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atDNA Case Study: Two Parents and One Child

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On 6 Jan 2017, blogger Blaine Bettinger, "The Genetic Genealogist," wrote The Danger of Distant Matches - a discussion of how small-segment atDNA matches often aren't true matches at all. Since a child inherits all of his atDNA from one parent or the other, Bettinger correctly argues that atDNA matches that are found for a child but aren't shared by a parent identify flaws in today's widely-used low-cost DNA testing chips.

I thought it would be interesting to reproduce Bettinger's methodology and compare them to the atDNA results for myself and my parents. I've provided a second set of my data as of 14 Aug 2017.

One caveat: my father and I were tested using the AncestryDNA v1 chipset; my mother's test used the v2 chipset.

My Parents' Matches at AncestryDNA

As of 7 Jan 2017, my father has 22,867 atDNA matches, of which 1,004 (4.4%) are rated by AncestryDNA as "close" matches - estimated as 4th cousins or closer, with 20cM or more of shared DNA. All three of his sisters have also been tested - for more information, read atDNA Case Study: Four Siblings. Their maternal first cousin has also been tested, as has their paternal second cousin. Articles analyzing those matches will be presented soon.

My mother has a much smaller set of 13,910 matches; 301 (2.2%) of them are rated "close." One paternal and one maternal first cousin have also been tested; more on them soon.

As of 14 Aug 2017, my father has 39,179 matches of which 1,683 (4.3%) are "close" - greater than or equal to 20cM. My mother now has 23,951 matches; 497 (2.1%) are close.

Our Matches at AncestryDNA

As of 7 Jan 2017, I had a total of 18,020 matches; Bettinger writes that he has 16,193. On 14 Aug 2017, I had 30,557 matches - an increase of 70% in seven months. The matches break down like this:

Shared atDNA Bettinger Ireland
7 Jan 2017
Ireland
14 Aug 2017
Total Matches 16,193 18,020 30,557
Share 50 cM or more 39 33 47
Share 25 cM or more 169 248 415
Share 20 cM or more 411 551 930
Share 15 cM or more 1,130 1,503 2,480
Share 10 cM or more 4,190 5,037 8,427
Share less than 10cM 12,003 (75%) 12,983 (72%) 22,130 (72%)
Share 6-7cM 5,224 (32%) 5,480 (30%) 9,318 (30%)

Shared With Our Parents

Shared atDNA Bettinger Ireland
7 Jan 2017
Ireland
14 Aug 2017
Total Matches 16,193 18,020 30,557
Shared with Father 7,144 (44%) 9,298 (51.6%) 15,813 (51.7%)
Share with Mother 3,977 (25%) 5,467 (30.3%) 9,285 (30.4%)
Matches to Both Parents 93 81 151
Not Matched to Either Parent 5,135 (32%) 3,336 (18.5%) 5,608 (18.4%)

Not Shared With Our Parents

Here are the matches not shared with our parents; all percentages are based only on the number of matches not shared with either parent:

Shared atDNA Bettinger Ireland
7 Jan 2017
Ireland
14 Aug 2017
Total Matches 16,193 18,020 30,557
Not Matched to Either Parent 5,135 (32%) 3,336 (18.5%) 5,608 (18.4%)
Largest Match 19.1 cM 17.2 cM 17.2 cM
Share 15cM or More 8 14 17
Share 10cM or More 261 (5%) 163 (5%) 243 (4.3%)
Share 7 to 10cM 1,784 (35%) 1,005 (30%) 1,681 (30%)
Share 6-7cM 3,090 (60%) 2,166 (65%) 3,682 (65.7%)

I'm not sure I agree with all of Bettinger's conclusions, but he raises some very interesting points.

Further Reading

A number of people have written similar analyses:

Send me a link to your analysis at and I'll include it here.

 


Are we related?

Here are the GEDmatch Kit #s for my father and mother:

GI: A909282
CL: A216073


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