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1. How might pedigrees for an autosomal recessive and an autosomal dominant trait differ? 2. Mel and Barbara are healthy, but they know from a blood test that they are each carriers of Tay-Sachs disease. If their first three children are healthy, what is the probability that their fourth child will inherit the disease? 3. Calculate the genotypic and phenotypic ratios for the following crosses in peas for height, determined by the T gene: 4. This unusual pedigree depicts the Ptolemy dynasty, which began in 323 B.C. and ended with Cleopatra in 30 B.C. What is unusual about the pedigree? (refer to art in the text) 5. Which genetic principle does each of the following examples illustrate? 6. In cats with the Manx trait, the M allele causes a short or absent tail whereas the m allele confers a normal, long tail. Cats of genotype MM die as embryos. If two Manx cats mate, what is the probability that each living kitten has a long tail? 7. The autosomal dominant disorder, distal symphalangism, causes the fingers and toes to be short with tiny nails. How can this disorder be both incompletely penetrant and variably expressive? 8. Domesticated hens with white feathers and large, single combs mate with roosters that have dark feathers and small combs. The offspring all resemble their mothers for these two traits. 9. Two genes carried on different chromosomes impart pigment to potato skin. The D gene provides red color, and the P gene provides blue. F1, the dominant allele of the D gene, is present, however, the potatoes are red, no matter which P gene allele is present. Which phenomenon that can alter Mendelian ratios does this illustrate? 10. Define complex, multifactorial, and polygenic traits. 11. In cats, several genes control coat color. If a dominant allele is present for either the white gene (w) or the orange gene (O), the other pigment genes are not expressed. What phenomenon does this illustrate?
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