… or does it?
It’s one of the most-commonly-repeated statements in genetic genealogy:
“DNA doesn’t lie.”
It’s usually coupled with: “Families do.”
And The Legal Genealogist isn’t going to take on either of those.
But — as with almost everything in genealogy — there’s more to the story.
And boy was that hammered home for me yesterday.
I’m in northern Virginia attending and speaking at the Professional Management Conference of the Association of Professional Genealogists. I gave the Friday keynote about professional ethics; Blaine T. Bettinger — who blogs as The Genetic Genealogist — gave yesterday’s keynote about using DNA evidence to prove a genealogical conclusion.
Blaine had no sooner finished his prepared remarks when a member of the audience said this one phrase — “DNA doesn’t lie” — should be eliminated from what we say as genetic genealogists, and his example was a man whose autosomal DNA did not match that of his own mother.
Now before you dismiss this as pure fiction let me assure you, the member of the audience was telling the absolute unvarnished truth: this tested man had autosomal DNA that did not match that of his own biological mother.
How is that possible?
When the person tested has had a stem cell or bone marrow transplant. The autosomal DNA in that case will match the donor — and not the donee’s own biological parent.
And Blaine himself showed an example of a case where each and every one of us, looking at the result, would have concluded that the two people tested were parent and child. The one-to-one comparison of DNA at GedMatch showed 3586.7 cM of DNA in common and a 1.0 generation difference between the two.
There isn’t a man-jack among us who wouldn’t look at that and say parent-child. And there isn’t a man-jack among us who wouldn’t have been dead wrong.
Because the two being compared were aunt and niece — the aunt happens to be an identical twin to the niece’s mother.
Powerful evidence, isn’t it?
So… should we stop saying “DNA doesn’t lie”?
No.
Because of something else that Blaine said that was even more powerful.
He reminded us that DNA alone can never be enough to prove a genealogical relationship. There’s got to be at least one more piece of information to be able to properly interpret the DNA evidence you get.
In the one-to-one comparison case, the one more piece of information we needed was that one of the people tested was an identical twin. That one more piece of information would have been enough to stop us from making the erroneous assumption that this had to be a parent-child relationship and would have clued us in to the possibility (correct in this case) that the other person tested was the twin and not the parent.
In the no-match-to-mother case, the one more piece of information we needed was that the person tested had had the stem cell transplant. That one more piece of information would have been enough to stop us from mistakenly assuming that we were dealing with a case of misattributed parentage.
No, DNA doesn’t lie.
Our interpretation can be wrong.
And in every single solitary case, bar none, without fail, we are going to need at least one more piece of information to be able to prove a genealogical relationship.
Whate about haplogroups and and deep lineage treatment of y chromosome analysis
Many or all of intrested people with this field say it does’t lie ??
And take its result as facts without any doubt
Is it lie or doe’t lie?
The haplogroup itself is simply a fact. What the haplogroup means in a particular case is a matter of interpretation, and that’s where the additional data points are essential.
And another possibility is that samples were mixed or switched — either by the person sending them in, or rarely – by the lab itself. No one is perfect, people do make mistakes. I have seen patients told they have HIV or leukemia when in fact they did not. I always tell people to do another test first before going into a panic. DNA is not perfect. Humans are not perfect. Mistakes happen.
We often advise a second opinion in many life-changing situations. This is no different. But before we even get to whether a second opinion is needed, we need to be sure we’re not leaping to conclusions based on unfounded assumptions.
Thank you for this. I had been wondering about things like this. My grand-daughter received plasma a number of times while in the NICU. Have been curious if that would change her DNA.
Mere blood or plasma transfusions shouldn’t have a permanent effect on DNA results. The impact on DNA results should dissipate within a fairly short time.
As always, Judy, a very good epistle.
As with any investigation, we must not confuse facts with interpretations or conclusions.
“Jimmy and Sue match and share 3500 cM” is a fact. It is the test result. Now whether the two people actually share 3500 cM, that is, is the test accurate, depends on the test methodology (end-to-end). The test companies tell us that it is and that their methods comply with industry standards for accuracy. “Jimmy is Sue’s father” is an interpretation of the fact. Without knowing the ages and other details, I could have just as easily said “Sue is Jimmy’s mother”.
“John’s DNA was found at the murder scene” is a statement of fact (let’s assume the test was valid, etc.). John is the murderer is interpretation.
DNA evidence is not sufficient for a complete interpretation by itself.
Science, like the law, is complicated and it requires thoughtful study and experience to draw valid conclusions
All genealogical evidence needs to be thoroughly tested through processes of reasonably exhaustive research, analysis and correlation, followed by resolution of conflicts, before we reach any sort of sound conclusion.
I was wondering, if the stem cell or bone marrow transplant occur before a child is conceived, will the donee’s child reflect the DNA of the donor or the donee? Or do we know yet?
It’s my understanding that the egg cells of the mother are created at the time of her conception– long before she would have had a stem cell or bone marrow transplant. Whether the DNA within those eggs would be impacted is something I simply don’t know. Sperm cells are created in real time (as far as I understand it — and remember, I went to law school, not medical school! ) and so could be impacted, I’d think.
You are correct. You’re born with all the eggs you will ever have– that’s why they degrade as they age. Sperm are produced 24/7.
When you think about it, we humans are wondrous and amazing creatures! That’s fascinating…
For a while now I have been saying, “DNA does not lie … when interpreted correctly.” That last part is so important; the additional information is required to make the correct interpretation.
And you are sooooooooooo right about that!!
HI I am a bone marrow recipient lovingly with my sister as the donor. So she had her DNA done with Ancestry, believes’ everything she gets back as truth! lol
I wanted to get mine tested too, she said no, we’d be the same cause of same parents. Your article got me wondering will my DNA not be of my moms, but of my sister’s if I do have it tested?
Chances are quite strong, given the bone marrow transplant, that your DNA would closely mirror your sister even if you were born with somewhat different DNA. But the reason is because of the transplant, not because of your shared parents. Siblings really do show significant differences, but those were probably lost with the transplant.
“Once you’ve eliminated the impossible, whatever is left, no matter how improbable, must be the truth.”
Given that stem cell/bone marrow transplants and identical siblings are not the usual scenario, can we say “DNA doesn’t lie*” with a footnote? I also think we’re going to be seeing more bona fide “outliers” as the databases continue to grow. I recently came across half-siblings who shared only 1157 cM on Ancestry. The same person also shared 2006 cM with another half-sibling from the same parent.
Occam’s Razor is certainly a factor, as is the rule that when we hear hoofbeats, we should think horses and not zebras. But the fact that the circus was in town might well make us stop and think.
I will remember this one. I have always thought horses, but one never knows…does one
Not unless we ask for that one more data point! 🙂
Judy, Very interesting about bone marrow transplant in regard to autosomal DNA, never knew this.
I wasn’t fully aware of the long term impact, but did some more reading afterwards. It really is fascinating stuff.
Might be the mother was a chimera!
Although it’s not impossible (again we’d need more data points), that’s not the most likely case, of course. We go with the known facts to begin with.
Several years ago I saw a program on TV about a woman (Lydia Fairchild) who applied for public assistance. When her DNA did not match the children’s DNA, she was suspected of welfare fraud and almost lost custody of her children. After hearing about a similiar case written up in a medical journal, DNA samples were taken from different parts of Ms. Fairchild’s body and finally a DNA match was made to prove she was the biological mother of her 4 children.
My mother and her sister are also identical twins, and my mother was quite shocked, a few weeks ago, when she saw that 23 and Me had identified my cousin (son of her sister) as my half-brother. I told her that her mother, a doctor, had attended a medical conference in the 1960’s where she was told that the children of her identical-twin daughters were biologically half-siblings to each other. My grandmother had told me at the time, and I said, basically, “Why, yes — of course that’s how it would be,” and only thought about it again when someone makes a sweeping statement about relationships, or crime evidence, etc. — the thought, “does this apply to identical twin situations?” always pops into my head.
It’s amazing what seems to be crazy and then makes perfect sense if only we stop and think about it… 🙂
a number of years ago, I remember reading an article about a set of identical twin brothers who married a set of identical twin sisters. It was explained that although the children of one couple might be 1st cousins to the children of the other couple, the genetic relationship of all the children of both couples was that of full brothers and sisters, which I suppose means that in the following generation of descendants, the DNA of 2d cousins might be indistinguishable from that of 1st cousins.
As a medical technologist with more than 20 years experience in Transfusion medicine and bone marrow transplant, I have never seen a report on the changes seen in the epithelial cells of bone marrow transplants. Although the epithelial cells may be used in the evaluation of graft vs. host disease (the donor cells make antibodies to the recipient’s cells) I haven’t that testing of DNA in epithelial cells change to that of the donor. Blood cells (red and white cell ) will change to the donor type, but often show chimerism. DNA testing post transplant and pre transplant is usually done via marrow cells and not epithelial cells.
Epithelial cells are only part of what’s tested for genealogical purposes, however, and that I think is what is at the heart of the problem for genetic genealogy.
Right, for saliva tests they’re collecting and testing blood cells in the saliva, not buccal cells.
Thanks for that info, Blaine!
I share 1513 centimorgans with my first cousin. That’s some way beyond the upper range of Blaine Bettinger’s Shared Cm project. FTDNA predicted we are half-siblings. Did the DNA lie?
Well no, it didn’t. But you would need to know something more than just the test results to know what’s going on. That something is that our grandparents were rather more closely related than was legal, so that all their kids got a double helping of the same DNA which was duly passed on to me and my cousins.
Had we not found this out by conventional means years ago, those test results would have been an obvious ‘lie’ and we would have been climbing trees wondering what was going on.
There’s that “at least one additional piece of information” again… Great example!
And don’t forget about DNA mosaic in. https://en.m.wikipedia.org/wiki/Mosaic_(genetics)
One individual can exhibit different genomes depending on what tissue is sampled
This, to me, is what makes researching collateral lines so imperative; oftentimes that piece of information that is needed to interpret the DNA results correctly is found somewhere in a collateral line.
We had unexpected yDNA results in our family, but- thanks to collateral line research and additional yDNA testing- we believe we have narrowed down the NPE to the birth of my 3rd great grandfather around the year 1818. We also believe we have both families of origin, narrowed down to two generations in each family.
On a (somewhat) related note, is there anything we can do to try to narrow that lineage down even further? To determine if he was born to one woman or to which of her specific daughters? And if he was fathered by one man or which of his specific sons/relatives? This is further complicated by the fact that one of her daughters married one of his sons, so we have many autosomal matches to both families.
I accidentally had my husband test twice on one DNA testing service. A person wrote to me thinking they were a father and son. When I told her they were both for the same person, she said the results were different. Is that possible?
Slightly different, yes, because (a) the platforms used by the companies change over time and (b) the analysis changes over time.
I am reading this several months after you first published it. Thank you – good to know that there are “other” right answers that should be considered.
When we are saying that DNA results will change as a result of bone marrow transplant which test does this apply to? Y? Mitachondrial? autosomal? I know my spelling is terrible but I think you can know the question.