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Genetic Interactions Review Practice Problems

By — McGraw-Hill Professional
Updated on Aug 19, 2011

Review the following concepts if needed:

Problems

Matching Questions   Match the expected phenotypic ratios (right column) in progeny from dihybrid parents with the conditions specified in the left column.

1. Dominant epistasis A. 9 : 6 : 1
2. Recessive epistasis B. 9 : 3 : 3 : 1
3. Duplicate genes with cumulative action C. 9 : 3 : 4
4. Duplicate dominant interaction D. 13 : 3
5. Duplicate recessive interaction E. 12 : 3 : 1
6. Dominant and recessive interaction F. 15 : 1
7. No interaction G. 9 : 7

Vocabulary   For each of the following definitions, give the appropriate term and spell it correctly

  1. Protein catalysts that speed the rate of chemical reactions.
  2. The material(s) acted upon and changed by the catalyst in question 1.
  3. The phenomenon in which a specific genotype(s) at one locus can prevent the phenotypic manifestation of a genotype (s) at one or more other loci.
  4. Adjective describing a locus whose phenotypic manifestation is suppressed by the phenomenon in question 3.
  5. A phenomenon wherein a single gene has more than one phenotypic effect.
  6. A collection of phenotypic effects that collectively defines a disease, genetic or otherwise.

Multiple-Choice Questions Questions   1–5 use the information in the diagram below.

Genetic Interactions Review Questions

  1. The genotype(s) capable of making C is/are     (g) G1g1G2g2     (h) G1G1g2g2     (i) G1g1g2g2     (j) g1g1G2G2     (k) more than one of the above
  2. In a cross between genotypes g1g1G2G2 × G1G1g2g2 what fraction of the F2 is expected to be phenotypically B-positive and C-negative?     (a) 1/16     (b) 3/16     (c) 3/8     (d) 1/4     (e) none of the above
  3. What fraction of the F2 in the above cross (question 2) is expected to be C-negative?     (a) 3/4     (b) 1/2     (c) 9/16     (d) 7/16     (e) none of the above
  4. What fraction of the F2 (in question 2) is expected to be able to make enzyme 2, but not enzyme 1?     (a) 3/4     (b) 3/16     (c) 9/16     (d) 3/8     (e) none of the above
  5. If a dihybrid is testcrossed, what fraction of the progeny is expected to be able to make substance C?     (a) 9/16     (b) 3/16     (c) 3/8     (d) 1/4     (e) none of the above
  6. Questions 6–10 use the information in the following diagram. Enzyme e3 becomes inactivated by binding to substance P.

    Genetic Interactions Review Questions

  7. If the phenotype is determined by the presence or absence of substance N, what type of interaction exists?     (a) dominant and recessive     (b) duplicate recessive     (c) duplicate dominant     (d) duplicate genes with cumulative action     (e) none of the above
  8. Approximately (within rounding error) what percentage of the F1 from G3g3G4g4 parents is expected to be N-positive?     (a) 56     (b) 19     (c) 25     (d) 38     (e) none of the above
  9. When dihybrids are testcrossed, the percentage of their progeny expected to be N-negative is     (a) 25     (b) 81     (c) 75     (d) 38     (e) none of the above
  10. Among the N-positive progeny from dihybrid parents, what fraction is expected to be P-positive?     (a) 3/4     (b) 1/2     (c) 2/3     (d) 5/6     (e) none of the above
  11. What fraction of the progeny from dihybrid parents is expected to be P-positive and N-negative?     (a) 9/16     (b) 7/16     (c) 6/16     (d) 3/4     (e) none of the above

Answers

Matching Questions

1. E   2. C   3. A   4. F   5. G   6. D   7. B

Vocabulary

1. enzymes 2. substrate(s) 3. epistasis 4. hypostatic 5. pleiotropism 6. syndrome

Multiple-Choice Questions

  1. a
  2. b
  3. d
  4. b
  5. d
  6. a
  7. b
  8. c
  9. a (zero)
  10. d
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