BIOL 1411 1st Edition Lecture 33 Outline of Last Lecture I Variation in Population Outline of Current Lecture II Variation in Population a Selection b Hardy Weinberg Lecture Individual Fitness o Natural selection acts on the phenotype rather than directly on the genotype o The reproductive contribution of a phenotype to subsequent generations relative to other phenotypes is called fitness o Fitness of a phenotype is determined by the rate of survival and reproduction of individuals with that phenotype relative to others Sexual Selection acts on characters that determine reproductive success o If an individual survives but does not reproduce it makes no contribution to the nest generation o Sexual selection favors traits that increase the chances of reproduction o Intrasexual with into one sex o Intersexual opposite sex o Stabilizing Selection preserves average phenotype o Directional Selection favors individuals that vary in one direction o Disruptive selection favors individuals that vary in opposite directions from the mean Allele Frequencies o If p is the frequency of allele A and q is the frequency of allele a P q 1 Q 1 p o If there is only one allele at a locus its frequency 1 The population is monomorphic at the locus the allele is said to be fixed Hardy Weinberg Model o Frequencies of different alleles at each locus and frequencies of genotypes in a Mendelian population make up the genetic structure of the population These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o Hardy Weinberg equilibrium describes a model population in which allele and genotype frequencies do not change o The hardy Weinberg model predicts genotype frequencies in a sexual population simply as a product of allele frequencies Assumptions of the Hardy Weinberg Model o Mating is random o Population size is infinite o No gene flow no migration into or out of the population o No mutation o Natural selection does not affect survival of any genotypes Hardy Weinberg Equilibrium o Allele frequencies remain constant o After one generation genotype frequencies occur in there proportions Genotype AA As aa Frequency p 2 2pq q 2 Hardy Weinberg Equation o P 2 2pq q 2 1 o At equilibrium allele and genotype frequencies remain constant Utility of the Hardy Weinberg model o Populations in nature never exhibit the conditions of equilibrium o However it is useful for predicting genotype frequencies fro allele frequencies and many populations fit these predictions o Also because the model describes conditions that would result in no evolution deviations from the model s predictions are used to identify mechanisms of evolution
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