The phenomenon by which a new set of population is formed from the change in frequency of some genes

The phenomenon you are describing is known as "genetic drift." Genetic drift refers to the random changes in allele frequencies within a population across generations. This can lead to the development of a new set of frequencies for certain genes, particularly in small populations where the effects of chance events are more pronounced.

There are several factors that contribute to genetic drift, including:

1. Founder Effect: When a small group from a larger population establishes a new population, the genetic makeup of this founding group may differ significantly from that of the original population.

2. Bottleneck Effect: This occurs when a significant reduction in population size (due to a natural disaster, human activity, etc.) leads to a loss of genetic variation. The surviving population may have a different genetic structure than the original population.

Overall, genetic drift is an important mechanism of evolution, alongside natural selection, mutation, and gene flow, as it can influence the genetic diversity and adaptability of populations over time.