SexLinked Punnett Square Notes What is this persons

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: XHY ¡ Male with Hemophilia: Xh. Y ¡ Normal female (not a carrier for hemophilia – homozygous): XHXH ¡ Normal female (carrier for hemophilia – heterozygous): XHXh h h ¡ Female with Hemophilia: X X ¡

Sample Problems

1. H h X X x Chances of: ¡ a. hemophiliac child? ¼ or 25% ¡ b. hemophiliac son? ½ or 50% XH ¡ c. hemophiliac daughter? 0/2 or 0% ¡ d. daughter Y who is carrier? ½ or 50% H X Y ¡ XH Xh X HX H X HX h X HY X h. Y

2. A woman who is a carrier for hemophilia marries a hemophiliac man. Chances of: ¡ a. hemophiliac child? 2/4 or 50% ¡ b. hemophiliac Xh son? ½ or 50% ¡ c. hemophiliac daughter? Y ½ or 50% ¡ X HX h x X h. Y XH Xh X HX h X h X HY X h. Y

3. A normal man marries a Homozygous normal woman. Chances of: ¡ a. Will any of their kids be hemophiliacs? X HX H x X HY ¡ 0/4 or 0% XH XH Y XH X HX H X HY

A normal woman (whose father is a hemophiliac) marries a hemophiliac man. ¡ What are their genotypes? Her dad - Xh. Y X HX ? X h. Y XHXh and Xh. Y