mutation genetic variation
1 Mutations are changes in the DNA. 2  A single mutation can have a large effect, but in many cases, evolutionary change is based on the accumulation of many mutations. 3  Gene flow is any movement of genes from one population to another and is an important source of genetic variation.ithout genetic variation, some of the basic mechanisms of evolutionary change cannot operate. There are three primary sources of genetic variation, which we will learn more about: 1  Mutations are changes in the DNA.