Question

1) In humans,hemophilia (a disease that affects the blood clotting process) is x-linked. A young man,John, has hemophilia but his parents do not.

a)What are the genotypes of John and his parents?

b)If John’s   parents have     additional children,   what are   the probabilities that John’s   future   sisters and   brothers   will not   have hemophilia?

c) Of   John’s   4 grandparents, only his   father’s father   has hemophilia. What are the possible genotypes of the 4 grandparents? From   which   of the grandparents could John have inherited hemophilia?             

Answer 1

Xh=hemophilia allele

X=normal allele

In an X linked recessive inheritance, two copies of a disease allele on the X chromosome are required for an individual with two X chromosomes (a female) to be affected with an X-linked recessive trait.

Genotypes of John and his parents

Father= XY

Mother= XhX

If John’s parents have additional children,what are the probabilities that John’s future sisters and brothers will not have hemophilia?

XY x XhX

XXh, XX, XhY, XY

None of John’s sister's would suffer from hemophilia, whereas 50% of John’s brothers would suffer from it.

Of John’s   4 grandparents,   only his father’s father   has hemophilia.       What are the possible genotypes of the 4 grandparents? From    which of the grandparents    could    John have inherited hemophilia?

John's paternal grandfather’s genotype= XhY

John's paternal grandmother's genotype= XhX

John's maternal grandfather’s genotype= XY

John's maternal grandmother’s genotype= XhX