Population Genetics and Speciation

population genetics

the study of how populations change genetically over time

Microevolution

Change in allele frequencies in a population over generations.

bell curve

distribution of scores in which the bulk of the scores fall toward the middle, with progressively fewer scores toward the "tails" or extremes

Population

A group of individuals that belong to the same species and live in the same area

gene pool

Combined genetic information of all the members of a particular population

Phenotype

An organism's physical appearance, or visible traits.

Genotype

genetic makeup of an organism

Hardy-Weinberg equilibrium

condition that occurs when the frequency of alleles in a particular gene pool remain constant over time

allele frequency

Number of times that an allele occurs in a gene pool compared with the number of alleles in that pool for the same gene

phenotypic frequency

proportion of individuals in a population that express a particular phenotype

Mutation

A change in a gene or chromosome.

gene flow

movement of alleles from one population to another

Immigration

Movement of individuals into a population

Emigration

movement of individuals out of an area

genetic drift

A change in the allele frequency of a population as a result of chance events rather than natural selection.

bottleneck effect

A change in allele frequency following a dramatic reduction in the size of a population

Founders effect

genetic drift that occurs after a small number of individuals colonize a new area

nonrandom mating

Mating among individuals on the basis of their phenotypic similarities or differences, rather than mating on a random basis

sexual selection

A form of natural selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates.

stabilizing selection

Natural selection that favors intermediate variants by acting against extreme phenotypes

disruptive selection

form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle

directional selection

Form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve

Speciation

Formation of new species

Morphology

study of form

biological species concept

Species is a group of populations whose members have the potential to produce fertile offspring.

geographic isolation

form of reproductive isolation in which two populations are separated physically by geographic barriers such as rivers, mountains, or stretches of water

allopatric speciation

The formation of new species in populations that are geographically isolated from one another.

reproductive isolation

Separation of species or populations so that they cannot interbreed and produce fertile offspring

sympatric speciation

The formation of a new species as a result of a genetic change that produces a reproductive barrier between the changed population (mutants) and the parent population. No geographic barrier is present.

Gradualism

The theory that evolution occurs slowly but steadily

punctuated equilibrium

Pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change