Individuals in the same species look different (have different phenotypes). This is called variation.

Variation is caused by;

  1. The genotype of the individual (i.e. which alleles they have).
  2. The environment.

Genetic diversity describes the range of different genotypes within a species. If there are few genotypes the genetic diversity is small. If there are lots of genotypes the genetic diversity is large.


  1. Independent Assortment
  2. Mutation
  3. Random fusion
  4. Crossing Over

Independent Assortment = which allele of each pair goes into which gamete. This is caused by the orientation of homologous pairs of chromosomes during metaphase 2 of meiosis.

Changes in the sequence of bases in codons (mutation) cause genetic variation. This usually occurs  by DNA being improperly copied or damaged. Chemicals (mutagens) and radiation can do this.

Each gamete is different. Therefore, by combining different gametes new variation occurs (random fusion).

During meiosis sections of DNA are swapped between homologous chromosomes (pairs of chromosomes). This creates more variation by creating new combinations of alleles (crossing over). (See fig. 5.18 on p18).