Macroevolution

allopatric speciation

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

allopolyploid

A fertile individual that has more than two chromosome sets as a result of two different species interbreeding and combining their chromosomes.

autopolyploid

(ot'-ō-pol'-ē-ployd) An individual that has more than two chromosome sets that are all derived from a single species.

biological species concept

Definition of a species as a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but do not produce viable, fertile offspring with members of other such groups

ecological species concept

Definition of a species in terms of ecological niche, the sum of how members of the species interact with the nonliving and living parts of their environment.

hybrid

Offspring that results from the mating of individuals from two different species or from two true-breeding varieties of the same species.

hybrid zone

A geographic region in which members of different species meet and mate, producing at least some offspring of mixed ancestry.

microevolution

Evolutionary change below the species level; change in the allele frequencies in a population over generations

morphological species concept

Definition of a species in terms of measurable anatomical criteria.

polyploidy

A chromosomal alteration in which the organism possesses more than two complete chromosome sets. It is the result of an accident of cell division.

postzygotic barrier

A reproductive barrier that prevents hybrid zygotes produced by two different species from developing into viable, fertile adults.

prezygotic barrier

A reproductive barrier that impedes mating between species or hinders fertilization if interspecific mating is attempted.

punctuated equilibria

In the fossil record, long periods of apparent stasis, in which a species undergoes little or no morphological change, interrupted by relatively brief periods of sudden change.

reproductive isolation

The existence of biological factors (barriers) that impede members of two species from producing viable, fertile offspring.

speciation

An evolutionary process in which one species splits into two or more species

species

A population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but do not produce viable, fertile offspring with members of other such groups.

sympatric speciation

The formation of new species in populations that live in the same geographic area.