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Population Genetics Modern Synthesis of Evolution Integrates discoveries and ideas from many different fields, including paleontology, taxonomy, biogeography, and population genetics Emphasizes Populations evolve, not individuals Natural selection is the most important mechanism of evolution Gradualism – large changes evolve as an accumulation of small changes over a long time Population A population is a group of organisms of the same species that live in a certain area A gene pool is composed of all the genes in a population The Hardy-Weinberg Theorem It states: “The frequency of alleles and genotypes in a population’s gene pool will remain constant over the generations unless acted upon by agents other than sexual recombination” WHAT?? The number of alleles and genotypes is not going to change in a given population is not going to change (unless the population is NOT in equilibrium) 5 Conditions Required for Hardy-Weinberg Equilibrium 1. 2. 3. 4. 5. Very large population size Isolation from other populations No net mutations Random mating No natural selection The Hardy-Weinberg Equations p2 + 2 pq + q2 = 1 p+q=1 p=frequency of dominant allele (A) q=frequency of recessive allele (a) p2=frequency of AA q2= frequency of aa 2pq=frequency of Aa The Hardy-Weinberg Theorem How is it helpful? Although the Hardy-Weinberg theorem describes a gene pool in equilibrium (ie. one that is NOT evolving), it can help us understand that evolution DOES occur If p and q change over time, then the population is evolving. We can gauge how quickly the population is evolving by how much p & q change over time.