Biology (B)

Hardy-Weinberg Equilibrium

The Hardy-Weinberg model (sometimes called a law) states that a population will remain at genetic equilibrium - with constant (unchanging) allele and genotype frequencies and no evolution - as long as five conditions are met:

1. No mutation (no change in the DNA sequence)
2. No migration (no moving into or out of a population)
3. Very large population size
4. Random mating (mating not based on preference)
5. No natural selection.

These five conditions rarely occur in nature. For example, it is highly unlikely that new mutations are not constantly generated. If these five conditions are met, the frequencies of genotypes within a population can be determined given the phenotypic frequencies.

Genetic Drift

Recall that the third requirement for Hardy-Weinberg equilibrium is a very large population size. This is because variations in allele frequencies that occur by chance are minimal in large populations. In small populations, random variations in allele frequencies can significantly influence the "survival" of any allele. Random changes in allele frequencies in small populations is known as genetic drift. As the population (and therefore the gene pool) is small, genetic drift could have substantial effects on the traits and diversity of a population. Many biologists think that genetic drift is a major cause of microevolution.

CK-12 Foundation, Biology. http://creativecommons.org/licenses/by-nc-sa/3.0/