evolution

• Genetic drift is the change in the frequency of an existing gene variant in a population due to random chance.
• • This applies when any group of individuals are isolated from a larger breeding population
  • The alleles found in a small group will inevitably be more limited than in a larger group so there is a loss of genetic variation. E.g. I do not have the allele for red hair or blue eyes.
  • Because there is a limited number of individuals this means any alleles possessed by them will inevitably become amplified in subsequent generations
• • Isolation – two populations must not be allowed to breed
  • Environmental variation – There must be differences in the two environments
  • Genetic variation – there must be differences between organisms
  • Natural selection – alleles that help an animal survive are selected for meaning over millions of years they change
  • Speciation – The populations become so different they cannot breed successfull
• • Allopatric is the most prevalent speciation method. Involves physically separating two populations and wait for them to evolve differently
  • If a species evolves in isolation e.g. on an island it is said to be endemic to that island
• • sympatric speciation is Speciation due to reproductive/ behavioural/ seasonal/ mechanical isolation
  • More rare because it is more difficult to totally eliminate gene flow
  • DNA analysis now shows us that often species undergo some sort of geographical isolation in their ancestry as well in order to undergo sympatric speciation succefully