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Population Genetics

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.

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Population Genetics

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  1. Population Genetics Hardy-Weinberg and More

  2. Variation of Traits in a Population • Bell Curve • Extremes at each end • Causes of Variation • Environment and heredity • Mutation • Recombination • Random fusion of gametes

  3. 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

  4. 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.

  5. What is Microevolution?

  6. 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

  7. 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

  8. 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

  9. Disruption of Genetic Equilibrium

  10. Disruption of Genetic Equilibrium • Natural Selection • Stabilizing selection • Individuals with average form of trait have highest fitness • Extreme forms have lower fitness • Directional selection • One extreme form has greater fitness then average • Disruptive Selection • Either extreme have greater fitness

  11. Disruption of Genetic Equilibrium • Sexual Selection • Colors • Females choose males based on certain traits • Extreme traits give female indication of quality of males genes

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