How Theodosius Dobzhansky integrated genetics with evolution

In 1859, Charles Darwin proposed his theory of natural selection which acts on variations present in the populations and better varieties are produced in the course of time. Darwin's theory of natural selection is important, and acts as the main guiding force of evolution. However, he lacked the knowledge of genetics and could not explain the basis of variations. It is only those variations which are important in evolution that have a genetic basis and are inheritable. This gap was filled by Theodosius Dobzhansky who provided the genetic basis of evolution through his book in which he explained various mechanisms of evolution having genetic basis. Dobzhansky also provided the experimental evidence in favour of evolution through his work on Drosophila. He was the first to provide the genetic basis of evolution showing the action of natural selection on genetic variability. He defined evolution as a change in genetic composition of a population. Further, he also contributed to the development of the modern synthetic theory of evolution. That is why the author says Dobzhansky integrated genetics with evolution.