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?
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.