SexLinked Traits SexLinked Traits o Most sexlinked traits

Sex-Linked Traits

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

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 o o X-linked Disorders - occur mainly in males because they only have one X chromosome; the mother donates the sexlinked 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

X-Linked Traits o Colorblindness is an X-linked recessive disorder. ex: X X - female, normal Xc. X - female, normal (carrier for colorblindness) Xc. Xc - female, colorblind X Y - male, normal Xc. Y - male, colorblind

Colorblindness is an X-linked recessive disorder. Show a cross between a colorblind female and a male who is not. X c XX Y c XY X c Xc X Xc Y How many are colorblind? 50% How many are carriers? 50%

X-Linked Traits o Hemophilia is an X-linked recessive disorder. ex: X X - female, normal Xh. X - female, normal (carrier for hemophilia) Xh. Xh - female, hemophilia X Y - male, normal Xh. Y - male, hemophilia

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

Hemophilia is x-linked recessive. Suppose that a man with hemophilia marries a woman who does not have the disorder. n What are the chances that their offspring will have hemophilia? h 0% X Y X XXh XY

Inheritance of Sex-Linked Traits o 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 ylinked disorders. o The Y chromosome is very small and contains few genes. Hence, there are very-few Y-linked diseases. X Y

Hairy ears is a Y-linked trait. Suppose that a man with hairy ears marries a woman with normal ears. n What are the chances that their offspring will have hairy ears? h 50% n Can females ever have hairy ears? X Y X XX XYh No, they have no Y chromosome