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Modern Genetic Analysis Answers to Selected Problems
Chapter 18*

2.

a. Shank length:

H2 = 0.200h2 = 0.150

Neck length:

H2 = 0.600h2 = 0.010

Fat content:

H2 = 0.500h2 = 0.400

b. Fat content would respond best to selection.
c. 8.9%
See question

3.

a. p(homozygotic at 1 locus) = 3(1/2)3 = 3/8

p(homozygotic at 2 loci) = 3(1/2)3 = 3/8

p(homozygotic at 3 loci) = (1/2)3 = 1/8

b. p(0 capital letters) = 1/64 p(4 capital letters) = 15/64

p(1 capital letter) = 3/32 p(5 capital letters) = 3/32

p(2 capital letters) = 15/64 p(6 capital letters) = 1/64

p(3 capital letters) = 10/32

See question

5. | The population described would be distributed as follows: Note that the 3-bristle class contains 7 different genotypes, the 2-bristle class contains 19 different genotypes, and the 1-bristle class contains only 1 genotype. It would be very difficult to determine the underlying genetic situation by doing controlled crosses and determining progeny frequencies. See question

7. | Mean = 4.7 Variance = 0.2619 Standard deviation = 0.5117 See question

9.

a. H2 has meaning only with respect to the population that was studied in the environment in which it was studied. Otherwise, it has no meaning.
b. Neither H2 nor h2 is a reliable measure that can be used to generalize from a particular sample to a "universe" of the human population. They certainly should not be used in social decision making (as implied by the terms eugenics and dysgenics).
c. Again, H2 and h2 are not reliable measures, and they should not be used in any decision making with regard to social problems.
See question

11. | First, define alcoholism in behavioral terms. Next, realize that all observations must be limited to the behavior used in the definition and that all conclusions from your observations are applicable only to that behavior. To do your data gathering, you must work with a population in which familiarity is distinguished from heritability. In practical terms, this means using individuals who are genetically close but who are found in all environments possible. See question

14.

a. If you assume that individuals at the extreme of any spectrum are homozygous, then their offspring are more likely to be heterozygous than the original individuals. That is, they will be less extreme.
b. For Galton's data, regression is an estimate of heritability (h2), assuming that there were few environmental differences between father and son.
See question

© 1999 by W. H. Freeman and Company. All rights reserved.