Hardy-Weinberg

Today you will learn about a principle known as Hardy-Weinberg Equilibrium.

Populations are always evolving, but two scientists developed a way to determine the gene pool in a population if the population is not evolving (called Hardy-Weinberg Equilibrium). So, Hardy-Weinberg Equilibrium is when a population remains constant with the number of dominant and recessive alleles stays the same, or in other words the population is not evolving since evolution means change.

First you will determine the factors that cause populations to change/evolve. These are the factors that cause a population NOT to be in Hardy-Weinberg equilibrium since the population is changing.
Go to this webpage and scroll down until you see = When the Hardy-Weinberg Law Fails to Apply = Read all the factors and make a short outline list of them with what they are and a brief explanation of what they mean and how they cause the population to change.

Second you will learn to use the Hardy-Weinberg equation to solve problems.
The Hardy-Weinberg equation allows us to figure out the percent of the population that is homozygous dominant, heterozygous and homozygous recessive if we assume the population is not changing. It also allows us to determine the percent of the dominant allele in the gene pool and the percent of the recessive allele in the gene pool. The first equation is as follows p + q = 1 p is the fraction of dominant alleles in the population q is the fraction of recessive alleles in the population This equation tells us that if 60% of the alleles in a population are dominant then p=0.6. If we know p then we can find q (recessive alleles). 1 - p = q, so 1 - 0.6 = .4. So 40% of the alleles in the population are recessive.

The second part of the equation is as follows
 * 1 = p2 ** + ** 2pq ** + ** q2 **


 * p 2 is the fraction of the population that is homozygous dominant. **


 * 2pq is the fraction of the population that is heterozygous **

So if 60% of the population has the dominant gene then you square 0.6 to get 0.36. In other words 36% of the population would be homozygous dominant (** p 2)  **. If 40% of the population has the recessive gene then you square 0.4 to get 0.16. In other words 16% of the population would be homozygous recessive (** q 2  **). Then 2 * 0.6 * 0.4 would be .48 or 48% of the population would be heterozygous (2pq).
 * q 2 is the fraction of the population that is homozygous recessive **

See this sample problem More samples And here is a video media type="youtube" key="xPkOAnK20kw" width="560" height="315"