Changes

==Genetic Drift as it Relates to Allele Frequencies==

==Genetic Drift as it Relates to Allele Frequencies==

Different forms of a [[gene]] are called [[allele|alleles]]. Individual members of a [[population]] have different alleles. Together, all the alleles for all the genes in a population constitute the "gene pool" of the population. Through reproduction, individuals pass their genes on to the next generation. Considering only the effect of genetic drift, the larger the population is, the more stable the frequency of different alleles in the gene pool will be over time; this is because random chance will play less of a role in determining who breeds. In small populations, allele frequencies are likely to change rapidly and dramatically over very few generations, or "drift," because of chance events. This rapid change can occur in small populations because each individual's alleles represent a large fraction of the gene pool, and if an individual did not reproduce it could have a much larger effect than in the case of an individual in a large population not reproducing. Also, alleles that are found infrequently are more likely to be lost due to random chance.

Different forms of a [[gene]] are called [[allele]]s. Individual members of a [[population]] have different alleles. Together, all the alleles for all the genes in a population constitute the "gene pool" of the population. Through reproduction, individuals pass their genes on to the next generation. Considering only the effect of genetic drift, the larger the population is, the more stable the frequency of different alleles in the gene pool will be over time; this is because random chance will play less of a role in determining who breeds. In small populations, allele frequencies are likely to change rapidly and dramatically over very few generations, or "drift," because of chance events. This rapid change can occur in small populations because each individual's alleles represent a large fraction of the gene pool, and if an individual did not reproduce it could have a much larger effect than in the case of an individual in a large population not reproducing. Also, alleles that are found infrequently are more likely to be lost due to random chance.

After many generations, if only genetic drift is operating, populations (even large populations) will eventually contain only one allele of a particular gene, becoming "monomorphic," or fixed for this allele. This can be seen as a loss of information in the population, though in real populations, this process is prevented by [[mutation]]s. As a general rule, the chances of an allele becoming fixed in the population are equal to its frequency in that population. For example, if a population has a frequency of 0.8 for allele ''A'', then ''A'' has an 80 percent chance of being fixed.

After many generations, if only genetic drift is operating, populations (even large populations) will eventually contain only one allele of a particular gene, becoming "monomorphic," or fixed for this allele. This can be seen as a loss of information in the population, though in real populations, this process is prevented by [[mutation]]s. As a general rule, the chances of an allele becoming fixed in the population are equal to its frequency in that population. For example, if a population has a frequency of 0.8 for allele ''A'', then ''A'' has an 80 percent chance of being fixed.

In the neutral theory of molecular evolution, genetic drift is seen as the most important element causing evolutionary change at the [[DNA]] sequence level: Since most changes at the molecular level are neither good (beneficial) nor bad (deleterious), but neutral, these changes must "drift" to fixation.

In the neutral theory of molecular evolution, genetic drift is seen as the most important element causing evolutionary change at the [[DNA]] sequence level: Since most changes at the molecular level are neither good (beneficial) nor bad (deleterious), but neutral, these changes must "drift" to fixation.

==Further Reading==

==Further reading==

:Avise, John C. Molecular Markers, Natural History and Evolution. New York: Chapman and Hall, 1994.

:Avise, John C. Molecular Markers, Natural History and Evolution. New York: Chapman and Hall, 1994.

:Mayr, Ernst. Evolution and the Diversity of Life: Selected Essays. Cambridge, MA: Belknap Press, 1976.

:Mayr, Ernst. Evolution and the Diversity of Life: Selected Essays. Cambridge, MA: Belknap Press, 1976.

:Weaver, Robert F., and Philip W. Hedrick. Genetics, 2nd ed. Dubuque, IA: William C. Brown, 1992.

:Weaver, Robert F., and Philip W. Hedrick. Genetics, 2nd ed. Dubuque, IA: William C. Brown, 1992.

[[Category:Genetics]]

[[Category:Genetics]]