Sex-Linked Traits

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

Examples of Sex-linked Traits: Colorblindness Baldness Hemophilia Duchenne Muscular Dystrophy (fatal)

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

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

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

Example of a Sex-Linked Recessive Trait H = Normal blood clotting h = Hemophilia XHY Normal Male: Male with Hemophilia: Normal Female: Normal Female (carrier): Female with Hemophilia: XhY XHXH XHXh XhXh

Sample Problems

c. hemophiliac daughter? d. daughter who is carrier? ¼ or 25% 1. A woman who is a carrier for hemophilia marries a man with normal blood clotting. 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% XHY XhY 0% ½ or 50%

2. A woman who has normal vision but is a carrier marries a man who is colorblind. Chances of: a. colorblind child? b. colorblind son? c. colorblind daughter? XC Xc 2/4 or 50% Xc Y XCXc XcXc ½ or 50% XCY XcY 1/2 or 50%

What percent will be carriers of the trait? NO Xb Y XBXb XBXb 3. A bald man marries a woman who does not carry the trait for baldness. a. Will any of their kids be bald? What percent will be carriers of the trait? XB XB NO Xb Y XBXb XBXb XBY XBY 2/4 or 50%