Genetic drift. Sewall Wright effect.
Changes in gene frequency of a population by chance and not by natural selection on mutation.
- Small population with certain gene frequency than the rest of population might get isolated or non random mating over long period creates different gene frequency.
- Suppose population has frequency of blood groups as O blood group with 90% a with 9.5% and 0.5% B blood group. But somehow a population with 50% B blood group gets isolated then over time am AM 10% a and 20% O blood group.
- Amish people migrated from Germany to Pennsylvania in 1720 and remained socially isolated. they have high frequency of rare alleles that cause dwarfism malformed heart and extra finger in hand.
- Causes of drift
- Natural calamities. Migration. isolation by inbreeding. Behavioral isolation like caste endogamy.
- It creates a bottleneck effect where many other genes are limited and only few remain and allowed to thrive. Generally by natural disaster or war
- Founder effect when migration.
- But if the population starts breathing with outsiders the effect may dissolve.
