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Evolution of Populations Raven Ch. 21 AP Biology 2007-2008 Doonesbury - Sunday February 8, 2004 Populations evolve Natural selection acts on individuals Variation results in: differential survival “survival of the fittest” differential reproductive success who bears more offspring Populations evolve genetic makeup of population changes over time favorable traits (greater fitness) AP Biology become more common Mummichog Individuals DON’Tare evolve… Individuals survive orselected don’t survive… Populations evolve Individuals reproduce or don’t… AP Biology 2007-2008 Variation & natural selection Variation is the raw material for natural selection there have to be differences within population some individuals must be more fit than others Fitness- Survival & Reproductive success AP Biology individuals with one phenotype leave more surviving offspring Where does Variation come from? random changes to DNA errors in mitosis & meiosis Wet year Beak depth Mutation Dry year Dry year environmental damage mixing of alleles recombination of alleles new arrangements in every offspring new combinations = new phenotypes spreads variation offspring inherit traits from parent AP Biology 1980 1982 1984 11 Beak depth of offspring (mm) Sex 1977 Dry year 10 9 8 Medium ground finch 8 9 10 11 Mean beak depth of parents (mm) Changes in populations Bent Grass on toxic mine site Pocket Mice in desert lava flows Pesticide molecule Target site Resistant target site Insect cell site Target membrane Insecticide resistance AP Biology Decreased number of target sites 5 Agents of evolutionary change Mutation Gene Flow Genetic Drift AP Biology Non-random mating Selection 1. Mutation & Variation Mutation creates variation Mutation rates in individuals are low (1 in 100,000 division) But are constantly appearing in populations Mutation changes DNA sequence. As a result, may change: Protein amino acid sequence may change protein structure? may change protein function? changes in protein may AP Biology change phenotype & therefore change fitness 2. Gene Flow Movement of individuals & alleles in & out of populations seed & pollen distribution by wind & insect migration of animals sub-populations may have different allele frequencies causes genetic mixing across regions reduce differences between populations AP Biology Human evolution today Gene flow in human populations is increasing today transferring alleles between populations Are we moving towards a blended world? AP Biology 3. Non-random mating Sexual selection AP Biology 4. Genetic drift Effect of chance events founder effect small group splinters off & starts a new colony bottleneck some factor (disaster) reduces population to small number & then population recovers & expands again AP Biology 5. Natural selection Differential survival & reproduction due to changing environmental conditions climate change food source availability predators, parasites, diseases toxins combinations of alleles that provide “fitness” increase in the population adaptive evolutionary change AP Biology 5 Agents of evolutionary change Mutation Gene Flow Genetic Drift AP Biology Non-random mating Selection Any Questions?? AP Biology 2005-2006