Evolution may lead to speciation

• Define evolution

  A change in the frequency of alleles in a population over time
• Define a gene pool

  All the alleles in a population
• Define speciation

  One species evolving from another
• Define allopatric speciation

  1. Environmental change causes several of an original population to become geographically isolated from the rest
  2. The gene pools do not mix
  3. There is already genetic variation in the isolated groups due to random DNA mutations
  4. Different selection pressures give different alleles the advantage, and these are passed on in reproduction, so increase in frequency
  5. Over time, the two groups become different species as they can no longer produce fertile offspring
  6. This is disruptive selection
• Define sympatric speciation

  1. A mutation that causes reproductive isolation is passed on to a small number of an original population not geographically isolated
  2. The gene pools do not mix
  3. There is already genetic variation in the isolated groups due to random DNA mutations
  4. Different selection pressures give different alleles the advantage, and these are passed on in reproduction, so increase in frequency
  5. Over time, the two groups become different species as they can no longer produce fertile offspring
  6. This is disruptive selection
• Describe how genetic drift leads to evolution

  In small populations, the frequency of alleles can change due to chance