1. POPULATION GENETICS & EVOLUTION -Overview DR. KOFI OWUSU-DAAKU
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2. Clown, Fool, or Simply Well Adapted?
The blue-footed booby has many specialized characteristics that are very functional in water but less useful on land
Such evolutionary adaptations are inherited traits that enhance an organism's ability to survive and reproduce in its particular environment
Evolution is the changes in organisms over time
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3. LE 13-7a
Webbing
No webbing
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5. DARWIN'S THEORY OF EVOLUTION
A sea voyage helped Darwin frame his theory of evolution
Pre-Darwinian ideas about the origin of species
Early Greek philosophers: Simpler life forms preceded more complex ones
Aristotle: Species are fixed and do not evolve; had a great impact on Western thinking
Judeo-Christian biblical view: All species were individually designed by a divine creator
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6. PRE-DARWINIAN IDEAS
In the century prior to Darwin, only a few scientists questioned the belief that species are fixed
Buffon: The study of fossils suggested that Earth is older than 6,000 years, and fossil forms might be early versions of modern forms
Lamarck: Fossils are related to modern forms because life evolves; acquired characteristics are inherited
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7. DARWIN’S VOYAGE
Charles Darwin made a round-the-world sea voyage as a naturalist on HMS Beagle in the 1830s
Darwin observed similarities between living and fossil organisms and the diversity of life on the Galápagos Islands
Darwin's experiences during the voyage helped him frame his ideas about evolution
Lyell's Principles of Geology led him to realize that still-operating natural forces gradually change Earth
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9. LE 13-1b 27th January 2016 POP GEN & EVOL LECTURE 1 Great Britain
Europe
Asia
North
America
ATLANTIC
OCEAN
PACIFIC
OCEAN
Africa
PACIFIC
OCEAN
Equator
The
Galápagos
Islands
South
America
PACIFIC
OCEAN
Pinta
Genovesa
Australia
Marchena
Equator
Santiago
Andes
Cape of
Good Hope
Daphne
Islands
Fernandina
Pinzón
Tasmania
Isabela
Santa
Cruz
Cape Horn
New
Zealand
Santa Fe
San
Cristobal
Tierra del Fuego
40 km
Florenza
Española
40 miles
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10. DARWINS AFTER VOYAGE IDEAS
After his return, Darwin began to document his observations and his new theory of evolution
Alfred Wallace conceived a theory almost identical to Darwin's; both works were presented to the scientific community
Darwin's On the Origin of Species by Means of Natural Selection was published in 1859
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11. "Descent with modification" summarizes Darwin's view of life
All organisms are related through descent from a remote common ancestor
Descendants spread into diverse habitats over millions of years and acquired adaptations to their environments
The history of life resembles a tree with multiple branchings from a common trunk
Species that are closely related share characteristics
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12. Darwin proposed natural selection as the mechanism of evolution
The essence of Darwin's theory of natural selection is differential success in reproduction
Organisms produce more offspring than the environment can support
Organisms vary in many characteristics that can be inherited
Excessive numbers of organisms lead to a struggle for survival
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13. Natural selection is supported by evidence from artificial selection
Individuals whose characteristics are best adapted to their environment are more likely to survive and reproduce
The unequal ability of individuals to survive and reproduce leads to a gradual change in the characteristics of a population over generations
Natural selection is supported by evidence from artificial selection
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14. SELECTION IN ACTION -ARTIFICIAL
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15. LE 13-2c African wild dog Coyote Wolf Fox Jackal Thousands to
millions of years
of natural selection
Ancestral canine
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16. FOSSILS AS EVIDENCE OF EVOLUTION
The study of fossils provides strong evidence for evolution
Fossils are the hard parts of organisms that remain after organic materials decay
Rarely, an entire organism is fossilized
The fossil record strongly supports the theory of evolution
Changes in sea level and drying and refilling of lakes over time result in rock strata that trap organisms
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17. Fossils appear in an ordered array within layers of sedimentary rocks
The fossil record reveals that organisms have evolved in a historical sequence
Many fossils link early extinct species with species living today
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27. OTHER EVIDENCE FOR EVOLUTION
A mass of other evidence reinforces the evolutionary view of life
Biogeography
The geographic distribution of species suggested to Darwin that organisms evolve from common ancestors
Isolated organisms resemble each other more than organisms in similar but distant places
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28. Comparative anatomy
Homologous structures are features that often have different functions but are structurally similar because of common ancestry
Vestigial structures are remnants of structures that served important functions in an organism's ancestors
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29. LE 13-4a Human Cat Whale Bat 27th January 2016
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30. Comparative embryology
Common embryonic structures in all vertebrates are evidence for common descent
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31. LE 13-4b Pharyngeal pouches Post-anal tail Chick embryo Human embryo
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32. Molecular biology
Comparisons of DNA and amino acid sequences between different organisms reveal evolutionary relationships
Molecular biology provides strong evidence that all life forms are related
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34. CONNECTION Scientists can observe natural selection in action
Examples of evolutionary adaptation observed over a short time
Different camouflage adaptations in different environments
Development of pesticide resistance in insects
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36. conferring resistance to pesticide
LE 13-5b
Chromosome with gene
conferring resistance
to pesticide
Pesticide application
Additional
applications of the
same pesticide will
be less effective, and
the frequency of
resistant insects in
the population
will grow
Survivor
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37. Natural selection is contingent on time and place
Examples of evolutionary adaptation reveal three key points about natural selection
Natural selection is more of an editing process than a creative mechanism
Natural selection is contingent on time and place
Significant evolutionary change can occur in a short time
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38. POPULATION GENETICS AND THE MODERN SYNTHESIS
13.6 Populations are the units of evolution
Population
A group of individuals of the same species living in the same place at the same time
May be isolated from other groups or concentrated
The smallest unit that can evolve
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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40. Connects population genetics with other sciences
Combines Darwin's and Mendel's ideas in studying how populations change genetically over time
The modern synthesis
Connects population genetics with other sciences
Focuses on population as the unit of evolution and central role of natural selection
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41. Studying evolution at the population level
Evolution: change in the prevalence of certain heritable characteristics in a population over a span of generations
Gene pool: the total collection of genes in a population at any one time
Microevolution: a change in the relative frequencies of alleles in a gene pool
Species: a group of populations capable of interbreeding and producing fertile offspring
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42. The gene pool of a nonevolving population remains constant over the generations
In a nonevolving population, the shuffling of alleles that accompanies sexual reproduction does not alter the genetic makeup of the population
In Hardy-Weinberg equilibrium, the frequency of each allele in the gene pool will remain constant unless acted upon by other agents
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43. The population is very large The population is isolated
For a population to be in Hardy-Weinberg equilibrium, it must satisfy five main conditions
The population is very large
The population is isolated
Mutations do not alter the gene pool
Mating is random
All individuals are equal in reproductive success
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44. The Hardy-Weinberg conditions are rarely met in nature
We can follow alleles in a population to observe if Hardy-Weinberg equilibrium exists
Hardy-Weinberg equilibrium provides a basis for understanding how populations evolve
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45. CONNECTION
The Hardy-Weinberg equation is useful in public health science
Public health scientists use the Hardy-Weinberg equation to estimate frequencies of disease-causing alleles in the human population
Example: phenylketonuria (PKU)
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46. OTHER FACTORS POWERING EVOLUTION
In addition to natural selection, genetic drift and gene flow can contribute to evolution
Genetic drift: change in the gene pool of a population due to chance
Can alter allele frequencies in a population
The smaller the population, the greater the impact
Bottleneck effect: an event that drastically reduces population size
Founder effect: colonization of a new location by a small number of individuals
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47. Original population Bottlenecking event Surviving population
LE 13-9a
Original
population
Bottlenecking
event
Surviving
population
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49. Gene flow: the movement of individuals or gametes between populations
Can alter allele frequencies in a population
Tends to reduce differences between populations
Natural selection
Best-adapted individuals have the most reproductive success
Results in accumulation of traits that adapt a population to its environment
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50. CONNECTION Endangered species often have reduced variation
Loss of genetic variability due to bottlenecking may reduce a population's ability to adapt to environmental change
Particularly threatening to endangered species such as the cheetah
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51. VARIATION AND NATURAL SELECTION
Variation is extensive in most populations
Individual variation exists in all sexually reproducing populations
Heritable variation results from a combination of genotype and environmental influences
Polymorphism: two or more forms of phenotypic characteristics
Geographic variation: variation of an inherited characteristic from place to place
May occur along a geographic continuum (a cline)
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53. Mutation and sexual recombination generate variation
Mutations-changes in the nucleotide sequence of DNA-can create new alleles
Only mutations in cells that produce gametes can affect a population's gene pool
A mutation may rarely improve adaptation to the environment and thus contribute to evolution
Sexual recombination generates variation by shuffling alleles during meiosis
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54. A1 A1 A2 A3 Parents  Meiosis A1 A2 A3 Gametes LE 13-12a
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55. A1 A2 A3 A1 A2 A1 A3 Gametes Fertilization Offspring, with new
LE 13-12b A1 A2 A3
Gametes
Fertilization A1 A2 A1 A3
Offspring,
with new
combinations
of alleles
and
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56. CONNECTION
The evolution of antibiotic resistance in bacteria is a serious public health concern
Natural selection has led to the evolution of antibiotic-resistant bacteria
Overuse and misuse of antibiotics has contributed to the proliferation of antibiotic-resistant strains
Example: tuberculosis
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58. Diploidy and balancing selection preserve variation
Diploidy (two sets of chromosomes) helps to prevent populations from becoming genetically uniform
Recessive alleles are "hidden" from natural selection and remain in the population
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59. Balanced polymorphism may result from
Balancing selection allows two or more phenotypic forms in a population
Balanced polymorphism may result from
Heterozygote advantage; example: sickle-cell disease
Frequency-dependent selection
Neutral variation provides no apparent advantage or disadvantage
Example: fingerprints
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61. The perpetuation of genes defines evolutionary fitness
Evolutionary fitness is the relative contribution an individual makes to the gene pool of the next generation
Survival of genes depends on production of fertile offspring
Selection indirectly adapts a population to its environment by acting on phenotype
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62. Natural selection can alter variation in a population in three ways
Stabilizing selection: favors intermediate phenotypes
Directional selection: acts against individuals at one of the phenotypic extremes
Disruptive selection: favors individuals at both extremes of the phenotypic range
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63. LE 13-16 27th January 2016 POP GEN & EVOL LECTURE 1 Original
population
Frequency of individuals
Phenotypes (fur color)
Original
population
Evolved
population
Stabilizing selection
Directional selection
Disruptive selection
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64. Sexual selection may produce sexual dimorphism Sexual dimorphism
The distinction in appearance between males and females of a species
Sexual selection
The determining of "who mates with whom"
Leads to the evolution of secondary sexual characteristics that may give individuals an advantage in mating
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67. Natural selection cannot fashion perfect organisms
There are at least four reasons why natural selection cannot produce perfection
Organisms are limited by historical constraints
Adaptations are often compromises
Chance and natural selection interact
Selection can only edit existing variations
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