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. A genetic pedigree is shown. Irene is a carrier. Her husband is not a carrier. Her children Waldemar and Henry have hemophilia. What is the best evidence to prove that Irene was heterozygous for hemophilia?