Genetic Drift, Founder Effect & Bottleneck Effect - Practice Questions & MCQ

• Genetic drift is one of the basic mechanisms of evolution.
• In each generation, some individuals may, just by chance, leave behind a few more descendants (and genes) than other individuals. 
• The genes of the next generation will be the genes of the individuals that happen to survive by chance and not necessarily by favorable variations.
• The effect of genetic drift is stronger in small populations as compared to the larger ones.
• Because genes are becoming prominent due to a chance event, it does not matter if they confer benefit or harm to the individual.
• It is also called Sewall Wright effect, named after American geneticist Sewall Wright who realized its evolutionary significance.

Founder Effect

• When a small group of individuals leaves their parent population to establish a new colony, they are called founders.
• Founders may not have the degree of genetic variability as seen in the parent population and the new colony would be isolated from other populations.
• Therefore, alleles in the founding population may be present at different frequencies than in the original population, and some alleles may be missing altogether.
• This is called the founder effect.
• It is seen when a colony of individuals is established.

Bottleneck Effect

• It is an extreme condition of genetic drift when the size of the population is severely reduced.
• It can occur due to natural disasters that can decimate the size of a population.
• Only a small group of survivors remain and the allele frequencies in this group may be very different from those of the population prior to the event, and some alleles may be missing entirely. 
• Hence, bottleneck effect results in a severe reduction in the gene diversity of a population.
• Bottleneck is similar to the founder effect. The only difference is that it occurs due to a catastrophic event whereas the founder effect is due to colonization.