Microevolution and Changing Alleles (The Hardy-Weinberg Principle) (Chap. 19)

1. Microevolution and Changing Alleles (The Hardy-Weinberg Principle)(Chap. 19) • Know from text: population, gene pool, population genetics, allele frequency

2. Hardy Weinberg Principle/Equation • In genetics, frequency refers to a proportion or percentage • both the allele and genotype frequencies will remain unchanged (genetic equilibrium) unless outside forces change those frequencies. • can be used to test for natural selection • if allele and genotype freq. in a pop. are in equilibrium for a particular gene, natural selection (among other things) is not affecting the population and there is no evolution happening

3. Rationale behind HW Principle • What are the probabilities of obtaining various gametic combinations? • prob. of A from male & A from female: • pm x pf = p2 • prob. of a from male & a from female: • qm x qf  = q2 • prob. of A from male & a from female, or a from male & A from female:     • (pm x qf ) + (pf x qm ) = 2pq • What is the result of the binomial expansion of p & q in males & females • (pm + qm) (pf + qf) = p2 + 2pq + q2

4. p= frequency of dominant allele • q = frequency of recessive allele • the sum of the frequencies of the alleles within a population must always equal 1 • p + q = 1 • ex. A + a = 1 • the sum of genotypes must also equal 1. • p2 + 2pq + q2 = 1 • p2 = freq. of AA genotype • 2pq = freq. of Aa genotype • q2 = freq. of aa genotype • ex) AA + Aa + aa must total 1

5. Restrictions of the Hardy-Weinberg Principle • mating is random • no mutation • no immigration nor emigration • alleles must segregate (Mendel’s first law) • population and sample are infinitely large • no natural selection operating on the population