1. Sex-Linked Traits

2. Sex-Linked Traits
Most sex-linked traits are found on the X chromosome NOT on the Y chromosome X Y

3. Sex-Linked Recessive Traits
Females XX – carry 2 alleles for a sex-linked trait
Males XY – carry only 1 allele for a sex-linked trait, so it is easier for males to get sex-linked disorders

4. Males receive sex-linked traits from their mother because their mother gives them the X chromosome; the father gives them the Y chromosome

5. Inheritance of Sex-Linked Traits
X-linked Disorders - occur mainly in males because they only have one X chromosome; the mother donates the sex-linked recessive allele
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 to their offspring

6. 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

7. Colorblindness is an X-linked recessive disorder
Colorblindness is an X-linked recessive disorder. Show a cross between a colorblind female 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%

8. 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

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

10. 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

11. Inheritance of Sex-Linked Traits
Y-linked Disorders – the allele is on the Y chromosome, therefore only males have the disorder because they only have Y chromosomes; there are no carriers for y-linked disorders.
The Y chromosome is very small and contains few genes. Hence, there are very-few Y-linked diseases. X Y

12. 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
ever have
hairy ears?
X Yh
50% X XX
XYh XX
XYh
No, they have no
Y chromosome