Evolution and speciation GapFill

The major source of genetic variation within a population is from  epigeneticsRNA interferencemutationepistasis, but sexually reproducing organisms also vary as a result of  mitosisinversionmeiosishydrolysis. Discontinuous characteristics are generally determined solely by genes, but other characteristics may be influenced by  epistasisgenomesex-linkageenvironment. Selection pressures differentiate between individuals based on their phenotypes - for example, poorly adapted prey animals are more likely to be at risk from  hybridisationrestrictionpredationextinction. As such, natural selection determines the  genomegene poolallele mixhybrid collection of a population.

There are three main types of selection which can act on populations:

It is not the mutation rate which is affected by changing conditions, just the frequency of  mutant allelesbase substitutionfertile offspringloci transitions throughout the population

The evolution of a new species from an existing one is called  colonisationepigenesisoncogenesisspeciation. This tends to happen only if populations become reproductively separated. In smaller populations, any changes in allelic frequencies are likely to quickly have a huge effect on the whole population; this is known as  mutant accumulationgenotype innovationspecies diversificationgenetic drift. Reproductive separation may occur as a result of a physical barrier - this geographic separation is known as  topographicforeignallopatricboundary speciation. Alternatively,  habitualparapatricnon-divisivesympatric speciation occurs when populations in the same region become reproductively separated. This can happen for many reasons, e.g.  ecologicalgameticculturaltemporal speciation occurs when the breeding seasons of two populations do not coincide.