What linux distribution is Android based on? Did Google use some existing distribution (Debian, Red Hat, etc.) to create Android, or did they use the bare essentials (kernel, file system and some mandatory files)?
Android shares very little with a typical Linux distribution. In fact, this is where Richard Stallman's "GNU/Linux" distinction comes in handy — Android isn't really a Unix-like general purpose operating system with a Linux kernel. It's a new system which happens to use the Linux kernel. This goes all the way down to its own custom libc implementation (called "Bionic"), which does not necessarily attempt POSIX compliance.

This article from ZDNet covers a talk which gives a pretty good overview of the system, and although it's a couple of years old it's still basically correct and helpful.