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Chapter 16 Evolution of Populations

Chapter 16 Evolution of Populations. Two main sources of genetic variation. Mutations—change in genes (DNA sequence) or chromosomes Gene recombination—mixing of genes that result from meiosis and sexual reproduction.

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Chapter 16 Evolution of Populations

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  1. Chapter 16Evolution of Populations

  2. Two main sources of genetic variation Mutations—change in genes (DNA sequence) or chromosomes Gene recombination—mixing of genes that result from meiosis and sexual reproduction

  3. Gene Pool—the combined genetic information of all the members of a particular populaiton

  4. Speciation—formation of a new species through reproductive isolation Example: Galapagos Island finches Ground Squirrels **Quick Speciation Activity**

  5. Fig. 24-6 A. harrisi A. leucurus

  6. Types of reproductive isolation Behavioral isolation (sympatric) Geographical isolation (allopatric) Which type did we demonstrate in our activity? If one of the Earth’s plates moves 1.9 cm a yr., in 1 million years it would move 12 miles

  7. Geographic Isolation Some birds from species A cross to a second island. The two populations no longer share a gene pool.

  8. Changes in the Gene Pool Seed sizes on the second island favor birds with large beaks. The population on the second island evolves into population B, with larger beaks.

  9. Fig. 22-6 (a) Cactus-eater (c) Seed-eater (b) Insect-eater

  10. Species—a group of similar organisms that can breed and produce fertile offspring

  11. Fig. 24-2a (a) Similarity between different species

  12. Exit Slip • List the conditions required for a population to become a species.

  13. Types of selection

  14. 1. Disruptive Selection • Selection that splits a population into 2 groups. • Removes individuals with average traits, but keeps those with more extreme traits.

  15. 2. Stabilizing Selection • Eliminates extreme expressions of a trait when the average expression leads to higher fitness. • Most common form of natural selection.

  16. 3. Directional Selection • An extreme version of a trait makes an organism more fit.

  17. Height Selection Activity: • Only extremely tall and extremely short • Only medium • Only extremely tall

  18. 4. Sexual Selection • Operates in populations where males and females look very differently. • Typically, males will be larger and more colorful.

  19. Types of Evolution

  20. Adaptive radiation (divergent evolution)— a single species evolves into several new species that live in different ways

  21. Convergent evolution—unrelated species independently evolve similarities when adapting to similar environments

  22. Coevolution— two species evolve in response to changes in each other over timeExample: mutualism Moth pollinates the comet orchid

  23. Rate of Evolution

  24. Catastrophism • Evolution occurs after a catastrophy

  25. Gradualism • Evolution proceeds in small, gradual steps

  26. Punctuated Equilibrium • Rapid spurts of genetic change that cause species to diverge quickly. • These periods disrupt much longer periods when the species exhibit little change. • Instances of abrupt transitions.

  27. Chapter 17The History of Life

  28. If one of the Earth’s plates moves 1.9 cm a yr., in 1 million years it would move 12 miles

  29. Fossil record—information about past life that has been obtained from fossils-it is incomplete

  30. Most organisms are now extinct2. fossils occur in a particular order3. groups of organisms have changed over time

  31. Extinct—a species that has died out

  32. Where do most fossils form? Most fossils form in sedimentary rock as weight compresses layers of sediment in bodies of water

  33. Index Fossil—an easily recognized species used to compare the relative ages of fossils

  34. Sedimentary rocks form in horizontal layers. When part of Earth’s crust is compressed, a bend in a rock forms, tilting the rock layers. As the surface erodes due to water, wind, waves, or glaciers, the older rock surface is exposed. New sediment is then deposited above the exposed older rock surface.

  35. Water carries small rock particles to lakes and seas. Dead organisms are buried by layers of sediment, which forms new rock. The preserved remains may later be discovered and studied.

  36. Relative dating—the age of a fossil is determined by comparing its placement with fossils in other layers The oldest layers are on the bottom

  37. Half-life—the length of time required for half of the radioactive atoms in a sample to decay Carbon-14 5770 Uranium-235 713 million yrs Potassium-40 1.3 billion yrs Uranium-238 4.5 billion yrs

  38. Radioactive dating—scientists use half-life to calculate the age of fossils based on the amount of remaining radioactive isotopes

  39. Microfossils—microscopic fossil

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