Your DNA may be entirely optional.
I maintain a family tree on Ancestry that is limited in numbers, but very complete within its scope. About six months ago I was contacted by a woman who was adopted at birth and was searching for her biological father. She had taken Ancestry's DNA test and had about a dozen relatively close matches who all listed relatives who were on my family tree. It took me less than an hour of reviewing the various family trees to identify their most recent common relative - my great-great-grandmother. A few more hours of research and I was able to eliminate all but one family of my great-great-grandmother's descendants. The woman then supplied a couple of tidbits of biographical information: where and when she was born, that her mother had been an unmarried teen, and her father had been a middle-aged married man working in a particular industry. In short, I identified the woman's biological father in less than a day and without any of his DNA being available. Luckily for him, I do not make my family tree information about living persons publicly available.