Hahaha I always ask them this and they stutter, and ponder and then there answer is something like "This is a trick question he doesn't exist" and I wanna cry :'(---that's horrible. I feel sorry for people who don't know who Uriah is.
The whole book is a quagmire of faux-science nonsense about genetics. listless, anti-climactic, and you really get the sense that Roth know where she was going with the story. Also, Tris dies in a deeply unsatisfying, unnecessary way.