# Hardy Weinberg Equilibrium Equation

The Hardy Weinberg Equilibrium Equation is an equation used to measure allele frequency in a population. It has set factors on the population being there is no Immigration or migration from the locale, as well it depends on random mating and mutations within the population. If these parameters are disrupted this will affect the outcome of the equations results. The crux of the equation is that allele frequency will remain constant within the given population as long as these parameters are kept.

The equation in it's simplest form is:

p2 + 2pq + q2 =1

this comes from a simple punnett square:

 p q p p2 pq q pq q2

If there are more than 2 alleles, the total allele frequencies must still app up to 1, (e.g. p + q + r = 1).

The equation for 3 alleles is written as:

p2 + q2 + r2 + 2pq + 2pr + 2qr = 1 or (p + q + r)

### When does Hardy-Weinberg not apply?

For the Hardy-Weinberg equilibrium to work a large population is needed so gene frequency doesn't change, this is known as genetic drift. Random mating must also occur, as a preference for certain characteristics will result in an increase in the frequency of certain genes. For the equilibrium to work. There must also be no evolutionary forces, as this will also change the frequency of certain genes, this is known as natural selection.

### Refferences

1. McClean, P., 1997. The Hardy-Weinberg Law. Population and Evolutionary Genetics. Available at: http://www.ndsu.edu/pubweb/~mcclean/plsc431/popgen3.htm [Accessed November 21, 2014].
2. M.Krempels, D., Hardy Weinberg calculations for multiple alleles at a single locus. College of Arts Sciences. Available at: www.bio.maimi.edu/dada/dox/trinomial.html [Accessed November 21, 2014].
3. McClean, P., 1997. The Hardy-Weinberg Law. Population and Evolutionary Genetics. Available at: http://www.ndsu.edu/pubweb/~mcclean/plsc431/popgen3.htm [Accessed November 21, 2014].
4. McClean, P., 1997. The Hardy-Weinberg Law. Population and Evolutionary Genetics. Available at: http://www.ndsu.edu/pubweb/~mcclean/plsc431/popgen3.htm [Accessed November 21, 2014].
5. McClean, P., 1997. The Hardy-Weinberg Law. Population and Evolutionary Genetics. Available at: http://www.ndsu.edu/pubweb/~mcclean/plsc431/popgen3.htm [Accessed November 21, 2014].