1. Chapter 13 Population Genetics

2. Question? u How did the diversity of life originate? u Through the process of Evolution.

3. Evolution u The processes that have transformed life on earth u Evolution: A change in a population’s gene pool over time.

4. Types of Evolution u Microevolution: Changes within a species (dozens or hundreds of generations) u Macroevolution: Origin of new species (much longer periods of time)

5. Galapagos Finches

6. Darwinian View u History of life is like a tree with branches over time from a common source. u Current diversity of life is caused by the forks from common ancestors.

7. Example

8. Darwin’s Voyage u Took a voyage on HMS Beagle u Used observations to make inferences about descent with modification

9. Observations: Observation 1 – Members of a population often vary greatly in their traits..

10. Observation 2 u Traits are inherited from parents to offspring.

11. Observation 3 All species are capable of producing more offspring than their environment can support.

12. Observation 4 u Due to lack of food or other resources, many of these offspring do not survive.

13. Inference 1 u Individuals whose inherited traits give them a higher probability of surviving and reproducing, tend to leave more offspring than other individuals.

14. Inference 2 u This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations.

15. Natural selection u Nature determines which characteristics are favorable.

16. Natural Selection in action

17. Artificial Selection u When man determines the characteristics that are favorable u Result - the various breeds of animals and plants we’ve developed.

18. Ex - Mustard Plant Original Cultivars

20. Evolution Success Measured By u Survival u Reproduction u Whoever lives long enough and has the most kids is the “winner” in evolution.

21. Requirements u In order for Natural Selection to work, you must have: u Variations within a population. u Long periods of time (according to Darwin).

22. Subtleties of Natural Selection 1. Populations are the units of Evolution. 2. Only inherited characteristics can evolve.

23. Changes in gene pools u Gene pool: all of the available genes in a population. u Allele frequency: How often an allele appears in a population u If evolution is not happening: allele frequency is not changing over time. u If evolution is happening: Allele frequency will change

24. Mechanisms for change u 1. Natural selection: increased reproductive success leads to increased allele frequency and vice versa.

25. Mechanisms for change u 2. Genetic drift: Random changes in small populations u Founder effect- a small founding population u Bottleneck- only a small population is left due to death

27. Mechanisms for change u 3. Gene flow: change in gene pool resulting from migration of individuals between populations

28. Mechanisms for change u 4. Mutation: direct conversion of one allele to another u Some will be good u Some will be bad u Most will be neutral

29. Genetic Variation u Variation allows for populations to adapt u 3 ways to get variation u Mutations u Crossing Over u Independent Assortment

30. Inbreeding depression u Happens when variation is low because of small original population u Everyone is more closely related (more similar=less genetic variation)

31. Causes of Inbreeding Depression u Founder Effect u Bottleneck Effect u Both start with small population and little genetic variation

32. Example u Cheetahs: Hunted to near extinction for hides u Small population that survived reproduced u Little genetic variation u Prone to virus like HIV u Prone to sterility

33. End of Part 1

34. Speciation

35. Species and Speciation u What is a species? u A group of organisms capable of breeding and producing fertile offspring under natural conditions

36. Keeping species separate u 1. potential mates do not meet u 2. potential mates meet but do not breed u 3. potential mates meet and breed but do not produce fertile or viable offspring

37. Speciation u Speciation: the creation of new species u Happens when 2 populations of organisms become so different in their genetic makeup that they can no longer breed

38. Speciation u Mostly happens when a small population is isolated from the rest of the species 2 things that speed up speciation u Bottleneck u Founder

39. Types of Speciation u Allopatric- Speciation due to a physical barrier u Sympatric- Speciation in the same area (due to another type of barrier)

40. Reproductive Barriers u Any barrier that separates members of the same population into two different ones u Eventually these populations could become different species based on different selection factors

41. Isolating mechanisms u Prezygotic- isolation that happens before the zygote is formed. u Geographical: u Behavioral u Temporal u Gametic u Mechanical u Ecological

42. Prezygotic barriers Isolation Geographical Behavioral Temporal Mechanical Gametic Ecological Separated by: Physical barriers Courting rituals Time -Day or Season Anatomical features Sperm and egg markers Different niches

43. Isolating mechanisms u Postzygotic- after zygote is formed u Hybrid inviability- won’t live u Hybrid sterility- sterile u Hybrid breakdown – hybrid’s offspring won’t live

44. Adaptive Radiation u Rapid emergence of several species from a common ancestor ( often Allopatric speciation) u Common in island and mountain top populations or other “empty” environments.

45. Mechanism u Resources are temporarily infinite. u Most offspring survive. u Result - little Natural Selection and the gene pool can become very diverse.

46. When the Environment Saturates u Natural Selection resumes. u New species form rapidly if isolation mechanisms work.

47. Speed of speciation? u How long does it take a new species to form? u How many genes are involved?

48. Gradualism Evolution u Darwinian style evolution. u Small gradual changes over long periods time.

49. Gradualism Predicts: u Long periods of time are needed for evolution. u Fossils should show continuous links.

50. Punctuated Equilibrium u Evolution has two speeds of change: 1. Gradualism or slow change 2. Rapid bursts of speciation

52. Possible Mechanism u Rapid: Adaptive Radiation, especially after mass extinction events u Gradual: Saturated environments favor gradual changes

53. End of Part 2