Genetic drift is only for the alleles that have no effect on the fitness of an organism (which means these alleles are not under natural selection).
https://biologydictionary.net/genetic-drift/
Genetic drift is a change in allele frequency in a population, due to a random selection of certain genes.
Types of genetic drift:
- Bottleneck effect
- Founder effect
1. Bottleneck effect
https://biologydictionary.net/genetic-drift/
A Bottleneck effect (population bottleneck) is a type of genetic drift in which a population’s size severely decreases. Competition, disease, or predation leads to these massive decreases in population size. The allele pool is now determined by the organisms which did not die. Some alleles increase in frequency simply because they are the only alleles left.
2. Founder effect
https://biologydictionary.net/genetic-drift/
In another type of genetic drift known as the founder effect, a new population is formed, or “founded”, in a new location. If this new population does not interact and reproduce with the main population, the allele frequencies in this population will be much different from that of the parent population.
