Changes to the Gene Pool: Microevolution
There can be many different forms of a gene for each species. The combination of all of the versions of all of the genes for a population is called the gene pool. The gene pool does not always stay the same. Over generations, small changes in the amount of each type of gene can happen because of several processes.
- Gene mutation: If there is an error during cell division, a new type of gene might show up in an individual. That new gene is part of the gene pool and can be passed on to the next generation. If the new gene is advantageous, it might become a common part of the gene pool.
- Gene flow: if new individuals of the species move into or out of the region, it can affect the gene pool. For instance, the only people in North America were once Native Americans. Immigration from other parts of the world over the last several hundred years has changed the gene pool significantly.
- Genetic drift: Gene frequencies in a population change over time because of chance events. For instance, if a few individuals leave a population and establish a new one, by chance their gene pool may not have the same frequency of genes as in the population they left. For example, plants that get to islands as seeds stuck to the feet of birds or in their stomachs may not be typical of their species, but they become the gene pool on the island.
- Natural selection: Some genetic differences will enhance survival of individuals in a population that possess them. For instance, hawks with large sharp talons may be more likely to survive than hawks with small talons. Since the surviving ones make the next generation, the genes for large talons are more likely to be passed on. Thus, eventually, the gene pool shifts towards large talons.
Microevolution is changes in the gene pool of a population over time that result in changes to the varieties of organisms in a population. Examples of microevolution include bacterial strains that have become resistant to antibiotics, or a change in a species' coloring or size. If the changes are over a very long time and are significant enough that the population is no longer able to interbreed with other populations, it is considered a different species. This is called macroevolution.