Population Genetics

Population Genetics - Would Cuvier have supported the law...

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10/13/09 1 Lecture 5 The Genetics of Populations Reading Ch 23 Would Cuvier have supported the law of succession? Which of the following explains your answer? a. Yes, his work showed that species went extinct b. Yes, he understood that older fossils were more dissimilar than younger fossils to current life forms c. Yes, his work demonstrated that all species are related d. All of the above e. None of the above Overview I. What is a population II. Probability III. Hardy Weinberg Equilibrium IV. Violations of Hardy Weinberg Species - group whose members have the potential to interbreed in nature and produce viable offspring Population – group of individuals from the same species that live in the same area and interbreed Devil’s hole pupfish Northern flicker II. Probability Probability – formal study of the laws of chance How likely is it that something will happen? Probabilities are always between 0 and 1 1. Chance of two events happening: Chance of getting heads on toss of penny = 1/2 Chance of getting heads on toss of another penny = 1/2 Chance of tossing one penny AND another penny and getting heads on both = 1/2 * 1/2 = 1/4 Combined chance of 2 independent events - multiplication problem

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10/13/09 2 2. Chance of one OR another event happening: Chance of getting 6 on one roll of die = 1/6 Chance of getting a 5 on one roll of a die = 1/6 Chance of getting a 6 OR a 5 on one roll is 1/6 + 1/6 = 2/6 = 1/3 Chance of one OR other independent events - addition problem III. Hardy-Weinberg Equilibrium Principle What would the genetic composition of a population be, if that population were NOT evolving? What would the genetic composition of a population be, if that population were NOT evolving? Why is this an interesting question? Null model – basis for comparison Definitions - review gene - the functional unit of heredity allele – alternative forms of a gene locus – location on a chromosome (pl. loci) For now, we are concerned with a population: diploid sexually reproducing 2 possible alleles at a locus (A 1 , A 2 )
10/13/09 3 Definitions - review homozygote - same 2 alleles at a locus (AA, A 1 A 1 , etc.) heterozygote - different alleles at a locus (Aa, A 1 A 2 , etc.) gametes (egg & sperm) are haploid zygote - fertilized egg, diploid Hardy-Weinberg Equilibrium Principle What would the genetic composition of a population be, if that population were NOT evolving? (general case) (specific case) Imagine you have a population of alleles, sample at random to create zygote If we know allele frequencies, can calculate genotype frequencies homozygote = p + q = 1 1. Chance of two events happening: Chance of getting heads on toss of penny = 1/2 Chance of getting heads on toss of another penny = 1/2 Chance of tossing one penny AND another penny and getting heads on both = 1/2 * 1/2 = 1/4 Combined chance of 2 independent events - multiplication problem (general case) (specific case) If we know allele frequencies, can calculate genotype frequencies A 1 A 1 homozygote = p 2 A 2 A 2 homozygote = q 2 (general case) (specific case) If we know allele frequencies, can calculate genotype frequencies heterozygote =

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