Hardy Weinberg What the heck is that?

Let’s look at Evolution What is a gene pool? includes all the alleles for all the genes present in the population So what does this mean? Means we can calculate different types of frequencies Allele frequencies Genotype frequencies

Suppose for example, that there are 1000 people in a population and they have the following genotypes for a trait: Genotype Number AA 490 people Aa 420 people aa 90 people Total: 1000 people

What is the genotype frequency? Genotype Number AA 490 ppl Aa 420 aa 90 Total: 1000 490/1000 = 0.49 420/1000 = 0.42 90/1000 = 0.09 Add all the genotype frequencies up and they should equal 1.0.

What is the phenotype frequency? Genotype Number AA 490 ppl Aa 420 aa 90 910/1000 = 0.91 90/1000 = 0.09 Equals 1.0 There are 2 phenotypes Dominant Recessive How many dominant individuals are there? 490 + 420 = 910 How many recessive individuals are there? 90

What is the allele frequency? Genotype Number AA 490 ppl Aa 420 aa 90 1400/2000 = 0.7 600/2000 = 0.3 Total is 1.0 There are 2 alleles A a So how many individuals have A? 490+490+420 = 1400 How many individuals have a? 420 + 90 + 90 = 600

Yes, if evolution was occurring Do you think these frequences (genotype, phenotype and allelic) would change over time? Yes, if evolution was occurring

These frequencies _________ change if the population was in genetic equilibrium. WOULD NOT

So these 2 guys, Hardy and Weinberg got together and said that if certain conditions are kept constant, large populations will not change their frequencies. So what are these conditions?

Five conditions are: Random mating – no selection of mates No net mutations Large population size No migration (immigration or emigration) No natural selection – no favoring of phenotypes

The best thing about Hardy Weinberg is It can be represented mathematically! And I know how much you guys LOVE math 

Symbols to memorize P = frequency of dominant allele (A) Q = frequency of recessive allele (a) And P+Q = 1; why? Because all students in the population are either dominant or recessive

Equations to memorize P2 = frequency of homozygous dominant (AA) 2pq = frequency of heterozygous dominant (Aa) Q2 = frequency of the recessive (aa) Also, P2 + 2pq + Q2 = 1; why? Because all people fall in one of those 3 groups above

So from our example earlier, What is Q2? What is Q? What is P? Does P + Q =1 in this example? What is P2? What is 2pq? Does , P2 + 2pq + Q2 = 1 in this example? 0.09 Genotype Number AA 490 ppl Aa 420 aa 90 0.3 0.7; remember p+q=1 0.7+0.3 = 1; yes P = 0.7, so (0.7)2 = 0.49 2(0.7)(0.3) = 0.42 0.49 + 0.42 + 0.09 = 1; yes