Google Answers DNA – Who’s yer daddy?

Google Answers DNA – Who’s yer daddy?

by Dr. Hsien-Hsien Lei
Posted August 16, 2007 in DNA @ Google Answers, DNA Testing

Although Google shut down the Google Answers service at the end of November 2006, it’s still a wealth of information on a variety of topics including genetics and DNA. In this new series at Eye on DNA, I’ll be choosing the most interesting to share with you.

happy father's dayThe Question:

Who’s yer daddy?

The Answer:

For many people, this is a simple issue: yer daddy is the person who is married to yer mommy. However, modern society has found many ways of complicating this question. Nevertheless, regardless of the different emotional roles differnet people may play in your life, there is only one male in the world who can be your biological father. For those cases where the answer to your question is not clear, the only resource to turn to is DNA testing.

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(28 comments)


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28 Comments

Comment by Krissy Poopyhands Subscribed to comments via email

The thing that has always struck me about genetic testing for paternity is the unknown prevalance of Chimeras.

Like the woman who’s kids were tested for bone marrow transplant who found that her reproductive organs were that of a vanished fraternal twin (so technically three of her four kids weren’t genetically hers, or they were, if your support of internal organs gives you ownership rights).

I always think about that when they are up to Possible Babydaddy 416 on Maury. What if a man’s sperm isn’t his but the sperm of his vanished fraternal twin? So he is the one that did the implanting, but the child won’t carry any of his genes including any of his DNA?

Also a problem, I think, with DNA testing exonerating criminals.

Not enough of the population has been tested to determine how prevalant Chimeraism is.

I find it fascinating.

Comment by Hsien

Great point, Krissy! And I got an answer for you right here from the Howard Hughes Medical Institute:

Chimeric organisms certainly complicate paternity (and even maternity!) determination based on DNA analysis and other forensic DNA-based approaches. From what we understand about the biology of chimeras, one may have to sample many tissues from a chimeric organism to arrive at the one that would match the DNA of the children or parents in question.

 
 
Comment by Hsien

And here’s the full story from New Scientist in 2003 about the chimeric mother and her sons.

EXPLAIN this. You are a doctor and one of your patients, a 52-year-old woman, comes to see you, very upset. Tests have revealed something unbelievable about two of her three grown-up sons. Although she conceived them naturally with her husband, who is definitely their father, the tests say she isn’t their biological mother. Somehow she has given birth to somebody else’s children.

 
Comment by Krissy Poopyhands Subscribed to comments via email

No, I know what a Chimera is, what I’m saying is that so little of the general population has been tested for DNA sequencing that we don’t know how many of us are likely carrying parts of a vanished twin.

Is it common? How common? Does it usuall affect an organ or two or three? How would you go about testing it?

Without knowing how common it is, or how common reproductive organs are affected, it throws a real wrench into the paternity testing bicycle.

Comment by Hsien

lol I know you know but I put the link to the New Scientist story for other interested people. ;)

 
 
Comment by Krissy Poopyhands Subscribed to comments via email

So, basically the Hughes site says, “Once thought to be rare we now think that there’s more chimeras than we thought.”

That’s all well and good, but how many? And how do you control for it?

Comment by Hsien

In the paragraph I quoted from the HHMI article above, he says multi-sampling from different tissues should solve the problem. I assume that you’d only have to do this if there were unexpected results so probably not too often in most cases since it’s been so little heard of in the news.

 
 
Comment by Krissy Poopyhands Subscribed to comments via email

I know that’s what they said, but then they have to operate under the assumption that you don’t ever get a false positive, but a negative might always be false. They don’t know what the prevalance is of just one organ being affected, or more than one being affected.

So say I get a paternatity test on TT and it’s negative. Do we then move to testing a different part of him? Do we test his sperm specifically? What if his reproductive organs are chimera and half his sperm carry his host DNA and the other half carry his vanished twin’s DNA and we test the wrong sperm?

Just how deep does the rabbit hole go? What percentage of folks who get negative paternity or crime scene DNA tests are getting simply the wrong DNA from the right person?

And if repeated testing is necessary, how much repeated testing? And who’s going to pay for it?

This is what bugs me about the “infallability” of DNA testing. Yes, when the results are positive, but Not Necessarily when the results are negative, and science has yet to answer the chimera question with any real numbers or information.

Comment by Hsien

You’re right. The probability of a false negative is higher than false positive because 16 markers are tested in the average paternity test with a positive being 99.999+% accurate in most cases.

I don’t think anyone thinks DNA testing is “infallible.” Aside from the issue of chimeras, there can be problems with sample contamination, procedural errors, misinterpretation of results, and other mix-ups. However, I’d have to believe that questions of paternity don’t come up for most people. For instance, I know for sure who the father of my child is and I have no reason to doubt it unless we’re talking immaculate conception.

 
 
Comment by Krissy Poopyhands Subscribed to comments via email

” For instance, I know for sure who the father of my child is and I have no reason to doubt it unless we’re talking immaculate conception.”

Well, yes, but then you’re unlikely to have a paternity dispute that requires that you get tested. I wasn’t talking about the general population where paternity isn’t in question, but those where paternity is in question.

In those cases often there are things at stake, and each side has a reason to want it to go one way or another. Think of the damage a false negative could do to a man wanting to prove paternity, or a false negative could do to a woman wanting to prove paternity for child support.

Also, I do think that the general population consideres DNA testing to be conclusive. Convictions are overturned based on the results of DNA testing, and on Maury Povich he doesn’t say, “There is a large chance you are not the father, however we will have to retest you using swabs from X, Y andZ”. He says, “Ralph, you… ARE NOT THE FATHER of baby Sally”. Begin the running, screaming, in-your-face hysteria.

For most of America, I’d think, DNA positive or negative is considered decisive.

Comment by Hsien

“For most of America, I’d think, DNA positive or negative is considered decisive.”

And I don’t think that’s a false assumption.

While chimerism may be more common than we believe, I still think it’s most likely quite rare. It wouldn’t be logical for anyone to reject a negative paternity test based on this reason because an absorbed/vanished fraternal twin would still share 50% of the person’s genetic material which would lead to results that would raise questions beyond the typical negative paternity test. I would recommend arguing faulty lab procedures over chimerism if there was going to be a dispute over results. Occam’s Razor….

Comment by Krissy Poopyhands Subscribed to comments via email

But… but the woman who got the negative maternity connection wasn’t told that she had interesting markers, was she? She was told that she wasn’t the mother of two of her boys.

I mean, obviously they caught it because it was that or a weird hospital switch that almost never happens, so you’re right about the red flag there, but what if the dad got the results that said that he wasn’t the father of two of his kids?

Maybe I’m just uncomfortable with the assumption that it’s very rare until science actually figures out how rare it is.

But I is not a scientist.

Seriously, sometimes I’m absolutely certain that you follow up your responses to me with “you frikkin moron” under your breath. ;-)

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Comment by Hsien

I do not! It’s great that you think outside of the box because I tend to be a little more complacent and accepting of the “evidence.” In most cases of a paternity dispute, I don’t think chimerism should be a concern. But, if something really weird were to show up, such as a parent’s absolute certainty that she’s the mother of her child, hopefully it would be investigated.

 
 
 
 
Comment by Krissy Poopyhands Subscribed to comments via email

“a parent’s absolute certainty that she’s the mother of her child, hopefully it would be investigated.”

What about a mother’s absolute certainty that the man is the father of her child?

You need to watch more Maury.

Comment by Hsien

LOLOL Believe me, I have watched several clips on YouTube and it is insane. I haven’t seen any woman, though, who was absolutely certain a particular guy was the father otherwise how would they be able to keep dragging guys up on stage show after show??

Comment by Krissy Poopyhands Subscribed to comments via email

But if you’re absolutely sure that Ralph is the father, but the paternity test says no, then what do you do? You cast your mind back for who it could be and drag that guy on.

If Ralph really is the father but the paternity test is incorrect, then you drag 17 guys up there hoping to get a positive match.

Sometimes I think that guy number 17 must have been “When I was 16 I dated this one guy”…

Sure, there are hos who have 30 person orgies, but at some point sometimes you have to question the validity of the test, and nobody does.

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Comment by Hsien

Well, that’s what’s so sad about it all! Not saying that Maury wouldn’t be on the up-and-up but let’s just say something got screwed up in the paternity test for one or more of these women. Do they have the resources to get a re-test on their own or to demand one from the show? In any case, what say some of those crazy sagas aren’t even real anyway. Wasn’t Jerry Springer staging some of his shows?

 
 
 
 
Comment by NA Subscribed to comments via email

I doubt that chimeras are common. Only one egg is released (usually), and the chances of a sperm not being the fathers DNA is also very rare. There are a couple of cases in the United States where this has occurred and the states wanted to take their children away from their parents.

This would be an interesting test to do, but funding should be put forth first for understanding disease mechanisms before finding out how rare a chimera event is.

Just so everyone is on the same page, a chimera is formed when two fertilized eggs or early embryos fuse together or a fertilized egg is fused with an unfertilized egg or a fertilized egg is fused with an extra sperm. These events do occur, but it’s very rare. There is research that shows the likelihood of releasing two eggs at the same time and the chances of two embryos fusing together (I don’t have access to the literature as I type this to show the research).

As stated already, the way to test this for is to just test different tissue samples. One tissue would have different chromosome information then another tissue if this type of event were to occur. This type of testing should only be done when one of the parents is being questioned as a parent of a child. Chimerism can be detected in DNA testing.

There can also be cases where fetal cells become apart of the mother’s body. The fetal cells can live up to 38 years in the mother.

Comment by Hsien

I am amazed at your wealth of knowledge, NA! Thanks for the great explanation.

 
 
Comment by NA Subscribed to comments via email

“Like the woman who’s kids were tested for bone marrow transplant who found that her reproductive organs were that of a vanished fraternal twin (so technically three of her four kids weren’t genetically hers, or they were, if your support of internal organs gives you ownership rights).”

One does have ownership rights of their organs. Choosing to be an organ donor or not is ownership.

 
Comment by NA Subscribed to comments via email

“No, I know what a Chimera is, what I’m saying is that so little of the general population has been tested for DNA sequencing that we don’t know how many of us are likely carrying parts of a vanished twin.”

This is due to DNA sequencing being very expensive and time consuming. We are only a few years passed having the human genome sequence. Time will come when our DNA sequence will cost less then 1,000 dollars and can be done as fast and as long as you want it to depending on how many SNPs that need to be sequenced.

 
Comment by NA Subscribed to comments via email

“I know that’s what they said, but then they have to operate under the assumption that you don’t ever get a false positive, but a negative might always be false. They don’t know what the prevalance is of just one organ being affected, or more than one being affected.”

I suspect that one wouldn’t find any common prevalence for the number of organs affected in a population group. Not like you would find the prevalence of a disorder being present in a population. It all depends on which germ line the organ develops from. I advise to read up on the three germ lines and how the process of development occurs up to about week 16.

 
Comment by NA Subscribed to comments via email

So when should one suspect mosaicism in a genetic disorder? I looked in my genetic disorder notes and I wrote down a case about a male and a female (2 different families) that had mosaicism occur in von Hippel-Lindau. Both patients had clinical VHL disease but were negative for VHL mutations. Each and an offspring with known clinical VHL disease and both offspring had a documented germline mutation in the VHL tumor suppressor gene. I also wrote down a case
Mosaicism can also be a reason why some females miscarry at the same time of embryonic development in each pregnancy (e.g., 3 months). The mother can have a karyotype done and it can come back normal, but it can also come back a turner syndrome chromosome number.

 
Comment by Shatara Subscribed to comments via email

Although The Maury Show is certainly not a reliable source, I have to admit that I began to wonder about some of the women on the show after I learned about chimerism. I mean, really, some of them come back over and over again with more than one man at a time. It’s like, ok I’m trying to do the math here, according to how many men these particular women have had tested so far, they were pretty damn busy for those 3 weeks out of the month. they would have had to sleep with at least one different guy every night of those 21 days in order to actually think all of these guys could be a potential father. Sure got me to thinking, wonder if the father was already tested and told he wasn’t the father so he went on his merry way while the mother is loosing her frikin mind.
I read that a sign of chimerism could be that a person has eyes that are each a different color, or patches of hair that are different colors from the rest of the hair. I personally know a guy who has one brown eye and one blue. when I was in school, there was a kid there with one brown eye and one dark gray. Get’s me to thinking, what if one of these guys get’s into a situation where he has a woman claiming he’s the father of her child and she wants child support. he doubts her claim, so the office of child support says they will administer a dna test, it comes back negative, but he is actually the father. The father walks away happy, the mother is left confused and trying to retrace her steps, the child support office goes about it’s business. Kid grows up with no father, and no one cares.
I think this thing happens far more than anyone in the government would want to admint. That would mean they have to admit screwing up on countless cases where criminals were set free, or homes were broken up and/or children were left fatherless and possibly poor.
The government doesn’t want that, but someone should push the issue. I think it is very important.

Comment by Hsien

Shatara, Thanks for the comment. I have no idea how often paternity tests come back with a false negative. With respect to Maury, I think some of the situations have to be staged.

 
 
Comment by Lee dallman

My husband who is 68 years old and I have located his birth daughter who is now 45 years old after searching for her for 23 years.They have had two DNA tests that have come back that he is not the birth father. The birth mother says that he definitely is. Any imput? This is causing a lot of trouble. Any help would be appreciated. Thank -you

Comment by B Subscribed to comments via email

Lee dallman,

We have almost the exact circumstance with my son and his biological father. I know..I was there. I have searched my mind over and over..
I hope they will forget the stupid test and just go with their gut.

 
 
Comment by Scott Cohn Subscribed to comments via email

Hi there!

Here’s the scenario in my head which brought about this line of questioning. If the biological father and mother go to court because he believes she’s cheated and wants a dna test for he and their son, and results say he isn’t the father when he actually is, what’s the course of action test wise to finally prove it? Is there a scenario in which they would test to see if he’s an actual chimera when he didn’t know to begin with? How might it come up later that he would get tested and/to prove it? Like a disease that crops up maybe? I imagine the tests are much more limited than for a woman. And I don’t imagine people immediately think “let’s see if he’s a chimera” when a test comes back negative. The father in this scenario would not be a hermaphrodite.

Any and all characteristics of this would be appreciated! (i.e. Would the son have ANY characteristics of the father? Or is it his twin’s the son would share? And how does that work when the father is the chimera in a parental scenario?) Sorry, I have a million questions, but this fascinates me.

I saw the show, “I am my own twin”, but they only dealt with 2 women, and the only answer I found was on here. My father ran the clinical labs at CHoP, as well as taught biochemistry at Univ of Penn, but he unfortunately didn’t know enough to answer my question. I may have to trade him in. ;)

I’m sure you’re extremely busy, but if you get the chance to answer this, I’d appreciate it! Thanks!

- Scott

 

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