1) (a) What are the agents of evolution?
(b)Which of these agents can introduce new variations to the population?
(c) What are the primary components of natural selection?
(d) Selection acts on a traits in three different ways, stabilizing selection, directional selection and disruptive selection. Explain each type using examples.
2. Assume that you sample a population of Gryllus crickets over a period of 4 years. You find 50, 200, 100 and 10 animals in years, 1, 2, 3, and 4 respectively.
a. Given this information, what is the effective population size (Ne) of this population? Show your work.
b. Your estimate of the effective population size from (a) may actually be an overestimate of the true effective population size. What other factors might reduce the effective population size?
3) Assume that you are studying sickle cell anemia in Africa in the 1900's. You find two alleles, sickled hemoglobin (HbS) and normal hemoglobin (HbA). You sample the population across two generations. Assume that each generation has a population size of 200. In generation 1 you find that the frequency of HbS is 0.5. In the adult population of generation 2 you find the frequency of HbS homozygotes is 0.0 and the frequency of heterozygotes is 0.50.
a. What are the allelic frequencies of adults in generation 1?
b. Had there been random assortment of alleles, what would the genotype frequencies have been in generation 2? (hint: use the Hardy Weinberg equilibrium equation)
c. What are the actual genotypic frequencies in generation 2 for all three genotypes?
d. Use the chi-square goodness of fit test to test whether the generation 2 observed genotype frequencies are significantly different from Hardy Weinberg expectation. Test with an alpha value of 0.05 and use the "critical values of the chi square distribution" table that is posted on Blackboard. Interpret your results.
e. Is evolution occurring? Why or why not?
4. (a) Define absolute fitness and relative fitness
(b) Assume there is a Mendelian trait determined by two alleles, A anda. The allele frequencies in the populationare A=0.9,a=0.1. Assuming that there is no immediate selection on this trait, what are the genotype frequencies? What are the number of individuals with each genotype (Assume population size is 200)
(c) After spraying an insecticide the number of individuals survived is given below. Calculate the absolute fitness of each genotype. Round up the answers to three decimal points.
|
Genotype
|
Number of individuals survived
|
|
AA
|
20
|
|
aa
|
2
|
|
Aa
|
30
|
(d) Calculate the relative fitness and selection coefficient for each genotype.
(e) Which genotype has the highest selection coefficient? What does this mean?