Genetics 2450 Lab
March 2, 2011
Genetic Drift as an Evolutionary Force
Genetic drift, along with natural selection, mutation, and gene flow, is one of the basic evolutionary forces of evolution. Evolution is the method by which allele frequencies in a population change over time. This process can be random, where the changes occur through genetic drift (Hahn and Bentley 2003). Genetic drift causes these random changes in allele frequencies, which result from random fluctuations across generations. Genetic drift happens in ALL populations, large and small, but affects them to a different degree based on size. Smaller populations tend to be significantly affected by genetic drift, while populations of a much larger size might experience some resistance. Although genetic drift usually occurs with one or more of the other evolutionary forces, genetic drift itself can cause extreme changes in allele and genotype frequencies. By chance alone, it can cause the elimination of a particular allele. Population genetics uses genetic drift, natural selection, mutation, and migration as tools to understand how and why populations undergo changes in allele and genotype frequencies, as well as its effects for future generations.
To recognize the effects of genetic drift on a population, an understanding of the Hardy-Weinberg Equilibrium must be met. This theory states that if certain conditions are met there will be no evolution occurring in a population. Simply put, if a population is in HWE, then that population is not evolving, and you can expect the population to stay frozen from one generation to the next in terms of allele and genotype frequencies. Conditions to be met include: 1.) the population must be infinitely large, 2.) no natural selection occurring, 3.) no mutation occurring, 4.) no migration (gene flow) occurring, and 5.) random mating...