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MECHANISMS FOR EVOLUTION
Honors Biology
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REVIEW
• Evidence for Evolution and Examples• What is Natural Selection?• How did Darwin develop theory of Natural Selection?
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PATTERNS OF EVOLUTION
• Coevolution:– 2 or more species evolve in association with one
another– Predators and Prey– Plants and Pollinators– Bats and Flowers
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PATTERNS OF EVOLUTION
• Convergent Evolution:– Organisms that look similar but are not related– Analogous features– Similar environments– Sharks and Dolphins
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PATTERNS OF EVOLUTION
• Divergent Evolution– 2 or more related populations or species become
more and more dissimilar – Usually a response to new habitat– Can result in new species– Adaptive radiation– Artificial Breeding– Humans and Chimps
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POPULATION GENETICS AND EVOLUTION
• What did Darwin know?– Environment is important– Competition for Resources– Natural Selection: Individuals with traits more
suitable for a particular environment are more likely to survive AND reproduce
• What did Darwin not know?– Where does variation come from
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POPULATION GENETICS
• We now know that variation comes from genetics; no variation extinction
• Population genetics: study of evolution from genetic point of view
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WHAT CAUSES VARIATION
• Need to think about variation in GENOTYPE– Mutation: change in DNA/chromosomes– Recombination: during meiosis– Random fusion of gametes
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OTHER MECHANISMS FOR EVOLUTION
• Things that upset genetic equilibrium• Using Hardy Weinberg you can predict
genotypes; Only in hypothetical populations
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MUTATION
• Change in DNA or chromosomes• Make new alleles for a trait• Many are harmful• Can be neutral (code for same amino acid)• Some are beneficial
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MIGRATION/GENE FLOW
• Call it gene flow• Populations exchange genes• Increases within group variation• Decreases between group variation• DOESN’T HAVE TO BE MIGRATION
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GENETIC DRIFT
• Occurs in small populations• Allele frequencies shift as a result of RANDOM
events• Coin Toss• Founders Effect; Bottleneck
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NONRANDOM MATING
• Sexual Selection• Positive assortative mating – mate with
someone similar• Negative assortative mating: redheads!
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NATURAL SELECTION
• Darwin and neoDarwinians believe is the most important way evolution occurs
• Types of Selection
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STABILIZING SELECTION
• Average form are selected for• Lizards:– Predators caught slow small and large visible– Select for medium size
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DIRECTIONAL SELECTION
• Individuals with an extreme trait are selected for
• Anteaters with long tongues
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DISRUPTIVE SELECTION
• Individuals with either extreme are selected for
• Limpet shell color; light and dark on different surfaces
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SEXUAL SELECTION
• Choosing mates based on traits• Intersexual Selection• Intrasexual Selection• Bird Color
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SPECIATION
• If enough changes accumulate new species• Biological concept of species: organisms can
mate and produce fertile offspring; not just morphological (what they look like)
• Isolating mechanisms speciation– Geographic isolation– Reproductive isolation
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SPECIATION
• Rates of speciation– Gradualism: species evolve gradually over time– Punctuated equilibrium: species go through times of fast change and slow or no change