Mechanisms of Evolution

1. 15 Mechanisms of Evolution

2. Chapter 15 Mechanisms of Evolution • Key Concepts • 15.1 Evolution Is Both Factual and the Basis of Broader Theory • 15.2 Mutation, Selection, Gene Flow, Genetic Drift, and Nonrandom Mating Result in Evolution • 15.3 Evolution Can Be Measured by Changes in Allele Frequencies • 15.4 Selection Can Be Stabilizing, Directional, or Disruptive

3. Chapter 15 Mechanisms of Evolution Key Concepts 15.5 Genomes Reveal Both Neutral and Selective Processes of Evolution 15.6 Recombination, Lateral Gene Transfer, and Gene Duplication Can Result in New Features 15.7 Evolutionary Theory Has Practical Applications

4. Chapter 15 Opening Question How do biologists use evolutionary theory to develop better flu vaccines?

5. Concept 15.1 Evolution Is Both Factual and the Basis of Broader Theory • Biological populations change over time, or evolve. • Evolutionary change is observed in laboratory experiments, in natural populations, and in the fossil record.

6. Concept 15.1 Evolution Is Both Factual and the Basis of Broader Theory Evolutionary theory—understanding the mechanisms of evolutionary change. It has many applications: study and treatment of diseases, development of crops and industrial processes, understanding the diversification of life, and how species interact. It also allows us to make predictions about the biological world.

7. Concept 15.1 Evolution Is Both Factual and the Basis of Broader Theory Theory—In everyday speech, an untested hypothesis or a guess. Evolutionary theory is not a single hypothesis, but refers to our understanding of the mechanisms that result in genetic changes in populations over time and to our use of that understanding to interpret changes in and interactions among living organisms.

8. Concept 15.1 Evolution Is Both Factual and the Basis of Broader Theory Even before Darwin, biologists had suggested that species had changed over time, but no one had proposed a convincing mechanism for evolution.

9. Concept 15.1 Evolution Is Both Factual and the Basis of Broader Theory Charles Darwin was interested in geology and natural history.

10. Concept 15.1 Evolution Is Both Factual and the Basis of Broader Theory In 1831, Darwin began a 5-year voyage around the world on a Navy survey vessel, the HMS Beagle.

11. Figure 15.1 The Voyage of the Beagle

12. Concept 15.1 Evolution Is Both Factual and the Basis of Broader Theory From the observations and insights made on the voyage, and new ideas from geologists on the age of the Earth, Darwin developed an explanatory theory for evolutionary change: • Species change over time. • Divergent species share a common ancestor. • The mechanism that produces change is natural selection.

13. Concept 15.1 Evolution Is Both Factual and the Basis of Broader Theory In 1858, Darwin received a paper from Alfred Russel Wallace with an explanation of natural selection nearly identical to Darwin’s. Both men are credited for the idea of natural selection. Darwin’s book, The Origin of Species, was published in 1859.

14. Concept 15.1 Evolution Is Both Factual and the Basis of Broader Theory By 1900, the fact of evolution was established, but the genetic basis of evolution was not yet understood. Then the work of Gregor Mendel was rediscovered, and during the 20th century, work continued on the genetic basis of evolution. A “modern synthesis” of genetics and evolution took place 1936–1947.

15. Figure 15.2 Milestones in the Development of Evolutionary Theory

16. Concept 15.1 Evolution Is Both Factual and the Basis of Broader Theory The structure of DNA was established by 1953 by Watson and Crick. In the 1970s, technology developed for sequencing long stretches of DNA and amino acid sequences in proteins. Evolutionary biologists now study gene structure and evolutionary change using molecular techniques.

17. Concept 15.2 Mutation, Selection, Gene Flow,Genetic Drift, and Nonrandom Mating Result in Evolution Biological evolution refers to changes in the genetic makeup of populations over time. Population—a group of individuals of a single species that live and interbreed in a particular geographic area at the same time. Individuals do not evolve; populations do.

18. Concept 15.2 Mutation, Selection, Gene Flow,Genetic Drift, and Nonrandom Mating Result in Evolution The origin of genetic variation is mutation. Mutation—any change in nucleotide sequences. Mutations occur randomly with respect to an organism’s needs; natural selection acts on this random variation and results in adaptation.

19. Concept 15.2 Mutation, Selection, Gene Flow,Genetic Drift, and Nonrandom Mating Result in Evolution Mutations can be deleterious, beneficial, or have no effect (neutral). Mutation both creates and helps maintain genetic variation in populations. Mutation rates vary, but even low rates create considerable variation.

20. Concept 15.2 Mutation, Selection, Gene Flow,Genetic Drift, and Nonrandom Mating Result in Evolution Because of mutation, different forms of a gene, or alleles, may exist at a locus. Gene pool—sum of all copies of all alleles at all loci in a population. Allele frequency—proportion of each allele in the gene pool. Genotype frequency—proportion of each genotype among individuals in the population.

21. Figure 15.3 A Gene Pool

22. Concept 15.2 Mutation, Selection, Gene Flow,Genetic Drift, and Nonrandom Mating Result in Evolution Many of Darwin’s observations came from artificial selection of domesticated plants and animals. Selection on different characters in a single species of wild mustard produced many crop plants.

23. Figure 15.4 Many Vegetables from One Species

24. Concept 15.2 Mutation, Selection, Gene Flow,Genetic Drift, and Nonrandom Mating Result in Evolution Darwin bred pigeons and recognized similarities between selection by breeders and selection in nature.

25. Figure 15.5 Artificial Selection

26. Concept 15.2 Mutation, Selection, Gene Flow,Genetic Drift, and Nonrandom Mating Result in Evolution Laboratory experiments also show genetic variation in populations. Selection for certain traits in the fruit fly Drosophila melanogaster resulted in new combinations of genes that were not present in the original population.

27. Figure 15.6 Artificial Selection Reveals Genetic Variation

28. Concept 15.2 Mutation, Selection, Gene Flow,Genetic Drift, and Nonrandom Mating Result in Evolution Natural selection: Far more individuals are born than survive to reproduce. Offspring tend to resemble their parents, but are not identical to their parents or to one another. Differences among individuals affect their chances to survive and reproduce, which will increase frequency of favored traits in the next generation.

29. Concept 15.2 Mutation, Selection, Gene Flow,Genetic Drift, and Nonrandom Mating Result in Evolution Adaptation—a favored trait that evolves through natural selection. Adaptation also describes the process that produces the trait. Individuals with deleterious mutations are less likely to survive and reproduce and to pass their alleles on to the next generation.

30. Concept 15.2 Mutation, Selection, Gene Flow,Genetic Drift, and Nonrandom Mating Result in Evolution Migration of individuals between populations results in gene flow, which can change allele frequencies.

31. Concept 15.2 Mutation, Selection, Gene Flow,Genetic Drift, and Nonrandom Mating Result in Evolution Genetic drift—random changes in allele frequencies from one generation to the next. In small populations, it can change allele frequencies. Harmful alleles may increase in frequency, or rare advantageous alleles may be lost.

32. Concept 15.2 Mutation, Selection, Gene Flow,Genetic Drift, and Nonrandom Mating Result in Evolution A population bottleneck—an environmental event results in survival of only a few individuals. Genetic drift can change allele frequencies. Populations that go through bottlenecks loose much of their genetic variation.

33. Figure 15.7 A Population Bottleneck

34. Concept 15.2 Mutation, Selection, Gene Flow,Genetic Drift, and Nonrandom Mating Result in Evolution Founder effect—genetic drift changes allele frequencies when a few individuals colonize a new area.

35. Concept 15.2 Mutation, Selection, Gene Flow,Genetic Drift, and Nonrandom Mating Result in Evolution Nonrandom mating: Selfing, or self-fertilization is common in plants. Homozygous genotypes will increase in frequency and heterozygous genotypes will decrease.

36. Concept 15.2 Mutation, Selection, Gene Flow,Genetic Drift, and Nonrandom Mating Result in Evolution Sexual selection—mates are chosen based on phenotype, e.g., bright-colored feathers of male birds. There may be a trade-off between attracting mates (more likely to reproduce) and attracting predators (less likely to survive).

37. Concept 15.2 Mutation, Selection, Gene Flow,Genetic Drift, and Nonrandom Mating Result in Evolution Or, phenotype may indicate a successful genotype, e.g., female frogs are attracted to males with low-frequency calls, which are larger and older (hence successful). Studies of African long-tailed widowbirds showed that females preferred males with longer tails, which may indicate greater health and vigor.

38. Figure 15.8 What Is the Advantage?

39. Figure 15.9 Sexual Selection in Action (Part 1)

40. Figure 15.9 Sexual Selection in Action (Part 2)

41. Concept 15.3 Evolution Can Be Measured by Changes in Allele Frequencies Evolution can be measured by change in allele frequencies. Allele frequency =

42. Concept 15.3 Evolution Can Be Measured by Changes in Allele Frequencies For two alleles at a locus, A and a, three genotypes are possible: AA, Aa, and aa. p = frequency of A;q = frequency of a

43. Figure 15.10 Calculating Allele and Genotype Frequencies

44. Concept 15.3 Evolution Can Be Measured by Changes in Allele Frequencies For each population, p + q = 1, and q = 1 – p. Monomorphic: only one allele at a locus, frequency = 1. The allele is fixed. Polymorphic: more than one allele at a locus. Genetic structure—frequency of alleles and genotypes of a population.

45. Concept 15.3 Evolution Can Be Measured by Changes in Allele Frequencies Hardy–Weinberg equilibrium—allele frequencies do not change across generations; genotype frequencies can be calculated from allele frequencies. If a population is at Hardy-Weinberg equilibrium, there must be no mutation, no gene flow, no selection of genotypes, infinite population size, and random mating.

46. Concept 15.3 Evolution Can Be Measured by Changes in Allele Frequencies At Hardy-Weinberg equilibrium, allele frequencies don’t change. Genotypes frequencies: Genotype AA Aa aa Frequency p2 2pq q2

47. Figure 15.11 One Generation of Random Mating Restores Hardy–Weinberg Equilibrium (Part 1)

48. Figure 15.11 One Generation of Random Mating Restores Hardy–Weinberg Equilibrium (Part 2)

49. Concept 15.3 Evolution Can Be Measured by Changes in Allele Frequencies Probability of 2 A-gametes coming together: Probability of 2 a-gametes coming together: Overall probability of obtaining a heterozygote:

50. Concept 15.3 Evolution Can Be Measured by Changes in Allele Frequencies Populations in nature never meet the conditions of Hardy–Weinberg equilibrium—all biological populations evolve. The model is useful for predicting approximate genotype frequencies of a population. Specific patterns of deviation from Hardy–Weinberg equilibrium help identify mechanisms of evolutionary change.