Genetics is the study of HEREDITY
(the passing down of traits)
Which is a heterozygous genotype?
A mouse is homozygous dominant for black
fur (BB). The other parent is heterozygous for
black fur with a recessive trait for brown fur (Bb).
What percentage of the offspring will be brown?
Genetics
Genetics is the study of how traits are passed
from one generation to the next.
Gregor Mendel
• Gregor Mendel was an
Austrian monk
• He is known as the
“father of genetics”
• Mendel did research
with pea plants
• Mendel used pea plants
because they
reproduced sexually and
he could easily control
this
Mendel’s Experiments
• Mendel cross pollinated plants to observe the
passed down traits
• Mendel observed seven main traits. Some of
these traits were: tall/short, yellow seeds/green
seeds, and wrinkled seed/smooth seed
• Mendel came up with 3 rules: rule of unit
factors, rule of dominance, and the law of
segregation
Rule of Unit Factors
• The rule of unit factors states that each
organism has 2 genes that control each trait
• These genes are located on chromosomes
• The different genes are called alleles
• One allele is inherited from the female parent,
and the other from the male parent
The Rule of Dominance
• The rule of dominance states that some alleles are
dominant and some are recessive
• An uppercase letter represents a dominant allele
• A lowercase letter represents a recessive allele
• A gene that has two dominant or two recessive alleles is
called homozygous (such as TT or tt)
• A gene that has one dominant and one recessive allele
is called heterozygous (such as Tt)
Punnett Squares
• Punnett squares are a short-hand version of finding
expected genotypes of a cross
• A genotype is the allele combination in an organism
• Remember that genotypes can be heterozygous (Tt) or
homozygous (TT, tt)
• Phenotypes are the physical characteristics expressed by a
certain genotype. For instance TT (genotype) = tall
plant (phenotype)
Which is a heterozygous genotype?
A mouse is homozygous dominant for black
fur (BB). The other parent is heterozygous for
black fur with a recessive trait for brown fur (Bb).
What percentage of the offspring will be brown?
Punnett Squares
Step 1: Draw a square with a t inside
Step 2: Place the parent 1 on the top of the square
and parent 2 on the left side of the square.
Step 3: Bring the Parent 1 alleles down into both
boxes and bring Parent 2 alleles across into both
boxes.
Step 4: Write out your genotype (letters) and your
phenotypes (what you see) in a percentage.
* The whole square should equal 100 percent
Generations: P, F1, F2
• P stands for “parental”. These are the two
original organisms mating. P groups produce F1
group
• F1 groups are the offspring of the P group.
When two organisms from F1 reproduce, they
produce F2 group
• F2 groups are the offspring of the F1 group.
A man who has a genotype, Aa, marries a woman
with the genotype, AA. What is the probability
that their offspring will have the genotype, Aa?
•
A
25%
•
B
33%
•
C
50%
•
D 75%
Which is a heterozygous genotype?
A.
B
B.
Brown and white fur
C.
BB
D.
Bb
A mouse is homozygous dominant for black fur (BB). The other
parent is heterozygous for black fur with a recessive trait for brown
fur (Bb). What percentage of the offspring will be brown?
A.
100%
B.
50%
C.
25%
D.
0%
Exceptions to Mendel’s Work
• Sometimes, traits are not simply dominant or
recessive
• Traits can also have incomplete dominance,
codominance, multiple alleles, or be polygenic traits
Incomplete Dominance
• Incomplete dominance happens when neither
allele is completely dominant over the other
• This results in a blending of traits
• For example: a red snap-dragon flower crossed
with a white snap-dragon flower will result in
pink snap-dragon flower offspring
Codominance
• Codominance occurs when both alleles
contribute to the phenotype
• This results in an organism that expresses both
alleles equally
• For example: a white chicken mated with a black
chicken will produce black and white striped
chickens
Multiple Alleles
• Many genes have more than two possible alleles
• An example would be human blood type
• There are 4 main types of human blood: A, B,
AB, and O
• Blood types A and B can be coded for in 2
different ways
Polygenic Traits
• Polygenic traits are traits controlled by two or
more genes
• Polygenic traits show a wide variety of
phenotypes
• Examples would be height, skin color, and
finger prints
Blood Typing
• Before a human can get a blood transfusion, their blood
type must be identified
• There are 3 alleles for the blood gene:
IA, IB, and i
And four possible blood types:
A, B, AB or O
• The alleles IA and IB are codominant and produce blood type
AB
• The allele i is recessive and produces blood type O
Sex-Linked Traits
• Genes that are found on the sex chromosomes (X, Y) are
called sex-linked traits
• The X chromosome is larger and has more genes than the
smaller Y chromosome
• Sex-linked traits are more often found in males
• This is because males have only one X chromosome, so if
a gene is located on the X chromosome it will always be
expressed (even if it’s recessive)
• In order for a recessive allele to be expressed in a female,
the female would have to have the recessive allele in both X
chromosomes
Colorblindness
• Colorblindness is a sex-linked disorder
• In humans, 3 genes associated with color are
located on the X chromosome
• In a male, a defect in any one of these will result
in colorblindness
• Color blindness is found in 1 in 10 males, and 1
in 100 females
Hemophilia
• Hemophilia is a sex-linked disorder
• Two genes carried on the X chromosome help
control blood clotting
• A defect in these genes will result in a missing
protein used in blood clotting
• People with hemophilia can bleed to death from a
small cut, or have severe internal bleeding from a
bump or bruise
• Hemophilia can be treated by injections of the
missing proteins
• What type of inheritance controls blood types in
humans?
A
incomplete dominance
B
polygenic inheritance
C
multiple alleles
D recessive genes
43. This diagram shows a pedigree for a
recessive disorder. What is the genotype of
individual 6?
What are Pedigrees?
 A “family tree” record
that shows how a trait
is inherited over
several generations is
called a Pedigree.
 Pedigrees are very
helpful because they
allow people to trace
genetic disorders over
several generations.
What do we need to know? The SYMBOLS
1. A
represents a male and a
represents a female.
2. A shaded
unshaded
represents a male with a trait but an
represents a male without a trait.
3. A shaded
unshaded
represents a female with a trait but an
represents a female without a trait.
4. A marriage is symbolized by a horizontal line connecting a
male and a female (or can mean they had a child).
5. Offspring are
symbolized by
brackets
below the
parents.
Example: These two parents
have two daughters. One of the
daughters has the trait, and the
other daughter does not.
Pedigree #1
 Mr. Heilemann is a biology teacher who
wants to make a pedigree tracing a
simple trait throughout three generations
of his family. He decided to trace the
inheritance of the “hitchhiker thumb” trait.
Blackened symbols represent people
with hitchhikers thumb.
Hitchhiker’s thumb is a recessive allele
Fred
Maria
Tami
Don
Generations
P
1
F
Pam
Joe
Jade
Matt
Ric
Barb
Todd
Ellen
1
F
Anya
Mr.H
Chris
Nina
2
All the people with hitchhiker’s thumb have to be
nn because hitchhikers thumb is a recessive trait
Fred
Maria
Tami
Don
P
nn
1
nn nn
Pam
Joe
Jade
Matt
F
Ric
Barb
nn
nn
Anya
Mr.H
Todd
Ellen
1
F
Chris
Nina
2
What would Ric and Barb’s genotype need to be to
have a child with Hitchhiker’s thumb?
Fred
Maria
Tami
Don
P
nn
1
nn nn
Pam
Joe
Jade
Matt
F
Ric
Barb
nn
nn
Anya
Mr.H
Todd
Ellen
1
F
Chris
Nina
2
They both have to be Nn because neither one has
hitchhiker’s thumb, but they need to pass the allele
to their son.
Fred
Maria
Tami
Don
P
nn
Nn
nn nn Nn
Pam
Joe
Jade
Matt
1
Ric
Barb
F
Todd
Ellen
1
nn
nn
N?
N?
F
Anya
Mr.H
Chris
Nina
2
Nn
Joe
Fred
Maria
Don
Tami
Nn
Nn
nn
N?
Nn
nn nn Nn
Pam
Matt
Jade
Nn
Ric
Barb
P
1
Nn Nn
Todd
Ellen
F
1
nn
nn
N?
N?
F
Anya
Mr.H
Chris
Nina
2
MORE PRACTICE!!
 Online Activity
Why Pedigrees are Important
• Pedigrees show the passing down of traits
genetically
• A genetic counselor can study a pedigree and
determine whether or not a certain trait will be
passed down
141. The inheritance of colorblindness is an x-linked,
recessive trait. If a woman who carries the trait and a
man without the trait have children, what would be
the most likely result?
A All their sons would be color-blind, and half of their
daughters would be carriers.
B Half of their sons would be color-blind, and half of
their daughters would be carriers.
C Half of their sons would be color-blind, and all of
their daughters would be carriers.
Which of the following is not a
polygenic trait?
a. Eye color
b. Hair color
c. Skin color
d. Height
Show the cross for two heterozygous
guinea pigs.
a. What percentage of the offspring will
have short hair? ________
b. What percentage of the offspring will
have long hair? _______
1. Which process produces the most variation within a species?
A. asexual reproduction
B. sexual reproduction
C. mitosis
D. cloning
2. During which phase of the cell cycle is the cell growing and
preparing for cellular division?
A. cytokinesis
B. anaphase
C.
prophase
D. Interphase
3. Why is the process of meiosis important to sexual
reproduction?
A. It provides genetic variation in offspring.
B. It doubles the number of chromosomes in offspring.
C. It reduces the number of alleles from parent to offspring.
D.
It produces a hybrid of all genetic traits in offspring.
Non-disjunction of chromosomes
• Non-disjuction: Failure of
chromosomes to separate
during meiosis I or II
• Both chromosomes stay
together and BOTH go to one
gamete. The other gamete gets
NOTHING.
• If non-disjunction occurs, one
gamete get both chromosomes,
the other gamete gets nothing.
Autosomal Disorders
• Recall that trisomy means having 3 copies of
chromosomes, instead of 2
• The most common form of trisomy occurs on
the 21st chromosome in humans and is called
Down syndrome
• People with Down syndrome will have mild to
severe mental retardation
Karyotype
• A karyotype is a picture of chromosomes
arranged in pairs
• In humans, we have 46 chromosomes, or 23 pairs
of chromosomes
• 44 chromosomes are known as autosomes (body
cells)
• 2 chromosomes are known as sex chromosomes
• In humans, a male is XY and a female is XX
Turner’s and Klinefelter’s Syndrome
• In females, nondisjunction can lead to Turner’s
syndrome. This female will only inherit one X
chromosome, instead of 2
• In males, nondisjunction can lead to
Klinefelter’s syndrome. The male will inherit
an extra X chromosome, and will be XXY
Down Syndrome- Trisomy 21
Question of the day
. This diagram shows a pedigree for a
recessive disorder. What is the genotype of
individual 6?
• A. XHXH
• B. XHXh
• C. XHY
• D. XhY
Human Genetic Disorders
• Most genetic disorders have no cure, yet.
• Scientists are working on the technology that
will repair/fix the “bad” genes in an organism
using GENE THERAPY.
• Genetic Counseling: Helps parents at risk of
having children with a genetic disorder. Helps
them understand the options and the needs that
the child would have
Genetic Disorders/Mutations
1. Cystic Fibrosis
2. Sickle Cell Anemia
3. Hemophilia
4. Phenylketonuria
5. Tay-Sachs disease
6. Huntington’s disease
Genetic Disorders/Non-disjunction
1. Down syndrome (Trisomy 21)
2. Klinefelter syndrome (trisomy)
3. Turner symdrome (monosomy)
1. CYSTIC FIBROSIS
Chase:
Before and after Lung
Transplant
• Caused by a recessive gene on chromosome #7.
Fatal. With the current technology people with CF
can live into their late 20’s
• Cystic fibrosis is caused by a deletion of one amino
acid, which causes the protein to not form correctly
• People with just one copy of the allele are unaffected
• Body secretions are abnormal—mucus is thick and
sticky.
• Mucus fills lungs  difficult breathing. Same
thing with digestive and reproductive systems.
• 1 out of 20 caucasian people carry the gene. CF
occurs in 1 in 1600 births. We can test for carriers
2. Sickle Cell Anemia
Caused by codominant alleles; chromosome 11
NN =normal RBC (red blood cells)
NS = both cells
SS = sickle RBC
- RBCs are sickle shaped, carry less oxygen and
clog blood vessels. Tissues and organs don’t get
oxygen and are damaged. People with sickle cell
anemia tend to be pale, tire easily, short of breath.
- More common in African populations. Affects about
1 in 400-600 African americans
- A test called hemoglobin electrophoresis can identify
people that carry the sickle cell trait.
- Sickle cell can cause physical weakness and damage to
the brain, heart and spleen
NN=normal RBC
NS=both cells
SS=sickle RBC
3. Hemophilia
• Caused by recessive allele on X
chromosome = Sex-linked
• “Bleeders” disease: individuals don’t have
the blood clotting protein.
• Need frequent transfusions or clotting factor
produced by transgenic bacteria.
• Clotting factor needs to be used under medical
supervision (too much and the bloods thickens
excessively)
4. Phenylketonuria -- PKU
Caused by a recessive gene; chromosome 12.
• People are missing and enzyme that converts the
amino acid phenylalanine into tyrosine. The build
up of phenylalanine affects the nervous system and
results in mental retardation.
• Children look normal at birth but become mentally
retarded by age 1.
• A test can be done at birth. If positive, the child is
put on a phenylalanine free diet.
• Phenylketonurics warning in foods!
• Occurs in 1 out of 14000 births.
Phenylketonuria testing at birth
Tay-Sachs Disease
Symptoms:
• Seizures
• Noticeable behavior changes, such as the infant stops
smiling, crawling or rolling over and loses the ability
to grasp or reach out
• Increased startle reaction
• Decreased eye contact
• Listlessness
• Increasing irritability
• Slow body growth
with increasing head size
• Delayed mental and
social skills
• Caused by a dominant gene
• Symptoms appear during middle age (3040’s) after most individuals have
reproduced.
• Nerve cells die earlier than usual and cause
mental deterioration and uncontrollable
movements.
• Fatal.
Klinefelter’s Syndrome XXY
Turner’s Syndrome - X
Down Syndrome- Trisomy 21
Caused by NONDISJUCTION- an extra
chromosome on the 21st pair
• Head and facial features often
associated with Down
Syndrome:
• Flattened back of head.
• Attractive Almond-shaped eyes,
with one eye lid a little droopy.
• Slightly flattened bridge across
nose.
• Smallish ears, positioned
slightly lower on the head, with
a small fold at the top of the ear.
• Smallish mouth.
• Slightly protruding tongue.
• Hand features often associated
with Down Syndrome:
• Horizontal crease in palm of
hand .
• Slightly shortened fingers.
• The little finger curves inward .
• Slightly shortened toes.
Caused by NONDISJUCTION- an extra
chromosome on the 21st pair
• Head and facial features often
associated with Down
Syndrome:
• Flattened back of head.
• Attractive Almond-shaped eyes,
with one eye lid a little droopy.
• Slightly flattened bridge across
nose.
• Smallish ears, positioned
slightly lower on the head, with
a small fold at the top of the ear.
• Smallish mouth.
• Slightly protruding tongue.
• Hand features often associated
with Down Syndrome:
• Horizontal crease in palm of
hand .
• Slightly shortened fingers.
• The little finger curves inward .
• Slightly shortened toes.
Klinefelter’s Syndrome XXY
Turner’s Syndrome - X
Other Important Genetic Disorders
•
•
•
•
Cystic fibrosis
Sickle cell anemia
Huntington’s disease
In both cystic fibrosis and sickle cell anemia, a
small change in the DNA of a single gene affects
the structure of a protein, causing serious
genetic disorders
Sickle Cell Anemia
• Sickle cell anemia is most commonly found in African
Americans
• Sickle cell is characterized by a bent and twisted shaped blood
cell (sickle shaped)
• Sickle cell can cause physical weakness and damage to the brain,
heart and spleen
• Those who are heterozygous for sickle cell (carry a “sickle cell
trait”) produce both normal red blood cells and sickle shaped
blood cells. This is an example of codominance
• People who have a sickle cell trait are resistant to the disease
malaria
Huntington’s Disease
• Huntington’s disease is a nervous system disorder
characterized by a progressive loss of muscle control
and mental function until death occurs
• People usually don’t show symptoms until they are
between 30 and 50 years old
• Huntington’s disease is caused by a rare dominant allele
• Therefore, everyone who has the allele for
Huntington’s disease will develop it
Important Diseases Overview
• Colorblindness: sex-linked trait (X chromosome)
• Hemophilia: sex-linked trait (X chromosome)
• Down syndrome: (trisomy) 3 chromosomes
found on the 21st pair
• Cystic fibrosis: recessive allele
• Sickle cell anemia: resistant to malaria, can be
expressed as codominance
• Huntington’s disease: dominant allele
In fruit flies, eye color is a sex-linked trait. Red eyes (XE) are
dominant to white eyes (Xe). If a white eyed female mates
with a red eyed male, what percentage of the male offspring
will have white eyes?
a. 0% c. 75%
b. 25%
d. 100%
When considering sickle cell anemia, the heterozygous
condition (Aa) results in resistance to malaria. If two
heterozygous parents have a child, what are the chances of
that child being resistant to malaria but not having sickle cell
anemia?
a. 25%
c. 50%
b. 75%
d. 100%
http://www.hom
eescapade.com
/what-ishuntingtonsdisease
Huntington’s Disease
Other Influences on Genes
• Things other than
inheritance can affect the
way a person looks or acts
• We call these “environmental
factors”
• Environmental factors can
be air quality, soil quality,
water availability, diet or
exercise
• Cause and effects
relationships