Wednesday, 23 August 2006

Genealogy by mtDNA

Yesterday I received an email from Family Tree DNA (FTDNA) informing me they had another client who exactly matches my mitochrondrial DNA (mtDNA) . For those not familiar with mtDNA, it's passed from generation to generation along the maternal line. I got mine for my mother, but as a male I won't ever pass it on to my children.

That makes three of us, clients of FTDNA, who share identical DNA in both Hypervariable regions 1 and 2 - that's a high resolution match. Because I've agreed to release of my name and email address to those who match I was able to see the new person's information.

A few hours later I received an email from that person giving his earliest know maternal line ancestor and asking about mine. From paper records I can trace my maternal line back seven generations, the earliest three of which were in one locality. That puts our earliest documented ancestors about a century and the North Atlantic Ocean apart.

mtDNA changes slowly which means that with present tests exact matches occur for people related quite distantly in time along their maternal lines. From the FTDNA web site, an exact high resolution mtDNA match has about a 50% chance of sharing a common ancestor within the last 28 generations (about 700 years). My new DNA cousin and I both have a lot of researching to do to get back that far!

FTDNA advertise they have about 31,000 clients who have taken mtDNA tests. I don't know if they all agreed to limited release of their results, but if so the three of us who share my mtDNA are about 1 in 10,000. With 300 million people in the USA, 60 million in the UK and 30 million in Canada, we could look for another 39,000 matches if everyone in those countries got a test. If they all descend from one woman 28 generations ago the intermediate generation daughters would have to have had daughters at a rate of 1.48 per generation. If the line started 54 generations ago the rate would be 1.22 per generation. That doesn't account for lines that don't produce daughters, so you'd expect the rate in surviving lines to be larger. What's the daughter production rate in your family history?

No comments: