Evolution of Populations Ch 17

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Evolution of Populations Ch 17

• Process of change over time
• A change in the genes!!!!!!!!

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Population Genetics

• The science of genetic change in population.
• Population all the members of a species that
  occupy a particular area at the same time
• Gene Pool all the genes in all the members of a
  population

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Genes and Variation

• Genetics Joins Evolutionary Theory
• Variation is the raw material for natural
  selection
• Gene pool consists of all the genes, including
  all the different alleles for each gene, that are
  present in a population
• Relative frequency the number of times that the
  allele occurs in a gene pool, compared with the
  number of times other alleles for the same gene
  occur
• Therefore evolution is any change in the
  relative frequency of alleles in the gene pool of
  a population over time
• 3 Sources of Genetic Variation
• Mutations
• Genetic Recombination in Sexual Reproduction (Ind
  assortment and crossing over)
• Lateral Gene Transfer (conjugation)
• Single-Gene (2 pheno) vs. Polygenic Traits (many
  pheno/bell curve)
• Natural Selection acts directly on PHENOTYPES
  not actual alleles some phenotypes are better
  suited to an environment than others and they
  will survive, reproduce and pass on their genes.

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Evolution as Genetic Change in Populations
How Natural Selection Works 3 Types

• Stabilizing Selection
• Individuals with the average form of a trait have
  the highest fitness
• Represents the optimum for most traits
• Results in a similar morphology between most
  members of the species

• Directional Selection
• Individuals that display a more extreme form of a
  trait have greater fitness than individuals with
  an average form of the trait
• A shift in one direction
• Peppered moth

• Disruptive Selection
• Individuals with either extreme variation of a
  trait have greater fitness than individuals with
  the average form of the trait
• A shift in both direction, away from the center
• Shell color (dark rocks and light sand)

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Genetic Drift

• Random changes in the frequency of a gene in the
  absence of natural selection ? occurs because of
  CHANCE
• Occurs efficiently in small populations because
  small changes affect more members
• Two examples
• a. Bottleneck effect
• b. Founder effect

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Genetic Drift
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a. Bottleneck Effect

• Genetic drift (reduction of alleles in a
  population) resulting from a disaster that
  drastically reduces population size.
• Examples
• 1. Earthquakes
• 2. Volcanos

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b. Founder Effect

• Genetic drift resulting from the colonization of
  a new location by a small number of individuals.
• Results in random change of the gene pool.
• Example
• 1. Islands
• (first Darwin finch)

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Hardy-Weinberg Principle

• Genetic Equilibrium situation in which allele
  frequencies in the gene pool of a population
  remain constant
• The concept that the shuffling of genes that
  occurs during sexual reproduction, by itself,
  cannot change the overall genetic makeup of a
  population.
• Shows mathematically and theoretically that there
  are situations where evolution DOES NOT OCCUR
• Seldom achieved in nature

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Hardy-Weinberg Principle

• This principle will be maintained in nature only
  if ALL five of the following conditions are met
• 1. Very large population
• 2. Isolation from other populations
• 3. No net mutations
• 4. Random mating
• 5. No natural selection
• Hardy-Weinberg Principle

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Species

• A group of populations whose individuals have the
  potential to interbreed and produce viable
  offspring.

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Speciation

• The evolution of new species. Species that
  occupy an otherwise unoccupied niche face no
  competition, they will therefore have a 100
  success rate

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Reproductive Isolation

• Any mechanism that impedes two species from
  producing fertile and/or viable hybrid offspring
  -factor necessary for the formation of a new
  species.
• Barriers
• 1. Geographic (rivers, mountains)
• 2. Behavorial - differences in courtship
  behavior
• 3. Temporal - fertile periods (time)

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Interpretations of Speciation

• Two theories
• 1. Gradualist Model (Neo-Darwinian)
• Slow changes in species overtime.
• 2. Punctuated Equilibrium
• Evolution occurs in spurts of relatively rapid
  change.

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Macroevolution

• The origin of taxonomic groups higher than the
  species level.

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Adaptive Radiationaka Divergent Evolution

• Emergence of numerous species from a common
  ancestor introduced to new and diverse
  environments.
• Example
• Darwins Finches
• Five steps to the 14 finch species on the
  Galapagos Islands
• 1) founders arrive
• 2) geographic isolation
• 3) changes in gene pools
• 4) behavioral isolation
• 5) competition and continued evolution

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Darwins Finches an example of Adaptive Radiation
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Convergent Evolution

• Species from different evolutionary branches may
  come to resemble one another if they live in very
  similar environments.
• Example
• 1. Ostrich (Africa) and Emu (Australia).
• 2. Sidewinder (Mojave Desert) and
• Horned Viper (Middle East Desert)
• 3. Shark and Dolphin

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Coevolution

• Evolutionary change, in which one species act as
  a selective force on a second species, inducing
  adaptations that in turn act as selective force
  on the first species.
• Example
• 1. Acacia ants and acacia trees
• 2. Humming birds and plants with flowers with
  long tubes

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The Age of the Earth and Fossils

• Fossils
• Trace the evolution of modern species from
  ancient/extinct ancestors
• Relative dating vs.
• Absolute dating

• Radiometric Dating
• When unstable nuclei release particles or radiant
  energy until the nuclei becomes stable
• Half-life The length of time it takes for
  one-half of a sample to decay to stable form

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The Earth is born
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Date Event Additional Info
4.6 bya Earth was born
4 bya Cooling of Earth, 1st solid rocks formed on earths surface
4-3.8 bya Volcanic activity meteorites release gases that produce earths atmosphere Contained H2O vapor, CO, CO2, H2, N2, NH3, CH4 It did NOT contain oxygen
3.8 bya Cooling continues, water appears, beginning of oceans Earth cool enough for liquid to stay on the ground
3.5 bya Age of first prokaryotic microfossils Heterotrophic obtained nutrients from organic soup Anaerobic able to live in oxygen-free environment
3.4 bya Appearance of 1st autotrophs Organic soup begins to run out Photosynthesis begins using H2S instead of water
2.2 bya Introduction of oxygen into the atmosphere More modern form of photosynthesis appeared Used H2O instead of H2S Caused earth to cool as they converted CO2 ? O2 Led to aerobic respiration Ozone layer protection
1.6-1.1 bya 1st eukaryotic cells evolved Sexual reproduction evolved Multicellular organisms arose Nucleus contains DNA, have membrane bound organelles, etc. Increased the speed of evolution Increased genetic variation
1700s Spontaneous Generation (abiogenesis) idea that life comes from non-life Disproven through Redi, Spallanzani, Pastuer
1953 Miller Urey mix methane, water, ammonia, and hydrogen with energy (sun lightning) Primordial Soup Amino acids other organic compounds are produced as by-products Provide glimpse at how molecules (proteins) may 1st have formed on the Earth
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The Age of the Earth and Fossils

• The Age of the Earth
• Earth had to be old enough for these proposed
  changes to occur
• Earth is 4.5 byo (determined by radioactive
  dating)

• History of Earth (24hours)
• 1200am Earth is formed
• 500am Prokaryotes appear
• 400pm Eukaryotes appear
• 1000pm Invasion of land
• 115930pm Humans appear

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Miller/Urey Experiment and Primordial Soup

• Oparin and Haldane hypothesized that the early
  atmosphere was composed of ammonia (NH3),
  hydrogen gas (H2), water vapor (H20), and
  compounds made of carbon and hydrogen, like
  methane (CH4). They thought that at high
  temperatures, simple organic compounds (like
  amino acids) could form. When earth cooled, and
  lakes and oceans formed, theses simple compounds
  could be found in the water and enter complex
  chemical reactions fueled by lightning and
  ultraviolet violet radiation resulting in
  macromolecules essential to life like proteins.
• Miller and Urey 1953 set up an apparatus to test
  Oparins hypotheses. Their experiment produced a
  variety of organic compounds, including amino
  acids

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EndosymbioticTheory

• What is the theory of endosymbiosis? Theory that
  large prokaryotic, unicellular organisms engulfed
  (ate) smaller prokaryotic, unicellular organisms.
  Engulfed prokaryotes eventually gave rise to
  modern mitochondria and chloroplasts.
• What evidence supports the hypothesis that
  mitochondria and chloroplasts were once free
  living prokaryotic cells? Replicate
  independently and replicate like prokaryotes
  (binary fission), have their own DNA and their
  own ribosomes (also similar to DNA and ribosomes
  of prokaryotes)

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