Review the following concepts if needed:

- Qualitative vs. Quantitative Traits for Genetics
- Polygenic Traits for Genetics
- The Normal Distribution for Genetics
- Types of Gene Action for Genetics
- Heritability for Genetics
- Selection Methods for Genetics
- Mating Methods for Genetics

### Problems

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

- The kind of phenotypic variation associated with quantitative traits. (One or two words.)
- A bell-shaped distribution of continuous phenotypic variation. (One or two words.)
- A squared standard deviation.
- A type of allelic interaction in which the phenotype of a heterozygote is outside the phenotypic limits of the corresponding homozygotes.
- The proportion of the phenotypic variance of a trait that is attributable to gene effects.
- A statistic expressing how much (on average) one sample variable may be expected to change per unit change in some other variable. (Two words.)
- A statistical measurement of how closely two sets of sample data are associated, having limits ±1. (Two words.)
- A method of estimating the breeding value of an individual by the performance or phenotype of its offspring. (Two words.)
- The mating of individuals that are more closely related than the average of the population to which they belong.
- The superior phenotypic quality of heterozygotes relative to that of homozygotes, commonly called "hybrid vigor."

**Multiple-Choice Questions** Choose the one best answer.

For problems 1–3, use the following information. Two pure lines of corn have mean cob lengths of 9 and 3 in, respectively. The polygenes involved in this trait all exhibit additive gene action.

- Crossing these two lines is expected to produce a progeny with mean cob length (in inches) of (
*a*) 12.0 (*b*) 7.5 (*c*) 6.0 (*d*) 2.75 (*e*) none of the above - If the variation in F1 cob length ranges from 5.5 to 6.5 in, this variation is estimated to be due to segregation at (
*a*) two loci (*b*) three loci (*c*) four loci (*d*) five loci (*e*) none of the above - If only two segregating loci contribute to cob length, and we represent the parental cross as
*AABB*(9-in average cob length) ×*aabb*(3-in average), the fraction of the F_{2}expected to be 4.5 in is (*a*) 1/8 (*b*) 1/16 (*c*) 3/32 (*d*) 3/16 (*e*) none of the above - If a mouse population has an average adult body weight of 25
*g*with a standard deviation of ±3*g*, the percentage of the population expected to weigh less than 22 g is approximately (*a*) 16 (*b*) 33 (*c*) 68 (*d*) 50 (*e*) 25 - With reference to problem 4 above, if the genetic variance in mouse body weight is 2.7, the environmental variance is approximately (
*a*) 22.3 (*b*) 6.3 (*c*) 0.3 (*d*) 3.3 (*e*) none of the above - In another population of mice, the total genetic variance of adult bodyweight is 4
*g*^{2}and the environmental variance is 12*g*^{2}. The broad estimate of heritability for this trait in this population is approximately (*a*) 0.15 (*b*) 0.20 (*c*) 0.25 (*d*) 0.33 (*e*) none of the above - If the correlation coefficient between body weight of full sibs is 0.15, then the heritability of this trait in this population is (
*a*) less than 0.15 (*b*) 0.25 (*c*) 0.3 (*d*) 0.6 (*e*) none of the above - The selection differential (in grams) is (
*a*) 0.5 (*b*) 4 (*c*) 3.5 (*d*) 2 (*e*) none of the above - The genetic gain (in grams) is (
*a*) 0.5 (*b*) 4 (*c*) 3.5 (*d*) 2 (*e*) none of the above - The heritability estimate for adult body weight in this population is (
*a*) 0.050 (*b*) 0.625 (*c*) 0.125 (*d*) 0.250 (*e*) none of the above

For problems 8-10, use the following information. A population of adult mice has a mean body weight of 30 *g*. The average weight of mice selected for breeding purposes is 34*g*. The progeny produced by random mating among the selected parents average 30.5*g*.

### Answers

### Vocabulary

- continuous variation
- normal (or Gaussian) distribution
- variance
- overdominance
- heritability (broad definition)
- regression coefficient
- correlation coefficient
- progeny test
- inbreeding
- heterosis

### Multiple-Choice Questions

- c
- e (environmental)
- e (1/4)
- a
- b
- c
- c
- b
- a
- c

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