Question

4. Using the pedigree illustrating the inheritance of hemophilia among members of Europe's monarchy, answer the following questions. Hemophilia is a sex-linked recessive disorder. Normal daughter XX Camer daughter EdwTO Duke of Kent Victoria Prince of Sam Coburg Normalson Son with hemophilia Queen Victoria of England (no affected descendants Emperor Free of Germany Duke of Albany King Edward VII of England Beatrice Victoria Modern English royal family Alice Alix (Alexandra Tsar Nicholas ll of Russia Irene Prince Henry of Prussia King Alonso xil of Spain Victoria Rupert German Royal Family Olga Marie Alexis Tatiana Anastasia Russian Royal Family Alfonso Gonzalo Spanish royal family Key Noncarrier female Carrier (heterozygous female) Possible carrier female Hayden-McNeil. ULC Normal male Affected male a. Who gave Duke Leopold of Albany his defective X chromosome (containing the hemophilia allele)? b. In generation three, explain why Alice is only a carrier for hemophilia. c. Do you trust the pedigree when it claims that all of the daughters of Tsar Nicholas and Empress Alexandra are carriers of hemophilia? Defend your answer.

Answer 1

a. Queen Victoria passed on defective X-chromosome with the hemophilia allele to Duke Leopold of Albany.

This is because fathers always pass on their Y chromosomes to sons. So -linked defective allele will come from mother.

b.Alice can be a carrier because she received a normal allele from her father. Mother passes on only a One X chromosome and father passes on another X-chromosme.

c. Empress Alexandra is a carrier. Which means she has one X-chromosome with the defective allele. Another chromosome is normal So , 50% of her gametes will be normal and 50% will be with defective X-chromosome. So any of the gametes can fertilize with the normal male gametes to make the females carrier or normal. It is all a chance which gamete fertilizes with what gamete of the female. So there is a possibility that all female can be carriers if defective female gametes fertilize. Similarly there will be a possibility that all females may be normal if all the other 50% of the Alexandra gametes fertilize with the normal male gametes.

Alexandra is a carrier because her mother Alice is a carrier. She has got the defective X-chromosome from her mother.