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Genetics_Prob_Answers

Genetics_Prob_Answers - Practice Problems ANSWERS(Available...

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Answers Practice Problems 33 Practice Problems: ANSWERS (Available on-line for students). Q1) Generate a Punnett Square for a heterozygous individual (a+/a) crossed with a heterozygous individual (a+/a). In this case the mutation is recessive. Determine the genotypic ratio and phenotypic ratio. For phenotypic ratio do not refer to specific a+ or a phenotype but instead refer to them as dominant or recessive. Can this trait be sex linked in humans? Answer: see 1) in table below. Can’t be sex-linked in humans because males can’t be heterozygous (except in very rare cases). Typically males are hemizygous. Q2) Generate a Punnett Square for a heterozygous individual crossed with a heterozygous individual. Make the mutation dominant. Notice that the phenotypic ratio for dominant/recessive is identical to Q1 (3/4 Dominant, 1/4 recessive) except you now have to realize your mutation is Dominant and wild type is recessive. Answer: see 2) in table below. Note that the answer with respect to ratios is identical to Q1 except the notation is different in that you use upper case because the mutation is dominant. Q3) Generate a Punnett Square for a heterozygous individual crossed with a homozygous recessive individual. Make the mutation recessive. Determine the genotypic ratio and phenotypic ratio. Can this trait be sex linked in humans? Answer: see 3) in table below. Can’t be sex-linked in humans because males can’t be heterozygous (except in very rare cases) or homozygous (except in very rare cases). Typically males are hemizygous. Q4) Generate a Punnett Square for a heterozygous individual crossed with a homozygous dominant individual. Make the mutation recessive. Determine the genotypic ratio and phenotypic ratio. Can this trait be sex linked in humans? How does your answer compare to 3? Answer: see 4) in table below. Note in this case that all of the offspring must have the dominant allele and must therefore have the dominant phenotype. Again this can’t be sex-linked because males are typically hemizygous. Q5) Generate a Punnett Square for a homozygous recessive individual crossed with a homozygous recessive individual. Determine the genotypic ratio and phenotypic ratio. Can this trait be sex linked in humans? How does your answer compare to 3? See # 5 below. All offspring will have the same genotype and the same phenotype – homozygous recessive and they will display the recessive phenotype. Again this can’t be sex-linked because males are typically hemizygous (not homozygous). Q6) Generate a Punnett Square for a homozygous dominant individual crossed with a homozygous dominant individual. Determine the genotypic ratio and phenotypic ratio. Can this trait be sex linked in humans? How does your answer compare to 5? See #6 below. All offspring will have the same genotype and the same phenotype – homozygous dominant and they will display the dominant phenotype. Again this can’t be sex-linked because males are typically hemizygous (not homozygous).
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