Genetic Drift: Bottleneck Effect

AGenetic Drift is the variation in a population’s allele frequencies from one generation to the next as a result of chance events. Genetic Drift may cause some genes to disappear, and overall reducing the genetic variation in a certain population. There are two types of Genetic Drift: Bottleneck Effect and Founder Effect . An example of Genetic Drift would be the American Bison, which suffered a huge reduction in population numbers, after succumbing to the bottleneck effect . Due to the quick killings of the Bison, many alleles died with their carriers, and genetic variation decreased exponentially. The American Bison has been gaining numbers in the past couple decades but the genetic variation amongst the different animals is very small. Another example of Genetic Drift would be that of the Northern elephant seals. Also being the target of hunters, the N.Elephant seals population reduced to a shocking 20 individuals at the end of the 19th century . Even though their population is steadily increasing, their genes still carry the effects of the bottleneck. They N. Elephant

Natural Selection will maintain both alleles at the locus, if the alleles allow for the heterozygote individual to have an advantage in reproduction and survival over competitors. An example of Heterozygote Advantage would be the Sickle-Cell trait, which protects against malaria in heterozygotes however it causes a disease in homozygotes . Another example of Heterozygote advantage is cystic fibrosis – the most fatal genetic disorder of Caucasians . Which is still currently being debated, however studies with mice have shown that a heterozygote mouse with the CF mutant when exposed to cholera didn’t succumb to death, and thus had an advantage over those mice who weren’t heterozygous and did succumb to death