Linkage and Chromosome Mapping Review Practice Problems

By — McGraw-Hill Professional
Updated on Apr 25, 2014

Review the following concepts if needed:


Vocabulary   For each of the following definitions, give the appropriate term and spell it correctly. Terms are single words unless indicated otherwise.

  1. The recovery and investigation of all the products of a single meiotic event (as occurs in ascomycete fungi).
  2. A cross-shaped cytological structure that is observed in paired homologous chromosomes during first meiotic prophase, and that is formed by the reciprocal breaking and rejoining of nonsister chromatids.
  3. The genetic event that recombines linked genes. (Two words.)
  4. The linkage arrangement in a dihybrid in which the two dominant genes are on one chromosome and their corresponding recessive alleles are on the homologous chromosome. (Two words.)
  5. The linkage arrangement in a dihybrid in which, on each chromosome of a homologous pair, there is one dominant and one recessive gene. (Two words.)
  6. A unit of map distance equivalent to 1% crossing over.
  7. The ratio of the double-crossover progeny observed in a three-point testcross relative to the double-crossover progeny expected on the basis of treating map units as if they were independent variables. (One to three words.)
  8. The complement of the coefficient of coincidence.
  9. A genetic system that can maintain dihybrid genotypes in repulsion-phase generation after generation. (Two words.)
  10. Investigation of the products of a given meiotic event in ascomycete fungi. (Two words.)

Multiple-Choice Questions   Choose the one best answer.

  1. If a chiasma forms between the loci of genes A and B in 20% of the tetrads of an individual of genotype AB/ab, the percentage of gametes expected to be Ab is   (a) 40   (b) 20   (c) 10   (d) 5   (e) none of the above
  2. The average number of chiasmata that forms in one pair of homologous chromosomes is 1.2. The total length (in map units) for this linkage group is expected to be   (a) 120   (b) 60   (c) 50   (d) 30   (e) none of the above

For questions 3–7, use the following information. Distances AB=15 map units, BC = 8 map units, and AC = 23 map units.

  1. In an individual of genotype AbC/aBc, the percentage of gametes expected to be ABC is   (a) 23   (b) 11.5   (c) 5.75   (d) 0.6   (e) none of the above
  2. In the cross Abc/abC × abc/abc, the percentage of Abc/abc progeny expected is   (a) 39.7   (b) 23.4   (c) 77.1   (d) 48.6   (e) none of the above
  3. If from the cross ABC/abc × abc/abc we observe among 1000 progeny one ABC/abc and one aBc/abc, then the coefficient of coincidence is estimated to be approximately (within rounding error)   (a) 0.054   (b) 0.167   (c) 0.296   (d) 0.333   (e) none of the above
  4. The percentage of progeny expected to be ABC/abc from the cross ABC/abc × abc/abc is   (a) 15.0   (b) 7.5   (c) 6.9   (d) 23.0   (e) 18.7
  5. If the B–C distance of 8 map units is a weighted average of two experiments (experiment 1 = 7.3 map units based on a sample size of 100; experiment 2 = 8.4 map units), the sample size of experiment 2 was approximately (a) 116 (b) 144 (c) 167 (d) 175 (e) 190
  6. From the cross AB/ab × AB/ab we observe 9% of the progeny to be ab/ab. The estimate of the recombination percentage between these two loci is   (a) 50   (b) 40   (c) 35   (d) 20   (e) none of the above

The following information applies to questions 9 and 10.Atrihybrid testcross (order of loci unknown) produced 35 AbC/abc, 37 aBc/abc, 8 ABc/abc, 10 abC/abc, 3 ABC/abc, 5 abc/abc, 1 Abc/abc, 1 aBC/abc

  1. The gene order   (a) is CBA   (b) is BAC   (c) is BCA   (d) cannot be determined from the information provided   (e) is none of the above
  2. The distance (in map units) between the A and C loci is estimated to be   (a) 30   (b) 25   (c) 20   (d) 15   (e) none of the above



  1. tetrad analysis
  2. chiasma, or X (chi)
  3. crossing over
  4. coupling phase
  5. repulsion phase
  6. centimorgan
  7. coincidence, coincidence coefficient, or coefficient of coincidence
  8. interference
  9. balanced lethals
  10. tetrad analysis

Multiple-Choice Questions

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