Chp 23- The Evolution of Populations

microevolution

microevolution

the change in allele frequencies in a population over generations

genetic variation

the differences in genes or other DNA sequences among individuals

phenotype

the product of inherited genotype & environmental influences

genotype

the genetic makeup of an organism

3 mechanisms that cause allele frequency change

1. Natural selection- adaptation to the environment

2. Genetic drift- chance events alter allele frequencies

3. Gene flow- transfer of alleles between populations

sources of genetic variation

• Mutation

• Gene duplication

• Rapid reproduction

• Sexual reproduction

Hardy-Weinberg equation

used to test whether a population is evolving

population

a group of individuals of the same species that live in the same area

gene pool

consists of all copies of every allele at every locus in all members of the population

adaptive evolution

traits that enhance survival or reproduction increase in frequency over time

genetic drift

chance events cause allele frequencies to fluctuate unpredictably from one generation to the next

founder effect

occurs when a few individuals become isolated from a larger population

bottleneck effect

occurs when there is a drastic reduction in population size due to a sudden change in the environment

gene flow

consists of the movement of alleles among populations

relative fitness

the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals

directional selection

favors individuals at one extreme end

disruptive selection

favors individuals at both extremes

stabilizing selection

favors intermediate variants & acts against extreme phenotypes

sexual selection

individuals with certain heritable traits are more likely to obtain mates than other individuals of the same sex

sexual dimorphism

a difference in secondary sexual characteristics between the sexes

intrasexual selection

direct competition among individuals of one sex for mates of the opposite sex

intersexual selection

occurs when individuals of one sex are choosy in selecting their mates

frequency-dependent selection

the fitness of a phenotype depends on how common it is

heterozygote advantage

occurs when heterozygotes have a higher fitness than both kinds of homozygotes