Understanding the Term "Gene Pool" in Evolutionary Science

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DNA Molecule. Getty/Pasieka

In evolutionary science, the term gene pool refers to the collection of all available genes that are available to be passed down from parents to offspring in the population of a single species. The more diversity there is in that population, the larger the gene pool. The gene pool determines which phenotypes (visible characteristics) are present in the population at any given time.

How Gene Pools Change

The gene pool can change within a geographic area due to the migration of individuals into or out of a population. If individuals holding traits that are unique to the population emigrate away, then the gene pool shrinks in that population and the traits are no longer available to be passed along to offspring. On the other hand, if new individuals possessing new unique traits immigrate into the population, they increase the gene pool. As these new individuals interbreed with individuals already present, a new type of diversity is introduced within the population. 

The size of the gene pool directly affects the evolutionary trajectory of that population. The theory of evolution states that natural selection acts on a population to favor the desirable traits for that environment while simultaneously weeding out the unfavorable characteristics. As natural selection works on a population, the gene pool changes. The favorable adaptations become more plentiful within the gene pool, and the less desirable traits become less prevalent or may even disappear from the gene pool altogether.

Populations with larger gene pools are more likely to survive as the local environment changes than those with smaller gene pools. This is due to the fact that larger populations with more diversity have a wider range of characteristics, which gives them an advantage as the environment changes and requires new adaptations. A smaller and more homogeneous gene pool puts the population at risk for extinction if there are few or no individuals with the genetic diversity required to survive change. The more diverse the population, the better its chances for surviving major environmental changes. 

Examples of Gene Pools in Evolution

In bacteria populations, individuals that are antibiotic-resistant are more likely to survive any sort of medical intervention and live long enough to reproduce. Over time (rather quickly in the case of rapidly reproducing species such as bacteria) the gene pool changes to include only bacteria that are resistant to antibiotics. New strains of virulent bacteria are created in this way. 

A great many plants regarded as weeds by farmers and gardeners are so tenacious because they have a wide gene pool that allows them to adapt to a variety of environmental conditions. Specialized hybrids, on the other hand, often require very specific, even perfect conditions, because they have been bred to have a very narrow gene pool favoring certain characteristics, such as beautiful flowers or large fruit. Genetically speaking, it could be said that dandelions are superior to hybrid roses, at least when it comes to the size of their gene pools.

Fossil records show that a species of bear in Europe changed sizes during successive ice ages, with larger bear dominating during periods when sheets of ice covered the territory, and smaller bears dominating when the ice sheets retreated. This suggests that the species enjoyed a broad gene pool that included genes for both large and small individuals. Without this diversity, the species may have become extinct at some point during the ice age cycles.