VARIATION

• WHAT IS EVOLUTION?

  gradual changes in allele frequencies in a population over time
• WHAT LEADS TO EVOLUTION?

  natural selection
• WHAT DOES NATURAL SELECTION DEPEND ON?

  • organisms produce more offspring than can be supported by available supply
  • GENETIC VARIETY within populations of species
  • variety of phenotypes that selection operates against
• WHAT TYPES OF CAUSES DOES VARIATION HAVE?

  genetic, environmental
• GENETIC CAUSES FOR VARIATION?

  MUTATIONS

  • random change in DNA/ nucleotide base sequence

  INDEPENDENT SEGREGATION

  • homologous chromosomes (meiosis I)
  • chromatids (meiosis II)

  CROSSING OVER

  • non-sister chromatids (meiosis I)

  RANDOM FUSION OF GAMETES DURING FERTILISATION
• ENVIRONMENTAL CAUSES FOR VARIATION?

  • soil pH
  • mineral ion concentration
  • exposure to radiation
  • diet
  • light intensity
• MAIN SOURCE OF GENETIC VARIATION?

  mutations