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. What genetic traits were possible for the four sisters?
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 hemophilia is an X-linked recessive trait, the only way for a female to have the disease is if she inherits the allele from both parents. Since Nicholas II was normal (did not carry the allele), Alexis must have inherited the allele from his mother, Alexandra. Therefore, each sister had a 50% chance of inheriting the allele from their mother, making them carriers of the hemophilia allele. Hemophilia would only manifest in females if they inherited the allele from both their mother and father, which is highly unlikely. Therefore, at least one of the four sisters was a carrier of the allele, but none of them had hemophilia.

Hemophilia Is a Genetic Disease That Has Plagued the Royal