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Population Genetics and Hardy Weinburg Population Genetics • Study of the allele frequencies in a given population. • Gene Pool – All the genes (alleles) in a population What alleles do you see in this pig pop.? Hardy Weinberg Equations p+q=1 p = frequency of dominant allele q = frequency of recessive allele p2 + 2pq + q2 = 1 p2 = frequency or % homozygous dominant (AA) 2pq = frequency or % heterozygous (Aa) q2 = frequency or % homozygous recessive (aa) Let’s use Hardy’s rules to calculate the frequencies of the alleles and genotypes in a population. If a population has a recessive genotype frequency of .36, what is the frequency of the recessive allele? 1. 2. What information did the question give you? a. q2 = .36 (frequencies are usually written as decimals) What information does the problem ask for? a. q = .6 What if the problem ask for the dominant allele frequency? P = 1-q = .4 What other information can be determined? • What is the frequency of the recessive genotype? • What is the frequency of the homozgyous dominant genotype? • What is the frequency of the heterozygous genotype? • Out of 100 individuals, how many will have the dominant phenotype? Now what? Why use Hardy Weinberg equations? • To be able to compare the initial allele frequency with the final allele frequency. Ex: The same population was analyzed 5 years later. 25% of the population expressed the homozygous phenotype. What is the frequency of the recessive and dominant alleles now? p and q are both .5 The population has changed…. Hardy-Weinberg Principle • This principle will be maintained in nature only if all five of the following conditions are met: 1. Very large population 2. Isolation from other populations 3. No net mutations 4. Random mating 5. No natural selection If these conditions are met, the population is at genetic equilibrium. But…, populations are not isolated from variation. Frequencies can change depending on the conditions that exist in the environment. If the frequencies in a population change over time the population has evolved.