Natural selection requires genetic variation to exist within a population in order to allow for the differential targeting of heritable characteristics

• Genetic variation can be generated via mutations, meiotic divisions, sexual reproduction and gene flow 
  

Mutation

• A gene mutation is a change to the nucleotide sequence of a section of DNA that encodes a particular trait
  

• Mutations can give rise to new versions of a gene (called alleles) and hence change the characteristics of an organism
  

• Only germ line mutations (in gametes) produce heritable variation – somatic mutations (in body cells) are not passed on to offspring

Meiosis

• Meiosis is a reduction division that reassorts parental chromosomes to create new gene combinations in gametes
  

• The assortment of homologous chromosomes is random, meaning different combinations of chromosomes are generated upon each meiotic division
  

• Additionally, genetic information can be exchanged between homologous chromosomes (crossing over) to create novel gene combinations
  

Sexual Reproduction

• The fusion of gametes from two different parental sources will result in the production of offspring that are genetically distinctive
  

• Because every gamete is unique (due to random assortment), the fertilisation of an egg and sperm should always generate different zygotes
  

Gene Flow

• Gene flow describes the movement of alleles between interbreeding populations as a consequence of migration (or pollen transfer)
  

• Gene flow creates variation within a given population by introducing new alleles from an alternate population source
  

• Gene flow maintains the genetic compatibility between the two separate populations and hence functions to prevent speciation
  

Sources of Variation