Question

A child is born with hemophilia (inherited as an X-linked recessive) and Klinefelter's syndrome to parents who both have normal blood clotting. In which parent (mother or father) and during which round of meiosis (I or II) did the nondisjunction event occur

Answer 1

Answer:

mother  

Explanation:

Hemophilia is a sex-linked recessive disorder caused by a mutation in one of the genes responsible for encoding the clotting factor proteins (factor VIII or factor IX), which are located on the X chromosome. Moreover, the Klinefelter syndrome is caused by men having an additional X chromosome. In this case, the nondisjunction occurred from the mother because her gamete included an extra X, it is for that reason that all genes localized on the X chromosome, including the defective gene involved in hemophilia, can cause all of her sons to be affected by the disease in some generation. Thus, sister chromatids did not separate during meiosis (Anaphase II) and caused two copies of the defective allele for the hemophilia trait.