It's important to understand that not all of our genes are put to use. A shy person may have their "outgoing genes" permanently switched off by a few "master genes". Most of the 1% difference among humans can be found in the genes that act as master keys.
This implies that everyone carries all the genes for all human traits, including the capacity to be a psychopath, which is simply a more rare innate trait. (The only exception is male/female traits, since women don't have a Y chromosome.)
It's easy to see why this would be true. If shy people had to inherit hundreds of unique (specialized) shyness genes as a package, that trait would quickly deteriorate when the genes were passed down from parent to child. Having children tends to remix the genes, so keeping genes together (and keeping them separate from the genes for outgoing traits) would be impossible.