Crazy genetics: the doctors said she wasn't their mother

*“Any child from a mom and dad should inherit genes from both the mom and the dad. In Keegan’s case, it appeared that her two boys hadn’t inherited any of her DNA,” said Dr. Lynne Uhl, a pathologist and doctor of transfusion medicine at Beth Israel Deaconess Medical Center in Boston. “They weren’t hers. So we scratched our heads and said, ‘This is really unusual. How can this be?’” *


*The DNA that would match her sons’ DNA could have been anywhere in Keegan’s body. But her thyroid was where she matched her sons’ genetic code. *


*It’s a rare condition called chimerism, with only 30 documented cases worldwide. In Greek mythology, “chimera” means a monster: part goat, part lion, part snake.

In human biology, a chimera is an organism with at least two genetically distinct types of cells – or, in other words, someone meant to be a twin. But while in the mother’s womb, two fertilized eggs fuse, becoming one fetus that carries two distinct genetic codes – two separate strands of DNA. *

ETA: a long time ago I was studying the genetic relationship between Down Syndrome and Alzheimers. I thought some of them ended up as chimeras because part of the replication went awry, giving rise to a different line. I didn’t realize eggs fusing could also create a chimera.


Accidentally switched in the hospital.

Ah missed the edit window. From a single zygote it’s called a mosaic.

These people were featured on a Discovery Channel documentary a couple of years ago.

Bosda, both of the women had several children whose DNA didn’t match theirs. One baby was tested directly after birth and didn’t match. Plus, they did find pockets of cells in in one mother that did match half the DNA of the kids.

In vitro fertilization followed by implantation in a host mom. Happens every day in the New York subways at rush hour. .

Ah, sorry, thought it was breaking news. But while we’re on the subject, is the science stated correctly here?

Siblings will have about 50% of the same genetic material. If my brother were to impregnate a woman and she carried it to term, I would have some DNA in common with my nephew. I understand that the particular code my brother passed on is not going to match mine identically, but it will be closer than a totally unrelated individual. I thought the higher number of matching codes would show that lobotomyboy isn’t the father—he’s a relative, though. lobotomyBRO is the father.

I.e. my nephew has some of the same DNA I do but not because he got it from me. Isn’t it incorrect to say that her boys had none of her DNA?

Yes, it’s correct that your nephew should share some DNA with you. They’re looking for a total match though. For a simplified example:

if mom is ABCDE
and dad is FGHIJ
and baby is AFGKL

People are going to know something is wrong. The A in common between mom and baby isn’t enough proof that the baby’s hers, and there’s the question of where fragments K and L came from.

I wasn’t complaining about the age of the story, FTR. They rerun the documentary every so often, and it’s worth watching. I think it’s called I am my own Twin

One of the POTWs on House turned out to be like this.

Yeah, I figured they must have been startled by the lack of a perfect match. But I thought they’d notice a higher correspondence than you’d expect from a complete stranger. If the mom’s sibling (absorbed fraternal twin) donated the DNA to the children, it would be like the analogy to a brother and nephew, right?

Instead, suppose that the woman had kidnapped the children. The children’s results might come up


It seems like you should have:

Parent: 50% common genes with child
Sibling of parent: about 25% common genes with child
Non-relative: maybe 5-10% common genes?

Sounds like an interesting documentary!

“You can’t tell me what to do! You’re not my mother!”

A part of her probably agrees with that ;):eek::smack:

Right. At one point, the authorities asked the younger mom if the children belonged to her sibling instead of her.

The whole doc is on youtube in ten minute segments.

Thanks for the link! I’m watching it and at about 3:55, they say a normal mother child DNA test will match about 50%. Hers matched 0%. How could that be? Why not 25%?

I resent the implication! That is not my child!

I’m watching part 4…this is really good.

They tested one woman’s relatives—it turns out that if you take the profile of her BROTHER + her husband, DNA would say they’re the parents of her sons. How freaky is that?!

And it was used as a plot point on CSI a few years ago.

When you’re talking about actual people, it won’t be that simple, because the percentages of shared DNA sequences can vary between siblings. Also, a DNA test isn’t looking at every single sequence, just a few markers.

You might be interested in these threads:*+genes

Thanks for the links…I skimmed through them.

Hmm, maybe I’m thinking the DNA test is a high-powered microscope when in fact it’s a dirty magnifying glass.

Still, my inner mathematician is uber bothered by 100%, 50%, and 0%. ZERO percent?!When you look at the comparisons side by side, they seem to get a lot of data points…but (exaggerating to make a point) if they are looking at one chromosome, would it match up perfectly or not at all, i.e. all or nothing?

Isn’t it true that my father’s chromosome (say, #1) would contain a gene sequence like

AbCDEfghijKLmNOP…? And maybe my father’s second chromosome #1 may be

I think one of the threads cited implied that some of that may get switched around when daddy makes and donates his sperm, so looking at my example he might give me A or a, but he could only give me b and C. And the same would be true for the sperm he makes and donates for all of my brothers and sisters, hence his contribution to the resemblance among us.

I spoilered this before and I’m going to suppose that anybody who wanted to watch that youtube set has done so.

One of the chimeras had a son but DNA testing said it wasn’t hers. They tested people from her family—her mother and two brothers IIRC. It turned out that the missing puzzle piece (who’s the mother?) was her brother. One of the geneticists said if you put the husband and brother together, they’d produce the sons perfectly.

So maybe Karen Keegan got the A and absorbed a twin who got the a. Maybe some of her eggs carry A and others carry a. Her blood has the A, they test her baby for maternity but her baby got the a. That sounds like black and white results, except if she and her absorbed twin both got b and C, which is all she’d have to pass along.

If they’re asking if the kids belong to Lydia’s sister, how can that not contradict 0% matching results?

A hermaphrodite with this condition would be pretty surprised when he/she was in her/his early teens when they became a mommy/daddy.

I recall reading years ago of an actual hermaphrodite that was the result of chimerism. Both male and female; the result of male and female twins that fused in the womb. He/she also had striped hair and two different eye colors.