If you're a woman, they do a mitochondrial DNA which gives your maternal line. If you are a guy, then you only need to swab your own cheek. If your dad or brother does it (or paternal uncle, for that matter) YOU do not have to do it since ALL the men in your family with the same last name have the same Y chromosome as you.
This is not creepy at all. I want to do it. My brother is the last living male of our line. My father was the only son and my brother his only son. My brother has 2 daughters. He will go along with it but I just don't know what to do with the swab.
It seems a bit Brave New World, Apocalypse time kinda thing. Like some day, we'll carry our genetic code around like a Driver's License, and the markers will determine what we will or will not be able to do. I've probably read too much dystopian literature or seen one too many SF shows.
It may be a bit paranoid, but it's not beyond the realm of possibility. I guess I just don't want my DNA in a database somewhere. Heck, I don't even like to give out my Social Security number! I think I'll keep my markers to myself.
Still, it is intriguing. Maybe one day my curiosity will get the better of me.