DNA is like your phone line. As Northwestern University biophysicist Johnathan Widom put it in a talk recently, DNA simultaneously encodes multiple overlapping signals, just like your phone line that allows you to call home while you're surfing the net via DSL. Written into your DNA is the code for the amino acid sequences of the proteins produced by your genes, as well as the so-called 'non-coding' regulatory sequences which essentially encode when, where, and how much your genes are expressed.

That DNA evidence that could exonerate you? You don't have a right to it, says the US Supreme Court.

Actually, not being a lawyer or constitutional scholar, I don't know what kinds of evidence you have a constitutional right to when you go on trial, so I'm not going to comment on the correctness of the decision. But legal scholarship aside, two things are obvious:

1) When we try someone for a crime, we want the best, most reliable evidence possible. It's probably reasonably safe to say that most people with at least some wisps of sanity would like our criminal justice system to convict the guilty and acquit the innocent.