1. Mechanisms of Evolution15
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
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

3. Chapter 15 Opening Question
What evidence do biologists use to confirm the theory of evolution?

4. 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.
Use that understanding to interpret changes in and interactions among living organisms.
Evolution is based on factual evidence-genetics, fossils, phylogeny, morphology, embryology.

5. Figure 15.2 Milestones of Evidence in the Development of Evolutionary Theory

6. Chapter 15 Example of Micro Speciation video on finches

7. 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.

8. Even before Darwin, biologists had suggested that species had changed over time, but no one had proposed a convincing mechanism for evolution.
Charles Darwin was interested in geology and natural history.

9. Figure 15.1 The Voyage of the Beagle

10. 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.
ANIMATED TUTORIAL 15.1 Natural Selection

11. CHARLES RETURNS HOME
BECAME VERY POPULAR DUE TO ALL THE SPECIMENS, SAMPLES HE SENT BACK
HE BECAME FRIENDS WITH Charles Lyell, a GEOLOGIST
Lyell stated “The Earth must be very old, since geological formations are slow & gradual.”
Charles Lyell

12. . INFLUENCES ON DARWIN A. CHARLES LYELL & FARMERS
DARWIN thought GEOLOGICAL changes could change PLANT & ANIMAL forms CHARLES LYELL He observed farmers breeding animals for SELECTIVE TRAITS - ARTIFICIAL SELECTION His Mother bred fancy pigeons. Darwin suspected Selection also OCCURRED in NATURE -Natural Selection

13. B. THOMAS MALTHUS
CLERGYMAN who wrote about ECONOMICS ESSAY “PRINCIPLE OF POPULATION”
He said “THE HUMAN POPULATION WAS GROWING SO FAST THAT RESOURCES WOULD SOON RUN OUT, PEOPLE WOULD DIE DUE TO DISEASE, WAR & OTHER DISASTERS”

14. THOMAS MALTHUS CONT.
“PLANTS & ANIMALS PRODUCE FAR MORE OFFSPRING THAN CAN SURVIVE”
He even suggested that lower class family size be regulated so they could not produce more young than they could support economically.

15. Alfred Russell Wallace Had some of the same ideas as Darwin
He actually contacted Darwin for advice on publishing his theory on Evolution!
He also had a theory on Natural Selection, although he did not use this term.

16. 1.MODERN ORGANISMS ARISE THROUGH EVOLUTION
1859 “THE ORIGIN OF SPECIES” IS PUBLISHED 30 YRS. AFTER THE BEAGLE Fossil film clip
5 KEY CONCEPTS of Darwins Theory on Evolution:
1.MODERN ORGANISMS ARISE THROUGH EVOLUTION
2.EACH SPECIES comes from a PRECEDING ONE, they have a COMMON ANCESTOR. COMMON DESCENT
3.FITNESS comes from ADAPTATION
4. SUCCESSFUL ADAPTATION allows ORGANISMS to SURVIVE & REPRODUCE
5.ADAPTATION IS ANY CHARACTERISTIC THAT INCREASES AN ORGANISM’S FITNESS

17. 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.

18. 5 PRINCIPLES OF DARWIN’S THEORY OF EVOLUTION
1844 DARWIN wrote his theory on EVOLUTION-called it NATURAL SELECTION
THERE ARE 5 POINTS TO HIS THEORY
1. There is VARIATION in POPULATIONS-VARIATIONS ARE PASSED ON FROM PARENT TO OFFSPRING
His trip to the Galapagos
2. SOME VARIATIONS ARE FAVORABLE-IF FAVORABLE IT IMPROVES THE ORGANISMS ABILITY TO LIVE & REPRODUCE
INFLUENCE BY FARMERS/BREEDERS

19. DARWIN’S INFLUENCES MALTHUS & LYELL
3. MORE YOUNG are PRODUCED than CAN SURVIVE -Only a few live long enough to reproduce.
Malthus’ Essay
4. THOSE THAT SURVIVE & REPRODUCE HAVE FAVORABLE ____? A larger & larger portion of the next generations will inherit these favorable variations.
? Lamarck
5. GRADUALISM-Over a large amount of time, small changes accumulate & populations change
Lyell

20. 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.

21. 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.

22. Chapter 15 Micro v. Macroevolution
Two causes are drift and natural selection
Generation-to-generation change in frequencies of alleles.
Includes:
Genetic drift
Natural selection
Gene flow
Mutation
Macro
Above species levels
Refers to the bigger picture (e.g. evolution of mammals, flowering plants, large scale history of life)

23. 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.
LINK Concepts 8.1 and 8.2 Review the nature of alleles and genetic inheritance
VIDEO 15.1 Within-species diversity in Agrias butterflies

24. Figure A Gene Pool

25. Figure 15.4 Many Vegetables from One Species
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

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
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
Migration of individuals between populations results in gene flow, which can change allele frequencies.
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.
VIDEO 15.2 Animal adaptations: Leaf-mimicry in insects
VIDEO 15.3 Animal adaptations: Camouflage in swallowtail pupae
VIDEO 15.4 Animal adaptations: Development of mimicry in a swallowtail species

29. 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.

30. 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.

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

32. Concept 15.3 Evolution Can Be Measured by Changes in Allele Frequencies
Evolution can be measured by change in allele frequencies.
Allele frequency =
INTERACTIVE TUTORIAL 15.1 Genetic Drift

33. 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.

34. 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.

35. 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
ANIMATED TUTORIAL 15.2 Hardy–Weinberg Equilibrium

36. Figure 15.11 One Generation of Random Mating Restores Hardy–Weinberg Equilibrium

37. 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:
LINK Concept 8.1 Discussion of probability and inheritance
APPLY THE CONCEPT Evolution can be measured by changes in allele frequencies

38. 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.

39. Concept 15.4 Selection Can Be Stabilizing, Directional, or Disruptive
Qualitative traits—influenced by alleles at one locus; often discrete qualities (black versus white).
Quantitative traits—influenced by alleles at more than one locus; likely to show continuous variation (body size of individuals).

40. Figure 15.12 Natural Selection Can Operate in Several Ways
Natural selection can act on quantitative traits in three ways: • Stabilizing selection favors average individuals. • Directional selection favors individuals that vary in one direction from the mean. • Disruptive selection favors individuals that vary in both directions from the mean.

41. Figure 15.13 Human Birth Weight Is Influenced by Stabilizing Selection
Stabilizing selection reduces variation in populations, but does not change the mean.

42. Figure 15.14 Long Horns Are the Result of Directional Selection
Directional selection—individuals at one extreme of a character distribution contribute more offspring to the next generation.

43. Figure 15.15 Disruptive Selection Results in a Bimodal Character Distribution
Disruptive selection—individuals at opposite extremes of a character distribution contribute more offspring to the next generation.

44. Concept 15.5 Genomes Reveal Both Neutral and Selective Processes of Evolution
Fitness of genotypes:
Genotypes of higher fitness increase in frequency over time; those of lower fitness decrease over time.

45. Concept 15.5 Genomes Reveal Both Neutral and Selective Processes of Evolution
Genome size and organization also evolves.
Genome size varies greatly.
If only the protein and RNA coding portions of genomes are considered, there is much less variation in size.

46. Figure 15.20 Genome Size Varies Widely

47. Figure 15.21 A Large Proportion of DNA Is Noncoding

48. Concept 15.5 Genomes Reveal Both Neutral and Selective Processes of Evolution
Much of the noncoding DNA does not appear to have a function.
Some noncoding DNA can alter the expression of surrounding genes.
Some noncoding DNA consists of pseudogenes.
Some consists of parasitic transposable elements.

49. Concept 15.5 Genomes Reveal Both Neutral and Selective Processes of Evolution
The amount of nonconding DNA may be related to population size.
Noncoding sequences that are only slightly deleterious are likely to be purged by selection most efficiently in species with large population sizes.
In small populations genetic drift may overwhelm selection against these sequences.

50. Concept 15.6 Recombination, Lateral Gene Transfer, and Gene Duplication Can Result in New Features
Sexual reproduction results in new combinations of genes and produces genetic variety that increases evolutionary potential.
But in the short term, it has disadvantages:
Recombination can break up adaptive combinations of genes
Reduces rate at which females pass genes to offspring
Dividing offspring into genders reduces the overall reproductive rate

51. Concept 15.6 Recombination, Lateral Gene Transfer, and Gene Duplication Can Result in New Features
Why did sexual reproduction evolve? Possible advantages:
It facilitates repair of damaged DNA. Damage on one chromosome can be repaired by copying intact sequences on the other chromosome.
Elimination of deleterious mutations through recombination followed by selection.

52. Concept 15.6 Recombination, Lateral Gene Transfer, and Gene Duplication Can Result in New Features
In asexually reproducing species, deleterious mutations can accumulate; only death of the lineage can eliminate them
Muller called this the genetic ratchet—mutations accumulate or “ratchet up” at each replication; Muller’s ratchet.

53. Concept 15.6 Recombination, Lateral Gene Transfer, and Gene Duplication Can Result in New Features
The variety of genetic combinations in each generation can be advantageous (e.g., as defense against pathogens and parasites).
Sexual recombination does not directly influence the frequencies of alleles. Rather, it generates new combinations of alleles on which natural selection can act.

54. Concept 15.6 Recombination, Lateral Gene Transfer, and Gene Duplication Can Result in New Features
Lateral gene transfer—individual genes, organelles, or genome fragments move horizontally from one lineage to another.
Species may pick up DNA fragments directly from the environment.
Genes may be transferred to a new host in a viral genome.
Hybridization results in the transfer of many genes.

55. Concept 15.6 Recombination, Lateral Gene Transfer, and Gene Duplication Can Result in New Features
Lateral gene transfer can be advantageous to a species that incorporates novel genes.
Genes that confer antibiotic resistance are often transferred among bacteria species.

56. Concept 15.7 Evolutionary Theory Has Practical Applications
Molecular evolutionary principles are used to understand protein structure and function.
Puffer fish have a toxin (TTX) that blocks sodium ion channels and prevents nerve and muscle function.
Genes for sodium channel proteins in puffer fish have substitutions that prevent TTX from binding.
Study of these gene substitutions aid in understanding how sodium channels function.

57. Concept 15.7 Evolutionary Theory Has Practical Applications
Living organisms produce many compounds useful to humans. The search for such compounds is called bioprospecting.
These molecules result from millions of years of evolution.
But biologists can imagine molecules that have not yet evolved. In vitro evolution—new molecules are produced in the laboratory to perform novel and functions.

58. Concept 15.7 Evolutionary Theory Has Practical Applications
In agriculture, breeding programs have benefited from evolutionary principles, including incorporation of beneficial genes from wild species.
An understanding of how pest species evolve resistance to pesticides has resulted in more effective pesticide application and rotation schemes.

59. Concept 15.7 Evolutionary Theory Has Practical Applications
Molecular evolution is also used to study disease organisms.
All new viral diseases have been identified by evolutionary comparison of their genomes with those of known viruses.

60. Answer to Opening Question
Changes in surface proteins make influenza virus strains undetectable to the host’s immune system (positive selection for changes in surface proteins).
By comparing ratios of synonymous to nonsynonymous substitutions, biologists can detect which mutations are under positive selection.

61. Answer to Opening Question
They then assess which current flu strains show the greatest number of changes in these positively selected codons.
These flu strains are most likely to survive and lead to flu epidemics of the future, so they are the best targets for new vaccines.

62. Figure 15.24 Evolutionary Analysis of Surface Proteins Leads to Improved Flu Vaccines