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Adaptive evolution

The process by which populations change and develop over time through natural selection, where beneficial traits increase in frequency.

Allopatric speciation

A mode of speciation induced when an ancestral population becomes segregated by a geographic barrier.

Allopolyploid

A common type of polyploid species resulting from two different species interbreeding.

Autopolyploid

An individual with more than two chromosome sets, all derived from a single species.

Bottleneck effect

Genetic drift that occurs when a population is reduced and survivors do not represent the original population's gene pool.

Directional selection

Natural selection that favors individuals at one end of the phenotypic range.

Disruptive selection

A type of natural selection where individuals with extreme traits have higher fitness than intermediate traits.

Founder effect

Genetic drift that occurs when a few individuals become isolated from a larger population.

Gene flow

Genetic additions or subtractions from a population resulting from movement of individuals or gametes.

Gene pool

The total aggregate of genes in a population at any one time.

Genetic drift

Unpredictable fluctuations in allele frequencies due to a population's finite size.

Genetic variation

Differences in DNA sequences among individuals within a population.

Habitat differentiation

The process where populations of the same species evolve to occupy different habitats.

Hardy-Weinberg equilibrium

The condition describing a non-evolving population in genetic equilibrium.

Hybrid

The offspring resulting from the mating of two organisms of different varieties or species.

Hybrid zone

A region where two related populations interbreed after becoming geographically isolated.

Interspecific

Occurring or existing between different species.

Neutral variation

Genetic diversity that confers no apparent selective advantage.

Polyploidy

A chromosomal alteration where an organism possesses more than two complete chromosome sets.

Population

A localized group of individuals capable of interbreeding and producing fertile offspring.

Postzygotic barrier

Species-isolating mechanisms preventing hybrids from developing into viable, fertile adults.

Prezygotic barrier

A reproductive barrier that impedes mating between species.

Punctuated equilibria

Long periods of stasis interrupted by brief periods of sudden change.

Relative fitness

The contribution of one genotype to the next generation compared to alternative genotypes.

Sexual selection

Selection based on variation in secondary sex characteristics, enhancing sexual dimorphism.

Sister species

Two species that share a most recent common ancestor, each other's closest living relatives.

Speciation rate

The frequency at which new species emerge from existing ones through speciation.

Stabilizing selection

Natural selection that favors intermediate variants by acting against extreme phenotypes.

Sympatric speciation

Speciation occurring due to a radical genome change in a subpopulation, isolating it from the parent population.

Temporal isolation

A prezygotic reproductive barrier where species breed at different times, preventing interbreeding.