Evolution of Populations Genetic Drift and Genetic Equilibrium

Genetic Drift • Is a random change in allele frequency due to chance • Genetic drift becomes increasingly important as the size of a population decreases • The bottleneck effect is an example of genetic drift • A population bottleneck occurs when a population’s size is reduced for at least one generation

The Bottleneck Effect A population bottleneck can drastically alter allele frequency and reduce a population’s genetic diversity

An example of a population bottleneck The northern elephant seal population decreased to as few as 100 individuals in the 19 th century. While now numbering 150, 000 or more, genetic diversity has been greatly reduced. As a result, northern elephant seals may be more susceptible to disease and polluition.

• In genetic drift, a random event could lead to the death of the 3 brown frogs, leading to the removal of this allele from the population

Genetic Drift • Genetic drift may occur when a small group of individuals colonizes a new habitat • Individuals may carry alleles in different relative frequencies than did the larger population from which they came. • When allele frequencies change due to migration of a small subgroup of a population it is known as the founder effect

The Hardy-Weinberg Principle • The situation in which allele frequencies remain constant in a population is known as genetic equilibrium • The Hardy-Weinberg Principle states the 5 conditions necessary for allele frequencies to remain constant 1. there must be random mating, 2. the population must be very large, 3. there can be no movement into or out of the population, 4. there can be no mutations, and 5. there can be no natural selection.