Hemophilia is a genetic disease that has plagued the royal houses of Europe. The disease allele is recessive and X-linked. Queen Victoria was a carrier, and her granddaughter Alexandra married Nicholas II, the last czar of imperial Russia. Alexandra was a carrier for hemophilia; Nicholas was normal. Their son, Alexis, was afflicted with the disease. Alexis and his four sisters were killed in 1917. It's most likely that
A) none of the four sisters carried the hemophilia allele.
B) at least one of the sisters was a carrier of the allele.
C) all four sisters were carriers of the hemophilia allele.
D) at least one of the sisters had hemophilia like Alexis.

Question

Quizplus · Accepted Answer

Since Queen Victoria passed on the hemophilia allele to her daughter Alexandra, it is possible that Alexandra could have passed it on to her daughters. Since the disease allele is recessive and X-linked, only females can be carriers and males are the ones who show the disease. Therefore, it is possible that at least one of the sisters was a carrier of the allele. The fact that all four sisters were killed in 1917 does not provide any information about their carrier status. It is extremely unlikely that any of the sisters had hemophilia like Alexis, since they would have inherited the disease allele from both of their parents, Nicholas and Alexandra, which was not the case.

Hemophilia Is a Genetic Disease That Has Plagued the Royal