# genetics assignment

1. The phenotypic variance for scutellar bristles in a population of Drosophilia is .35. The population is moved to new, rigidly controlled conditions in which there is no environmental variation whatsoever. The phenotypic variance in the new conditions is .25.

a. What was the environmental variance under the old environmental conditions?

b. What was the heritability in the old environment?

c. What is the heritability in the new environment?

2 . 2. A population of birds has an average tarsus (part of the leg) length of 20 mm. The successful breeders in this population have an average tarsus length of 25 mm.

a. What is the selection differential?

b. If the narrow-sense heritability of tarsus length was 1.0, what would the average tarsus length of the offspring be?

c. If he narrow sense heritability of tarsus length was .5, what would the average tarsus length of the offspring be?

d. If the narrow sense heritability of tarsus length was 0, what would the average tarsus length of the offspring be?

3. 3. The mutation rate to a recessive allele is 10^{-5}. The selection against the recessive allele is 10^{-3}. What is the equilibrium frequency of the allele?

4. 4. The fitnesses of the genotypes AA, Aa, and aa are .8, 1, and .9, respectively. At equilibrium, which allele(s) will be present in the population? frequency of allele a?

5. 5. Recall that the average population size for determining the effect of genetic drift (called the *effective population size*, Ne, is not the arithmetic mean, but the harmonic mean, viz.

N_{e}=[E(1/N)/t]^{-1}

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where N is the population size and t is the number of generation) A population, over 5 generations, has a size of 2000, 2500, 125, 3000, and 2900.

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a. What is the arithmetic mean population size over these five generations?

b. What is the effective population size over this time?

c. Compare the two numbers. What does this comparison show the importance of?