Genetics 3301

Chapter 19: Population Genetics

Genetic variation:

Ä Goals of population genetics: 1) determine what is responsible for the current pattern of genetic variation or lack thereof, 2) determine how the pattern of genetic variation will change in the future.

Ä Phenomena that affect genetic variation (i.e. that drive evolution): mating patterns (i.e. random vs. inbreeding/assertive mating), genetic composition (immigration), introduction of genetic variation (mutation/recombination), reproduction and survival (genotypes that have different rates of reproduction and survival - natural selection), small population size (fluctuations in reproduction of different genotypes affect a small population) (19-1).

Ä Differences between populations - hemoglobin isoforms in Africa vs. USA, frequency of MN blood groups (T19-1); Calculating allele frequencies in a population (Box 19-1).

Hardy-Weinberg Equilibrium (HWE) (Box 19-2):

Ä HWE is the null model for population genetic variation in the absence of evolution (i.e. no migration, no selection, no mutation, infinite population size, random mating).

Ä Equilibrium distribution of A/A (p²): A/a (2pq): a/a (q²); proportions of genotypes in a population having different allelic frequencies (19-6); if no evolutionary forces, both allele and genotypic ratios will be stable over time (T19-7).

Ä Determining whether a population is in HWE: 1) determine observed genotype frequencies, 2) calculate allele frequencies, 3) calculate expected genotype frequencies, 4) compare observed vs. expected genotype frequencies using a c² test; If a population is not in HWE, assuming no evolutionary forces, population will reach HWE in one generation.

Key terms: Know the following terms: allele frequency, genotype frequency, Hardy-Weinberg equilibrium, polymorphism, population, population genetics, wild type.

Problems: 1-3.