Can nightmares be hereditary?

I believe that in some form that fear, and other emotions, of course, are inherited in terms of their magnitude due to the prior experience of loved ones. For eg. my wife's grandfather was a P.O.W. in WWII and could not talk about it. In the family tree that followed there are traces of memories that may be able to be linked to his experiences that can not be other wise explained. If you look at Jungian theory in psychology these are known as archetypes. I don't believe the relationship between DNA and RNA (RNA is produced by DNA and RNA is involved in memory) is fully understood in terms of how one effects the other. So in answer to your question are they hereditary, you've got my vote.