What is a single unit of hereditary information called?

What is a train line on a single rail called? What is a single residential building divided into three units called? What is a single-seat aircraft powered by a small motor called? What is a single show of a TV drama series called? Which sitcom starred a DeFazio and a Feeney? A sixth-round draft pick in 2000, which Michigan man found a bit of success as a QB for the Patriots? A skier in his free time, which Mercury Seven astronaut landed his Aurora 7 capsule 250 miles off course in 1962? A skirmish over the theft of one of the Discovery's boats led to which explorer's death in Hawaii in 1779?