Ch 2426

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Ch 24/26

• Hmwk
• Review for the exam
• Use study guide

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Causes of Microevolution

• Genetic Drift - changes in the gene pool of a
  small population due to chance the smaller the
  sample, the greater the chance of deviations from
  the expected result.
• Gene Flow genetic exchange due to migration of
  individuals or gametes between populations
• Mutation A change in the DNA found in the
  gametes.
• Nonrandom mating Making a choice.
• Natural Selection survival of the fittest

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Causes of Genetic Drift

• The bottleneck effect when a disaster such as
  an earthquake, flood or fire reduce the size of a
  population drastically, killing victims rather
  unselectively
• The founder effect When a few individuals from
  a population colonize an isolated island, lake,
  or some other new habitat.

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Nonrandom mating

• Proximity may lead to inbreeding
• Assortative mating individuals select partners
  that are like themselves in certain phenotypic
  characters (size)

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The substrate for natural selection is genetic
variation

• Polymorphism two or more forms
• Geographical variation
• Mutation
• Sexual recombination
• Diploidy
• Heterozygote advantage
• Hybrid vigor (crossbreeding between inbred
  varieties)

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Relative fitness

• The contribution of a genotype to the next
  generation compared to the contribution of
  alternative genotypes for the same locus
• If Pink flowers (AA or Aa) produce more offspring
  than white (aa), then they are given a relative
  fitness of 1. If white flowers produce only 80
  as many offspring, their relative fitness is 0.8.

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How does selection effect a population?

• Stabilizing selection acts against extreme
  phenotypes and favors the more common
  intermediates. - birth weight
• Directional selection common during periods of
  environmental change or when members of a
  population migrate to some new habitat with
  different environmental conditions. Shifts the
  frequency curve for some phenotypic character in
  one direction or the other by favoring relatively
  rare individuals. During glacial periods of the
  ice ages, black bears in Europe increased in
  size.
• Diversifying selection environmental conditions
  are varied in a way that favors individuals on
  both extremes of a phenotypic range. A finch
  population with two bill sizes

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The biological species concept

• Defines a species as a population or group of
  populations whose members have the potential to
  interbreed with one another in nature to produce
  viable, fertile offspring (in natural
  environments not labs or zoos etc).

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Prezygotic barriers

• Impede mating between species or hinder the
  fertilization of ova if members of different
  species attempt to mate
• Habitat Isolation
• Behavioral Isolation
• Temporal Isolation
• Mechanical Isolation
• Gametic Isolation

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Postzygotic Barriers

• Reduced Hybrid Viability abort development of
  the hybrid at some embryonic stage
• Reduced Hybrid Fertility offspring are
  completely or largely sterile (ex. Horse/donkey
  mule)
• Hybrid Breakdown offspring of the F2 and
  further generations are feeble or sterile.

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Biological species concept does not always work

• Extinct animals/plants
• Asexual organisms
• Even though coyotes interbreed with domestic dogs
  and wolves to rpoduce fertile hybrid
  offspiring, all three remain distinct.
• Some organisms have subspecies some interbreed
  some dont

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Other ways to i.d. a species

• Morphological species concept (physical features)
• Recognition species concept (mating adaptations)
• Ecological Species concept (where they live
  what they do)

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Modes of Speciation

• Allopatric speciation a geographic barrier that
  physically isolates populations
• Sympatric speciation chromosomal changes (in
  plants) and nonrandom mating (in animals)

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Sympatric Speciation

• For example, 200 years ago, the ancestors of
  apple maggot flies laid their eggs only on
  hawthornsbut today, these flies lay eggs on
  hawthorns (which are native to America) and
  domestic apples (which were introduced to America
  by immigrants and bred). Females generally choose
  to lay their eggs on the type of fruit they grew
  up in, and males tend to look for mates on the
  type of fruit they grew up in. So hawthorn flies
  generally end up mating with other hawthorn flies
  and apple flies generally end up mating with
  other apple flies. This means that gene flow
  between parts of the population that mate on
  different types of fruit is reduced. This host
  shift from hawthorns to apples may be the first
  step toward sympatric speciationin fewer than
  200 years, some genetic differences between these
  two groups of flies have evolved.

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Adaptive Radiation

• The evolution of many diversely adapted species
  from a common ancestor.
• Type of Allopatric or Sympatric Speciation?
  Finches on the Galapagos Islands?

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How fast does speciation occur?

• Punctuated equilibrium species diverge in
  spurts of rapid change
• Gradualism species descend from a common
  ancestor gradually diverging more and more as
  they acquire unique adaptations

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Table 25.1

• 4.5 billion years ago Earths origin
• 3.5 billion years ago oldest fossils
  prokaryotes
• 2.5 billion Oxygen begins to accumulate
• 1.7 billion oldest eukaryotic fossils
• 700 million Oldest animal fossils
• 570 million Cambrian Explosion most modern
  animal phyla
• 510 million Origin of plants marine algae
• 245 million cone-bearing plants dominate
  landscape
• 145 million Flowering plants appear many
  organisms (including most dinosaur lineages
  become extinct Cretaceous.
• 1.8 million Ice ages humans appear

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1953 Stanley Miller and Harold Urey

• Tested the hypothesis that the ancient world
  contained the chemical conditions and energy
  resources needed for the abiotic synthesis of
  organic molecules.
• Water, H2, CH4 (methane), and NH3 (ammonia)
  (atmosphere strongly reducing)
• Sparks mimicked lightening
• Warm flask of water primeval sea
• Condenser cooled the atmosphere raining water
  and dissolved compounds back to the miniature
  sea.
• After one week found a variety of organic
  compounds (some amino acids)

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The experiment has been repeated.

• Labs have produced all 20 amino acids commonly
  found in organisms, several sugars, lipids, the
  purine and pyramidine bases present in DNA and
  RNA and even ATP

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What came first?

• RNA probably the first genetic material

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Whos related to whom?
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Evidence for Evolution

• Biogeography the study of the past and present
  distribution of organisms in the world why are
  specific organisms found in Australia? They
  evolved from ancestral species there
• The Fossil Record oldest known fossils are
  prokaryotes chronological appearance of the
  different classes of vertebrates many
  evolutionary transitions have been discovered
  linking old to new species

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More Evidence

• Comparative Anatomy the forelegs, wings,
  flippers and arms of different mammals are
  variations on a common structural theme
  homologous structures similarities resulting
  from a common ancestor ex vestigial organs

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More Evidence..

• Comparative Embryology- closely related organisms
  go through similar stages in their embryonic
  development.
• Ontogeny the development of an individual
  organism is a replay of the evolutionary
  history of the species - phylogeny

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More Evidence.

• Molecular Biology evolutionary relationships
  among species are reflected in their DNA and
  proteins