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Population Genetics

Population Genetics. Questions for Lecture 1. What are some of the causes of variations? 2. What is an allele frequency, what is the equation used to find allele frequency? 3. How do you use allele frequency? 4. What is a gene pool?

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Population Genetics

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  1. Population Genetics Questions for Lecture 1. What are some of the causes of variations? 2. What is an allele frequency, what is the equation used to find allele frequency? 3. How do you use allele frequency? 4. What is a gene pool? 5. What is Hardy Weinberg Equilibrium, and what are the 5 assumptions of a population which doesn't not evolve? 6. What disrupts genetic equilibrium?

  2. I.Variation of Traits in a population A. Bell Curve 1. Extremes at each end B. Causes of Variation 1. Environment and heredity 2. Mutation 3. Recombination a) During meiosis by independent assortment and crossing over 4. Random fusion of gametes

  3. II. Allele frequencies and gene pool A. Total genetic information available in population B. 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 C. Predicting Phenotypes 1. Phenotype frequency a) Equal to the number of individuals with particular phenotype divided by the total number of individuals in the population. b) Same principle as allele frequencies c) P2 + 2PQ + Q2 = 1

  4. III. Hardy Weinberg Equilibrium A. Allele frequencies in a population remain the same from generation to generation unless acted on by outside influences. B. Assumptions about an ideal “made up” population that is not evolving 1. No net mutations occur; allele frequencies do not change because of mutation. 2. Individuals neither enter nor leave the population. 3. The population is large 4. Individuals mate randomly. 5. Natural Selection does not occur.

  5. IV. Disruption of Genetic Equilibrium A. Mutation 1. can produce totally new alleles for a trait 2. most harmful 3. beneficial are important for evolution B. Migration 1. Immigration a) Movement of individuals into a population 2. emigration a) movement of individuals out a population b) Gene flow (1) Process of genes moving from one population to another

  6. C. Genetic Drift 1. Allele frequencies change as a result of random events or chance 2. Small populations a) Founders effect b) Bottle neck D. NonRandom Mating 1. Many species do not mate randomly 2. based on a) geographic proximity b) similar physical characteristic (1) assortative mating

  7. E. Natural Selection 1. Stabilizing selection a) Individuals with average form of trait have highest fitness b) Extreme forms have lower fitness (1) Large – seen (2) Small – not fast 2. Directional selection a) One extreme form has greater fitness then average b) Anteaters longer tongue more effective 3. Disruptive Selection a) Either extreme have greater fitness

  8. F. Sexual Selection 1. Colors 2. Females choose males based on certain traits 3. Extreme traits give female indication of quality of males genes

  9. Summary • Causes of variation • predicting phenotype • Hardy Weinberg equilibrium • 6 things which disrupt genetic equilibrium

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