DNA is a series of Trap Cards that were first introduced in Pharaoh's Servant. The latest is "DNA Checkup" which was released in Crossroads of Chaos. Each "DNA" card depicts a doctor with three eyes and two nurses next to it doing something to a patient.
"DNA" cards focus on changing Types and Attributes of monsters. This can come in handy if you play cards like "System Down" which banish all Machine-Types. Cards like these are only used in combos (or Side Decks). They also work well in a "Charmer" Deck.