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A genetic isolate is a population of organisms that has little to no genetic mixing with other organisms of the same species due to geographic isolation or other factors that prevent reproduction. Genetic isolates form new species through an evolutionary process known as speciation .
The patterns of isolation by distance as shown among human genetic data representing 346 microsatellite loci taken from 1484 individuals in 78 human populations. The horizontal axis of both charts is geographic distance as measured along likely routes of human migration.
In addition to the genetic causes of reproductive isolation between species there is another factor that can cause post zygotic isolation: the presence of microorganisms in the cytoplasm of certain species. The presence of these organisms in a species and their absence in another causes the non-viability of the corresponding hybrid.
Habitat isolation is not equivalent to a geographic barrier like that of allopatric speciation. [1]: 182 Instead, it is based on genetic differences, where one species is unable to exploit a different environment, resulting from fitness advantages, fitness disadvantages, or resource competition. [1]: 182
Population genetic models can be used to identify which populations show significant genetic isolation from one another, and to reconstruct their history. [52] Subjecting a population to isolation leads to inbreeding depression. Migration into a population can introduce new genetic variants, [53] potentially contributing to evolutionary rescue.
Allopatric speciation (from Ancient Greek ἄλλος (állos) 'other' and πατρίς (patrís) 'fatherland') – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model [1]: 86 – is a mode of speciation that occurs when biological populations become geographically isolated from each other to an extent that prevents or interferes with gene flow.
Genetic divergence will always accompany reproductive isolation, either due to novel adaptations via selection and/or due to genetic drift, and is the principal mechanism underlying speciation. On a molecular genetics level, genetic divergence is due to changes in a small number of genes in a species, resulting in speciation. [2]
[39] Ecotypic variation is therefore described to have a genetic base, and are brought about by interactions between an individual's genes and the environment. [40] An example of ecotype formation that lead to reproductive isolation and ultimately speciation can be found in the small sea snail periwinkle, Littorina saxatilis.