Question

What do we call a mixing of genes as a result of migration?

Answer 1

Migration helps the genes to flow from one gene pool to other. I think if you are talking about 'mixing of genes' you actually mean addition of new alleles in the gene pool.

Explanation:

Gene flow which add new alleles to gene pool, may decrease genetic differences between two populations. On the other hand if 'mixing of genes' stops, related populations would become genetically different/unique. Hence, gene flow is identified as an important evolutionary force in speciation.