The logarithm of fitness as a function of the number of deleterious mutations. Synergistic epistasis is represented by the red line - each subsequent deleterious mutation has a larger proportionate effect on the organism's fitness. Antagonistic epistasis is in blue. The black line shows the non-epistatic case, where fitness is the product of the contributions from each of its loci.
Drosophila melanogaster
A graphical representation of the typical human karyotype.
Gene flow is the transfer of alleles from one population to another population through immigration of individuals. In this example, one of the birds from population A immigrates to population B, which has fewer of the dominant alleles, and through mating incorporates its alleles into the other population.
Varieties of maize in the office of the Russian plant geneticist Nikolai Vavilov
The Great Wall of China is an obstacle to gene flow of some terrestrial species.
Photomontage of planktonic organisms.
Current tree of life showing vertical and horizontal gene transfers.
A Tanzanian cheetah.

The academic field of population genetics includes several hypotheses and theories regarding genetic diversity.

- Genetic diversity

Theodosius Dobzhansky, a postdoctoral worker in T. H. Morgan's lab, had been influenced by the work on genetic diversity by Russian geneticists such as Sergei Chetverikov.

- Population genetics
The logarithm of fitness as a function of the number of deleterious mutations. Synergistic epistasis is represented by the red line - each subsequent deleterious mutation has a larger proportionate effect on the organism's fitness. Antagonistic epistasis is in blue. The black line shows the non-epistatic case, where fitness is the product of the contributions from each of its loci.

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Alpha

In this simulation, each black dot on a marble signifies that it has been chosen for copying (reproduction) one time. fixation in the blue "allele" occurs within five generations.

Genetic drift

Change in the frequency of an existing gene variant (allele) in a population due to random chance.

Change in the frequency of an existing gene variant (allele) in a population due to random chance.

In this simulation, each black dot on a marble signifies that it has been chosen for copying (reproduction) one time. fixation in the blue "allele" occurs within five generations.
Ten simulations of random genetic drift of a single given allele with an initial frequency distribution 0.5 measured over the course of 50 generations, repeated in three reproductively synchronous populations of different sizes. In these simulations, alleles drift to loss or fixation (frequency of 0.0 or 1.0) only in the smallest population.
Changes in a population's allele frequency following a population bottleneck: the rapid and radical decline in population size has reduced the population's genetic variation.
When very few members of a population migrate to form a separate new population, the founder effect occurs. For a period after the foundation, the small population experiences intensive drift. In the figure this results in fixation of the red allele.

This effect is visible in molecular data as a correlation between local recombination rate and genetic diversity, and negative correlation between gene density and diversity at noncoding DNA regions.

The corrected mathematical treatment and term "genetic drift" was later coined by a founder of population genetics, Sewall Wright.