No matter how expert you think you are, there is always something to be learned from others.
When I saw that Michelle Trostler of DNA Detectives on Facebook and Identify Family was giving a talk on getting started with AncestryDNA for my local DNA special interest group, the North San Diego County Genealogical Society, I knew I should go, and I am glad that I did.
Personally, I use the Ancestry.com DNA testing service the least of the big three because all my ancestors are relatively recent arrivals (late 1800s and 1930s) so I do not have as many DNA matches there as elsewhere. Thus I know far less about using that site than the others.
Michelle is a knowledgeable and confident speaker. You can hear her at the upcoming i4GG seminar in San Diego as well.
Here are some of the tips from her talk that I found particularly useful.
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Many people have the illusion that if their testing company says a person is a 3rd to 5th cousin they really will be. That is not the case.
The testing companies are just making the best guess they can from the data they have. They do not seem to take segment sizes into account, rather they primarily use total shared DNA measured in centimorgans (cMs) for their relatedness estimates, usually the sum of all matching segments of 5 cM or larger. Close relatives will always share larger chunks with each other and so size does matter here.
Recently I have received numerous questions from people trying to figure out if a new match is a half sibling or a niece or a grandchild. These are hard to tell apart without testing more relatives as they all share about 25% of their DNA with each other. So I decided to collect some detailed statistics on those specific relationships with a google form (click here) that includes total segments and segment sizes for a future blog post [UPDATE as of sept 2017: First round results are written up at https://blog.kittycooper.com/2017/09/the-25-relationship-a-first-look-at-the-data/ ]
The companies predict reasonably well for close family but it is just not possible to be accurate beyond that due to the randomness of DNA inheritance.
For example, here is a picture from the new 23andme of some of the DNA I share with Dick, a 2nd cousin on Dad’s paternal side so blue, and John, a 2nd cousin on Dad’s maternal side so red.
I share a third again as much DNA with John as I do with Dick, even excluding the 14 cM on the X. The expected amount for a 2nd cousin is 3.125% which is 212.50 cM, right in the middle between these two.
Checking my brother, I see the same effect – he has 282 cM with John versus 185 with Dick. Not surprisingly, when I look at Dad I find that he shares almost twice as much with John as with Dick. Clearly he just inherited more of the same DNA as John’s mother from their common grandparents. Conversely, he inherited less DNA shared with Dick’s mother from his other grandparents.
On the left is a comparison of my first cousin Henry with both Dick and John. The amount he shares with each 2nd cousin is practically identical, as long as you subtract the 40 cM that he shares with John on the X from the total shown by 23andme. Amazing how variable DNA inheritance can be among 2nd cousins.
Click here for the ISOGG wiki article on Autosomal DNA statistics which usually includes the current chart from Blaine Bettinger’s shared centimorgan DNA project.
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It is so delightful that you can now easily view your past correspondence with a 23andme match! To do this go to DNA relatives, which defaults to the People section, and click on the person. This takes you to a one-to-one comparison page partially shown below.
Your most recent message will appear in a box in the right hand column and you can scroll back in that box to see previous messages, both sent and received. Not all my oldest messages are there and I am not sure why. I did find one from 2012 and all the ones since 2014 seem to be available.
Past correspondence in the People view – as always, the red arrow has been added by me
I used to have to use the chrome add-on 23++ in order to search my inbox or outbox which took a long time with four years worth of messages to search. Sometimes it even crashed! This is much better.
More on the People view in DNA Relatives
Can’t find the person? You can use the search box on the right in the People view to find them, an improvement over the first roll-out of the new site. Note that the search in the DNA view works immediately as you type, no buttons to push, while the search in this People view requires you to press return. Annoying that they are different.
You can now download your aggregated results from the bottom of the People view page. Continue reading →