hard to remember evolution terms

gene flow

the movement of allelic variations through populations

gene drift

the generally random changing of allelic variation of a population.

Founder effect

Lack of gene flow due to generally random isolation of individuals within a population, creating different allelic variation. Allele frequencies that are normally recessive become more common, but depends on selective pressure. Long term founder populations generally show reduced variation due to smaller initial population. Can result in speciation due to different selective pressures and lack of gene flow. 

bottleneck effect

Random removal of individuals from a population resulting in reduced allelic frequency creating potentially altered/ reduced variation. 

allopatric speciation

Population is separated due to generally random geographical separation creating a random allele frequency. Different selective pressure creates different allelic variation. Speciation may occur due to different selective pressures and lack of gene flow.