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Romanovs and Revolution A Genetic History Mystery The Romanovs Tsar Nicholas II Alexandra Tatiana Marie Alexei Anastasia Olga The Romanov children Tsarevich Alexei Grigory Rasputin Hemophilia •Caused by a single, recessive allele. •This allele codes for a blood-clotting protein. If the protein is defective, then the blood does not clot properly. •Untreated, victims often die in childhood or teen years, rarely live to adulthood. The Windsor Pedigree This pedigree shows who had hemophilia in the Windsor family line. Why only males? And who are the carriers? The Completed Pedigree Notice only women can be carriers. Why? And here’s the real mystery: Why are there no carriers before Victoria? Sex-linkage • Sex-linked traits are carried on the sex chromosomes (X or Y). Women have two X chromosomes, while men have an X and a Y. • Most sex-linked traits that have been studied well are X-linked. Women need two copies of a recessive Xlinked trait to show the trait. Men only need one. How X-linkage works • Only women can be carriers of Xlinked traits, since they have two X chromosomes. • Men can pass an X or a Y to their children. Women only have an X. Red-Green Color Blindness - X-linked • If your vision is normal, these should read: A = 29, B = 45, C = abstract, D = 26. • If you are redgreen color blind, they might read: A = 70, B = nothing, C = 5, D = nothing. Color-blindness Inheritance If I have a brother who is red-green color blind (which I do), where did he get the color-blind gene from? Mom or Dad? What are the odds that I am a carrier? Things to Remember • When doing Punnett squares for Xlinked traits, we track not just the alleles, but the chromosomes they are carried on. • This is only for traits on the sex chromosomes, not for traits on the other(somatic) chromosomes.
