Sex-Linked Traits

Sex-Linked Traits 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 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

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

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

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

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

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

Inheritance of Sex-Linked Traits 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 y-linked disorders. 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.  What are the chances that their offspring will have hairy ears?  Can females ever have hairy ears? X Yh 50% X XX XYh XX XYh No, they have no Y chromosome