genprob - Biology 16 GENETICS PROBLEMS The best way to gain...

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Biology 16 GENETICS PROBLEMS The best way to gain an understanding of genetics is to work with it. The fundamental principles discussed will become clearer to you. You will grasp them more surely, if you carefully think through the following problems, which illustrate the various patterns of inheritance treated in this section of class. 1. In squash a gene for white color (W ) is dominant over its allele for yellow color (w ). Give the genotypic and phenotypic ratios for the results of each of the following crosses: a. WW x ww b. Ww x ww c. Ww x Ww 2. If pollen from the anthers of a heterozygous white-fruited squash plant is placed on the pistil of a yellow-fruited plant, show, using ratios, the genotypes and phenotypes you would expect the seeds from this cross to produce. 3. In human beings, brown eyes are usually dominant over blue eyes. Suppose a blue-eyed man marries a brown-eyed woman whose father was blue-eyed. What proportion of their children would you predict will have blue eyes? 4. If a brown-eyed man marries a blue-eyed woman and they have ten children, all brown-eyed, can you be certain that the man is homozygous? If the eleventh child has blue eyes, what will that show about the father’s genotype? 5. A brown-eyed man whose father was brown-eyed and whose mother was blue-eyed married a blue-eyed woman whose father and mother were both brown-eyed. The couple has a blue-eyed son. For which of the individuals mentioned can you be sure of the genotypes? What are their genotypes? 6. If the litter resulting from the mating of two short-tailed cats contains three kittens without tails, two with long tails, and six with short tails, what would be the simplest way of explaining the inheritance of tail length in
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these cats? Show genotypes. 7. When Mexican Hairless dogs are crossed with normally-haired dogs, about half the pups are hairless and half have hair. When, however, two Mexican Hairless dogs are mated, about a third of the pups produced have hair, about two thirds are hairless, and some deformed puppies are born dead. Explain these results. 8. In peas a gene for tall plants (T ) is dominant over its allele for short plants (t ). The gene for smooth peas (S ) is dominant over its allele for wrinkled peas (s ). Calculate both phenotypic ratios and genotypic ratios for the results of each of the following crosses: a. Tt Ss x Tt Ss c. tt Ss x Tt ss b. Tt ss x tt ss d. TT ss x tt SS 9. In hogs a gene that produces a white belt around the animal’s body is dominant over its allele for a uniformly colored body. Another independent gene produces fusion of the two hoofs on each foot (an instance of
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genprob - Biology 16 GENETICS PROBLEMS The best way to gain...

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