Answer: The gene flow is responsible for the (b) genetic variation.
The gene flow is a concept of genetics where the genes or alleles move between the individuals in an interbreeding population of species. When a member belonging to a particular gene pool (collection of unique genes) mates with another member of a different gene pool, the gene frequencies change for the various genes in the progeny. This helps in maintaining the genetic variation in the population of the interbreeding species.