The gene pool is the complete set of genetic information in a population.

Population genetics investigates how allele frequencies within populations change over time. Changes in allele frequency are the basis of evolution.

Genetic diversity leads to variation within a population, which is essential in the process of natural selection, allowing a population to adapt to changes over time.

Small populations with limited genetic diversity cannot adapt to change as easily and are more likely to become extinct.

Genetic drift is a change in allele frequency that occurs by chance, not as a result of natural selection. It is most likely to happen when a small number of individuals are separated from the rest of a large population.

In small populations, genetic drift can lead to a loss of genetic variation, as certain alleles may be lost purely by chance, not due to natural selection.

The founder effect is an extreme example of genetic drift, where small populations arise due to the establishment of new colonies by a few isolated individuals.

The founder effect leads to smaller gene pools and less genetic diversity in a population, compared with the original population. Rare alleles in the original population may have a much higher frequency in the new population.

The bottleneck effect is a large reduction in population size that lasts for at least one generation.

A genetic bottleneck greatly reduces the gene pool, and so greatly reduces the genetic diversity in a population, which can lead to problems of inbreeding and reduced fertility.

However, a beneficial mutation may also have a much greater impact.

The founder effect occurs when a small group splits from a larger population.

The bottleneck effect occurs when a large population experiences a significant decrease in size.

1. Mutation - forms new alleles that lead to genetic variation
2. Gene flow - movement of alleles between populations changing the allele frequency within a population
3. Genetic drift - changing allele frequencies in smaller populations has a larger effect
4. Natural selection - increases the frequency of alleles coding for traits that improve survival and so reproduction success
5. Sexual selection - increases the frequency of alleles coding for traits that improve reproductive success specifically

Density-dependent factors are dependent on population size and include competition, predation, parasitism, and disease.

Density-independent factors affect all populations regardless of their size and include climate change, natural disasters, and human activities.