>> > one reason I haven't sent a DNA sample to 23andMe, etc., is because I can't control what happens to my data after that point, and I'm not even sure if I can find out.

https://www.23andme.com/privacy/

Research participation

23andMe offers customers the opportunity to participate in a new way of conducting research (at home and online). Participating in our research is completely voluntary. Customers can choose not to consent to research and doing so will not impact their 23andMe experience.