Population Genetics

# Population Genetics - Population Genetics pp 676 697...

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Population Genetics pp. 676 - 697 Terminology 0. Population 0. a group of individuals of the same species that can interbreed with each other 1. gene pool 1. the total of all alleles carried in all members of a population 2. polymorphism 2. "many forms" 3. many traits display variation within a population o phenotypic frequency o the proportion of individuals in a population that are a particular phenotype o genotypic frequency the proportion of total individuals in a population that are of a particular genotype. Number of individuals with a particular genotype in a population Total number of all individuals in a population o allelic frequency the proportion of all of the copies of a gene in a population that are of a given allele type. Number of copies of an allele in a population Total number of all individuals in a population Genotypic frequency 3. 182 RR, 172 Rr, or 44 rr f (RR) = number of RR individuals = 182/398 = .457 = 46% N f (Rr) = number of Rr individuals = 172/398 = .432 = 43% N f (rr) = number of rr individuals = 44/398 = .11 = 11% N

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Allelic frequencies 4. two alleles, R and r f (R) = 2n(RR) + n(Rr) = p 2N f (r) = 2n(rr) + n(Rr) = q 2N p = f (R) = 2(182) +172 = 536 = .673 = 67% 2(398) 796 q = f (R) = 2(44) +172 = 260 = .327 = 33% 2(398) 796 can be calculated from genotypic frequencies too p = f (R) = f (RR) + ½ f (Rr) = .437 + ½ (.432) = .673 q = f (r) = f (rr) + ½ f (Rr) = .111 + ½ (.432) = .327 Hardy-Weinberg 5. AKA H-W expression, H-W equilibrium, H-W equation, etc. 6. used to show the relationship between allelic and genotypic frequencies in populations 7. Based on an "idealized" population 4. no migration 5. random mating 6. no natural selection 7. no mutation 8. very large (infinitely large) Allelic frequencies genotypic frequencies p + q = 1 p 2 + 2pq + q 2 = 1
To summarize 8. genotypic frequencies are 9. p 2 for RR 10.2pq for Rr 11. q 2 for rr 9. known as Hardy-Weinberg proportions 10.Since these genotypic frequencies represent the total of all genotypes in population, they MUST add up to one Properties of Ideal Population o The frequency of alleles does not change from generation to generation o After one generation of random mating, offspring genotypic frequencies can be predicted from parental allelic frequencies

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## This note was uploaded on 05/12/2008 for the course BSCI 222 taught by Professor Gdovin during the Spring '08 term at Maryland.

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Population Genetics - Population Genetics pp 676 697...

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