speciation

• allopatric speciation

  caused by geographical barrier

  diff selection pressures in the diff environments causes diff species and advantageous alleles

  stops gene flow
• sympatric speciation

  less common

  formation of new species when populations aren't geographically isolated but reproductively isolated

  reduced gene flow

  can occur in plants
• genetic drift

  change in allele frequency (increase)

  occurs in small populations

  reduced gene pool

  does not discriminate if an allele is advantageous

  increase in harmful alleles (allele freq)

  alleles may become fixed
• what can cause genetic drift?

  founder effect e.g colonisation

  disease

  natural disasters

  famine

  genetic bottleneck
• founder effect - occurs when a small number of individuals from a large parent population start a new population
• genetic bottleneck: very quick, large reduction decrease in population size