DNA genealogy, a classic good news / bad news scenario. The good news is that YDNA is past down from father to son so every direct male ancestor of mine would have the same YDNA as me, kinda. Nothing is perfect. There are certain YDNA makers that are known as fast mutating markers. So what does that mean? It means that you can be off by a few markers and still be related. Which means it's very difficult to get an exact match with anyone.
For example, I first took a 46 marker YDNA test through ancestor.com. I was so excited when my results came back. Finally I was going to find my direct ancestors. On my first database search I had over 500 matches. Then there is this statical time period thing that estimates how many generations back you are related to a specific match. I love it, the feed back shows that you and this other YDNA person have a 99% probability of having a common ancestor in the past 50 generations. That's cool except 50 generations ago was way before we were using surnames. So what good id the match?
Then there are websites that have surname groups but you must take your YDNA from that site in order to join in the surname group. So off I go and spend another $100+ for a 37 marker test so I can join the group. Guess what? The results from this new test don't match my results from the first test. The 37 marker test was off by 2 markers from the 46 marker test. Which means that I have a high probability of being related to me in the past 5 generations. Hint: remember those fast mutating markers. On two of those markers my two tests were off by 1 on two known fast mutating markers.
So I join this surname group to find out that I'm not matching up with anyone in the group. But if I mess around with the mutating markers I find I'm matching a lot of the members. OK, what does messing around mean? It means that if I “assumed” that if a mutating marker was only off by one point then I counted it as a match. After all my two miss matched markers were only off by one marker each and I know I'm related to me. Then I decided what happens if I don't count mutating markers at all?
Good news is that after playing some games with mutating markers I came up with a handful of high matches. Bad news is all I know about the matching people is their kit number. Why would someone pay to get their YDNA, then post it for the world to see but not give you anyway to contact them to see if you are truly related.
No problem, the web site for the surname group has a message stating contact your surname group administrator for assistance. They should have mention that the administrator may or may not reply to your email. Mine didn't
I could go on and on but the bottom line is that the various types of DNA have the potential of being a great tool for genealogy. I think the science is good and getting better all the time. My grip focuses on the process involved in the interpretation of your results.
Man, it feels good to have said all this even if I'm only saying it to the other me. (joke)