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.