random genetic drift


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Fig. 265 Random genetic drift . The frequency of one allele of a gene over many generations. The continuous line represents population A, the broken line population B.

random genetic drift (RGD) or Sewall Wright effect

changes in ALLELE frequency in a population from one generation to another due to chance fluctuations. RGD is important in small populations which are subject to sampling error and where an allele can be lost (0% frequency) or fixed (100%).

The phenomenon was first described by the American geneticist Sewall Wright.

References in periodicals archive ?
Therefore, the effect of random genetic drift is stronger with lower [f.sub.ge]/[f.sub.e] ratio.
Recessive alleles are therefore selected more strongly when rare due to FS, and become less sensitive to random genetic drift. Dominant alleles are more sensitive to loss due to random genetic drift because of their lower frequencies, as illustrated by the stationary frequency distribution [ILLUSTRATION FOR FIGURE 3 OMITTED] and the conditional probabilities of loss (Table 8).
This phenomenon is called random genetic drift. Analogously, changes in species-genus ratios due to sampling effects may be called random colonization drift.
Random genetic drift and other factor (such as bottleneck) jointly contributed about 37% of the total loss of genetic diversity.
However, mutations with effects much greater than 1/[N.sub.e] have negligible chances of accumulating via random genetic drift. Thus, the extent to which variance in mutational effects will increase the vulnerability of a population to extinction depends on the form of the distribution as well as on the effective size of the population.
Linkage tends to make the two pleiotropic systems more similar by coupling the behavior of one-trait-only and shared loci, but in finite populations it also enhances the dispersive effect of random genetic drift. This can be best observed in Table 2: when Nih is small, the number of wrong-way responses grows sharply when loci are closely linked for both pleiotropic systems.
A particular characteristic might result from random genetic drift, the novel use of a feature adapted for a different function, or could occur as an incidental by-product of an adaptation, Lewontin and Gould pointed out.
Therefore, the fixation index for each population, which corresponds to the loss of within-population heterozygosity (Table 5), most likely reflects the expected inbreeding due to random genetic drift rather than selection and fixation of genes linked to the marker loci used in this study.
The degree of genetic subdivision also controls the balance between evolutionary change by natural selection or the combination of random genetic drift and the fixation of neutral variants due to sampling in finite populations (Lande 1976; Kimura 1986; Turner 1992).
Mallet (1986), on the other hand, invokes the SB process, suggesting that random genetic drift establishes a novel pattern in a small region.
The potential for random genetic drift is a major concern in the relatively small populations associated with regeneration.