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Mechanisms for Evolution

Mechanisms for Evolution. Natural selection traits that improve survival or reproduction accumulate in the population ADAPTIVE change Genetic drift frequency of traits changes in a population due to chance events RANDOM change. Natural Selection.

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Mechanisms for Evolution

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  1. Mechanisms for Evolution • Natural selection • traits that improve survival or reproduction accumulate in the population • ADAPTIVE change • Genetic drift • frequency of traits changes in a population due to chance events • RANDOM change

  2. Natural Selection • Selection acts on any trait that affects survival or reproduction • predation selection (speed, camouflage, defenses) • physiological selection (disease resistance, protection from injury) • sexual selection (attractiveness, fertility)

  3. Modes of Selection Directional: Darker mice are favored because they live in dark rocks. Disruptive: Intermediate color at a disadvantage. Mice live in both light and dark rocks. Stabilizing: Intermediate color is advantaged, extremes are not favored.

  4. Genetic Drift • Chance events change frequency of traits in a population • not adaptation to environmental conditions • Founder effect • Bottleneck

  5. CWCW CRCR CRCR CRCR CRCR CRCR CRCW CRCR CRCW Only 5 of 10 plants leave offspring Only 2 of 10 plants leave offspring CRCR CRCR CWCW CRCR CWCW CRCR CRCW CRCW CRCR CRCR CRCR CWCW CRCR CRCW CRCR CRCR CRCR CRCR CRCW CRCW CRCW Generation 2 p = 0.5 q = 0.5 Generation 1 p (frequency of CR) = 0.7 q (frequency of CW) = 0.3 Generation 3 p = 1.0 q = 0.0  Genetic drift (can greatly affect small populations)

  6. albino deer Seneca Army Depot Founder effect (Genetic drift) • A new population is started by a small group of individuals or are isolated from other population • just by chance somerare traits may be at high frequency; others may be missing • skews the gene pool of new population • less genetic diversity

  7. Example: Distribution of blood types • Distribution of the O type blood allele in native populations of the world reflects original settlement

  8. Bottleneck effect (genetic drift) • A large population drastically reduced by a disaster • famine, natural disaster, loss of habitat… • loss of variation by chance event • narrows the gene pool

  9. Example: Cheetahs • All cheetahs share a small number of alleles • less than 1% diversity • as if all cheetahs are identical twins • 2 bottlenecks • 10,000 years ago • Ice Age • last 100 years • poaching & loss of habitat

  10. Question??? • What do you think is the definition of a species? • Pair up and write down your definition of a species and how do we get new species?

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