Physiology 31 Lecture
Chromosomes, DNA, & Genetics
I. Overview
A. Chromosomes, DNA, and Genes
B. DNA Replicates Prior to Cell Division
C. Genetic Inheritance
D. Genes Direct the Formation of Proteins
II. Chromosomes, DNA, and Genes
A. ____________ are rod like bodies found mainly in the cell nucleus and composed of
1. Tightly coiled strands of ______ containing genes, the hereditary material, and
2. Proteins (mostly __________)
B. ______ (deoxyribonucleic acid) is double helix molecule composed of nucleotide subunits
1. ____________ include a phosphate group, deoxyribose sugar, and a nitrogenous base
2. DNA Nitrogenous _________ include:
a. _____________ - have a double ring structure and include adenine (A) and guanine
(G)
b. ______________ - have a single ring and include thymine (T) and cytosine (C)
3. DNA consists of two strands of nucleotides twisted together in a double ___________,
like a twisted ladder
a. ________-phosphate groups make up the sides of the ladder, and nitrogenous
_________ form the rungs
b. Nitrogenous bases are ___________, meaning that a pyrimidine always forms
___________ bonds with a purine
1) Adenine always bonds with Thymine (___-___)
2) Cytosine always bonds with Guanine (___-___)
C. Functions of DNA include
1. Genes in DNA store information needed to build ______ in a cell
2. Genes provide the basis for _____________ in an organism’s offspring. A _______
a. Is a segment of _____ that controls the synthesis of a protein
b. Acts as a unit of ____________ that can be transmitted from generation to generation
III. DNA replicates itself prior to cell division
A. Two types of cell ________ occur in the body: mitosis and meiosis
1. ____________ - one diploid somatic (body) cell divides into two diploid genetically
identical cells
a. ___________ (2n) cells have two of each type of chromosome
b. A normal human cell has ___ _______________ pairs of chromosomes in its nucleus,
one of each pair from the mother and one from the father
1) 22 pairs of _____________ and
2) 1 pair of ____ chromosomes (___ in females, ___ in males)
c. Mitosis occurs in many body cells during ________ and ______ processes
2. ____________ - one diploid sex cell divides into four haploid ____________ (sperm or
eggs) that are not genetically identical
a. _________ (n) cells have only one of each type of chromosome
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b. Meiosis occurs only in the ovaries or ________ for reproductive purposes
B. Mitosis follows interphase in the cell ________
1. ____________ – the cell prepares itself for division by replicating its chromosomes (with
DNA) into identical ____________, in addition to its other organelles
2. ____________ (cell division) can be divided into 4 phases: prophase, metaphase,
anaphase, and telophase
a. __________ – chromosomes coil and become visible; nuclear envelope dissolves;
centrioles migrate to opposite ends of cell; spindle microtubules attach to chromatid
____________
b. ___________ – chromosomes arrange themselves in dyads (identical chromatid pairs)
across the ________ (equator) of the cell
c. ___________ – centromeres connecting chromatids ________, and individual
chromosomes are pulled to ____________ ends of the cell by spindle microtubules
d. ________ – nuclear envelopes reform around the chromosomes at opposite ends of the
cells; spindle microtubules are disassembled, and the cell divides (___________) into
two genetically identical diploid cells
C. DNA replicates when the chromosomes replicate
1. During ______________, DNA unwinds & “unzips.”
2. Helicase unwinds DNA & breaks the _________ bonds between nitrogenous base
pairs.
3. Nucleotides in the nucleus are joined to complementary bases of separated, single
DNA strands by DNA ______________.
4. Two ______________ DNA double helices result.
5. Called _____________ replication because each resulting double helix has one
parental strand and one new strand.
D. _____________ alter the sequence of DNA
1. A _______ mutation is a change in one nucleotide of DNA, due to a deletion, addition,
or substitution of a base
2. Mutations can cause a change in a _______ product, which could be minor, or result in
something that can kill the cell or organism
3. ____________ are factors that cause mutations, such as harmful chemicals and ionizing
radiation
4. Mutations that occur in the DNA of the _________ can be passed on to children that
result from fertilization
5. _________ mutations occur in body cells, and can spread in the body as mitosis occurs
E. Oncogenes and Cancer
1. ________-oncogenes are normal genes that code for proteins that regulate cell growth,
cell division, and cell adhesion
2. Mutations in proto-oncogenes can cause them to become _________ that cause
uncontrolled mitosis, also known as ______
3. ________ are often responsible for cancerous mutations in proto-oncogenes
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F. _________ is also preceded by interphase, but the cell goes through ___ stages of cell
division to reduce the chromosome number by ___
1. Meiosis I – similar to mitosis, except ___________ chromosome pairs (not chromatids)
are separated during __________ I, and the end result is two __________ daughter cells
2. Meiosis II – same stages as mitosis, with the separation of identical _________ during
anaphase II; overall result is ___ haploid ___________ that are not genetically identical
IV. Genetic Inheritance
A. A __________ is a photograph of all the chromosomes from a cell arranged by
homologous pairs in a fixed order.
B. __________ are alternate forms of a ______ in the same position on a pair of homologous
chromosomes, and affecting the same trait.
C. Alleles are represented by paired __________ (e.g.: BB, Bb, bb)
1. __________ allele: gene that controls for a trait that is ________ whether it’s paired
with another dominant allele or with a recessive allele.
a. _______________ dominant has 2 of the _____ dominant alleles (e.g.: ____).
b. _______________ has one dominant and one recessive allele (e.g.: ___). An
individual that is heterozygous for a trait is often called a _________ of the trait.
2. ___________ allele: gene that controls a trait that is only evident if the allele is paired
with another _________ allele.
a. ______zygous recessive has 2 of the ______ recessive alleles (e.g.: ___).
C. Genetic ________ are genotypic and phenotypic
1. ____________ - type of genes an individual has for a particular trait(s) (e.g.: ___ =
homozygous dominant; ___ = heterozygous; ___ = homozygous recessive).
2. ___________ - physical or observable characteristics that result from the genotype
(e.g.: brown eyes vs. blue eyes)
3. A ________ Square - device used to determine the probabilities of possible genotypes
and phenotypes of simple genetic crosses. (Widow’s peak activity)
a. Determine ___________ of P (parental) generation and all possible _________ in
their gametes [e.g.: monohybrids are heterozygous (Ww), so gametes would contain
a dominant (W) or a recessive (w) allele].
b. Align all possible combinations of ______ vertically and ____ horizontally (or vice
versa).
c. ________ egg & sperm alleles in converging _________, then determine probable
proportions of genotypes and phenotypes of children (F = filial generation).
d. ___________ cross always results in 3:1 phenotypic ratio of offspring.
e. Chance has no memory - each new child has the same ___________ of genotypes
& phenotypes.
D. Autosomal Dominant genetic disorders
1. Caused by a __________ allele on an autosomal chromosome.
2. A child and at least one _________ is affected.
3. Example: _____________ Disease
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a.
b.
c.
Caused by abnormal gene on chromosome ___.
Disease does not usually develop until ___________ age.
Causes degeneration of _______ cells; person gradually loses control of muscle
function and dies.
4. Do punnett square of autosomal dominant disorder.
E. Autosomal Recessive genetic disorders
1. Disorder is only present if both alleles for the trait are ________ on homologous
chromosomes.
2. Parents are usually heterozygous ________ of a recessive gene.
3. Homozygous recessive child is affected but _________ are not
4. Example: Phenylketonuria (_____)
a. Caused by abnormal gene on chromosome ___.
b. Causes defective _________ to break down phenylalanine.
c. Phenyl_________ accumulate in blood & urine.
d. Newborns are routinely ________ for PKU in hospital.
e. Diet low in _____________ can prevent mental retardation.
5. Do Punnett square of autosomal recessive disorder
F. ______________ Dominance genetic disorders
1. Both alleles are expressed such that _______zygous individuals exhibit an ___________
trait between the dominant and recessive traits
2. Parents of severely affected individuals are often heterozygous _________ of the trait
3. Example: Familial Hypercholesterolemia (___)
a. Caused by an abnormal gene on chromosome ____
b. Causes a defective LDL ________ protein
c. ____ can’t be taken into the cell and broken down, thus __________ deposits in
arterial walls and causes arteriosclerosis
d. Homozygous __________ have very high plasma cholesterol levels, sometimes in
excess of _____ mg/dl
e. _______zygotes (1 in every 500 births) have high cholesterol levels around ____
mg/dl
f. Homozygous _________ have normal cholesterol levels (<___ mg/dl)
4. Do Punnett square of incomplete dominance problem
G. ____-linked genetic disorders are usually associated with the ___ chromosome
1. Some genes on __ chromosome determine _______ development.
2. Gene on __ chromosome determines _______ development.
3. Other traits on sex chromosomes called ____-linked traits.
4. Alleles on small Y chromosome called __-linked.
5. Alleles on larger X chromosome called __-linked.
6. Male receives X-linked condition from his _________
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7.
Female must receive recessive alleles from _____ mother and father to express X-linked
condition.
8. X-linked Inheritance Disorder example: _______-Blindness.
a. Color vision ______ are found only on the ___ chromosome, no corresponding
genes on the Y chromosome.
b. XB = _________ vision; Xb = color _________
c. XBXB = homozygous female with ________ vision.
d. XBXb = __________ female with normal vision.
e. XbXb = color-_______ female.
f. XBY = _________ vision male.
g. XbY = color-______ male.
9. Do Punnett Square Color-blindness problem
H. Multiple Alleles & Codominance
1. Within a population, there may be ___ or more ________ that affect the same trait.
2. Each person still has only ____ of the alleles for the trait.
3. Example: ______ Blood Types
a. Type A has A antigen on RBC surface; alleles are ___ or ____ (A is dominant).
b. Type B has B antigen on RBC surface; alleles are ___ or ___ (B is dominant).
c. Type AB has A & B antigens on RBC surface; alleles are ____ (_____________
= both are equally expressed).
d. Type O has no antigens on RBC surface; alleles are ____ (recessive alleles).
4. Do Punnett square of how to determine blood type.
V. Genes direct the formation of proteins
A. Overview (DNA  mRNA  tRNA + A.A.  Protein)
1.
2.
_____ in the nucleus is like a cookbook containing gene “recipes” for proteins.
DNA unwinds at a _______ and the “recipe” is rewritten (______________) as
messenger RNA (mRNA).
3. ______ moves from nucleus to cytoplasm and is “clamped” onto the E. R. protein
assembly line by _________ (rRNA).
4. Transfer RNA (_____) then brings appropriate amino acid “ingredients” to mRNA
(___________) to make the protein.
B. Structure of _______
1. Mostly ________-stranded, not helical.
2. Composed of nucleotides, but has _________ sugar instead of deoxyribose.
3. Thymine of DNA is replaced by _______ in RNA, thus adenine pairs with uracil in
RNA.
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C. Three types of _____ in Protein Synthesis:
1.
2.
3.
______ - carries coded sequence of bases in 3 base _______ from DNA in nucleus to
ribosomes in cytoplasm.
______ - major component of ribosomes produced in the nucleolus; ribosomes bind
to mRNA during protein synthesis
_____ - carries an __________ specific for its 3 base anticodon to a complementary
mRNA codon.
D. The Genetic Code
1.
2.
3.
4.
5.
6.
7.
The order of ______ bases ultimately codes for the order of ____________ in
proteins.
The _________ code of four bases supplies 43=___ triplets, more than enough for the
___ amino acids.
A ______ is a “3 letter” unit of 3 nucleotides in mRNA.
All 64 mRNA codons have been determined, as to which _____ _______ will be
brought to them (see chart)
___ codons correspond to particular amino acids (usually more than one codon per
amino acid)
Three are ______ codons (UAA, UAG, UGA).
One codon (AUG) for methionine is a _______ codon to begin protein synthesis.
E. Transcription - first stage in protein synthesis: DNA is “__________” to mRNA;
occurs in the nucleus
1. A portion of DNA (______) unwinds and unzips.
2. Complementary ______ nucleotides pair with DNA nucleotides of the sense strand,
via RNA __________
3. RNA __________ pairs with DNA adenine.
4. Resulting mRNA is processed by RNA enzymes to remove _______ (nonexpressed
sequences) and leave _____ (expressed sequences).
5. Processed _____ exits nucleus through nuclear membrane pores to ____________ in
cytoplasm.
F. Translation - second stage in protein synthesis in which the sequence of mRNA
nucleotide codons is “____________” into a specific sequence of amino acids brought by
tRNA (in the cell cytoplasm)
1. Initiation - ______ binds to a ribosome on the E. R.
2. Elongation
a. ______s with anticodons complementary to mRNA codons bring specific ______
_______ one at a time in the sequence dictated by mRNA.
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b.
3.
4.
Each new amino acid forms a __________ bond with the previous amino acid to
form the polypeptide chain.
Termination - Translation ends when tRNA binds to _______ codon on mRNA;
ribosomes dissociate from mRNA.
_____ribosomes are several ribosomes that move along mRNA at one time, thus
several polypeptides are made at once.
G. Review of Gene Expression
1. _____ in the nucleus contains a triplet code; each group of 3 bases corresponds to a
2.
3.
4.
5.
specific _______ ______
During _____________, a segment (gene) of DNA serves as a template for the
formation of _______ (DNA  mRNA)
mRNA carries its sequence of _________ to ribosomes in the cytoplasm
During ___________, tRNAs with anticodons complementary to the mRNA codons
bring specific ______ _____ to the mRNA
The linear sequence of the _____ codons determines the order of amino acids in the
resulting polypeptide.