Pedigrees are used to geneticists understand how traits are inherited between generations. the romanovs, a russian royal family, had a history of hemophilia, a sex-linked disorder that is determined by a recessive allele on the x chromosome.

The question is the following :
What is the best evidence to prove that Irene was heterozygous for hemophilia?
A) Alice carried the recessive allele.
B) Alexandra carried the recessive allele.
C) Frederick carried the recessive allele.
D) Waldemar carried the recessive allele.

The correct answer is A

In the pedigree, marked with blue are the carriers of the X recessive allele ( they have one X that has the mutation and the other that doesn't).
Alice was Irene's' mother, and since both Alice and iIrene have the allele, it is safe to conclude that Irene inherited the recessive allele from Alice.

Ithink the answer is d.