Briefly describe Sewall-Wright effect.

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Hint: Sewall-Wright effect is related with the genetics of the living being. It is also called genetic drift or allelic drift and causes gene variants to disappear completely and thereby reduce genetic variation. When there are few copies of an allele, the effect is large but when there are large copies of alleles its effect is small. This theory is linked with the gene frequency of reproducing a small population called Sewall-Wright effect or genetic drift. This effect was described in 1930 by Sewall Wright. It will remain a major factor which determines the origin of new species in an isolated place or an island.

Complete answer:
Sewall-Wright effect is dependent on the gene frequency of reproducing a small population which is also called genetic drift. Genetic drift causes disappearance of gene variants completely and thereby causes reduction in genetic variation. It can also lead to increase in certain rare alleles in an organism. The genetic change in the population after a long time occurs due to genetic drift acting on neutral mutations. Repeated mating causes a reduction in proportions of heterozygotes and results in an increase in number of homozygotes. When a small population of individuals creates a new population with the help of genetic drift it is known as the founder principle.

Note:
New population which is formed with the help of genetic drift in a small population has different genotype frequencies from the parent population. The change in frequencies in large and small populations is not possible due to occurrence of genotypic frequencies. These different genotypic frequencies lead to change in characters in the population and that results in formation of a new population.