Question

30. What is the source of genetic variation? How does meiosis contribute to the maintenance of genetic diversity?

31. Describe the preconditions for natural selection to operate and what the results of the natural selection will be.

32. Use the HW equations to solve simple population genetics problems with and without selection.

33. Hardy-Weinberg equilibrium tells us the conditions under which populations will not evolve. So what types of things may lead to a population evolving? How do these things lead to populations evolving (gene frequencies changing)?

34. When is genetic drift the strongest?

Answer 1

30. a) Crossing over, seggregation, independent assortment of chromosomes are the sources of genetic variation.

b) During deplotene of meiosis-I chrosome segments of homologous chromosomes are exchanged to produce recombinant chromosomes.

c) During Metaphase-I of meiosis-I the recombinant chromosomes are segregated to each daught cell to produce four haploid gametes by the end of meiosis.

31. Four conditions are required for natural selection. They are a) Reproduction b) Heredity c) Variations in fitness of organisms and d) Variation in individual characters among members of population.

32. Consider a population of 100 cats with 84 black(BB) and 16 white cats(bb). What is the genotypic and phenotypic freuency of both cats?

1. Respective frequencies of black and white are 0.84 and 0.16.

2. Hardy-Weinberg equaltion can be expressed as binomial expansion, that is (p+q)² = p²+2pq+q^2.

^3. Black triat is represented with p and white character is represented with q.

4. If q² is 0.16 then the q = 0.4, therefore the frequency of allel B would be 0.6 (1- 0.4, (q=1-q)).

5. We can calcuate genotype frequencies: there are p²= (0.6)² x 100 = 36.homozygous dominant(BB)

6. Heterozygous individuals would be 2pq = (2 x 0.6 x 0.4) x 100 = 48.

33. The things that lead to population evolution are 1) Mutation 2) Gene flow 3) Non-random mating 4) Genetic drift and 5) Selection. These all agents change the Hardy-Weinberg equlibrium.

34. Genetic drift is stronger in small population. Small samples can vary from larger sets from which they are selected than larger samples. .