1. Sex-Linked Traits

2. Inheritance of Sex-Linked Traits
X-linked Disorders – the allele is on the X chromosome, it occurs mainly in males because the mother usually donates the recessive allele and since males only have one X chromosome they get the disorder automatically
Carriers – are individuals who are heterozygous for an inherited disorder but do not show symptoms of the disorder; they can pass the allele for the disorder on to their offspring; seen only in x-linked disorders
Y-linked Disorders – the allele is on the Y chromosome, therefore males have the disorder because they only have Y chromosomes; there are no carriers for y-linked disorders.

3. X-Linked Traits Colorblindness is an X-linked recessive disorder.
ex: X X - female, normal
XcX - female, normal
(carrier for colorblindness)
XcXc female, colorblind
X Y - male, normal
XcY - male, colorblind

4. Colorblindness is an X-linked recessive disorder
Colorblindness is an X-linked recessive disorder. Show a cross between a female who is colorblind and a male who is not. X c X c
How many are colorblind?
How many are carriers?
XcX
XcX
50% X Y
XcY
XcY
50%

5. X-Linked Traits Hemophilia is an X-linked recessive disorder.
ex: X X - female, normal
XhX - female, normal
(carrier for hemophilia)
XhXh female, hemophilia
X Y - male, normal
XhY - male, hemophilia

6. Show a cross between a female who is a carrier of hemophilia with a male who has the disorder.
How many have hemophilia?
How are carriers of hemophilia?
How many are normal? h X X h X
50%
XhXh
XhX Y
XhY XY
25%
25%

7. Hemophilia is x-linked recessive.
Suppose that a man with hemophilia marries a woman who does not have the disorder. 
What are the chances that their offspring will have hemophilia? 
Xh Y 0% X
XXh XY
XXh XY

8. Hairy ears is a Y-linked trait.
Suppose that a man with hairy ears marries a woman with normal ears. 
What are the chances that their offspring will have hairy ears? 
Can females
have hairy
ears?
X Yh
50% X XX
XYh XX
XYh No

9. Blood type inheritance is somewhat complicated, with three forms of the gene and 4 possible phenotypes. (A, B, AB, O) AB
AA - Homozygous A
AO - Heterozygous A
BB - Homozygous B
BO - Heterozygous B OO

10. A B B O AB BB AO BO Blood Types: 25% 50% 25%
Suppose a woman with blood type AB marries a man who is heterozygous B. What are the chances that their children will have blood type A?
blood type B?
blood type AB?
25%
A B
50%
25% B O AB BB AO BO