Question

Pedigrees are used to help 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.
What is the best evidence to prove that Irene was heterozygous for hemophilia?

Alice has the recessive allele.
Alexandra has the recessive allele.
Frederick has the recessive allele.
Waldemar has the recessive allele.

Answer 1

Me and my friend say its Alice's fault, she is a carrier and she passes on the gene for the disease, also it helps that she is the mother.

Answer 2

Answer : Alice has the recessive allele.

In the pedigree it is shown that Alice passes the gene to Irene. Which is also a haemophiliac. Irene is a female and hemophilia can determined by recessive allele on the X chromosome. So if only one of the allele is recessive for haemophilia in the allelic pair than the condition will be heterozygous as only one allele is responsible to cause haemophilia in females. This is why Irene is heterozygous for haemophilia.