1. Chapter 22-24 Review Notes

2. 1. Explain Darwin’s two main ideas: descent with modification and natural selection caused by adaptive radiation.

3. The Origin of Species Darwin developed two main ideas: –Descent with modification explains life’s unity and diversity –Natural selection is a cause of adaptive evolution Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

4. 2. Define and give an example of artificial selection.

5. Artificial Selection, Natural Selection, and Adaptation Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

6. 3. Give an example of Darwin’s four observations and two inferences on natural selection.

7. Darwin then described four observations of nature and from these drew two inferences Observation #1: Members of a population often vary greatly in their traits Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

8. Observation #2: Traits are inherited from parents to offspring Observation #3: All species are capable of producing more offspring than the environment can support Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

9. Observation #4: Owing to lack of food or other resources, many of these offspring do not survive Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

10. Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

11. Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

12. 4. Explain the statement that populations, not individuals, evolve over time.

13. Note that individuals do not evolve; populations evolve over time Natural selection can only increase or decrease heritable traits in a population Adaptations vary with different environments Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

14. 5. Compare and contrast homology and analogy in terms of evolution.

15. Homology Homology is similarity resulting from common ancestry There are anatomical and molecular homologies. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

16. Fig. 22-17 Humerus Radius Ulna Carpals Metacarpals Phalanges HumanWhale Cat Bat Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor

17. 6. How is comparative embryology used in evolutionary studies?

18. Fig. 22-18 Human embryoChick embryo (LM) Pharyngeal pouches Post-anal tail Comparative embryology reveals anatomical homologies not visible in adult organisms

19. 7. Describe how scientists use vestigial structures to make a phylogenetic tree.

20. Vestigial structures are remnants of features that served important functions in the organism’s ancestors (appendix, pelvic bones in whales) Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

21. Fig. 22-19 Hawks and other birds Ostriches Crocodiles Lizards and snakes Amphibians Mammals Lungfishes Tetrapod limbs Amnion Feathers Homologous characteristic Branch point (common ancestor) Tetrapods Amniotes Birds 6 5 4 3 2 1

22. 7. Define convergent evolution and give an example.

23. Convergent Evolution Convergent evolution is the evolution of similar, or analogous, features in distantly related groups Analogous traits arise when groups independently adapt to similar environments in similar ways Convergent evolution does not provide information about ancestry Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

24. 8. What is an endemic species and why is it important?

25. Biogeography Darwin’s observations of biogeography, the geographic distribution of species, formed an important part of his theory of evolution Islands have many endemic species that are often closely related to species on the nearest mainland or island Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

26. 9. Define a cline and how it is shown on a graph.

27. Variation Between Populations Most species exhibit geographic variation, differences between gene pools of separate populations or population subgroups Some examples of geographic variation occur as a cline, which is a graded change in a trait along a geographic axis

28. Genetic Drift The smaller a sample, the greater the chance of deviation from a predicted result Genetic drift describes how allele frequencies fluctuate unpredictably from one generation to the next Genetic drift tends to reduce genetic variation through losses of alleles

29. 10. Differentiate between gene flow and genetic drift. What role does the founder effect play upon it?

30. Fig. 23-9 Original population Bottlenecking event Surviving population

31. The Founder Effect The founder effect occurs when a few individuals become isolated from a larger population Allele frequencies in the small founder population can be different from those in the larger parent population

32. Gene Flow Gene flow consists of the movement of alleles among populations Alleles can be transferred through the movement of fertile individuals or gametes (for example, pollen) Gene flow tends to reduce differences between populations over time Gene flow is more likely than mutation to alter allele frequencies directly

33. 11. Describe the ways in which gene flow can increase/decrease the fitness in a population.

34. In bent grass, alleles for copper tolerance are beneficial in populations near copper mines, but harmful to populations in other soils Windblown pollen moves these alleles between populations The movement of unfavorable alleles into a population results in a decrease in fitness between organism and environment Gene flow can decrease the fitness of a population

35. Insecticides have been used to target mosquitoes that carry West Nile virus and malaria Alleles have evolved in some populations that can offer insecticide resistance to these mosquitoes The flow of insecticide resistance alleles into a population can cause an increase in fitness Gene flow can increase the fitness of a population

36. 12. Differentiate between directional, disruptive, and stabilizing and give examples of each.

37. Directional, Disruptive, and Stabilizing Selection Three modes of selection: –Directional selection favors individuals at one end of the phenotypic range –Disruptive selection favors individuals at both extremes of the phenotypic range –Stabilizing selection favors intermediate variants and acts against extreme phenotypes

38. Fig. 23-13 Original population (c) Stabilizing selection (b) Disruptive selection (a) Directional selection Phenotypes (fur color) Frequency of individuals Original population Evolved population

39. 13. Define balancing selection. Where would find this in nature?

40. Balancing Selection Balancing selection occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population

41. 14. Describe heterozygote advantage in terms of sickle-cell and malaria.

42. Heterozygote advantage occurs when heterozygotes have a higher fitness than do both homozygotes Natural selection will tend to maintain two or more alleles at that locus The sickle-cell allele causes mutations in hemoglobin but also confers malaria resistance Heterozygote Advantage

43. 15. Define hybrid vigor and neutral variation.

44. Frequency-Dependent Selection In frequency-dependent selection, the fitness of a phenotype declines if it becomes too common in the population Selection can favor whichever phenotype is less common in a population Hybrid vigor-crossbreeding between 2 purebred Stocks produce hardy hybrids (ex. Corn)

45. Neutral Variation Neutral variation is genetic variation that appears to confer no selective advantage or disadvantage For example, –Variation in noncoding regions of DNA –Variation in proteins that have little effect on protein function or reproductive fitness

46. 16. Give two reasons why natural selection cannot fashion a perfect organism.

47. Why Natural Selection Cannot Fashion Perfect Organisms 1.Selection can act only on existing variations 2.Evolution is limited by historical constraints 3.Adaptations are often compromises 4.Chance, natural selection, and the environment interact

48. Fig. 23-6 Frequencies of alleles Alleles in the population Gametes produced Each egg:Each sperm: 80% chance 80% chance 20% chance 20% chance q = frequency of p = frequency of C R allele = 0.8 C W allele = 0.2

49. Hardy-Weinberg equilibrium describes the constant frequency of alleles in such a gene pool If p and q represent the relative frequencies of the only two possible alleles in a population at a particular locus, then –p 2 + 2pq + q 2 = 1 –where p 2 and q 2 represent the frequencies of the homozygous genotypes and 2pq represents the frequency of the heterozygous genotype

50. Ex. White flowers are caused by a recessive allele. 4% of the population of plants have white flowers. What percent of the population are carriers ? q 2 =.04 q=.2 p= 1-.2 =.8 Carrier frequency =2pq = 2 (.2)(.8) =.32 32% of the population is a carrier

51. 17. What are the five conditions to be met for population to not be evolving?

52. The five conditions for nonevolving populations are rarely met in nature: –No mutations –Random mating –No natural selection –Extremely large population size –No gene flow

53. 18. Define the biological species concept.

54. The Biological Species Concept The biological species concept states that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations Gene flow between populations holds the phenotype of a population together

55. 19. Give the definition of a hybrid and reproductive isolation.

56. Reproductive Isolation Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring Hybrids are the offspring of crosses between different species Reproductive isolation can be classified by whether factors act before or after fertilization

57. 20. List three pre-zygotic barriers for hybridization.

58. Prezygotic barriers block fertilization from occurring by: –Impeding different species from attempting to mate –Preventing the successful completion of mating –Hindering fertilization if mating is successful

59. Fig. 24-4a Habitat IsolationTemporal Isolation Prezygotic barriers Behavioral Isolation Mating attempt Mechanical Isolation (f) (e) (c) (a) (b) (d) Individuals of different species

60. 21. List two post-zygotic barriers for hybridization.

61. Fig. 24-4i Prezygotic barriers Gametic Isolation Fertilization Reduced Hybrid Viability Postzygotic barriers Reduced Hybrid FertilityHybrid Breakdown Viable, fertile offspring (g) (h) (i) (j) (l) (k)

62. 22. Compare and contrast the morphological, ecological, phylogenetic species concepts.

63. Other Definitions of Species Other species concepts emphasize the unity within a species rather than the separateness of different species The morphological species concept defines a species by structural features –It applies to sexual and asexual species but relies on subjective criteria

64. The ecological species concept views a species in terms of its ecological niche –It applies to sexual and asexual species and emphasizes the role of disruptive selection The phylogenetic species concept: defines a species as the smallest group of individuals on a phylogenetic tree –It applies to sexual and asexual species, but it can be difficult to determine the degree of difference required for separate species

65. 22. Differentiate between allopatric and sympatric speciation. How can sympatric speciation occur?

66. Concept 24.2: Speciation can take place with or without geographic separation Speciation can occur in two ways: –Allopatric speciation –Sympatric speciation

67. Sympatric (“Same Country”) Speciation In sympatric speciation, speciation takes place in geographically overlapping populations Can occur if gene flow is reduced by factors such as a. Polyploidy b. Habitat differentiation c. Sexual selection

68. 23. Differentiate between allopolyploidy and autopolyploidy.

69. a. Polyploidy Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division Polyploidy is much more common in plants than in animals (ex. gray tree frog) Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploids

70. An autopolyploid is an individual with more than two chromosome sets, derived from one species

71. An allopolyploid is a species with multiple sets of chromosomes derived from different species

72. 24. Describe the three possible outcomes of hybrid zones.

73. Fig. 24-14-4 Gene flow Population (five individuals are shown) Barrier to gene flow Isolated population diverges Hybrid zone Hybrid Possible outcomes: Reinforcement OR Fusion Stability

74. 25. What is punctuated equilibrium?

75. Speciation Rates The punctuated pattern in the fossil record and evidence from lab studies suggests that speciation can be rapid The interval between speciation events can range from 4,000 years (some cichlids) to 40,000,000 years (some beetles), with an average of 6,500,000 years