Genetics Problems- Set 1

Genetics Problems- Set 1 - Genetics Problems Set#1 1 Assume...

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Genetics Problems: Set #1 1. Assume that white color is dominant over yellow color in squash. If pollen from the anthers of a heterozygous white-fruited plant is placed on the pistil of a yellow-fruited plant, what would be the ratios among the genotypes and among the phenotypes of plants grown from the resulting seeds? F = white fruit f = yellow fruit ♂ = Ff ♀= ff f f f ff ff Ff F Ff genotypes 1 Ff : 1 ff phenotypes 1 white: 1 yellow 2. In human beings, brown eyes are usually dominant over blue eyes. Suppose a blue-eyed man marries a brown-eyed woman whose father had blue eyes. What proportion of their children would you predict will have blue eyes? B = brown eyes b = blue eyes ♂ : bb ♀ : B_ (but her father has blue eyes, so she is Bb ) b b Bb bb Bb b bb genotypes 1 Bb : 1 bb phenotypes 1 brown : 1 blue B 3. If a brown-eyed man marries a blue-eyed woman and they have 10 children, all with brown eyes, can you be certain that the man is homozygous for eye color? If the eleventh child has brown eyes, will that prove what the father’s genotype is? : B_ x bb If 11 children are brown eyed you DO NOT know the man’s genotype. Each child is a separate probabilistic event. (If he is Bb, the probability of having 11 brown-eyed children is: (1/2) 11 = .00049 or 1 in 2048)
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4. A brown-eyed man whose father had brown eyes and whose mother had blue eyes married a blue- eyed woman whose father and mother both had brown eyes. The couple has a blue-eyed son. Construct a pedigree for this family, showing all the genotypes for which you can be certain, and indicate the possible genotypes of individuals whose genotypes cannot be determined from the information given. What further information could you use to determine the genotypes of those individuals? bb B_ Bb Bb Bb bb bb If a child is blue-eyed both parents must carry the blue allele (b). Thus, the father in this case must be Bb. Her mother was blue-eyed, so each of her brown-eyed parents must be heterozygotes. 5. Two short-tailed cats were mated, and produced a little of 11 kittens – 3 with no tails, 2 with long tails, and 6 with short tails. What would be the simplest explanation of the inheritance of tail length in these cats? Show the genotypes of each kind. short tails x short tails offspring: 3 no tails 2 long tails 6 short tails 3/11 no tails = .27 = about 1/4 6/11 short tails = .54 = about 1/2 2/11 long tails = .18 = about 1/4 If TT = long tails tt = no tails Tt = short tails } long tail is incompletely dominant to tailless short tails = heterozygotes
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6. In the fruit fly Drosophila melanogaster , vestigial wings and hairy body are produced by two recessive alleles carried on different chromosomes. The normal alleles, long wings and hairless body, are dominant. If a vestigial-winged, hairy male is crossed with a female homozygous for both of the normal traits, what would be the phenotypes and genotypes of their progeny?
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