Good news, bad news, mixed news
There’s good news and bad news in the genetic genealogy world this week.
The good news is, things are changing.
The bad news is, thing are changing.
Good good news
Unabashedly good news came from AncestryDNA, which finally started officially reporting how much DNA any two people who match each other have in common.
With any match open, there is now a little icon with the predicted relationship that’s a letter i in a circle. Click on that and you get information we never got before.
Measured in centimorgans (cM), we can now see that someone reported as an extremely high confidence match as a predicted second (actual third) cousin shares 140 cM of DNA with The Legal Genealogist — a very good match indeed, and one well worth spending a lot of time collaborating with.
We can also see, at the other end of the spectrum, that a match reported as a moderate confidence match and distant cousin shares only five cM of DNA with me — and, quite frankly, that’s a match at a level where we’re unlikely ever to identify the common ancestor.
This level of reporting is a very welcome addition to the information from AncestryDNA — the first really solid analytical data that isn’t tree-dependent.
So kudos to AncestryDNA for providing this!
The bad good news
AncestryDNA also reports, with the amount of DNA we share with a match, how many segments we have in common with that match: how many individual pieces of DNA are likely shared because of common descent.
This isn’t as useful as the total amount of DNA in common, because part of the algorithm used by AncestryDNA results in skewing these numbers particularly for close matches.
Here’s the deal: AncestryDNA has a system called Timber that identifies, and removes, areas from its reporting system where it looks like there are huge numbers of people who share those segments just because they’re human, or European, or Greek — rather than because they share a common ancestor.
That’s a good thing, usually, since it removes a lot of false positive matches. But the result is that it really wreaks havoc with the number of segments reported.
Every parent should share exactly one very long segment on every autosomal chromosome with each of that parent’s children. That’s because each child inherits one entire chromosome out of each autosomal pair of chromosomes from each parent. So — on any given autosomal chromosome — there should be one, and only one, shared segment between a parent and a child. Twenty-two autosomal chromosomes, 22 autosomal segments shared.
But when you remove those Timber segments from consideration, what you get instead of one long shared segment is lots of smaller shorter segments shared between parent and child. My first cousin has had both of her parents tested: AncestryDNA reports that she shares 89 segments with her father and 102 with her mother.
So, for the time being at least, the Timber system combined with the segment reporting system isn’t good news at all.
The really mixed news
The biggest changes on the horizon are those over at 23andMe where the entire reporting system is about to be up-ended. An entire new set of rules go into effect this Wednesday, November 11th, so time is running out for those of us who’ve tested there to collect information about existing matches that could very well disappear as of Wednesday.
I’d give you an entire laundry list of things you can do to maximize your chances of keeping information you already have and being able to ensure that you are best positioned to take advantage of the changes there… but I don’t need to.
Shannon Christmas has already done it, yesterday, in a post on his blog, Through the Trees. The post, Prepare for The New 23andMe, gives you step by step instructions, with screen captures, on just what to do to make sure you keep as much as can be kept of the utility of the existing 23andMe system and position yourself to benefit the most from the new system there.
The winds of change are a-blowing… and we all need to keep abreast of what’s happening to make the most of our DNA test results.