1. Sex-Linked Punnett Square Notes

2. What is this person’s sex?
female

3. Sex-Linked Traits
Those traits whose genes are found on the X chromosome but NOT on the Y chromosome
Females = XX –carry 2 alleles for a sex-linked trait
Males = XY – only carry 1 allele for a sex-linked trait, so it is easier for them to get sex-linked diseases

4. Sex-Linked Traits, cont.
Males receive sex-linked traits from their mother because their mother gives them the X chromosome and their father gives them the Y chromosome

5. Examples of Sex-Linked Traits
H = Normal blood clotting
h = Hemophilia
Normal male:
Male with Hemophilia:
Normal female (not a carrier for hemophilia – homozygous):
Normal female (carrier for hemophilia – heterozygous):
Female with Hemophilia:
XHY
XhY
XHXH
XHXh
XhXh

6. Sample Problems

7. 1. XHXh x XHY Chances of: a. hemophiliac child? b. hemophiliac son?
c. hemophiliac daughter?
d. daughter who is carrier?
¼ or 25%
XH Xh XH Y
XHXh
XHXH
½ or 50%
0/2 or 0%
XHY
XhY
½ or 50%

8. 2. A woman who is a carrier for hemophilia marries a hemophiliac man.
XHXh x XhY
Chances of:
a. hemophiliac child?
b. hemophiliac son?
c. hemophiliac daughter?
XH Xh
2/4 or 50% Xh Y
XhXh
XHXh
½ or 50%
XHY
XhY
½ or 50%

9. 3. A normal man marries a Homozygous normal woman.
XHXH x XHY
Chances of:
a. Will any of their kids be hemophiliacs?
XH XH XH Y
XHXH
XHXH
0/4 or 0%
XHY
XHY

10. Her dad - XhY XHX? XhY XHXh and XhY
A normal woman (whose father is a hemophiliac) marries a hemophiliac man.
What are their genotypes?
Her dad - XhY
XHX?
XhY
XHXh and XhY