1.15.2009 Previous lecture continued continued Genetic drift - Increases the chance of evolution with smaller population sizes Natural Selection Founder?s Effect: Look at the map: native populations. Gene flow Can sometimes keep higher levels of evolution from moving forward Exchange of genetic material between populations of the same species Alleles spread through gene flow even when selection is not operating on the alleles Species: group of related organisms whose members can interbreed to produce offspring that live and reproduce. Gene flow can prevent speciation ? the formation of a new species Macroevolution ? accumulation of changes in a species until they become biologically distinct (i.e. a new species) Mutation Mistakes in copying DNA Important for generating and maintaining variation Rates are typically low ? it?s a rare occurance [Hidden variation]* Evolutionary Forces Evolution is a change in a population?s genotype frequencies Evolutionary forces: Natural selection Genetic drift Gene flow mutation when these forces are inactive, population is said to be in equilibrium (gene flow and mutation occur at a low rate, so they are almost in equilibrium) Hardy Weinberg Equilibrium When no evolutionary forces effect a population and there is random mating, populations will be in H-W Equilibrium after one generation If population does not show an H-W Equilibrium, evolutionary forces must be at work H-W Equilibrium: Frequency of aa = q^2 Frequency of Aa = 2pq Frequency of AA = p^2
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