mendel studied autosomal gene traits the “either-or” traits that were seen in your tutorial....
TRANSCRIPT
• Mendel studied autosomal gene traits• The “either-or” traits that
were seen in your tutorial.• Genes found on
autosomes (1-22 for humans) = autosomal traits
• Genes found on sex chromosomes (pair 23 for humans) = sex-linked traits
KEY CONCEPT The chromosomes on which genes are located can
affect the expression of traits.
Males and females can differ in sex-linked traits.
– 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 sex-linked genes are expressed.
– Males have no second copies of sex-linked genes.
– Because of this, males can never be “carriers” of sex-linked traits or disorders.
– Ex: Colorblindness, Hemophilia, Muscular dystrophy
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
Sample Colorblind Tests
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 ofgetting:
• 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 ofgetting:
• 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?25%
• Healthy daughter?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
Let’s try a sex-linked 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) ½ daughter x ½ carrier = 25%b) ½ son x ½ c.b. = 25%