Genetic Drift
Genetic drift is also called allelic drift. It is change that occurs in the frequency of gene variant or allele in the population. Genetic drift is caused by random sampling. Alleles that are found in an offspring are samples of the ones found in the parents. In addition, chance plays a role in determining if an individual offspring survives and successfully reproduces.
Allele frequency of a population refers to a fraction of copies of a gene sharing a particular form. Gene variants can disappear completely due to genetic drift. This reduces genetic variation. In cases where allele copies are few, genetic drift’s effect is larger. When allele copies are many, there is a smaller effect.
Vigorous debates have occurred over relative importance of the natural selection process versus the neutral processes such as genetic drift. Some scientists such as Ronald Fisher are of the view that the entire process of genetic drift plays a minor role in the evolution process. This has remained a dominant view over the years.
Motoo Kimura in 1968 rekindled this debate with the neutral theory of the molecular evolution. The claims are that most instances of genetic change spread across the population. However, these are not necessarily phenotypes’ changes. They result from genetic drift.
Many scientists view genetic drifts in statistical drift in a population over time due to the effects that random sampling have in successive generations’ formation. In a narrower sense, genetic drift can be seen as expected dynamics of a population of the neutral alleles. Neutral alleles are the ones that are defined as comprising negative and positive impact on the reproductive fitness. They are predicted to becoming fixed at 100 percent or zero frequency eventually in absence of other mechanisms that affect the distribution of allele.
Genetic drift can cause a loss of genetic traits in a population. A genetic trait can also become widespread in the population irrespective of the reproductive or survival value of the involved alleles. Random statistical effect of genetic drift can be seen in small and isolated populations where there is small gene pool that is sufficient to allow chance to change its makeup significantly.
In a larger population, specific allele can be carried by many individuals making it almost certain that it will be transmitted by some organisms of the population unless if it is unfavorable biologically. Nevertheless, genetic drift, mutation, migration and natural selection are the basic mechanisms that facilitate evolution.
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Sources
http://en.wikipedia.org/wiki/Genetic_drift
http://evolution.berkeley.edu/evolibrary/article/evo_24
http://www.sciencedaily.com/articles/g/genetic_drift.htm
http://www.britannica.com/EBchecked/topic/228886/genetic-drift