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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 genetics of ethological isolation barriers will be discussed first. Pre-copulatory isolation occurs when the genes necessary for the sexual reproduction of one species differ from the equivalent genes of another species, such that if a male of species A and a female of species B are placed together they are unable to copulate.
[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.
Post-mating isolation occurs between the process of copulation (or pollination) and fertilization—also known as gametic isolation. [1]: 232 Some studies involving gametic isolation in Drosophila fruit flies, [93] ground crickets, [94] and Helianthus plants [95] suggest that there may be a role in ecology; however it is undetermined. [4]
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 is the process in which two or more populations of an ancestral species accumulate independent genetic changes through time, often leading to reproductive isolation and continued mutation even after the populations have become reproductively isolated for some period of time, as there is not any genetic exchange anymore. [1]
Eventually, if reproductive isolation is achieved, it may lead to a separate species. However, reproductive isolation between hybrids and their parents is particularly difficult to achieve and thus hybrid speciation is considered an extremely rare event. The Mariana mallard is thought to have arisen from hybrid speciation. [citation needed]
A genetic species as defined by Robert Baker and Robert Bradley is a set of genetically isolated interbreeding populations. This is similar to Mayr's Biological Species Concept, but stresses genetic rather than reproductive isolation. [47] In the 21st century, a genetic species could be established by comparing DNA sequences.