(a) Evolution 

• The changes in organisms over generations as a result of genomic variations.

(b) Selection

• Natural selection is the non-random increase in frequency of DNA sequences that increase survival and the non-random reduction in the frequency of deleterious sequences.

• The changes in phenotype frequency as a result of stabilising, directional and disruptive selection.

  • In stabilising selection, an average phenotype is selected for and extremes of the phenotype range are selected against.

  • In directional selection, one extreme of the phenotype range is selected for.

  • In disruptive selection, two or more phenotypes are selected for.

  • Horizontal gene transfer is where genes are transferred between individuals in the same generation.

• Natural selection is more rapid in prokaryotes. 

• Prokaryotes can exchange genetic material horizontally, resulting in faster evolutionary change than in organisms that only use vertical transfer.

  • Vertical gene transfer is where genes are transferred from parent to offspring as a result of sexual or asexual reproduction.

(c) Speciation

• Speciation is the generation of new biological species by evolution as a result of isolation, mutation and selection.

  • A species is a group of organisms capable of interbreeding and producing fertile offspring, and which does not normally breed with other groups.

• The importance of isolation barriers in preventing gene flow between sub-populations during speciation.

• Geographical barriers lead to allopatric speciation and behavioural or ecological barriers lead to sympatric speciation.