Hardy Weinberg Population Genetics

In 1908 G.H. Hardy and W. Weinberg independently suggested a scheme whereby evolution could be viewed as changes in the frequency of alleles in a population of organisms. In this scheme, if (A) and (A) are alleles for a particular gene locus and each diploid individual has two such loci then (p) can be designated as the frequency of the (A) allele and (q) as the frequency of the a allele. Thus in a population of 100 individuals (each with two loci) in which 40% of the alleles are (A), (p) would be .40. The rest of the alleles (60%) would be (a), and (q) would be .60. (i.e. p + q = 1.0).

These are referred to as allele frequencies. The frequency of the possible diploid combinations of these alleles (AA, Aa, and aa) is expressed as (p² + 2pq + q² = 1.0).

Hardy and Weinberg also argued that if five conditions are met, the populations allele and genotype frequencies will remain constant from generation to generation. These conditions are as follows:

1. The breeding population is large.
2. Mating is random.
3. There is no mutation of the alleles.
4. No differential migration occurs.
5. There is no selection.

Purpose

Students will learn about the Hardy Weinberg law of genetic equilibrium. The students will study the relationship between evolution and changes in allele frequency of a population by using the Net Logo Hardy Weinberg computer modeling simulation.

Learning Objectives

1. Understand how natural selection can alter allelic frequencies in a population.

2. Apply the Hardy Weinberg equation and its use in determining the frequency of alleles in a population.

3. Analyze the effects on allelic frequencies of selection against the homozygous recessive population or other genotypes.

4. Explain natural selection and other causes of microevolution as deviations from the conditions required to maintain Hardy Weinberg equilibrium.