Transcript Document

KEY CONCEPT
The chromosomes on which genes are located
can affect the expression of traits.
Two copies of each autosomal gene affect
phenotype.
• Mendel studied autosomal
gene traits (these genes are
on autosomes), like hair
texture.
• The “either-or” traits that
were seen in your tutorial.
• Mendel’s rules of inheritance apply to autosomal
genetic disorders.
– A heterozygote for a recessive disorder is a carrier.
– Disorders caused by dominant alleles are uncommon, but
possible.
(dominant)
• What about genes located on sex
chromosomes? What are these traits called?
Males and females can differ in sexlinked traits.
• Genes on sex chromosomes are called sex-linked genes.
– Y chromosome genes in mammals are responsible for male
characteristics.
– X chromosome genes in mammals affect many traits.
• Male mammals have an XY genotype.
– All of a male’s sexlinked genes are
expressed.
– Males have no
second copies of
sex-linked genes.
– Because of this,
males can never be
“carriers” of sexlinked traits or
disorders.
– Ex: Colorblindness,
Hemophilia, Muscular
dystrophy
Sample Colorblind
Tests
4 Sex-Linked Traits:
1. Normal Color Vision:
A: 29, B: 45, C: --, D: 26
2. Red-Green Color-Blind:
A: 70, B: --, C: 5, D: -3. Red Color-blind:
A: 70, B: --, C: 5, D: 6
4. Green Color-Blind:
A: 70, B: --, C: 5, D: 2
Let’s take a look at…
Lynda is a healthy carrier of colorblindess
and her husband, Jim, has no family history
of colorblindness.
Lynda’s genotype:
XXd
Jim’s genotype:
XY
What is the probability of
getting:
• A colorblind daughter?
0%
• Carrier child?
25%
• A colorblind child?
25%
• Two healthy children?
¾ x ¾ = 9/16 (56%)
Jen is a healthy carrier of hemophilia and Adam has
no history in his family.
What is the probability of
getting:
• Daughter with hemophilia?
0%
• Carrier child?
25%
• Child with hemophilia?
25%
• Two healthy children?
¾ x ¾ = 9/16 (56%)
Kelly is a healthy carrier of hemophilia, but Joe
suffers from the disease.
What is the probability of
getting a:
• Healthy son?
½ son x ½ hemophilia= ¼ or
25%
• Healthy daughter?
½ girl x ½ hemophilia= ¼ or 25%
• Child with hemophilia?
50%
• Carrier child?
25%
We use PEDIGREES to trace:
• Autosomal traits
• Sex-linked traits
• Autosomal disorders or
diseases
• Sex-linked disorders or
diseases
A pedigree is a chart for tracing genes in
a family.
• Phenotypes are used to infer genotypes on a pedigree.
• Autosomal genes show different patterns on a pedigree
than sex-linked genes.
•
If the phenotype is more common in males, the gene is likely sex-linked.
Creating a Pedigree
Key
Hh
Hh
H = Healthy
h = PKU
hh
H?
H?
• 1) Manny and Rosa are married and both are healthy.
• 2) They have 3 children.
• 3) Their oldest child, Jacob, has a recessive disorder called
PKU.
• 4) Their middle child Erica and their youngest Matthew are
healthy.
• If healthy is dominant to PKU, fill in the missing genotypes.
(start with what you know)
The Next Generation
Key
H = Healthy
Hh
Hh
h = PKU
H?
hh
• 5) Erica meets Moe at college and the two become
married.
• 6) Erica and Moe have 2 daughters.
• 7) Their youngest daughter Jamie shows signs of PKU while
Amy does not.
• Fill in the genotypes of the four individuals. (start with what
you know)
Fill in the X-linked Pedigree
Sickle cell anemia (recessive) pedigree
Hint: 3 unknown
H?
Hh
hh
hh
Hh
hh
Hh
Hh
hh
Hh
Hh
H?
Key
H?
H = Healthy
h = Sickle cell anemia
Let’s try a problem:
A man and a woman marry.
The woman is a carrier of
colorblindness, an X-linked disorder.
?
They have 4 children, 3 boys and one
girl.
Two of the boys are colorblind, and
the girl is a carrier.
The carrier daughter marries a healthy
man.
a)What is the probability they will
have carrier daughters?
b)What is the probability they will
have sons that are colorblind?
a)
b)
½ daughter x ½ carrier
= 25%
½ son x ½ c.b. = 25%
Try this on your own…
A man and a woman marry. The man has DMD (a muscular dystrophy disease),
which is an X-linked disease. They have 4 children, 2 carrier daughters and 2
completely healthy boys. One of the carrier daughters marries a healthy man
and has 3 children. They have two boys with DMD, and a healthy, non carrier
daughter. What is the probability that one of the boys will have sons with
disorders if he marries a healthy, non carrier woman?
Now this…
Jack and Jill get married. As Jill falls down the hill, she cuts herself and bleeds
profusely. She goes to the doctors and realizes that she has hemophilia, an Xlinked blood disorder. They have 5 children, 3 boys and 2 girls, all of which get
tested for hemophilia. They discover that 2 boys have hemophilia and one of
the daughters is a carrier. One of the affected sons marries a healthy non
carrier woman and has twin carrier children. What is the sex of these carrier
children? Explain your answer.