Genetic divergence is the process in which two or more populations of an ancestral species accumulate independent genetic changes (

mutations In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mi ...

) 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 isn’t genetic exchange anymore. In some cases, subpopulations living in ecologically distinct peripheral environments can exhibit genetic divergence from the remainder of a population, especially where the range of a population is very large (see parapatric speciation). The genetic differences among divergent populations can involve silent mutations (that have no effect on the

phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological pro ...

) or give rise to significant morphological and/or

physiological Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chem ...

changes. 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 Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution with ...

. On a molecular genetics level, genetic divergence is due to changes in a small number of

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ...

s in a species, resulting in

. However, researchers argue that it is unlikely that divergence is a result of a significant, single, dominant mutation in a genetic

locus Locus (plural loci) is Latin for "place". It may refer to: Entertainment * Locus (comics), a Marvel Comics mutant villainess, a member of the Mutant Liberation Front * ''Locus'' (magazine), science fiction and fantasy magazine ** '' Locus Awar ...

because if that were so, the individual with that mutation would have zero fitness. Consequently, they could not reproduce and pass the mutation on to further generations. Hence, it is more likely that divergence, and subsequently

reproductive isolation The mechanisms of reproductive isolation are a collection of evolutionary mechanisms, behaviors and physiological processes critical for speciation. They prevent members of different species from producing offspring, or ensure that any offsprin ...

, are the outcomes of multiple small mutations over evolutionary time accumulating in a population isolated from

gene flow In population genetics, gene flow (also known as gene migration or geneflow and allele flow) is the transfer of genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent a ...

Causes

Founder effect

One possible cause of genetic divergence is the

founder effect In population genetics, the founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population. It was first fully outlined by Ernst Mayr in 1942, usi ...

, which is when a few individuals become isolated from their original population. Those individuals might overrepresent a certain genetic pattern, which means that certain biological characteristics are overrepresented. These individuals can form a new population with different

gene pool The gene pool is the set of all genes, or genetic information, in any population, usually of a particular species. Description A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can surv ...

s from the original population. For example, 10% of the original population has blue eyes and 90% has brown eyes. By chance, 10 individuals are separated from the original population. If this small group has 80% blue eyes and 20% brown eyes, then their offspring would be more likely to have the allele for the blue eyes. As a result, the percentage of the population with blue eyes would be higher than the population with brown eyes, which is different from the original population.

Bottleneck effect

Another possible cause of genetic divergence is the bottleneck effect. The bottleneck effect is when an event, such as a natural disaster, causes a large portion of the population to die. By chance, certain genetic patterns will be overrepresented in the remaining population, which is similar to what happens with the

Disruptive selection

Genetic divergence can occur without geographic separation, through

Disruptive selection Disruptive selection, also called diversifying selection, describes changes in population genetics in which extreme values for a trait are favored over intermediate values. In this case, the variance of the trait increases and the populati ...

. This occurs when individuals in a population with both high and low phenotypic extremes are fitter than the intermediate phenotype. These individuals occupy two different niches, within each niche there is Gaussian trait distribution. If the genetic variation between niches is high then there will be strong reproductive isolation. If genetic variation is below a certain threshold than

introgression Introgression, also known as introgressive hybridization, in genetics is the transfer of genetic material from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species. In ...

will occur but if variation is above a certain threshold the population can split resulting in speciation. Disruptive selection is seen in the bimodal population of

Darwin's finches Darwin's finches (also known as the Galápagos finches) are a group of about 18 species of passerine birds. They are well known for their remarkable diversity in beak form and function. They are often classified as the subfamily Geospizinae or t ...

, ''

Geospiza fortis The medium ground finch (''Geospiza fortis'') is a species of bird in the family Thraupidae. It is endemic to the Galapagos Islands. Its primary natural habitat is tropical shrubland. One of Darwin's finches, the species was the first which scie ...

''. The two modes specialize in eating different types of seeds small and soft versus large and hard, this results in beaks of different sizes with different force capacities. Individuals with intermediate beak sizes are selected against. The song structure and response to song also differs between the two modes. There is minimal

between the two modes of ''G. fortis.''

References

{{DEFAULTSORT:Genetic Divergence Evolutionary biology Population genetics