1. Chapter 16 Evolution 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

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

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

9. 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

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

11. 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.

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

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

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

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

17. Types of selection

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

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

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

21. Height Selection Activity:
Only extremely tall and extremely short
Only medium
Only extremely tall

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

23. Types of Evolution

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

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

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

28. Rate of Evolution

29. Catastrophism
Evolution occurs after a catastrophy

30. Gradualism
Evolution proceeds in small, gradual steps

31. 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.

33. Chapter 17 The History of Life

34. If one of the Earth’s plates moves 1. 9 cm a yr
If one of the Earth’s plates moves 1.9 cm a yr., in 1 million years it would move 12 miles

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

40. Most organisms are now extinct 2. fossils occur in a particular order 3. groups of organisms have changed over time

41. Extinct—a species that has died out

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

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

44. 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.

46. 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.

47. The oldest layers are on the bottom
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

48. Potassium-40 1.3 billion yrs
Half-life—the length of time required for half of the radioactive atoms in a sample to decay
Carbon
Uranium million yrs
Potassium billion yrs
Uranium billion yrs

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

50. Microfossils—microscopic fossil

54. Mass Extinction—many types of living things become extinct in a short period of time
Example: Dinosaurs