The subject of DNA is a difficult one. Explaining human life on a molecular level tells most people far more than they can understand or care to know. Cops and prosecutors love what DNA can do. They hate to talk about it scientifically. Few of them understand it. The old joke is, most people can't even spell DNA. I explain that nuclear DNA is what we get when cells with nuclei are present, such as with blood, tissue, seminal fluid and hair roots. Nuclear DNA is inherited equally from both parents, so if we have someone's nuclear DNA we have, in a sense, all of him, and can compare his DNA profile to any other biological sample this same person has left at, say, another crime scene.