I was an early DNA tester: the Beatty DNA project is one of the biggest (and oldest) and has a couple of DNA scientists who've taken our project to extremes. After I signed up for a Y test, I decided to get the MtDNA also. So many years ago I had very few hits but I seem to get a new one every few months and I must have 30 or 40 matches with zero distance matches. In other words, a perfect match on all 16,569 markers.
Just yesterday a new tester who is a zero match to me emailed and asked if I had a tree he could look at. It turns out that his family is huge into genealogy (they have been for nearly two centuries) and they have the family tree well plotted out to the 17th century. He said that he has a good paper trail on his maternal line back to England in the last 1600's. And so he's wondering, how is his maternal line Swedish?
I have wondered the same question - my line is for sure Swedish - maternal Grandma was a first generation American and both of her parents came from Sweden. Sweden has exported a lot of people over the last dozen centuries but hasn't had many migrants until recent days. Yes, I have 0 distance matches in Ireland, England, northern Germany, and some in the Baltic States. I've often wondered if this MtDNA line goes back to Viking times?
I checked FtDNA's page on MtDNA and they claim that if you have a 0 distance match, there is a 50% chance that your most recent common ancestor (MCRA) is within the past 5 generations, or about 125 years. I have a hard paper trail on my maternal line (yay for Swedish records!) back 7 generations and 253 years. Hmmmm.... doesn't sound right. Well, I must be in the other 50% right? What about the matches in other countries? I suppose Swedish immigration during the 1800's to England because of famine refugees but to Germany, to Latvia?
And so, I began to read up on MtDNA and I found this article and it confirmed what I've long suspected. Your MtDNA most recent mutation could be one generation, or it could be 2,000, 3,000, or even 5,000 years past.
Concepts – Genetic Distance
It is a fascinating article and I highly recommend giving it a read. It covers both YDNA and Mitochondrial. The author confirms my suspicions, that my matches in Latvia and Ireland may be remnants of old Viking colonies.