Chapter 19: The Evolution of Populations

adaptive evolution

increase in frequency of beneficial alleles and decrease in deleterious alleles due to selection

allele frequency

(also, gene frequency) rate at which a specific allele appears within a population

assortative mating

when individuals tend to mate with those who are phenotypically similar to themselves

bottleneck effect

magnification of genetic drift as a result of natural events or catastrophes

cline

gradual geographic variation across an ecological gradient

directional selection

selection that favors phenotypes at one end of the spectrum of existing variation

diversifying selection

selection that favors two or more distinct phenotypes

evolutionary fitness

(also, Darwinian fitness) individual’s ability to survive and reproduce

fitness

measure of successful reproduction, the passing on alleles to the next generation

founder effect

event that initiates an allele frequency change in part of the population, which is not typical of the original population

frequency-dependent selection

selection that favors phenotypes that are either common (positive frequency-dependent selection) or rare (negative frequency-dependent selection)

gene flow

flow of alleles in and out of a population due to the migration of individuals or gametes

gene pool

all of the alleles carried by all of the individuals in the population

genetic drift

effect of chance on a population’s gene pool

genetic structure

distribution of the different possible genotypes in a population

genetic variability

diversity of alleles and genotypes in a population

genotype frequency

the proportion of a specific genotype in a population relative to all other genotypes for those genes that are present in the population

geographical variation

differences in the phenotypic variation between populations that are separated geographically

good genes hypothesis

theory of sexual selection that argues individuals develop impressive ornaments to show off their efficient metabolism or ability to fight disease

handicap principle

theory of sexual selection that argues only the fittest individuals can afford costly traits

Hardy–Weinberg principle of equilibrium

a stable, non-evolving state of a population in which allelic frequencies are stable over time

heritability

fraction of population variation that can be attributed to its genetic variability

honest signal

trait that gives a truthful impression of an individual’s fitness

inbreeding

mating of closely related individuals

inbreeding depression

increase in abnormalities and disease in inbreeding populations

macroevolution

broader scale evolutionary changes seen over paleontological time

microevolution

changes in a population’s genetic structure

modern synthesis

overarching evolutionary paradigm that took shape by the 1940s and is generally accepted today

nonrandom mating

changes in a population’s gene pool due to mate choice or other forces that cause individuals to mate with certain phenotypes more than others

polymorphisms

variations in phenotype within individuals of a population

population genetics

study of how selective forces change the allele frequencies in a population over time

population variation

distribution of phenotypes in a population

relative fitness

individual’s ability to survive and reproduce relative to the rest of the population

selective pressure

environmental factor that causes one phenotype to be better than another

sexual dimorphism

phenotypic difference between the males and females of a population

stabilizing selection

selection that favors average phenotypes