles can be expressed together. The A allele does not mask the B allele, and the B allele
does not mask the A allele. They are both dominant, and the phenotype of this person will be type AB blood.
OO is the last genotype that could exist. In this case, the person has two recessive alleles together
(homozygous recessive). The recessive trait will be expressed and the person’s phenotype will be type O.
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Page 48

SUMMARY
Codominance is when two alleles express themselves instead of one dominating another. This can
be seen with alleles for blood types. The alleles for blood types are an example of a multiple allele
system. There are three possible alleles for blood type: A, B and O. A and B are both dominant. AA or
AO genotype will result in an A blood type, and BB or BO will result in a B blood type. However, when
both A and B alleles are present, a person will have an AB blood type. O blood type will only occur
when a person has two O alleles. Keep up the learning and have a great day!
Source: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND

TERMS TO KNOW
Codominance
When two alleles express themselves vs. one dominating the other; an example would be A and B
blood types.
Multiple Allele System
A gene that has three or more alleles or alternative sets of genes, again an example would be the
A.B.O. blood group.
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Polygenic Traits and Pleiotropy
by Sophia Tutorial

WHAT'S COVERED
This lesson will cover how different traits can be expressed by covering:
1. Polygenic Traits
2. Penetrance
3. Pleiotropy
1. Polygenic Traits
Polygenic traits are traits the combined expressions of multiple genes. In other words, these traits are not
determined by just one single gene. Most of the traits that are expressed are determined by many genes, with
very few traits determined by one single gene.
 EXAMPLE The color of your eyes, hair or skin are all polygenic traits.
Polygenic traits can show continuous variation within a population. Height is a good example of a polygenic
trait because, within a given population, we could have a wide range of continuous differences of that trait.
Height is also a multifactorial trait, meaning that it is determined by multiple factors such as the combination of
a person’s genes and environment.
 EXAMPLE Nutrition is an example of an environmental factor that can influence height.

TERMS TO KNOW
Polygenic Trait
A trait that is determined by several genes.
Continuous Variation
Variation of a trait that shows up in a population of people; body height is an example of continuous variation.
Multifactorial Trait
A gene that is partially controlled by genetics and partially controlled by the environment; for example, body
height is influenced by genetics, but nutrition growing up also influences height.
2. Penetrance
Penetrance is the varying degree to which someone expresses a trait that's associated with an allele.
Incomplete penetrance means that some people who inherit a disease allele will not manifest the disease in
their phenotype. For example, mutations in the BCRA1 gene cause familial breast cancer. 80% of people who
inherit one of these mutant alleles will contract breast cancer at some point during their lifetime. That means
that the penetrance of these alleles is 80%; just because you have the allele doesn't guarantee the phenotypic
outcome.
Cystic fibrosis is an example of a trait that would be completely penetrant. This means that 100% of people
who are homozygous recessive will have cystic fibrosis.
Polydactyly would be an example of a trait that would be incompletely penetrant. Polydactyly relates to the
number of digits that a person has. Some people who carry the genes for polydactyly might have the normal
ten fingers, while some people who have that trait might have more than ten fingers. There are varying
degrees to which someone expresses this trait.
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
TERM TO KNOW
Penetrance
The degree to which an inherited allele is expressed in the phenotype; an example would be familial breast
cancer due to mutations in the BRCA1 gene.
3. Pleiotropy
Pleiotropy is the expression of one gene that affects multiple traits. An example of this is the gene that causes
sickle-cell anemia. This gene produces various effects throughout the body and can affect the way the blood
carries oxygen, other internal organs, et cetera.

TERMS TO KNOW
Pleiotropy
When one gene influences multiple phenotypic traits; an example is sickle-cell anemia: A mutation in one of
the hemoglobin genes results in phenotypic changes in the blood, the joints, etc.
Sickle-cell Anemia
An example of pleiotropy, a person who inherits the mutated HBs gene will contract sickle-cell anemia, which
damages erythrocytes, the spleen, and many other organs of the body.

SUMMARY
Polygenic traits are a combined expression of multiple genes. Examples would be the color of your
eyes, hair, and skin. These traits can show continuous variation in a population, and can also be
multifactorial. Penetrance is the varying degree to which a trait associated with an allele is expressed.
Pleiotropy is the expression of multiple traits from one gene, such is the case with the gene for sicklecell anemia. Keep up the learning and have a great day!
Source: SOURCE: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND

TERMS TO KNOW
Continuous Variation
Variation of a trait that shows up in a population of people, body height for instance.
Multifactorial Trait
A gene that is partially controlled by genetics and partially controlled by the environment. For
example, body height is genetic but nutrition growing up also influences height.
Penetrance
The degree to which an inherited allele is expressed in the phenotype. An example would be familial
breast cancer due to mutations in the BRCA1 gene. Of the people who inherit such a mutation, 80%
will develop breast cancer over their lifetime. The penetrance of this allele is 80%.
Pleiotropy
When one gene influences multiple phenotypic traits. An example is sickle-cell anemia: a mutation in
one of the hemoglobin genes results in phenotypic changes in the blood, the joints, etc.
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Polygenic Trait
A trait that is determined by several genes.
Sickle-cell Anemia
An example of pleiotropy, a person who inherits the mutated HBs gene will contract sickle-cell
anemia, which damages erythrocytes, the spleen, and many other organs of the body.
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Page 52
Pedigrees
by Sophia Tutorial

WHAT'S COVERED
This lesson will cover the use of pedigrees by looking at:
1. Pedigrees
2. Genetic Abnormality vs. Genetic Disorder
1. Pedigrees
Being able to identify family history is important because it allows parents to assess the risk of their child
inheriting a genetic disorder that runs in the family. Pedigrees are charts that can help to track the family
history of a particular trait.
A carrier is a person who is heterozygous for a recessive trait, meaning they have one dominant and one
recessive allele. If this recessive trait is for a disease, then they are considered a carrier for the disease. This
person only expresses the dominant phenotype, but they still possess the recessive allele. To display the
phenotype for that disease, someone would have to have two recessive alleles. The importance of knowing
who is a carrier if this person were to have a child with another carrier. Their children would then have a
chance of inheriting this recessive trait from both parents and contracting the disease.
IN CONTEXT
What are the odds two heterozygous parents (carriers) would have an offspring that expresses only
the recessive trait? How would you find this out?
To determine what the chances are, you would need to use a Punnett square:
If you cross two heterozygous people, the square shows there is a 25% chance that their child will
inherit that recessive trait.

TERMS TO KNOW
Pedigree
A chart used to track a trait through a family tree.
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Carrier
An individual who is carrying a trait genotypically but does not display it phenotypically.
2. Genetic Abnormality vs. Genetic Disorder
A genetic abnormality is a trait that a person can inherit that is an abnormal expression of that trait, but doesn't
necessarily cause a health problem.
 EXAMPLE A person that has six toes. It is an abnormal expression of a trait, but it's not going to cause
that person any health problems.
A genetic disorder, on the other hand, does cause health issues.
 EXAMPLE Huntington's disease is a genetic disorder that results in the breakdown of nerve cells in
the brain that results in severe mental and physical degeneration. Huntington's disease is therefore
termed a genetic disorder because it actually does cause health problems.

TERMS TO KNOW
Genetic Abnormality
A genetic characteristic that is not typical (example: Six toes, which does not prevent a person from enjoying a
healthy life).
Genetic Disorder
A genetic characteristic that causes health problems (example: Huntington's Disease, which causes the
breakdown of nerve cells in the brain, leading to severe physical and mental degeneration).

SUMMARY
Pedigrees are used to track the family history of a particular trait. This is useful in determining if
someone is a carrier for a trait like a recessive disease. If they are, and they have offspring with
another carrier for that trait, their offspring will have a chance of expressing that recessive trait.
Genetic abnormalities are abnormal traits a person can inherit that do not cause health problems,
while genetic disorders are inherited traits that do cause health problems. Keep up the learning and
have a great day!
Source: This work is adapted from Sophia author Amanda Soderlind.

TERMS TO KNOW
Carrier
An individual who is carrying a trait genotypically but does not display it phenotypically.
Genetic Abnormality
A genetic characteristic that is not typical (example: 6 toes, which does not prevent a person from
enjoying a healthy life).
Genetic Disorder
A genetic characteristic that causes health problems (example: Huntington's Disease, which causes
the breakdown of nerve cells in the brain, leading to severe physical and mental degeneration).
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Page 54
Pedigree
A chart used to track a trait through a family tree.
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Chromosome Structure Changes
by Sophia Tutorial

WHAT'S COVERED
This lesson is going to cover changes in chromosome structure by examining:
1. Gene Mutation
a. Deletions
b. Translocations
c. Duplications
2. Karyotypes
1. Gene Mutations
A gene mutation is the change in the nucleotides that make up a gene. Sometimes, chromosome structure
can be altered during cell division, which will lead to a certain type of gene mutation. These gene mutations
can include:
Deletions
Translocations
Duplications
1a. Deletions
A deletion is the removal of one or more nucleotides on the chromosome.
 EXAMPLE Cri-du-chat is a disorder that is caused by a deletion on chromosome number five. With this
type of disorder, a baby's larynx will not properly develop, so that when the baby cries, it will sound like a
meowing cat. This disorder can also be associated with abnormal mental development as well.

TERMS TO KNOW
Deletion
When part of a chromosome is deleted; sometimes it may not have any effect, while other times it does.
Cri-du-chat
A genetic disorder caused by the deletion of a section of the fifth chromosome; cri-du-chat is French for “cry
of the cat”and causes physical and cognitive abnormalities.
1b. Translocations
Translocation is when part of one chromosome switches place with a corresponding part of a different (nonhomologous) chromosome. This type of gene mutation can lead to certain types of cancers.
 EXAMPLE Say the original Chromosome 1 is made of A, B, C, D, E, F and Chromosome 2 contains G,
H, I, J, K, L. In a translocation, part of Chromosome 1 will switch places with a corresponding part of
Chromosome 2. In this example, perhaps the F and L parts of the chromosome could switch places so that
the translocated Chromosome 1 now reads ABCDEL and the translocated Chromosome 2 now reads
GHIJKF.

TERM TO KNOW
Translocation
A chromosome abnormality that occurs when pieces of different (non-homologous) chromosomes fuse
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Page 56
together.
1c. Duplication
Duplication is when a nucleotide sequence is repeated. Duplications can be harmful, as in the case of
Huntington's disease. The more repeats of a certain nucleotide sequence you have, the more likely you are to
contract Huntington's; an increase in this particular duplication also means you'll contract Huntington's earlier
in life. However, duplications can also be helpful. Our ancestors used to be unable to see green and yellow
color. A duplication of our red cone cell receptor gene, along with some slight mutation, resulted in a third
type of cone cell in our retina. This duplication allows us to see green and yellow light, as well as blue and red.
 EXAMPLE Say a chromosome is composed of A, B, C, D, E, F. If a duplication occurs, it might end up
with A, B, C, B, C, D, E, F with the B, C portion repeated.

TERM TO KNOW
Duplication
Sequences of nucleotides are repeated multiple times; Huntington's disease is an example of a genetic
disorder that results from duplication: The more times a certain sequence is repeated, the more likely and
earlier in life Huntington's is to strike.
2.Karyotypes
Karyotypes are the arrangement of a person's complete set of chromosomes by length, shape, and the
location of the centromere. These pictures are taken well in metaphase of mitosis because the chromosomes
at that point are most easy to identify. The chromosomes will be photographed through the microscope, cut
out, and arranged from the largest all the way down to the smallest. The last pair of chromosomes in a
karyotype are always the sex chromosomes. For a male, one is an X chromosome, and one is the Y
chromosome. For a female, they will both be X chromosomes.
These karyotypes allow you to see a picture of a person's chromosome. This can help to identify any
abnormalities. One abnormality that can be seen on a karyotype is Trisomy 21, a genetic disorder in which a
person has three copies of chromosome number 21. Here is an example of what this might look like:
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If there is a third chromosome in the 21st pair, then the person would have trisomy 21; also known as Down
Syndrome.

TERM TO KNOW
Karyotype
Looking at the number of chromosomes and their characteristics under a microscope; this is a critical tool in
assessing genetic disorders in a developing embryo.

SUMMARY
Gene mutations are changes in the nucleotide sequence. These mutations can includedeletions,
translocations and duplications. A deletion is the removal of one or more nucleotides on the
chromosome. Translocation is when part of a chromosome switches places with part of a different
(non-homologous) chromosome. Duplication occurs when part of a chromosome becomes repeated.
A karyotype looks at a person's chromosomes under a microscope to check for genetic
abnormalities. This can identify if someone has Down Syndrome. Keep up the learning and have a
great day!
Source: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND

ATTRIBUTIONS
Karotype | Author: Wikipeda | License: Public Domain
Trisomy 21 | Author: Wikipeda | License: Public Domain
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
TERMS TO KNOW
Cri-du-chat
A genetic disorder caused by the deletion of a section of the 5th chromosome; cri-du-chat is French
for “cry of the cat”. Cri-du-chat causes physical and cognitive abnormalities.
Deletion
When part of a chromosome is deleted; sometimes it may not have any effect while other times it
does.
Duplication
Sequences of nucleotides are repeated multiple times. Huntington's disease is an example of a
genetic disorder that results from duplication: the more times a certain sequence is repeated, the
more likely and earlier in life Huntington's is to strike.
Karyotype
Looking at the number of chromosomes and their characteristics under a microscope. This is a critical
tool in assessing genetic disorders in a developing embryo.
Translocation
A chromosome abnormality that occurs when pieces of different (non-homologous) chromosomes
fuse together.
© 2019 SOPHIA Learning, LLC. SOPHIA is a registered trademark of SOPHIA Learning, LLC.
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Chromosome Count Changes
by Sophia Tutorial

WHAT'S COVERED
This lesson will cover changes in chromosome number and the effects this has by looking at:
1. Nondisjunction
2. Changes in the Number of Sex Chromosomes
1. Nondisjunction
Chromosome numbers can change during mitosis or meiosis and are generally the result of nondisjunction.
During the metaphase portion of mitosis and meiosis II, sister chromatids are being pulled towards the poles
of the cell. Usually these sister chromatids separate, but sometimes they do not separate correctly.
Nondisjunction is the failure of one or more pairs of sister chromatids to separate during cell division, and this
results in some cells ending up with too many or too few chromosomes. Nondisjunction can lead to several
different disorders.
Down Syndrome, also called trisomy 21, is an example of nondisjunction. This disorder occurs when a person
ends up with an extra copy of chromosome 21. Instead of having two homologs of chromosome 21, a person
with Down Syndrome has three homologs.

TERMS TO KNOW
Nondisjunction
When chromosomes don’t separate during anaphase, causing cells (such as gametes) to have abnormal
numbers; Down syndrome is an example of a genetic disorder that results from nondisjunction.
Down Syndrome
A genetic disorder in which the 21st pair of chromosomes has three chromosomes vs. the normal pair, this is
called a trisomy.
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2. Changes in the Number of Sex Chromosomes
Turner syndrome, Klinefelter syndrome, and XYY condition are examples where there is an anomaly in the
number of sex chromosomes.
Turner syndrome is when an X chromosome is missing. Generally, a person who is missing an X
chromosome would be miscarried by the mother, but anyone who does survive is always going to be a
female. That female is going to end up with sexual abnormalities and, generally, a shortened life span.
Klinefelter syndrome occurs when sex chromosomes have an extra copy. The person’s genotype on their
sex chromosomes would be XXY, and the individual would be a male with an extra X chromosome. A
person with this disorder is going to have low fertility, the possibility of mental retardation, and small
testes. They will also have physical abnormalities because of the presence of this extra X chromosome.
XYY syndrome is another condition that affects the sex chromosome. This person would be male
because of the presence of the Y chromosome. The only real result of this is that the male is probably
going to be a little bit taller than average. There are no serious abnormalities caused by having an extra Y
chromosome.

TERMS TO KNOW
Turner Syndrome
A genetic condition in which an X chromosome is missing (XO instead of XX or XY); if the child is not
miscarried, the effects can range from non-life threatening to life-threatening.; people with Turner syndrome
are female due to the presence of only an X chromosome, are almost universally infertile and typically have
cardiovascular issues along with other organ system problems.
Klinefelter Syndrome
A condition in which a person has an XXY chromosomal pattern; males that inherit this are often infertile, may
develop breasts and other female secondary characteristics and possible mental retardation.
XYY Syndrome
A condition in which a male inherits an extra Y chromosome; XYY syndrome doesn’t express any cognitive or
life-threatening abnormalities, it just tends to make males taller than average.

SUMMARY
Nondisjunction is the failure of one or more pairs of sister chromatids to separate during cell division
and can lead to a change in chromosome number. This will result in cells that end up with too many
or too few chromosomes. Down Syndrome is an example of a disorder that is generally caused by
nondisjunction. Changes in the number of sex chromosomes can also cause problems. Turner
syndrome is caused when an X chromosome is missing, and Klinefelter syndrome is caused when an
extra X is present in a male. Both of these disorders can cause long term problems for the person
they affect. XYY condition causes no serious abnormalities. Keep up the learning and have a great
day!
Source: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND

ATTRIBUTIONS
Nondisjunction | Author: Wikipeda | License: Creative Commons

TERMS TO KNOW
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Down Syndrome
A genetic disorder in which the 21st pair of chromosomes has three chromosomes vs. the normal pair,
this is called a trisomy.
Klinefelter Syndrome
A condition in which a person has an XXY chromosomal pattern; males that inherit this are often
infertile, may develop breasts and other female secondary characteristics and possible mental
retardation.
Nondisjuction
When chromosomes don’t separate during anaphase, causing cells (such as gametes) to have
abnormal numbers. Down syndrome is an example of a genetic disorder that results from
nondisjunction.
Turner Syndrome
A genetic condition in which an X chromosome is missing (XO instead of XX or XY). If the child is not
miscarried, the effects can range from non-life threatening to life-threatening. People with Turner
syndrome are female due to the presence of only an X chromosome, are almost universally infertile
and typically have cardiovascular issues along with other organ system problems.
XYY Syndrome
A condition in which a male inherits an extra Y chromosome; XYY syndrome doesn’t express any
cognitive or life-threatening abnormalities, it just tends to make males taller than average.
© 2019 SOPHIA Learning, LLC. SOPHIA is a registered trademark of SOPHIA Learning, LLC.
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Autosomal Recessive Traits and Disorders
by Sophia Tutorial

WHAT'S COVERED
This lesson is going look at autosomal recessive traits and disorders by examining:
1. Autosomal Recessive
2. Autosomal Recessive Disorders
1.Autosomal Recessive
Autosomal recessive traits and disorders are caused by the inheritance of recessive traits on autosomes.
Autosomes are all the chromosomes in your body, excluding the sex chromosomes.
In order for a person to inherit an autosomal recessive trait or disorder, both parents must contribute
recessive alleles. A person with an autosomal recessive trait or disorder has a genotype with two recessive
alleles. They would be homozygous recessive.
What are the odds certain parents would end up with offspring that are homozygous recessive? Punnett
squares can be used to help find out the chances:
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The first square shows the odds two people who are both heterozygous (carriers) for a particular trait of
having an offspring that is homozygous recessive. A capital letter indicates that the trait is dominant, and the
lower case letter shows the recessive trait.
The second square shows a parent that is heterozygous (a carrier) for a trait with someone who is
homozygous recessive (someone whose phenotype shows the recessive trait).
The third square shows two people that are homozygous recessive.
There really is no need to make a square for two people that are both homozygous dominant because they
will always produce children with the dominant gene.
It is important to note that someone who is heterozygous for a trait is a carrier for the recessive trait. They
won't display the characteristics of it because they display the dominant trait, but they can still pass the
recessive allele on to their offspring.

TERM TO KNOW
Autosomal Recessive
A trait or disorder caused by the inheritance of two recessive alleles on an autosome.
2. Autosomal Recessive Disorders
Cystic fibrosis is a type of autosomal recessive disorder in which mucus will build up in the lungs along with
other different symptoms.
Phenylketonuria (PKU) is another autosomal recessive disorder in which the buildup of a certain amino acid
will get too high in a person's body. If they get too much of this certain amino acid built up in their body, it can
cause mental retardation. Diet can help lower the specific amino acid, and help prevent symptoms of this
disorder.

TERMS TO KNOW
Cystic Fibrosis
An autosomal recessive disorder that results in buildup of mucus in the lungs.
Phenylketonuria (PKU)
An autosomal recessive disorder that results in the buildup of phenylalanine (an amino acid) in the body that
can lead to mental retardation if levels exceed a certain point.

SUMMARY
Autosomal Recessive traits and disorders are caused by inheritance of recessive traits on the
autosomes. Autosomes are all the chromosomes in your body besides your sex chromosomes. For a
recessive trait to express in a person's phenotype, they must inherit recessive genes from both of
their parents. Some autosomal recessive disorders include cystic fibrosis and phenylketonuria. Keep
up the learning and have a great day!
Source: This work is adapted from Sophia Author Amanda Soderlind

TERMS TO KNOW
Autosomal Recessive
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Page 64
A trait or disorder caused by the inheritance of two recessive alleles on an autosome.
Cystic Fibrosis
An autosomal recessive disorder that results in build-up of mucus in the lungs.
Phenylketonuria (PKU)
An autosomal recessive disorder that results in the build-up of phenylalanine (an amino acid). This
build-up can lead to mental retardation if levels exceed a certain point.
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Autosomal Dominant Traits and Disorders
by Sophia Tutorial

WHAT'S COVERED
In this lesson, we'll discuss the characteristics and examples of autosomal dominant traits and
disorders. The specific areas of focus include:
1. Cause of Autosomal Dominant Traits
2. Punnett Squares with Autosomal Dominant Disorders
3. Common Autosomal Dominant Disorders
1. Cause of Autosomal Dominant Traits
Autosomal dominant traits or disorders are caused by the inheritance of at least one dominant allele on a
person's autosomes. As you learned in a previous lesson, autosomes are the chromosomes found in your
cells, excluding the sex chromosomes.
For each trait that you have, you possess two alleles for that trait, one inherited from your mother and one
inherited from your father. For a person to express an autosomal dominant trait, he or she needs to have at
least one dominant allele.
This means the person's genotypes could be either big A-little a (Aa) or big A-big A (AA). You only need one
dominant allele to phenotypically express an autosomal dominant trait; you can be homozygous dominant or
heterozygous, and still have that particular autosomal dominant trait.

TERM TO KNOW
Autosomal Dominant
A trait or disorder caused by the inheritance of at least one dominant allele on an autosome.
2. Punnett Squares with Autosomal Dominant
Disorders
Some traits are controlled by recessive alleles, and some traits are controlled by dominant alleles. Punnett
squares are thus one way to see how the genotypes of parents can affect the outcome of their children.
 EXAMPLE If a parent possesses at least one dominant allele, that parent will have that trait. The only
way that 100% of their potential children would be normal is if both parents were homozygous recessive.
In the Punnett square below, you can see that if both parents are homozygous recessive, meaning neither
possesses a single dominant allele, then they have a 100% chance of having all normal children. In this
case, the normal trait would be homozygous recessive; however, you only need one dominant allele to
possess a dominant trait.
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 EXAMPLE Say both parents are heterozygous, meaning they have an autosomal trait or disorder
because they both have at least one dominant allele. If you look at the Punnett Square below, you'll notice
that because they also each possess a recessive allele for the normal condition, they actually have a 25%
chance of having a child who is unaffected by the disease.
 EXAMPLE Now say one parent is heterozygous, and the other parent is homozygous recessive. The
first parent contains one allele for that autosomal dominant trait--that parent possesses the trait--while the
second parent is completely normal. As the Punnett square shows, this combination of parent alleles
means the parents have a 50% chance of having totally normal children.
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2. Common Autosomal Dominant Disorders
The following are examples of autosomal dominant disorders:
Huntington's Disease: A disease that can be inherited, but the symptoms don't show up until adulthood.
Often, people don't realize that they have Huntington's disease until they've already reproduced and
passed it on to their children.
Marfan Syndrome: This disorder causes a weakening of the aorta, meaning that the aorta can rupture
over time. Generally, people with this disorder are very, very tall and lanky. However, the weakening of
the aorta is the most serious aspect of Marfan syndrome since rupturing can occur with intense physical
activity.
Achondroplasia: This disorder results in a person who has short arms and legs, and who is short overall.
Most people with this type of disorder only get to be about 4 to 4.5 feet tall, so achondroplasia affects a
person's height, and then--as a result--causes shortness of the arms and legs.
Familial Hypercholesterolemia: This disorder leads to high blood cholesterol. This is because the
cholesterol in the blood of people with this disorder won't bind to LDLs, which is the first step in removing
the cholesterol from the body. Therefore, most people with familial hypercholesterolemia often don't
have as long of a lifespan as other people as a result of their very high cholesterol.

TERMS TO KNOW
Huntington's Disease
An autosomal dominant disorder which does not show up until later in life often after the gene has been
passed onto offspring; it is a neurodegenerative disorder that causes motor and cognitive impairment and
eventually becomes fatal.
Marfan Syndrome
A genetic disorder of connective tissue that causes people to have a certain appearance: Being abnormally
tall with long limbs and digits; it can also affect other connective tissues such as heart valves, and can be fatal.
Achondroplasia
An autosomal dominant disorder in which the person is abnormally short in stature with short arms and legs.
Familial Hypercholesterolemia
An autosomal dominant disorder in which a person has chronic high cholesterol.

SUMMARY
In this lesson, you learned that the cause of autosomal dominant traits or disorders is the inheritance
of at least one dominant allele on an autosome. In other words, if one parent has one dominant allele,
there is a chance that the children will have the dominant trait as well, even though the other parent
does not have that dominant allele, which can be shown in a Punnett square. You now understand
that some common examples of autosomal dominant disorders are Huntington's disease, Marfan
syndrome, achondroplasia, and familial hypercholesterolemia. Good luck!
Source: ADAPTED FROM SOPHIA TUTORIAL BY AMANDA SODERLIND.

TERMS TO KNOW
Achondroplasia
An autosomal dominant disorder in which the person is abnormally short in stature with short arms
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and legs.
Autosomal Dominant
A trait or disorder caused by the inheritance of at least one dominant allele on an autosome.
Familial Hypercholesterolemia
An autosomal dominant disorder in which a person has chronic high cholesterol.
Huntington's Disease
An autosomal dominant disorder which does not show up until later in life, often after the gene has
been passed onto offspring. It is a neurodegenerative disorder that causes motor and cognitive
impairment and eventually becomes fatal.
Marfan Syndrome
A genetic disorder of connective tissue that causes people to have a certain appearance: being
abnormally tall with long limbs and digits. It can also affect other connective tissues such as heart
valves, and can be fatal.
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Page 69
X-Linked Traits
by Sophia Tutorial

WHAT'S COVERED
This lesson will cover traits and disorders associated with the sex chromosomes by looking at:
1. X-Linked Traits & Disorders
a. X-linked Recessive Disorders
b. X-linked Dominant Disorders
2. Inheritance
1. X-Linked Traits and Disorders
Sex chromosomes are the chromosomes that are related to our gender. Human females have sex
chromosomes composed of two X chromosomes, and males have sex chromosomes composed of one X
chromosome and one Y chromosome. X-linked traits are disorders related to a person's X chromosomes.
Both males and females can be affected by X-linked traits; however, males are generally more at risk of being
afflicted by an X-linked trait because they only have one X. If one X chromosome is affected in a female, the
other X will generally mask the effect.

TERM TO KNOW
Sex Chromosome
The chromosomes that, when paired, determine the sex/gender of the organism, in humans XX = female
while XY = male.
1a. X-linked Recessive Disorders
X-linked traits or disorders can be caused by recessive alleles or a dominant mutant allele on an X
chromosome. The following are examples of X-linked recessive disorders:
Hemophilia: A bleeding disorder in which blood doesn't properly clot.
Red-green color blindness: A disorder where a person can't distinguish between the colors red and
green.
Duchenne's muscular dystrophy: A disorder in which muscles begin to degenerate over time.

TERMS TO KNOW
Hemophilia
An X-linked recessive disorder that affects the blood's ability to clot.
Red-Green Color Blindness
An X-linked recessive disorder in which a person cannot distinguish between the colors red and green.
Duchenne Muscular Dystrophy
An X-linked recessive disorder in which the muscles deteriorate over time.
1b. X-linked Dominant Disorders
Disorders caused by a dominant mutant allele on the X chromosome are much less common. Faulty enamel
trait is an example of an X-linked dominant disorder. The enamel that protects your teeth doesn't properly
develop in people with this disorder. Their teeth will rot easily because they don't have protective enamel on
their teeth.

TERM TO KNOW
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Faulty Enamel Trait
A disorder caused by a dominant mutant allele on the X chromosome in which enamel that protects teeth
does not properly develop.
2. Inheritance
Using hemophilia as an example, it is possible to look at how these types of disorders can be passed on. A
father can pass on a X and a Y allele, while the mother can pass on one of two X chromosomes.
On the Punnett square below, the alleles listed on the top are the sperm a father can supply, and the alleles
listed on the left side are the possible eggs a mother could supply. This example shows the mother as a
carrier for hemophilia. The X shown in red is the recessive allele that is affected.
Because the mother has a normal X chromosome, any effect the recessive X would have is probably masked.
She is only a carrier, and she has a 50% chance of passing this chromosome on to any of her children. The
Punnett square shows she has a 25% chance of creating a daughter that is a carrier like her, and a 25%
chance of having a son that has hemophilia. She also has a 50% chance of passing on a X that is not affected.
She has a 25% chance of having a daughter that is not a carrier and a 25% chance of a son that is not
affected.
This illustrates how X-linked traits can be passed on from parents to offspring and why males are generally
more susceptible to inheriting these disorders. If they inherit the X chromosome from their mother that is
affected, they will automatically get that disease.
Many X-linked disorders follow common patterns of inheritance. There are lots of different patterns of
inheritance like this that geneticists can study to understand these diseases and the patterns in which these
diseases are passed through generations. Pedigrees are another useful tool in tracking these disorders as
well because you can follow the family history of a disease.
 EXAMPLE One type of inheritance pattern is that only daughters can inherit recessive alleles from
their affected father because the sons will get the Y chromosome. In other words, if a father is affected, he
can only give an affected X chromosome. His daughters, therefore, will either be affected or be carriers.

SUMMARY
X-linked traits or disorders are those located on the X sex chromosome. They can be caused by a
recessive allele or a dominant mutant allele on the X chromosome. Hemophilia, red-green color
blindness and Duchenne’s muscular dystrophy are examples of X-linked recessive disorders, and
faulty enamel trait is a disorder caused by a dominant mutant allele. These disorders can be inherited.
Women are generally only carriers of X-linked recessive traits because the second X they have can
mask the affected X. Men are most susceptible to X-linked recessive disorders because they only
have one X. Geneticists can study patterns of inheritance to understand these diseases, and
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Page 71
pedigrees can be a helpful tool for them. Keep up the learning and have a great day!
Source: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND

TERMS TO KNOW
Duchenne Muscular Dystrophy
An X-linked recessive disorder in which the muscles deteriorate over time.
Faulty Enamel Trait
A disorder caused by a dominant mutant allele on the X chromosome, in which enamel that protects
teeth does not properly develop.
Hemophilia
An X-linked recessive disorder that affects the blood's ability to clot.
Red-Green Color Blindness
An X-linked recessive disorder in which a person cannot distinguish between the colors red and
green.
Sex Chromosome
The chromosomes that, when paired, determine the sex/gender of the organism, in humans XX =
female while XY = male.
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