The gene pool of a species includes all the genes in the population.
Click on image for full size
Windows to the Universe original image

Changes to the Gene Pool: Microevolution

There can be many different forms of a gene. All of the versions of the genes in a population of a species are together 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 for a number of reasons.

  • Gene mutation: An error during cell division can create a new type of gene. That new gene is a small part of the gene pool. It can be passed on to the next generation. If the new gene is useful, 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 a lot.
  • Genetic drift: The amount of each gene in a gene pool can 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 improve the chance of survival of individuals that have 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. 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 individuals in a population. Examples of microevolution include bacteria that have become unaffected by antibiotics, or a change in a species' coloring or size. If the changes are over a very long time and are large enough that the population is no longer able to breed with other populations, it is considered a different species. This is called macroevolution.

Last modified October 15, 2011 by Jennifer Bergman.

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Chromosomes, DNA and Genes: Tiny Things That Have a Huge Effect on Who We Are!

Do you look a bit like your brothers and sisters? Do you look a bit like your parents? The similarities are because, unless you were adopted, you and the other members of your family have genetic material...more

Fish Adapting to a Changing World

Scientists have been studying stickleback fish to learn more about how animals cope when their environment changes. Since the Earth is changing quickly because of global warming and other global changes,...more

Can there be Life in the Environment of Jupiter?

Jupiter's atmospheric environment is one of strong gravity, high pressure, strong winds, from 225 miles per hour to 1000 miles per hour, and cold temperatures of -270 degrees to +32 degrees (freezing temperature)....more

The possible discovery of Life on Mars

In July, 1996, it was announced that Dr. David McKay, along with a team of scientists at Johnson Space Center (a division of NASA), had discovered possible fossils of bacteria in a meteorite named ALH84...more

The Environment of Saturn

Saturn's atmospheric environment is one of strong gravity, high pressure, strong winds, from 225 miles per hour to 1000 miles per hour, and cold temperatures of -270 degrees to +80 degrees. With winds...more

Can there be Life in the Environment of Titan?

Titan's atmosphere is a lot like the Earth's, except that it is very cold, from -330 degrees to -290 degrees! Like the Earth, there is a lot of Nitrogen and other complex molecules. There also may be an...more


Autotrophs are organisms that can "make their own food" from an inorganic source of carbon (carbon dioxide) given a source of energy. Most autotrophs use sunlight in the process of photosynthesis to make...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA