IGA 8/e Chapter 2

Chapter Two 29Generation IV: a/aGenotypes of pedigree 2:Generation I: A/a, a/a, A/a, a/aGeneration II: a/a, a/a, A/a, A/a, a/a, a/a, A/a, A/a, a/aGeneration III: a/a, a/a, a/a, a/a, a/a, A/–, A/–, A/–, A/a, a/aGeneration IV: a/a, a/a, a/aGenotypes of pedigree 3:Generation I: A/–, a/aGeneration II: A/a, a/a, a/a, A/aGeneration III: a/a, A/a, a/a, a/a, A/a, a/aGeneration IV: a/a, A/a, A/a, A/a, a/a, a/aGenotypes of pedigree 4:Generation I: a/a, A/–, A/a, A/aGeneration II: A/a, A/a, A/a, a/a, A/–, a/a, A/–, A/–, A/–, A/–, A/–Generation III: A/a, a/a, A/a, A/a, a/a, A/a53. Tay-Sachs disease (infantile amaurotic idiocy) is a rare human disease in whichtoxic substances accumulate in nerve cells. The recessive allele responsible forthe disease is inherited in a simple Mendelian manner. For unknown reasons,the allele is more common in populations of Ashkenazi Jews of eastern Europe.A woman is planning to marry her first cousin, but the couple discovers thattheir shared grandfather’s sister died in infancy of Tay-Sachs disease.a. Draw the relevant parts of the pedigree, and show all the genotypes ascompletely as possible.b. What is the probability that the cousins’ first child will have Tay-Sachsdisease, assuming that all people who marry into the family are homozygousnormal?Answer:a. The pedigree isT/tT/tT/–t/tT/–T/–T/–?T/–