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| Modern Genetic Analysis Chapter 4. The Inheritance of Genes Human Pedigree Analysis Figure 4-25. The inheritance of the X-linked recessive condition hemophilia in the royal families of Europe. A recessive allele causing hemophilia (failure of blood clotting) arose in the reproductive cells of Queen Victoria, or one of her parents, through mutation. This hemophilia allele spread into other royal families by intermarriage. (a) This partial pedigree shows affected males and carrier females (heterozygotes). Most spouses marrying into the families have been omitted from the pedigree for simplicity. Can you deduce the likelihood of the present British royal family's harboring the recessive allele? (b) A painting showing Queen Victoria surrounded by her numer-ous descendants. [(a) Modified from C. Stern, Principles of Human Genetics, 3d ed. Copyright © 1973 by W. H. Freeman and Company. (b) Royal Collection, St. James's Palace. Copyright © Her Majesty Queen Elizabeth II.]

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