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Natural Selection

Natural Selection. Darwin vs Lamarck. Lamarck - animals passed on acquired traits Darwin - individuals are selected for survival by combinations of traits. Darwin observed…. More individuals are born than live to reproduce individuals vary from one another

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Natural Selection

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  1. Natural Selection

  2. Darwin vs Lamarck • Lamarck - animals passed on acquired traits • Darwin - individuals are selected for survival by combinations of traits

  3. Darwin observed… • More individuals are born than live to reproduce • individuals vary from one another • individuals compete with each other for resources • individuals with the best combination of traits for the given conditions will survive

  4. the combination of Darwinian natural selection and Mendelian genetics is called the synthetic theory of evolution

  5. Evidence of evolution • Fossil record • Comparative anatomy • Biogeography • Biochemistry

  6. Microevolution small gradual changes within a population over time. • Accounts for differences between populations of same species • For example, dark colored moths went from being 10% of population to 80% when soot made tree trunks dark and switched success of predators.

  7. Inheritance itself will not cause achange in allele frequencies • Allele frequencies will not change if • there is random mating • there are no mutations • there is no migration • there is no natural selection • UNDER THESE CONDITIONS THERE IS GENETIC EQUILIBRIUM!!!!

  8. Mutation • A random, permanent change in DNA • does not determine the direction of evolution (mutations occur randomly, not in response to need or conditions)

  9. Genetic Drift • Involves changes in allele frequencies of gene pool due to chance. • In small populations, there is greater chance that rare genotypes might not participate in next generation • When few individuals found a colony, only a fraction of total genetic diversity of original gene pool is represented—this is called the FOUNDER EFFECT

  10. The Founder Effect Amish of Lancaster, Pa. have recessive allele causing dwarfism and higher proportion of polydactylism (1:14 compared to 1:1000)

  11. Genetic Bottleneck • Populations subjected to near extinction because of a natural disaster endure a bottleneck. • Chance determines which few genotypes participate in production of the next generation. • For example, cheetahs have uniform enzymes, indicating this bottleneck caused certain alleles to be lost from a population.

  12. Types of Selection • Stabilizing selection - tends to make population more uniform (birth weight of human infants between 6.8 lbs and 7.7 lbs have better chance of surviving than weights on either extreme) • Directional selection - favors one extreme (Pesticide effects on insects and antibiotics on bacteria are directional selection agents producing resistant strains) • Disruptive selection - favors both extremes (land snails in low vegetation areas are eaten by thrushes if they have dark shells, and in forest areas banded shelled snails get eaten; result is a mixed population)

  13. Speciation occurs when one species gives rise to two species through reproductive isolation • Species - members freely breed with one another • Reproductive isolation - • temporal isolation (different times) • behavioral isolation (courtship patterns) • mechanical isolation

  14. Types of Speciation • Allopatric speciation - geographic separation results in new species • Sympatric speciation - divergence in same geographic area (insects)

  15. Adaptive Radiation proliferation of species by adaptation to new ways of life.

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