A gene pool is used to describe all the alleles present for a given gene in a particular population. Mutation, gene flow, natural selection and genetic drift; which are the four forces of evolution affect gene pool. For mutation, it creates a new genetic variation in the gene pool while gene flow and gene drift alter the allele frequencies in a gene pool. It is important to note that the composition of the gene pool of a population can change over time by means of evolution. Evolution is change in species over time.
A good example is how humans migrated from equatorial regions to the northern climates. In the northern climates, they experiences low amounts of sunlight and this resulted in a genetic change in the skin pigmentation over time. Thus, the skin color became lighter to augment the absorption of vitamin D from sunlight. These genetic modification in skin pigmentation is a part of many of the migrated populations' gene pools.
Smaller populations will naturally have smaller gene pools and may not be very successful or biologically fit whenever there is an environmental change. On the other hand, larger populations with a large gene pool, tend to be more successful in surviving whenever there is a change in the environmental condition. This is because the size of a population's gene pool can influence the ability of a population to survive and evolve.
Whenever there is inbreeding, restricted gene flow, genetic drift and a small population; this will cause a reduction in genetic diversity and as such; will reduce the gene pool. Take for instance, the platypus, Ornithorhynchus anatinus, that is found in eastern Australia has two island populations on King island in Bass Strait and Kangaroo island off the coast of South Australia.
The population on King island occurs naturally while that on Kangaroo island was from introductions of the platypus by Tasmanian and Victorian individuals. Now, Kangaroo island has a good population of platypuses. However, because of the restricted aquatic habitat and isolation on Kangaroo island, the population is likely to experience a small population size, inbreeding, and reduced genetic diversity over time.
National Library of Medicine