Genetic variation + mutation

• Crossing over


  When homologous pairs pf chromosome pair up the chromatids twists around each other and bits of chromatics swap over.

  Same genes but different combinations of alleles
• Independent segregation


  When homologous pairs are separated in meiosis 1, they randomly go to a different daughter cell

  Have random assortments of paternal and maternal chromosomes
• Random assortment


  The random organisation of chromosomes in the middle of the cell during the first stage of meiosis
• Substitution


  One base substituted with another
• Deletion


  One base is deleted
• Why don't all substitution mutations change the amino acid sequence

  The degenerate nature of the genetic code

  More than one DNA triplet can code for an amino acid
• Frame shift


  A genetic mutation which is caused by the deletion or insertion in a DNA sequence
• Directional selection


  Individuals with alleles for extreme characteristics are more likely to survive
• Stabilising selection


  Individuals with alleles for characteristics towards the middle range are more likely to survive