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.

This disease would be more common in the males than in the females, all female offspring of an affected male with a   normal female  would be carriers, there would be a 50% chance of a carrier woman to give birth to an affected male and all males born to an affected female would be affected even if the disease is recessive since males only have one copy of the x chromosome.