Question

what is the best evidence to prove that irene was heterozygous for hemophilia? elizabeth is not a carrier for the trait. tatiana carried the recessive allele. her brother has hemophilia and her sister is a carrier. two of her sons have hemophilia and one does not.

Explanation:

To determine if Irene is heterozygous for hemophilia (an X - linked recessive disorder), we analyze the inheritance pattern. Hemophilia is X - linked recessive, so for a female to be heterozygous (a carrier), she has one dominant and one recessive allele. If two of her sons have hemophilia (which requires them to inherit the recessive allele from their mother) and one does not (he inherited the dominant allele from her), this shows she has both alleles (heterozygous).

• Option 1: Elizabeth not being a carrier doesn't relate to Irene's genotype.
• Option 2: Tatiana's allele status doesn't directly prove Irene's heterozygosity.
• Option 3: Her brother having hemophilia and sister being a carrier doesn't directly show Irene's heterozygosity as strongly as her own offspring's genotypes.
• Option 4: Since hemophilia is X - linked recessive, sons inherit their X chromosome from their mother. If two sons have hemophilia (got the recessive X allele) and one does not (got the dominant X allele), it means Irene has both the dominant and recessive alleles (heterozygous).

Answer:

D. Two of her sons have hemophilia and one does not.