How does speciation start to take place on a genetic level between two isolated populations?

Speciation start to take place on a genetic level between two isolated populations by Allele frequencies change in different ways.

The field of study called the population genetics helps us to understand about the composition of a selected population and the frequencies of alleles and how they get changed over a specific period of time.  The mechanism called the adaptation mechanism ,mutation and gene flow determines the allele frequency changes in natural population.

Micro evolution refers to the changes in gene pool from one generation to another. Natural selection, mutation, genetic drift and gene flow are considered as the four forces of this evolution. When the allele frequencies starts to get changed in different ways, the Speciation starts to take place.