Speciation and Genetic Drift

• Speciation in the development of a new species from an existing species. It occurs when populations of the same species become reproductively isolated - changes in allele frequency cause changes in phenotype, which means they can no longer interbreed to produce fertile offspring.
• Reproductive isolation can occur when a physical barrier e.g. a flood or earthquake, divides a population of a species, causing some individuals to become separated from the main population. This is known as geographical isolation. There is no gene flow (transfer of genes) between the two populations, which can lead to allopatric speciation.
• Speciation can also occur when a population becomes reproductively isolated without any physical separation - sympatric speciation