Forces of evolution and species concepts

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Forces of evolution and species concepts
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• Evolutionary mechanisms
• 1. Mutation the only source of new genetic
  information.
• Mutation any heritable change in the structure
  or amount of genetic material.
• Different levels of mutation
• DNA point and frameshift mutations (mistakes
  made during DNA replication)
• Chromosome rearrangements
• /- of single chromosomes
• complete sets of chromosomes.
• Spontaneous (random) vs. induced mutations
• Only mutations occurring during meiosis can
  affect the next generation.

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2. Evolutionary forces Genetic Drift

• Natural interbreeding populations are finite in
  size.
• Geographically structured so that mating, within
  a species, is not random.
• In small, isolated populations (demes), the
  frequency of different alleles can fluctuate by
  chance (genetic drift).
• Therefore, by definition, genetic drift is an
  evolutionary force.
• But, direction cannot be predicted therefore,
  cannot reliably produce adaptations.

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Demes
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Computer modeling of genetic drift Start with 4
heterozygous individuals (A1/A2)
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(No Transcript)
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Example of genetic drift
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Desert 8,000 to 4,000 ybp Contiguous with SW
desert Then retreat of deserts to SW
Present oak-hickory forest Relictual
populations each with. c.12 lizards.
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• Humans
• Tristan da Cuhna island in southern Atlantic
  one of most isolated places on earth
  adminsstered by Great Britan.
• 1816 William Glass, wife, two daughters
• Joined later by a few additional settlers from
  England
• 1961 volcano eruption forced removal of all
  residents (294)
• In England, tested for various genetic traits.
• All residents homozygous (alleles fixed) for nine
  genetic markers.
• Clinodactyly (dominant) present in the Glass
  family.
• Alternative glucose-6-phosphate dehydrogenase
  allele arrived in 1827..gene flow.

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• 3. Founder Effect
• Occurs when a small segment of a population
  becomes geographically isolated from the larger
  population
• The smaller population has only a small fraction
  of the genetic variation of the larger
  population.

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Founder effect
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Frequency of blood type O)
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4. Population bottleneck What does it do?
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• 5. Gene Flow Individuals carry alleles from one
  population to another population.
• Gene flow refers to migration
• Influenced by culture and social structure.
• Gene flow (exchange of genes between populations)
  has increased over time.

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6. Natural selection directional selection
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Natural selection e.g. Stabilizing selection
19.2 lbs. c. 8.5 kg