A View of Life

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Population Genetics

• Genetic diversity in populations changes over
  generations
• Forces that cause populations to evolve
• Allele and genotype frequencies over generations

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Microevolution

• Change in gene frequencies between populations of
  a species over time
• Hardy-Weinberg Equilibrium
• Stable, non-evolving population

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The nitty-gritty p292 of text

• Random mating
• No selection (no reproductive advantages)
• No mutation
• No migration
• Large population

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Migration aka GENE FLOW

• Amount depends on
• Distance between populations
• Ability of individuals/gametes to move between
  populations
• behavior
• No migration can result in reproductive isolation

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Genetic Drift A result of small populations

• Chance events alter the gene pool
• Bottleneck effect
• Founder effect
• High level of inbreeding loss of diversity in
  the population

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Figure 24.9 Ensatina eschscholtzii, a ring
species
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How do we define a species?

• Morphological species
• Cryptic species
• Evolutionary species (fossils)
• Biological species

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Reproductive Isolation

• Incapable of interbreeding
• Formation of new species
• SPECIATION

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Speciation

• The splitting of one species into two or more
  species.
• OR
• The transformation of one species into a new
  species over time.

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Modes of Speciation

• Allopatric Speciation (Greek, different
  fatherland)a population forms a new species
  while geographically separated from its parent
  population.
• reproductive isolation occurs.
• Examples squirrels on either side of the
  Grand Canyon pupfish in springs in the deserts
  of California and Nevada adaptive radiation in
  island chains.

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Modes of Speciation continued

• 2. Sympatric Speciation (Greek, together,
  fatherland)a population develops two or more
  reproductively isolated groups without prior
  geographic isolation.
• Usually a mutation erects a reproductive
  barrier between the mutants and the parent
  population.
• Best evidence is found among plants where it
  can occur by means of polyploidy or by
  hybridization between two species followed by
  doubling of the chromosome number. These new
  plants can no longer reproduce with the parent
  species.

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Figure 24.6 Two modes of speciation
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Figure 24.7 Allopatric speciation of squirrels
in the Grand Canyon
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Figure 23.9 Geographic variation between
isolated populations of house mice
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Figure 24.8 Has speciation occurred during
geographic isolation?
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Figure 24.13 Sympatric speciation by
autopolyploidy in plants
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Figure 24.15 One mechanism for allopolyploid
speciation in plants
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Adaptive Radiation

• Is an example of allopatric speciation.
• The rapid development from a single ancestral
  species of many new species, which have spread
  out and become adapted to various ways of life.
• --as the parent population increases in size,
  daughter populations are subjected to the founder
  effect and the process of natural selection.
• --Examples 13 species of Galapagos finches
• 20 species of Hawaiian
  honeycreeper
• 500 species of Drosophila in Hawaii

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Types of evolution

• Divergent
• Parallel
• Convergent

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Rates of Evolution
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