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Evolution
Chapter 11
Evolution
• Descent with modification
• Aristotle understood all
natural things, not only
living things, as being
imperfec...
Darwin
• Theory—Natural Selection/Descent with
Modification
• HMS Beagle—Trip to explore the South
American coastline
– Ob...
Mechanisms of Evolution
• Descent with Modification—gradual changes
from an ancestral type
– Galapagos finches
• Survival ...
(a) Cactus-eater (b) Seed-eater (c) Insect-eater
Natural Selection
• Natural selection favors some traits over
others that enhance the relative fitness of an
organism
– Fi...
Modern
Evolutionary
Theory
• Genetic mutations cause
inherited variation,
natural selection uses
new genotypes for
natural...
Genetic Mechanisms for Evolution
• Natural selection acts on individuals, but
only populations evolve
• Genetic variations...
Genetic Mechanisms for Evolution
• Mutation/sexual reproduction
– produce variation in gene pools that contributes to
diff...
Hardy-Weinberg
• Occurs when genes are shuffled during sexual
reproduction
• Hardy-Weinberg principle—frequencies of allel...
Assumptions of Hardy-Weinberg
• Five conditions for nonevolving populations
are rarely met in nature:
– No mutations
– Ran...
Hardy-Weinberg
• p and q represent relative frequencies of
the only two possible alleles in a population
at a particular l...
Fig. 23-7-4
Gametes of this generation:
64% CR CR, 32% CR CW, and 4% CW CW
64% CR + 16% CR = 80% CR = 0.8 = p
4% CW + 16% ...
Females
A (p) A (q)
Males
A (p) AA (p2) Aa (pq)
A (q) Aa (qp) Aa (q2)
Expected genotype frequencies for
tetraploidy
Genoty...
H-W Example
• The occurrence of PKU is 1 per 10,000 births
– q2 = 0.0001
– q = 0.01
• The frequency of normal alleles is
–...
Types of Natural Selection
• Directional selection favors individuals at one
end of the phenotypic range
• Disruptive sele...
Selection
Types
Preservation of Genetic Variation
• Diploidy—We have a pair of alleles and lots of
variation is hidden in recessive allele...
Distribution of Malaria Distribution of Sickle-Cell Trait
Heterozygote Advantage
Illness Heterozygote Advantage
Cystic fibrosis resistance to cholera, protection from diarrhea,
som...
Genetic Drift
• Process where chance events cause
unpredictable fluctuations in allele frequencies.
• Most pronounced in s...
Founder Effect
• Effect of genetic drift—occurs when a few individuals
get isolated from a population and form a new
popul...
Bottleneck Effect
• Effect of genetic drift—occurs when size of
population is reduced and surviving population is no
longe...
Genetic Drift (summary)
• Genetic drift is significant in small populations
• Genetic drift causes allele frequencies to c...
Gene Flow
• Gene flow is the movement of alleles among
populations
• Alleles can be transferred through the movement
of fe...
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#11 evolution

Evidence of Evolution

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#11 evolution

  1. 1. Evolution Chapter 11
  2. 2. Evolution • Descent with modification • Aristotle understood all natural things, not only living things, as being imperfect actualizations of different fixed natural possibilities, known as “forms,” “ideas,” or “species.” 350 BCE • Buffon suggested that species could degenerate into different organisms. AD 1749 • Erasmus Darwin proposed that all warm-blooded animals could have descended from a single micro-organism (or “filament”). AD 1796 • Cuvier insisted that species were unrelated and fixed, their similarities reflecting divine design for functional needs. AD 1798 • Lamarck’s “transmutation” theory envisaged spontaneous generation continually producing simple forms of life that developed greater complexity in parallel lineages with an inherent progressive tendency, and that on a local level these lineages adapted to the environment by inheriting changes caused by use or disuse in parents. AD 1809 • William Paley took Ray’s ideas that each species can be defined by the features that perpetuate and developed them in a book Natural Theology or Evidences of the Existence and Attributes of the Deity (1802), which proposed complex adaptations as evidence of divine design, and was admired by Charles Darwin. AD 1802 • Darwin noted that population growth would lead to a "struggle for existence" where favorable variations could prevail as others perished. Each generation, many offspring fail to survive to reproduce because of limited resources. This could explain the diversity of animals and plants from a common ancestry through the working of natural laws working the same for all types of thing. AD 1859
  3. 3. Darwin • Theory—Natural Selection/Descent with Modification • HMS Beagle—Trip to explore the South American coastline – Observed species in temperate regions more closely resemble tropics not other temperate regions • Galapagos Islands – Adaptation
  4. 4. Mechanisms of Evolution • Descent with Modification—gradual changes from an ancestral type – Galapagos finches • Survival of the Fittest—Malthus—over time environmental challenges eliminate more poorly equipped genotypes • Natural Selection—environmental factors cause different reproductive success of individuals with different genotypes – Artificial selection—traits that are chosen ‘on purpose’ (dog breeds, genetically modified crops, etc.)
  5. 5. (a) Cactus-eater (b) Seed-eater (c) Insect-eater
  6. 6. Natural Selection • Natural selection favors some traits over others that enhance the relative fitness of an organism – Fitness—ability to pass on your genes to the next generation • The more fit, the more chance of passing on genes
  7. 7. Modern Evolutionary Theory • Genetic mutations cause inherited variation, natural selection uses new genotypes for natural selection 1859 •Darwin publishes On the Origin of Species. 1865 •Mendel reported that traits were inherited in a predictable manner 1915 •Sturtevant constructs crosses of three segregating genes, called “three-factor crosses.” 1920s–1930s •Modern evolutionary synthesis connected natural selection, mutation theory, and Mendelian inheritance into a unified theory that applied generally to any branch of biology 1953 •The publication of the structure of DNA by James Watson and Francis Crick demonstrated a physical basis for inheritance. 1973 •Peter and Rosemary Grants have spent six months of the year each year since 1973 capturing, tagging, and taking blood samples of the finches on the Galápagos Island named Daphne Major. 1977 •Woese defines the Archaea (a new domain of life), bringing the total of domains to three. 1990s •Genome sequencing begins. The first theoretical description of a pure pairwise end sequencing strategy, assuming fragments of constant length, was in 1991. In 1995, the genome of a bacterium was sequenced. Present •Research continues to reveal new information and redefine our understanding.
  8. 8. Genetic Mechanisms for Evolution • Natural selection acts on individuals, but only populations evolve • Genetic variations in populations contribute to evolution • Microevolution is a change in allele frequencies in a population over generations
  9. 9. Genetic Mechanisms for Evolution • Mutation/sexual reproduction – produce variation in gene pools that contributes to differences among individuals • Variation genotype = variation in phenotype • Not all phenotypic variation is passed on • Natural selection can only act on variation with a genetic component
  10. 10. Hardy-Weinberg • Occurs when genes are shuffled during sexual reproduction • Hardy-Weinberg principle—frequencies of alleles and genotypes in a population remain constant from generation to generation – The Hardy-Weinberg theorem describes a hypothetical population – In real populations, allele and genotype frequencies do change over time
  11. 11. Assumptions of Hardy-Weinberg • Five conditions for nonevolving populations are rarely met in nature: – No mutations – Random mating – No natural selection – Extremely large population size – No gene flow
  12. 12. Hardy-Weinberg • p and q represent relative frequencies of the only two possible alleles in a population at a particular locus – p2 + 2pq + q2 = 1 – p2 and q2 represent the frequencies of the homozygous genotypes and 2pq represents the frequency of the heterozygous genotype
  13. 13. Fig. 23-7-4 Gametes of this generation: 64% CR CR, 32% CR CW, and 4% CW CW 64% CR + 16% CR = 80% CR = 0.8 = p 4% CW + 16% CW = 20% CW = 0.2 = q 64% CR CR, 32% CR CW, and 4% CW CW plants Genotypes in the next generation: Sperm CR (80%) 80% CR (p = 0.8) CW (20%) 20% CW (q = 0.2) 16% ( pq) CR CW 4% (q2) CW CW 64% ( p2) CR CR 16% (qp) CR CW
  14. 14. Females A (p) A (q) Males A (p) AA (p2) Aa (pq) A (q) Aa (qp) Aa (q2) Expected genotype frequencies for tetraploidy Genotype Frequency AAAA p4 AAAa 4p3q AAaa 6p2q2 Aaaa 4pq3 aaaa q4
  15. 15. H-W Example • The occurrence of PKU is 1 per 10,000 births – q2 = 0.0001 – q = 0.01 • The frequency of normal alleles is – p = 1 – q = 1 – 0.01 = 0.99 • The frequency of carriers is – 2pq = 2 x 0.99 x 0.01 = 0.0198 – or approximately 2% of the U.S. population
  16. 16. Types of Natural 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
  17. 17. Selection Types
  18. 18. Preservation of Genetic Variation • Diploidy—We have a pair of alleles and lots of variation is hidden in recessive alleles • Balanced Polymorphism—When natural selection maintains 2 or more forms – Heterozygote Advantage – Frequency Dependent Selection
  19. 19. Distribution of Malaria Distribution of Sickle-Cell Trait
  20. 20. Heterozygote Advantage Illness Heterozygote Advantage Cystic fibrosis resistance to cholera, protection from diarrhea, some resistance to TB G6PD deficiency protective effect against Plasmodium falciparum and Plasmodium vivax malaria Phenylketonuria (PKU) protects to some extent against the fungal toxin ochratoxin A, which is potentially carcinogenic and can affect prenatal brain development Sickle cell disease protection against symptoms of malaria Tay–Sachs disease protects to some extent against tuberculosis Diabetes mellitus type 2 protects against starvation
  21. 21. Genetic Drift • Process where chance events cause unpredictable fluctuations in allele frequencies. • Most pronounced in small populations In this simulation, there is fixation in the blue "allele" within five generations.
  22. 22. Founder Effect • Effect of genetic drift—occurs when a few individuals get isolated from a population and form a new population.
  23. 23. Bottleneck Effect • Effect of genetic drift—occurs when size of population is reduced and surviving population is no longer representative of original population
  24. 24. Genetic Drift (summary) • Genetic drift is significant in small populations • Genetic drift causes allele frequencies to change at random • Genetic drift can lead to a loss of genetic variation within populations • Genetic drift can cause harmful alleles to become fixed
  25. 25. Gene Flow • Gene flow is 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

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