Evolution Vocabulary

population

A group of individuals of the same species that live in the same area.

allele frequency

a measure of how common a certain allele is in the population

gene pool

Combined genetic information (alleles) of all the members of a particular population

gene flow

Movement of alleles into or out of a population due to the migration of individuals to or from the population

allele

Different forms of a gene

genetic drift

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

Founders effect

genetic drift that occurs when a few numbers of a population colonize an isolated location; the smaller the number of individuals, the more limited the variability.

Bottleneck effect

Genetic drift resulting from the reduction of a population, typically by a natural disaster, such that the surviving population is no longer genetically representative of the original population.

reproductive isolation

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

speciation

The formation of new and distinct species in the course of evolution

behavioral isolation

Form of reproductive isolation in which two populations have differences in courtship rituals or other types of behavior that prevent them from interbreeding

temporal isolation

Form of reproductive isolation in which two populations have different breeding seasons which prevents them from interbreeding

mechanical isolation

matings fail because male and female reproductive structures are incompatible

geographic isolation

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

random mutation

A new mutation is introduced to a population

natural selection

A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits.

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

stabilizing selection

form of natural selection in which intermediate phenotypes survive or reproduce more successfully than do extreme phenotypes.

disruptive selection

Natural selection in which individuals on both extremes of a phenotypic range survive or reproduce more successfully than do individuals with intermediate phenotypes.

sexual selection

Natural selection arising through preference by one sex for certain characteristics in individuals of the other sex.

non-random mating

mating that can cause evolution to occur because it causes the allele frequencies in the population to either increase or decrease (Ex: bird mating rituals)

random mating

mating that is associated with maintaining genetic equilibrium and therefore a lack of natural selection and speciation

genetic equilibrium

condition in which the frequency of alleles in a population remains the same over generations

example of Founder effect

Afrikaner population of Dutch settlers in South Africa. This population has an abnormally high count of Huntington's Disease (nerve cells in brain degenerate) because the original Dutch settlers carried the gene with a higher frequency that the rest of the Dutch population.

example of Bottleneck effect

Northern elephant seals have reduced genetic variation most likely due to being hunted. Hunting reduced their population size to as few as 20 individuals at the end if the 19th century. Since then their population has rebounded to over 30,000 but the genes still carry the marks of their bottleneck. They have much less variation than a population of Southern Elephant seals that have not been hunted.

example of disruptive selection

Light tan limpets are covered in an area with light-colored rocks and dark brown limpets are favored in an area with dark colored rocks, but the brown limpet population is reduced drastically.

example of directional selection

Desert mice - habitat turned black from lava and dark haired mice thrived. Light colored did not.

example of stabilizing selection

Human birth weight: Human babies born at around 7.5 lbs (average) are more likely to survive than babies born either much smaller or much larger than average