Variation+Selection

• Define variation?


  The differences that exist between individuals
• What does variation within a species mean?


  That individuals in a population can show a wide range of different phenotypes
• Although individuals of the same species have the same genes....?

  They have different alleles - this causes genetic variation within a species
• What is another word for variation within a species?


  Intraspecific variation
• What is the main source of genetic variation?

  • Mutations
  • also during meiosis - crossing over , independent segregation
  • random fertilisation of gametes during sexual reproduction
• variation within a species can also be caused by what?


  differences in the environment eg climate, food , lifestyle
• Most variation within a species is caused by what?

  A combination of genetic and environmental factors
• ONLY GENETIC variation results in evolution
• what is evolution?


  A change in the frequency of an allele in a population over time
• How is one method by which evolution occurs?

  natural selection
• how else can evolution also occur?


  By genetic drift