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Unformatted text preview: Evolution, part II 1 BIOL 112 Evolution II Chapters 21–25 BIOL 112 Darwinian Theory ! By the end of the 19 th Cent., Darwin’s Theory was in trouble ! Couldn’t adequately explain inheritance ! If favorable gene combinations are selected for, how keep them together through several generations? ! Standard 19 th Cent. Inheritance model was Blending Inheritance ! No one read or understood Mendel’s work ! By turn of 20 th Cent., “rediscovery” of Mendel: Hugo de Vries, Dutch geneticist discovered mutations (new alleles), and found and publicized Mendel’s papers BIOL 112 Darwin vs. Mendel? ! Evolutionists realized need to revise Darwin’s Theory to incorporate Mendelian Genetics ! Synthesis of Darwin and Mendel done in 1920s and 1930s by Fisher, Wright and Haldane ! Product is Neo-Darwinian Theory of Evolution. Combined two paradigms into one: ! Darwin Natural Selection acting on variations in phenotypes ! Mendel Genetic Variability: mutations and recombinations; and Principles of Heredity ! Evolution: a change in the genetic content of a population over time BIOL 112 Mendel Applied to Populations? ! Godfrey Hardy, British Mathematician ! Wilhelm Weinberg, German Physician ! In 1908, both independently developed mathematical application of Mendel’s principles to populations ! Hardy-Weinberg model of Population Genetics BIOL 112 Terms ! Gene Pool Sum of all genetic information in a reproducing population ! Allele (Gene) Frequencies Relative proportion of alleles in a population ! Genotype Frequencies Relative proportion of genotypes in a population ! What happens if allele frequencies change? Evolution , by definition ! Population Genetics Application of Mendelian principles to populations of organisms BIOL 112 Evolution, part II 2 BIOL 112 BIOL 112 Differences from Classical Mendelian Genetics ! We are considering all eggs and all sperm (pollen) in the reproductive population, not just those from two individuals in one breeding pair ! Conditions to be met to work mathematics: ! Breeding population is very large ! No mutations in population ! No immigration or emigration ! Reproduction success (contribution of eggs or sperm to pool) not related to genotypes/phenotypes of members of population * Notice that Campbell text lists 5 conditions: text splits last condition into two separate criteria BIOL 112 Hardy-Weinberg Equilibrium ! If all conditions are met, population in stable state in which allele frequencies and genotype frequencies will not change from generation to generation: H-W Equilibrium ! Population in equilibrium will not evolve unless outside forces intervene. Thus, “outside forces” will tend to cause evolution (allele frequency change) BIOL 112 Mathematical Derivation of Hardy-Weinberg Model ! Binomial Equation ! Starting with allele frequencies: f(A) = p; f(a) = q; ! (p + q) 2 = 1; ! p 2 + 2pq + q 2 = 1 ! Thus, one can identify genotype frequencies: ! f(AA) = p 2 ; ! f(Aa) = 2pq; ! f(aa) = q 2 BIOL 112 Back Calculation from HW...
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