Effects Of Genetic Drift Essay

3534 words - 14 pages


Table of content
Introduction
Effects of genetic drift
Change in allele frequency
Loss of genetic variation
Loss of allelic diversity
Founder effects
Founder effect (i) genetic bottleneck
Case study: Greater Prairies Chickens
Founder effect (ii)
Fitness effect of genetic drift
Effective population size
Genetic drift and natural selection
Correlation between fitness and genetic diversity
Conclusion
References


Genetic drift in natural populations
Introduction
If you flip a coin 500 times, a result of 300 heads and 200 tails might make you suspicious about that coin. But you would not be surprised if you flip a coin to 10 times, and an outcome of 8 heads and 2 tails shows. The smaller the number of coin flips, the more likely it is that chance alone will cause a deviation from the predicted result (Campbell & Reece 2008). In this case, the prediction is an equal number of heads and tails. Allele frequencies fluctuate unpredictably as a result of chance events, from one generation to the next mostly in small populations. Genetic drift is an overall change of allele distribution especially in a small population due to a random variation in the allele frequencies of an individual. Genetic drift (also known as random drift) occurs mostly in small population caused by severe reduction in population size called bottlenecks and founder events where a new population starts from a small number of individuals. Genetic drift is an example of a stochastic process where the actual outcome cannot be predicted because it is affected by random chance (Allendorf & Luikart 2007). The population genetic theory predicts that when populations are finite and random genetic drift takes place, increase in population fragmentation and isolation will lead to stochastic differentiation between populations and an increase in the between-population component of genetic diversity (Yamamoto et al. 2004). As a result of genetic drift, allele frequencies change decreases an expected heterozygosity and increases homozygosity as well as inbreeding coefficient. As soon as this fixation of either one allele or another takes place, it is permanent. A new allele can be introduced only by a new mutation or gene flow from another population. If populations remain small and isolated for many generations they face two genetic threats which are as alleles are randomly fixed or lost from the population by drift, level of quantitative genetic variation necessary for adaptive evolution erode and simultaneously, deleterious mutations will tend to accumulate, because selection is less effective in small populations(Keller & Waller 2002). There is a fundamental difference between drift and selection. Selection also leads to changes in allele frequencies, but it is because some alleles are better suited for the given circumstances.

Effects of genetic drift in a population
Change in allele frequency
Because genetic drift is a random process, the allele frequencies...

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