How can a biological mother not have the same DNA as her children?

+9 votes

The case of Lydia Fairchild one of 30 known cases of chimera's, (people who have absorbed their twin in utero).. 

She had three children, and had to have them DNA tested to prove that they were hers.  They failed the test.  Turns out the skin cells are different that the cells of her uterus. 

This is the part I don't understand. 

The DNA of Fairchild's children matched that of Fairchild's mother to the extent expected of a grandmother. They also found that, although the DNA in Fairchild's skin and hair did not match her children's, the DNA from a cervical smear test did match. Fairchild was carrying two different sets of DNA, the defining characteristic of a chimera.

Siblilngs should be revealed as siblings via auDNA testing, so how can siblings have DNA one generation apart?



in WikiTree Tech by Living Farrar G2G6 Mach 1 (15.0k points)
retagged by Peter Roberts
Um, interesting?  No idea.

My grandson was born almost six weeks ago, his mother and him have entirely different blood group so the moment he was born she had to receive injections to counteract the blood that may enter after the umbilical cord was cut.  If her own son needed a blood transfusion she would not be able to help him. The moment he was born within an hour we could see both her (her nose) and my son (his hair and mouth). This was a natural conception eg no IV etc involved.

Strange as I'm the grandmother - mother-in-law but my blood group is fine for my grandson.

It makes you wonder - our dna/blood/genes are so much more complex that we know.
That is really interesting. Indeed our dna/blood/genes are incredibly complex. Mind muddling!

Another weird thing - if a mother is rhesus negative her body does not recognise a rhesus + baby as being of the same species as her!  An anti-d injection is needed after each child born who is rhesus + to stop mums body taking out the next baby if it is also rhesus +.
The children of Lydia Fairchild would indeed be Lydia Fairchild's mother's grand children. So I expect that the bold sentence says as much. In which case, she has the DNA of a fraternal sister.
Got that, then Lydia's children would show up as nephew and nieces. Correct?
T Cassidy...Yep, RH factor can cause problems for the next pregnancy if she doesn't get the shot during pregnancy and again after delivery. I had to have them with all of mine, as I am RH neg (A -) and hubby is RH pos (O+). It's extremely common!!!
@William, yes. Which as I recall reading that is the case.
The part that confuses me is the mt-dna. I have not read anything about this case beyond this thread, but all her mt-dna would have come from her mother wether she is chimera or not, and she would have passed that onto her children. Did the mt-dna not match?
What happens with mt-DNA - a woman can pass to her children, but only a daughter can pass it on to her children, who again, only a female child can pass it on.

E.g. my mtDNA - my mother and siblings, though my brother does not pass this on.

My mother's mother

My mother's mother's mother - passes it to all the children but only a girl/female passes it on - those female children can pass it on.

mtDNA literally stops at the male offspring - he cannot pass it on to his children.
Correct.  That is why I am confused. We are talking about a woman and her children.
I think you are wrong, mtDNA is passed on regardless of gender, XDNA is only passed on to females.

The skeleton found under the parking lot of what once had been Grey Friar's Abbey was identified as Richard III because his mtDNA matched that of Michael  Ibsen, who descends from Richards mother Cecily of Nevile via her daughter Anne of York.

Richard Plantagenet, Duke of York and Anne of Neville produced Anne of York, Michael Ibsen's, whose mtDNA was passed down through 16 females to him .
Hi Dawn,

I really don't know?

Hi William -

WikiTree is set up to show this - I was amazed.

mtDNA - can only be passed down from the woman, the male is a carrier but his offspring will not be carriers as it would be his spouse/partner who carries it.

Even in my tree, when I put in the mtDNA - it ran through upwards my mother, her children - my brother has it but his son does not. My son has it but his son does not.

My mother's mother - passed it to her three children (all girls)

My mother's mother's mother - passed it to her five children, the data stops at the boys, whereas the girls carried it through to her daughter and son, their sons has it, his offspring do not.

My mother's mother's mother's mother - passed it to her five children - four girls and one boy - the male - it stops.  The women passed it onto their children - likewise stops at the male offspring.

William  "XDNA is only passed on to females" is incorrect.  The X DNA is passed to males as well.  Males are XY whereas females are XX - males get an X from their mothers.  

Excuse me. I don't want to be argumentative, but feel that I am being talked down to. I am not an expert in DNA, but I do know somethings, like  Quoting you mtDNA - "can only be passed down from the woman, the male is a carrier but his offspring will not be carriers as it would be his spouse/partner who carries it."

I do believe that in my previous posts, I have said as much.

To wit: Michael Ibsen, 16 generations removed from Richard III, carries the mtDNA of Richard's mother, which was passed down 16 generations via the females in his line.

I envy him that he was able to trace 16 generations of female ancestors, I wish that I could. And if women were valued as equals to males and didn't change their surname when they married I probably could.


I misspoke, Apologies, Of course males get XDNA from the mother, and they pass it on to their daughters, but not their sons.

2 Answers

+4 votes
Well, the progeneter sex cells are separated out very early in development.  In fact it's really the non sex cells which separate out and become other sorts of cells.  So unless the mother's sex cells were tested you wouldn't know what had happened to the fraternal twins.  But I think perhaps "match" is being used two different ways, first an exact match as would be predicted for a mother child relationship and secondly as genealogical DNA testing measures it being a particular length of DNA match in one chromosome or in several such segments.  

That is, Fairfhilds mother looked like a gradmother because the test was seeing a mix as it were of two children but the cervical smear apparently has the mom's true original genome.
by Dave Dardinger G2G6 Pilot (411k points)
Identical twins share the same pacenta, thus a great chance of absorption, or so you would think.

Fraternal twins share different placenta's so  a lesser chance of fetal absorption? (Have no idea if the above absorption statements are true).

That the twins would show two different DNA's does indicate that they were fraternal twins.

Just saw something about an absorbed twin showing up as a tumor in the brain , with hair, bits of bone and teeth.

Makes the skin crawl.
As I understand it, the outer "shell" of Lydia Fairchild had the DNA of one twin, while the DNA of the "absorbed" twin is reflected in her internal organs (the skin is an external organ).

But the previous poster asked an unanswered question, Each twin would have had the same mtDNA. And their autDNA should show sibling., At best Lydia's DNA test would have suggested that, her children belonged to a sibling.

Unless, the fraternal twin that was "absorbed" (using that word for convenience sake and lack of a better term) was a male. Then I have no idea what the result would be,  Would Lydia be a true hermaphrodite? Or a pseudo hermaphrodite? Or neither, just have YDNA in the shell (skin), but internal DNA determined her gender and reproductive capability.

This in fact might be the case, as they tested for mtDNA , which they would not have found from cheek swabs, and since she was a female they would not have even suspected YDNA.

I wish that there was a more detailed discussion of the DNA tests of Lydia Fairchild.
Actually the intestinal tract tissue is derived from the "shell" tissue, not from the internal organs.  I've forgotten what the sex organs derive from but I expect it would be from the internal organs.  (actually there are three layer of tissue exoderm, endoderm (SP?) and mesoderm, but I'm simplifying so I don't get lost in google jail.
Are the tests public; I would assume that she would be at best highly ambivalent about DNA testing after such a traumatic experience. More importantly how should  I cite the parent child connection for the children in case I get around to adding that collateral branch to my wiki tree?
+4 votes

The Fairchild case is a very unique situation. I went and looked at the NEJM study, and the molecular analysis of the tissues and markers. The evidence shows that she is a tetragametic chimera. (This means 4 separate gametes- 2 eggs, 2 sperm contributed to her genetic material.) At her conception- two eggs and two sperm fused separately. Normally, this would become two separate fraternal twins (call them red twin and blue twin), with two separate sets of DNA (Red DNA and Blue DNA). These individuals would have the normal sibling ratios of DNA IBD segments; 1700 cM identical, and the additional 800-850 half identical DNA.

During the gestation of the biological mother, probably while these developing entities were still balls of cells called "blastula", somewhere in the first week of development.... the two balls of cells fused into one ball of cells. This is not the same as "destroying each other", it is much more like taking one ball of red clay and one ball of blue clay and mushing these two balls of clay into one ball of red and blue streaked clay. This ball then gastrulated (formed an inside layer and outside layer) and continued the process of development as one entity.

One of the tenets of cell theory that allows us to understand life is that "all cells are derived from the cells that came before"....As she developed, some of her cells grew from the red ball and some grew from the blue ball. Each of these cell lines thus has different genetic composition, because they each arose from different egg and sperm combinations. And yes, early in development, but after fusion- different cells based on their placement or location in the gastrulated structure would have become or "been assigned to become" different structures and tissue types through molecular tagging. 

In this case, when her children were tested for maternity, the technicians initially looked at her "red cells" that were derived from the "red ball of clay", but her oocytes "eggs" all developed from cells derived from the "blue ball of clay". So, the when the doctors and techs later examined multiple tissues through molecular typing- they found evidence of both the "red" and "blue" genotypes. That's how the chimerism was found. Some of her cells are genetically "blue" like her children's cells, but others are "red". She has both types of cells that have formed different tissues.

Now, to answer the math question. The simplest thing to do to understand this is look at DNA ratios more carefully. It's her "sibling" (blue) cells that formed the oocytes, remember that these cells would have been her sister, had the "balls of cells" not fused in early gestation. It should be noted that grandparent to grandchild AND aunt/uncle to niece/nephew share about 1700 cM of DNA... So saying that this is the "grandparent/grandchild" DNA ratio is technically correct and may be what the lawyer said, but also incomplete and misleading.

The ratios for both relationships are the same, anyone can check the iSOGG DNA table.... but it would be better to state that the biological chimeric mother shares DNA as an AUNT to a NIECE/NEPHEW. This is the accurate and correct genetic relationship by DNA evidence, which is what should have been stated in the wikipedia article you've referenced above, and wasn't. It is also technically incorrect to say that any of her cells are her "true genome" as the biological mother has two completely unique genomes in her somatic (body) cells, and from the evidence, gave rise to her gametic cells in her ovaries. Does this clarify?

PS- the "growth" referred to by WF is a form of "congenital cancer" called a teratoma, but the origin as an absorbed twin is a little controversial. The wikipedia is pretty informative without being too graphic if you want more info.

by Jess White-Phillip G2G1 (1.7k points)
edited by Jess White-Phillip
Very good and informative answer Jess. However, one exception

the Tetranoma, had hair, teeth, bone, which is not something you would find in a cancer, congential or not. I understand that certain facts are "controversial", but that is only because the specialist scientific community doesn't understand the causation, or has a social abhorrence to considering certain issues.  E.G. You used the term "eating the sibling" in utero, that creates an abhorrent social issue, leaving the impression that we, or the twin, was a cannibal (even if utero)  When there was "eating" a simple absorption of one set of cells by another, via a process apparently not yet understood.

Using the word "eating" in the discussion, creates mental images and changes the discussion from a dispassionate scientific discussion to an  emotional, cultural, value laden exclamation (not even a discussion).

Hi William,

"Teratoma" is the term.... and it is technically classified as a very unique type of congenital defect. Some teratoma are malignant, and thus are considered "cancerous", though most are benign growths.... 

A teratoma could simply arise from a set of cells within a single organism that recieved the incorrect developmental messages- or could possibly be products from the merger of two sets of cells in an incomplete resorptive process. In this case, the first develops normally, and the second that does not fully resorb subsequently receives incorrect developmental messages (instead of undergoing apoptosis) that cause the formation of tissues (such as those you mention) in improper areas of the developing fetus.

You're absolutely correct- the causation is not fully understood. That's all "controversial" really means, "having different or opposing views", though we often ascribe an adversarial connotation to the word, there is no negativity inherent within the word itself .... Wisdom and new knowledge come from reconciling opposing or controversial viewpoints, and 'controversial ideas' are often sources that stimulate new inquiries, which lead us to greater understanding of the world and ourselves. As humans, we should strive to seek these out and inqure to resolve them.  In the search for the solution, we will learn something that we did not know before, and may benefit from this knowledge.

The choice of term was used to correct a common misconception of chimerism- as the initial cells do not destroy (or consume) the secondary or merged cells- which is sometimes what happens in the case of twin resorption (vanishing twin). I did not use the technical term "resorb" or "resorption" because it's scientific jargon, and I try to avoid using specialized terms in posts, unless required based on context.

Adsorption was used in a previous post, which is also not the correct term- because this refers to particles "sticking to" or adhering to a solid surface or substrate, and forming a separate layer. Some examples of this would be like the particles in hard water depositing a separate layer of calcium on bath tile.... In this case, the calcium is still a separate layer, and does not become "part of" the bath tile. There is no evidence that the seconday or merged cells in this chimeric case formed a separate layer of mesoderm, endoderm, or ectoderm.... If the secondary cells had formed one layer of tissue during gastrulation, then the term Adsorption would be quite correct. 

Absorbed isn't accurate, either- because this term used in a biological sense does refer to "the uptake of particles during digestion"- which as you and I (in different ways) have both stated- is not what occurred in this case. I did not use this term because most people think about something like paper towels "absorbing water" and I believed that use of this term would create improper confusion. E.G. "The primary blastula did not absorb the cells from the secondary blastula...." A reader might look at this statement and wonder, if these two things became one thing, why were they not in fact "absorbed"?

None of the above terms (Adsorption, Absorption or Resorption) accurately describes what happened in the case of this gestation and development. That's what made this case so unique, the cells merged into one structure, without destruction (resorption) of the secondary or merged cell line

I have change the potentially perjorative word in my initial post (viz the section using the analogy involving inanimate balls of clay) to the  word "destroy"... I hope that satisfies your previous objection to the word choice and further, clarifies why I selected the initial "common" term instead of the incorrect term "adsorb", the potentially confusing term "absorb",  or the more technical but accurate term "resorb". 

Thank you for your comment, and feedback. I appreciate your thoughtful analysis and note that all NFT corrections joyfully accepted in the spirit of cooperation. :)

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