Eugenics
From Memory Alpha, the free Star Trek reference
Eugenics (also known as selective breeding) is the philosophy or practice of selectively breeding traits in or out of a group of organisms. While widely-used in botany and horticulture, eugenics via genetic engineering in sentient lifeforms is illegal in the Federation, except in cases of medical necessity. (DS9: "Doctor Bashir, I Presume", VOY: "Lineage")
In the late twentieth century, Human scientists on Earth used eugenics programs to attempt to improve the human species, sparking the Eugenics Wars. (TOS: "Space Seed")
Kodos used his own personal theory of eugenics when killing 4,000 people on Tarsus IV. (TOS: "The Conscience of the King")
The Dominion used selective breeding on the Jem'Hadar and the Vorta. (DS9: "Favor the Bold", "Treachery, Faith and the Great River")
