How does reducing gene flow cause speciation?

Reducing gene flow allows divergence to occur

If the rate of gene flow is high enough, then two populations will have equivalent allele frequencies and therefore can be considered a single effective population.

it's     c       this is a cell (b) with a nucleus (c) containing dna (a). the dna is organized into chromosomes (d). a section of the chromosome that codes for a trait is called a gene (e).