Genetic Drift

Genetic Drift

the random fluctuations in allele frequencies in a population over generations due to chance events.

It is a random process and affects all alleles regardless of their effects on fitness.

Effects of Genetic Drift

• More pronounced in small populations

• Can lead to the loss ( p = 0 ) or fixation ( p = 1 ) of alleles over time

Founder Effect

A small proportion of individuals starting a new population. Amish population in Pennsylvania with Ellis-van Creveld syndrome

Bottleneck Effect

A certain population drastically reduced by environmental or human factors. Cheetahs low genetic variability due to two drastic population reduction between 10,000 and 100,000 years ago.

Effective Population size

Number of individuals in a population who contribute to the next generation’s gene pool

It is affected by:

• Unequal sex ratio

• population fluctuations

• variation in reproductive success

Unequal population size: unequal sex ratio

It refers to an unequal proportion of females and males in the population.

In some species the number of breeding males is smaller because they mate multiple times or, like for the honey bees