The Gear screen opens from the main menu once you've finished a run. The Loadout is on the left, the bag (grouped by slot, best first) in the middle, and the inspected piece with Equip, Enhance, Combine and Dismantle on the right. Spare gear breaks down into nucleotides.
Break a spare piece down for nucleotides and some materials back. It can't be undone.
Equipped gear must be unequipped first, and locked gear unlocked: Lock keeps a piece from ever being dismantled, one at a time or in bulk (Pandemic Game Mode set rewards come locked)
Base yield of A and T: Common 30, Uncommon 60, Rare 120, Epic 220, Legendary 400, Mythic 700, Prismatic 1,200, plus about two-thirds as much C and a third as much G
The inspected piece shows the nucleotides it dismantles into, under "Dismantling gives"; the gear page after a run shows it too
+8% per item level above 1 and +25% per enhancement level
Also returns Polymerase Shards (1 for Common up to 18 for Prismatic) plus half the materials spent enhancing it
From the Codex
The building block of DNA and RNA: a sugar, a phosphate and a base (A, T, C, G in DNA; A, U, C, G in RNA).
Fun fact: Influenza stores its genes as RNA, so it uses U in place of T.