What are the roles of mutation, migration, and selection in bringing about speciation? Drag the terms n the left to the appropriate blanks on the right to complete the sentences. Not all terms will be used. ResetHelp Reproductive isolation reduces genetic differences between populations of a species and can decrease the level of genetic variation in some populations. Mutations that are favorable or detrimental are preserved or removed by natural selection . However, the frequency of the neutral alleles in a population will b