Eukaryotic genetic variation occurs with vertical gene transfer while prokaryotic genetic variation occurs with horizontal gene transfer.
Genetic variation is when the genetic content of the offsprings are different from that of the parents. It is a phenomenon achieved in different ways by different organisms. Eukaryotic organisms undergo sexual and asexual reproduction in which they transfer genetic material (DNA) to their offsprings. This process of transfer of DNA from parents to their offsprings is called VERTICAL GENE TRANSFER. In sexually reproducing organisms, meiosis is undergone where CROSSING-OVER is the process that increases the chances of genetic diversity.
However, in prokaryotic cells that use other methods like transformation, transduction and conjugation to increase genetic diversity among their species since asexual reproduction does not produce genetically different offsprings. Prokaryotes like bacteria transfer or receive genetic material (DNA) from other bacteria species that are not their offsprings. This process is called HORIZONTAL GENE TRANSFER.