Lecture 39: Population Genetics I

1. What is the basic difference in approach between the Mendelian genetic studies discussed at the beginning of the semester and the population genetic studies discussed at the end of the semester?

2. Write the basic Hardy-Weinberg equations for distribution of alleles in a population and distribution of genotypes in a population, and show how the two are related.

3. How can the relationship between allelic frequency and genotypic frequency be depicted visually? Draw an appropriate figure.

4. What conditions must be met in order for the Hardy Weinberg relationship to be applicable.

5. A rare recessive disease has a frequency of occurrence of X among the children of unrelated parents.

a. What is the allelic frequency of the allele that is homozygous in diseased individuals?

b. What is the frequency of heterozygous carriers of the disease in the general population?

c. What is the frequency of individuals who are neither afflicted nor carriers?

6. What pattern of change of allelic frequencies over time is expected in a large population with random mating and no selective advantage of any of the genotypes?

7. Explain the meaning of the symbols H, P, and Q, and relate each to allelic frequencies p and q.

8. Use a diagram to demonstrate how inbreeding leads to loss of heterozygosity.

9. What is meant by the term homozygosity by descent?

10. Define the inbreeding coefficient (F) in terms of loss of heterozygosity.

11. Use specific equations to show how the frequencies of homozygous genotypes (P and Q) are affected by the inbreeding coefficient.

12. What would the inbreeding coefficient be in each of the following cases?

a. For the children of a first cousin marriage (parents have the same grandparents).

b. For the children of a second cousin marriage (parents have the same great-grandparents)

c. For childdren of a marriage in which a grandson of a couple married a great-granddaughter. Assume that the grandson and great-granddaughter were descended from different children of the original couple. (Hint: construct the entire pedigree and determine the dilution of original parental alleles at each reproductive step, taking into account that there is one more generation on one side than on the other. Don't forget that there are four parental alleles.)

d. Brother-sixter matings of laboratory mice.

e. The offspring of the mating of a male laboratory rat with his female progeny (construct a pedigree and determine the dilution of alleles as in question c).

13. Alleles A and B are codominant. Calculate the relative frequencies of the three possible phenotypes for each of the following frequencies of A. (Assume that A and B are the only alternatives).

a. A = 0.5
b. A = 0.2
c. A = 0.1
d. A = 0.01
e. A = 0.001

14. Allele a is recessive to allele A. Calculate the relative phenotypic frequencies in each of the following situations. (Assume that A and a are the only alternatives).

a. a = 0.5
b. a = 0.2
c. a = 0.1
d. a = 0.01
e. a = 0.001

15. What is the highest frequency of heterozygosity that can exist is a population that is in Hardy-Weinberg equilibrium. What are the allelic frequencies that yield the highest fraction of heterozygosity. Hint: If you are not particularly skilled in mathematics, the best approach to this one is trial and error, coupled with a little bit of intuition.

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