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How Natural Selection works

How Natural Selection works. Natural selection works on phenotypes Natural Selection reduces variation. Normal Distribution. Bell shaped curve Most organisms have an average trait Has variation. Make sure you draw these in your notes!. Directional Selection.

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How Natural Selection works

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  1. How Natural Selection works

  2. Natural selection works on phenotypes Natural Selection reduces variation

  3. Normal Distribution Bell shaped curve Most organisms have an average trait Has variation Make sure you draw these in your notes!

  4. Directional Selection Favors one extreme of the trait…pushes the curve in one direction

  5. Disruptive Selection Aka diversifying selection Selects for both extremes of the trait

  6. Stabilizing Selection • Reduces the extremes (selects against them) • Favors the average for the trait • Ex: Birth weight in humans

  7. Sexual Selection Males normally compete for females, behavior or physical features that females look for in a suitable male are the basis for sexual selection. Ex. Peacock tails

  8. Adaption An inherited trait (variation) that increases the chance of survival and reproduction in a particular environment (3 classifications)

  9. Morphological Adaption • A structural adaption that increases an organisms likeness to survive • Ex: shape, coloration etc

  10. Physiological Adaption • An adaption that helps an organism do special things in order to survive better • Ex: venom!

  11. Behavioral Adaption • Inherited behavior (instincts) or the ability to learn • Ex: vocalizations and mating

  12. Speciation • The evolution of one or more species from a single ancestral species • New species can be formed by reproductive isolation mechanisms or RIMS – they can be considered either pre-zygotic or post-zygotic

  13. Geographic (Habitat) Isolation Pre-zygotic: When a population is separated from another section of the population. The separated population may respond to selection pressures differently and over time eventually become a new species

  14. Behavioral Isolation • Pre-zygotic: When two populations are capable of interbreeding but have differences in behavior which keeps them from breeding • Ex: courtship rituals Lady Amerhurst’s pheasants

  15. Temporal Isolation Pre-zygotic: When two or more different species reproduce at different times, which keeps them from interbreeding

  16. Mechanical Isolation Pre-zygotic: Parts of organisms do not work together.

  17. Gametic Isolation Pre-zygotic: Sperm will not fertilize the egg

  18. Hybrid Inviability Post-zygotic: Fetus does not survive

  19. Hybrid Sterility Post-zygotic: Hybrid offspring is sterile

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