# How useful are at-home DNA tests? **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [October 7, 2017, 8:44pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258 "2017-10-07T20:44:12Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Johnny\_Bravo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_bravo/32/493_2.png) [@Johnny\_Bravo](https://boards.straightdope.com/u/Johnny_Bravo)\ **Post date:** [October 9, 2017, 3:02pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/21 "2017-10-09T15:02:29Z")
> [@Qadgop\_the\_Mercotan](#): > > put me in touch with a few 3rd cousins I didn’t know I had, By matching you with other partially completed family trees, right? Not because the test can compare your DNA results with others in the database? ---
**Author:** ![Powers](https://avatars.discourse-cdn.com/v4/letter/p/edb3f5/32.png) [@Powers](https://boards.straightdope.com/u/Powers)\ **Post date:** [October 9, 2017, 3:16pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/22 "2017-10-09T15:16:18Z")
> [@Senegoid](#): > > What’s a Slanket? It’s a blanket with sleeves; another brand name is “Snuggie”. Both are often sold via TV ads. Powers &8^] ---
**Author:** ![Powers](https://avatars.discourse-cdn.com/v4/letter/p/edb3f5/32.png) [@Powers](https://boards.straightdope.com/u/Powers)\ **Post date:** [October 9, 2017, 3:17pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/23 "2017-10-09T15:17:22Z")
> [@Johnny\_Bravo](#): > > By matching you with other partially completed family trees, right? Not because the test can compare your DNA results with others in the database? I could be wrong, but I believe it does indeed look for other DNA profiles with a (relatively) large percentage of markers in common. Powers &8^] ---
**Author:** ![ThelmaLou](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/thelmalou/32/390_2.png) [@ThelmaLou](https://boards.straightdope.com/u/ThelmaLou)\ **Post date:** [October 9, 2017, 3:22pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/24 "2017-10-09T15:22:48Z")
> [@Siam\_Sam](#): > > When my wife gains US citizenship in a couple years’ time, will that result in a dramatic DNA shift? > … You’re just being silly here, right? :rolleyes: ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [October 9, 2017, 3:27pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/25 "2017-10-09T15:27:37Z")
> [@Johnny\_Bravo](#): > > By matching you with other partially completed family trees, right? Not because the test can compare your DNA results with others in the database? The DNA database linked me to a person identified as a 3rd or 4th cousin who had a surname that’s in my pedigree that I had little info on. He was indeed of that line, sharing great-great grandparents with me, and I was able to take the line back another two generations thanks to his family info. He filled in my partially completed tree, but I only was able to find him because the test compared our DNA results and concluded we were related, so offered up his name and contact info (as he allowed it do to so). ---
**Author:** ![Evan\_Drake](https://avatars.discourse-cdn.com/v4/letter/e/b487fb/32.png) [@Evan\_Drake](https://boards.straightdope.com/u/Evan_Drake)\ **Post date:** [October 9, 2017, 3:47pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/26 "2017-10-09T15:47:53Z")
> [@Dewey\_Finn](#): > > The best bit, though? Some white supremacists have taken these tests only to find African ancestry. I would be very surprised if any white southerner didn’t have some African blood — although in other cases, North African ( Berber etc… ) is not the same as Sub-Saharan ancestry; just as one would expect every European to have some Jewish ancestry. ---
**Author:** ![Johnny\_Bravo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_bravo/32/493_2.png) [@Johnny\_Bravo](https://boards.straightdope.com/u/Johnny_Bravo)\ **Post date:** [October 9, 2017, 4:00pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/27 "2017-10-09T16:00:45Z")
> [@Qadgop\_the\_Mercotan](#): > > He filled in my partially completed tree, but I only was able to find him because the test compared our DNA results and concluded we were related, so offered up his name and contact info (as he allowed it do to so). How cool! I didn’t know they were able to do that sort of matching. ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [October 9, 2017, 4:20pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/28 "2017-10-09T16:20:04Z")
> [@Johnny\_Bravo](#): > > How cool! I didn’t know they were able to do that sort of matching. It also identified distant cousins whom I already knew, or knew of. But finding new kinfolk in those less well defined branches of the family tree is like finding gold to us poor obsessed dead relative collectors. ---
**Author:** ![DSYoungEsq](https://avatars.discourse-cdn.com/v4/letter/d/c6cbf5/32.png) [@DSYoungEsq](https://boards.straightdope.com/u/DSYoungEsq)\ **Post date:** [October 9, 2017, 4:45pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/29 "2017-10-09T16:45:52Z")
> [@Qadgop\_the\_Mercotan](#): > > It also identified distant cousins whom I already knew, or knew of. But finding new kinfolk in those less well defined branches of the family tree is like finding gold to us poor obsessed dead relative collectors. Am I the only person who thinks Dead Relative Collectors would be a great band name?? 😛 ---
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [October 9, 2017, 5:30pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/30 "2017-10-09T17:30:10Z")
> [@Johnny\_Bravo](#): > > By matching you with other partially completed family trees, right? Not because the test can compare your DNA results with others in the database? The DNA our family has submitted to Ancestry _has no associated pedigree whatsoever visible to Ancestry.__ **All** _ of the 3rd cousin, 4th cousin, 5th cousin, etc. matches are derived solely from DNA comparisons. One distant cousin match shows an extensive pedigree. The only likely match is of an early 18th-century immigrant from Ulster with the same surname as my own ancestral immigrant from Ulster. I’ll guess the two women are sisters! (Unfortunately nothing is known of the parents of either sister. ☹ There is a will giving circumstantial evidence ours had two immigrant brothers. 🙂 But the brothers also lack known parents. ☹ ) ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [October 9, 2017, 5:42pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/31 "2017-10-09T17:42:56Z")
> [@septimus](#): > > The only likely match is of an early 18th-century immigrant from Ulster with the same surname as my own ancestral immigrant from Ulster. I am curious how one acquires information about the DNA of someone from the eighteenth century. ---
**Author:** ![Johnny\_Bravo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_bravo/32/493_2.png) [@Johnny\_Bravo](https://boards.straightdope.com/u/Johnny_Bravo)\ **Post date:** [October 9, 2017, 6:10pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/32 "2017-10-09T18:10:02Z")
Septimus is saying that the living cousin had already done extensive genealogy, and he used that work to identify a probable common ancestor. ---
**Author:** ![ThelmaLou](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/thelmalou/32/390_2.png) [@ThelmaLou](https://boards.straightdope.com/u/ThelmaLou)\ **Post date:** [October 9, 2017, 6:44pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/33 "2017-10-09T18:44:22Z")
> [@Qadgop\_the\_Mercotan](#): > > So is this a rant about the commercials? Or what? > > I got my DNA tested, because of my interest in genealogy. And the results have served me well, in that they confirmed a lot of what I’d suspected, provided some clues about some other suspicions, and put me in touch with a few 3rd cousins I didn’t know I had, and they were able to tell me more about some shared family lines that I’d drawn a blank on. That was fun. And continues to be fun, as they add more people to the data base. > > It also revealed I have some Ashkenazi genes, which was fun to discover. > > It confirmed I have one copy of the gene for CF, which I sadly already knew. > > In short, it fulfilled and even exceeded my expectation, which weren’t that high to begin with. I consider it a good investment of my resources. Which DNA testing service did you use? Was it the one advertised on [Ancestry.com](https://www.ancestry.com/dna/) or was it [23andme](https://www.23andme.com/)? I was going to start a thread and ask which was the better one, but this seems like a good place to ask. ---
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [October 9, 2017, 7:38pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/34 "2017-10-09T19:38:47Z")
> [@carnivorousplant](#): > > I am curious how one acquires information about the DNA of someone from the eighteenth century. It was all 21st-century DNA! If two people share a 6-great grandparent, about 0.003% of the persons’ DNA will be shared due to that connection! That seems very tiny, especially since unrelated people can share markers by chance. But the Ancestry test supposedly _ **reads 700,000 markers from each DNA testee!** _ Despite crossovers, there will be long sections of intact DNA since only 16 meiosis events separate these seventh cousins. I assume the Ancestry matching algorithm looks for\* long chains\* of matching markers rather than just a _raw total_ of matching markers. ---
**Author:** ![Cazzle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cazzle/32/75_2.png) [@Cazzle](https://boards.straightdope.com/u/Cazzle)\ **Post date:** [October 9, 2017, 8:41pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/35 "2017-10-09T20:41:14Z")
> [@Johnny\_Bravo](#): > > By matching you with other partially completed family trees, right? Not because the test can compare your DNA results with others in the database? Yes, by comparing results. Here’s a fun one. One of my matches has not uploaded a tree. He’s clearly a relative on my mother’s paternal side because Ancestry shows the closest matches we have in common are Mum’s (paternal) first cousin, a different first cousin’s granddaughter, and also a first cousin once removed - mum’s father’s aunt’s granddaughter. The amount of DNA I share with him is consistent with second cousins - that is, cousins who share great grandparents. I contacted him and he isn’t into genealogy - the test was a Christmas gift. He gave me the limited information he had about his family history, and I built his tree out from there. No obvious links between our families back to his great great grandparents. I dug further through the shared matches. He has matches to people related to my mother’s paternal grandfather, but also her paternal grandmother… and her maternal grandfather. Oh, and also her maternal grandmother. Until this person came along, the only people in the world who were known to have links to all four of my mother’s grandparents were their descendants. No other members of their family intermarried. So this person’s family tree shows he is no relation to me whatsoever, but he shares as much DNA with me as someone who is descended from my great grandparents would, and also he has matches to all of my tested cousins in my mum’s paternal family line, and also to descendants of siblings and cousins of all four of the relevant great grandparents. But looking at our trees, we are 100% no relation to each other. In fact, the only connection we’ve found between our families is that, when his mother was a child, her parents lived next door to my great uncle… what a coincidence, huh? ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [October 9, 2017, 9:01pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/36 "2017-10-09T21:01:54Z")
> [@ThelmaLou](#): > > Which DNA testing service did you use? Was it the one advertised on [Ancestry.com](https://www.ancestry.com/dna/) or was it [23andme](https://www.23andme.com/)? I was going to start a thread and ask which was the better one, but this seems like a good place to ask. I used 23andMe, but I can’t compare it to Ancestry’s. I suspect the former may have more genealogical utility; if so I may repeat the test using them. I found 23andMe interesting and useful. But I wish it did more. It identifies thousands of folks as relatives of some sort, but you can’t easily figure out which specific DNA bits you share with them unless you compare your profile to theirs directly, and look for bits that match. That function should be automatic and done by computer. Perhaps they will add that feature, they have been rapidly expanding what results they do offer. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [October 9, 2017, 9:16pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/37 "2017-10-09T21:16:39Z")
> [@Eliahna](#): > > So this person’s family tree shows he is no relation to me whatsoever, but he shares as much DNA with me as someone who is descended from my great grandparents would, and also he has matches to all of my tested cousins in my mum’s paternal family line, and also to descendants of siblings and cousins of all four of the relevant great grandparents. But looking at our trees, we are 100% no relation to each other. > > In fact, the only connection we’ve found between our families is that, when his mother was a child, her parents lived next door to my great uncle… what a coincidence, huh? :dubious: ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [October 9, 2017, 10:09pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/38 "2017-10-09T22:09:18Z")
> [@Qadgop\_the\_Mercotan](#): > > I used 23andMe, but I can’t compare it to Ancestry’s. I suspect the former may have more genealogical utility; if so I may repeat the test using them. :smack: _Latter_, not former. I suspect that the **Ancestry** product may have more genealogical utility than 23andMe. ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [October 9, 2017, 11:02pm UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/39 "2017-10-09T23:02:04Z")
> [@septimus](#): > > Large sections of our family tree are now confirmed to have no cuckolding. This slightly surprises me. I was under the impression that early experiance with blood transfusons was that a /really large number of children/ were not genetically related to their fathers. Just out of morbid couriosity, is anybody publishing that kind of data? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 10, 2017, 12:43am UTC](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258/40 "2017-10-10T00:43:26Z")
On the other hand, the Cohens have stayed true enough, for thousands of years, that there’s still a recognizable Y haplotype associated with the line. Though that could still allow for cuckolding by close male relatives, such as a father or brother. [Previous page](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258.md?page=1) [Next page](https://boards.straightdope.com/t/how-useful-are-at-home-dna-tests/798258.md?page=3)