Genetics is the field of science concerned with the study of genes, the method common to many species by which traits and characteristics are passed from one generation to the next in reproduction. The term is also used to refer to anything pertaining to genes.
Each individual has a unique genetic structure. Likewise, every alien race has a different genetic pattern. For example, Bajoran genes are quite different from those of Cardassians. This fact proved troublesome for the like of Seska, who was exposed as a Cardassian spy disguised as a Bajoran Starfleet officer when it was found that the genetic markers in her blood were those of a Cardassian. (VOY: "State of Flux")
Khan Noonien Singh and the other augments of the Eugenics Wars were products of "controlled genetics". Their genetic makeup was chosen through selective breeding and their DNA altered through the process of genetic engineering. (TOS: "Space Seed")