Genetics and Population Variation

Study Notes

Population: a localized group of interbreeding individuals
Gene pool: the sum of all gene copies at all loci in individuals is the population’s gene pool
Genotype frequencies: the percentages of individuals possessing each genotype
Allele frequencies: the relative abundance of the different alleles

Specifies the conditions under which a population of diploid organisms achieves genetic equilibrium
Conditions for Hardy-Weinberg equilibrium: very large population, no migration, no mutations, random mating, and no natural selection
If all conditions are met, allele frequencies and genotype frequencies will not change over time
Hardy-Weinberg Principle is a testable model to evaluate the circumstances under which evolution may occur
Natural populations are virtually never in Hardy-Weinberg equilibrium

Microevolution: change in allele frequencies of a population
Agents of microevolution: mutation, gene flow, non-random mating, genetic drift, and natural selection

Movement of alleles between populations
Introduces new alleles, shifting allele and genotype frequencies away from Hardy-Weinberg predictions
Common in animal species, facilitated by dispersal agents (e.g., pollen or seed-carrying animals) in plants

Mating between individuals with particular phenotypes (and underlying genotypes)
Causes deviation from Hardy-Weinberg predictions, leading to fewer heterozygous offspring and more homozygous offspring
Inbreeding: mating between genetically related individuals, increasing homozygosity and expression of lethal recessive alleles

Unpredictable change in allele frequency due to chance events in small populations
Results in loss of genetic alleles and reduced genetic variability
Major effects in smaller populations, particularly when population size is sharply reduced (bottleneck effect) or a small group splits off to found a colony (founder effect)