Sex-Linked Punnett Square Notes

What is this person’s sex? female

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

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

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

Sample Problems

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%

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%

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

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