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Population Genetics Hardy-Weinberg and More Variation of Traits in a Population • Bell Curve – Extremes at each end • Causes of Variation – – – – Environment and heredity Mutation Recombination Random fusion of gametes Allele frequencies and Gene Pool • • Total genetic information available in population Allele frequency is determined by dividing number of certain allele by total number of alleles. – • P+Q=1 – P = number of recessive/total number of alleles – Q =number of dominant/total number of alleles Predicting Phenotypes – Phenotype frequency • Equal to the number of individuals with particular phenotype divided by the total number of individuals in the population. • Same principle as allele frequencies • P2 + 2PQ + Q2 = 1 Hardy Weinberg Equilibrium • • Allele frequencies in a population remain the same from generation to generation unless acted on by outside influences. Assumptions about an ideal “made up” population that is not evolving – – – – – No net mutations occur Individuals neither enter nor leave the population. The population is large Individuals mate randomly. Natural Selection does not occur. What is Microevolution? What is Microevolution? • A change in the gene frequency of a population • Can be seen over short periods of time – One generation to the next – For example, the frequency of a gene for pesticide resistance in a population of crop pests increases – There can be many reasons for microevolution Disruption of Genetic Equilibrium • Mutation – Can produce totally new alleles for a trait – Most are harmful but the beneficial ones are important for evolution • Migration – Immigration: Movement of individuals into a population – Emigration: Movement of individuals out a population • This is gene flow, the process of genes moving from one population to another Disruption of Genetic Equilibrium • Genetic Drift – Allele frequencies change as a result of random events or chance – Small populations • a) Founders effect • b) Bottle neck • Non-Random Mating – Many species do not mate randomly – Based on geographic proximity and similar physical characteristic Disruption of Genetic Equilibrium Disruption of Genetic Equilibrium • Natural Selection – Stabilizing selection • • – Directional selection • – Individuals with average form of trait have highest fitness Extreme forms have lower fitness One extreme form has greater fitness then average Disruptive Selection • Either extreme have greater fitness Disruption of Genetic Equilibrium • Sexual Selection – Colors – Females choose males based on certain traits – Extreme traits give female indication of quality of males genes