Hardy-Weinberg Equation Intro

Introduction

The Hardy-Weinberg equilibrium is used to estimate the allele frequencies and genotype frequencies in a population that is not evolving.  For our purpose we will assume Mendelian inheritance in which there are only two possible alleles (dominant and recessive) for a given characteristic.  In a population containing two alleles (e.g., A and a) of the same gene, two individuals who are randomly mated would provide an A or an a allele to the offspring.  The frequencies p and q represent the probability of a member of the population having the alleles A or a, respectively.  

The Hardy-Weinberg equation is written as a binomial expansion as shown below.

= 1

Each variable (or letters) represent either an allele or genotype frequency:

• p = frequency of the dominant allele
• q = frequency of the recessive allele
• p² = frequency of the homozygous dominant genotype
• q² = frequency of the homozygous recessive genotype
• 2pq = frequency of the heterozygous genotype

Based on the equation we see that the sum of the two allele frequencies is 1 and the sum of the three genotype frequencies is also 1.  This means that when calculating frequencies, the answer should be equal to or less than 1.