BIO151 UNIT 4 CH. 23 EVOLUTION OF POPULATIONS

microevolution

a change in allele frequencies in a population over generations

genetic variation

differences among individuals in the composition of their genes

neutral variation

differences in DNA sequence that don’t confer a selective advantage or disadvantage

population

a group of individuals of the same species that live in the same area & interbreed, producing fertile offspring

gene pool

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

Hardy-Weinberg equilibrium

allele & genotype frequencies that remain constant from generation to generation, provided that only Mendelian segregation & recombination of alleles are at work; occurs in a population that doesn’t evolve

adaptive evolution

traits that enhance survival or reproduction, said traits increase in frequency over time since the alleles are favored

genetic drift

when allele frequencies fluctuate unexpectedly from one generation to the next, especially in small populations

founder effect

when a few individuals are isolated from a larger population, so the gene pool differs from the source population

bottleneck effect

caused by a severe drop in population size, certain alleles become overrepresented, others underrepresented, and others are absent

gene flow

the transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes

relative fitness

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

directional selection

occurs when conditions favor individuals exhibiting one extreme of a phenotypic range, shifting the frequency curve

disruptive selection

occurs when conditions favor individuals at both extremes of a phenotypic range over individuals with intermediate phenotypes

stabilizing selection

acts against both extreme phenotypes & favors intermediate variants to maintain status quo for particular phenotypic characters

sexual selection

a process in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates

sexual dimorphism

a difference in secondary sexual characteristics between males & females of the same species (size, color, behavior, etc..)

intrasexual selection

selection within the same sex, individuals of one sex compete directly for mates of the opposite sex

intersexual selection

individuals of one sex are picky in selecting their mates from the other sex

balancing selection

when two or more phenotypic forms are kept to preserve variation

frequency-dependent selection

the frequency of a trait failing and rising again in a regular manner

heterozygote advantage

individuals who are heterozygous at a particular locus having greater fitness than those who are homozygous