# Identical Twins marry identical twins **URL:** \ **Category:** Factual Questions\ **Created:** [December 18, 2000, 2:40am UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088 "2000-12-18T02:40:45Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Markxxx](https://avatars.discourse-cdn.com/v4/letter/m/5daacb/32.png) [@Markxxx](https://boards.straightdope.com/u/Markxxx)\ **Post date:** [December 18, 2000, 2:40am UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/1 "2000-12-18T02:40:45Z")
Suppose identical twins marry identical twins then both cheat on each other with the other twin. Babies are born. Is it correct to assume there is no way to tell who the father is. ---
**Author:** ![dragonlady](https://avatars.discourse-cdn.com/v4/letter/d/5f8ce5/32.png) [@dragonlady](https://boards.straightdope.com/u/dragonlady)\ **Post date:** [December 18, 2000, 3:03am UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/2 "2000-12-18T03:03:03Z")
Yes. There is case right now of identical twin brothers each claiming the other impregnated a girl who had a baby related to them both. DNA tests show that ONE of them is the father, but there is supposedly no way to tell which one. Identical twins = identical DNA. ---
**Author:** ![nowalls99](https://avatars.discourse-cdn.com/v4/letter/n/e68b1a/32.png) [@nowalls99](https://boards.straightdope.com/u/nowalls99)\ **Post date:** [December 18, 2000, 3:22am UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/3 "2000-12-18T03:22:07Z")
I know several sets of identical twins. Many of them have slight differences between them. For example, one is 2 inches shorter than his “identical” twin brother. If the cause of this difference is genetic, rather than environmental, there should be a difference in the genetic code. While these differences aren’t seen in all identical twins, I would think the percentage would be high enough for a determination to possibly be made. However, if these differences are environmental, the possibility of positively identifying the father would be mind boggling. Due to the complexity of DNA, and the amount of time it takes to decode the entire chain, it is currently impractical to use the entire chain for paternity testing, The lack of testing to determine if there are any differences between the DNA of twins also tends to support the fact that there may be slight genetic differences between twins that we are currently unaware of. I won’t go so far as to say that it is possible, but I cannot say that it is impossible, as the science behind using DNA for paternity tests is still in its infancy. We shall all wait and see what develops. ---
**Author:** ![Ringo](https://avatars.discourse-cdn.com/v4/letter/r/779978/32.png) [@Ringo](https://boards.straightdope.com/u/Ringo)\ **Post date:** [December 18, 2000, 3:28am UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/4 "2000-12-18T03:28:12Z")
> [@](#): > > For example, one is 2 inches shorter than his “identical” twin brother. Are you sure they’re not fraternal twins? ---
**Author:** ![Nefarious\_Chipmunk](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nefarious_chipmunk/32/1045_2.png) [@Nefarious\_Chipmunk](https://boards.straightdope.com/u/Nefarious_Chipmunk)\ **Post date:** [December 18, 2000, 3:39am UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/5 "2000-12-18T03:39:47Z")
Heraldgwena steps up to the plate. Ahhh, finally something I know about. As a multiple I can tell you right now that identical twins have identical DNA. There is no way to tell which one is the father. There are no difference. If the DNA is different the the twins are not identical. They are fraternal. Their DNA is no more similar then that of regular siblings. This doesn’t mean they can’t look almost totally identical. While my sisters and I are not identical, many people think that we are. ---
**Author:** ![DAVEW0071](https://avatars.discourse-cdn.com/v4/letter/d/e19b73/32.png) [@DAVEW0071](https://boards.straightdope.com/u/DAVEW0071)\ **Post date:** [December 18, 2000, 12:43pm UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/6 "2000-12-18T12:43:12Z")
> [@](#): > > There is case right now of identical twin brothers each claiming the other impregnated a girl who had a baby related to them both. DNA tests show that ONE of them is the father, but there is supposedly no way to tell which one. Identical twins = identical DNA. Too bad they can’t dust the lady for fingerprints. That oughta solve the problem. Alas, it’s no doubt too late for that now. This raises an interesting question about identical siblings, though. Just how different would their fingerprint patterns be? Enough to satisfy an expert in court, I would imagine. Actually, the question ought to be: how identical are the fingerprints of identicals? Anyone know the answer to this? Or should I start a new thread? ---
**Author:** ![AWB](https://avatars.discourse-cdn.com/v4/letter/a/bb73d2/32.png) [@AWB](https://boards.straightdope.com/u/AWB)\ **Post date:** [December 18, 2000, 1:29pm UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/7 "2000-12-18T13:29:31Z")
[QUOTE] \*Originally posted by DAVEW0071 \* \*\* > [@](#): > > This raises an interesting question about identical siblings, though. Just how different would their fingerprint patterns be? Enough to satisfy an expert in court, I would imagine. Actually, the question ought to be: how identical are the fingerprints of identicals? Anyone know the answer to this? Or should I start a new thread? \*\* Fingerprint traits do follow ethnic patterns, so with a certain degree of confidence an expert could determine the ethnicity of a fingerprint. Within families, patterns are even closer. But they are still different between individuals. ---
**Author:** ![AWB](https://avatars.discourse-cdn.com/v4/letter/a/bb73d2/32.png) [@AWB](https://boards.straightdope.com/u/AWB)\ **Post date:** [December 18, 2000, 1:33pm UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/8 "2000-12-18T13:33:46Z")
> [@](#): > > \*Originally posted by heraldgwena \* > \*\*Heraldgwena steps up to the plate. Ahhh, finally something I know about. As a multiple I can tell you right now that identical twins have identical DNA. There is no way to tell which one is the father. There are no difference. If the DNA is different the the twins are not identical. They are fraternal. Their DNA is no more similar then that of regular siblings. This doesn’t mean they can’t look almost totally identical. While my sisters and I are not identical, many people think that we are. \*\* The Olsen twins, Mary-Kate and Ashley, are also fraternal. (IIRC, they have different colored eyes.) Coulda fooled me otherwise. ---
**Author:** ![robinh](https://avatars.discourse-cdn.com/v4/letter/r/b77776/32.png) [@robinh](https://boards.straightdope.com/u/robinh)\ **Post date:** [December 18, 2000, 1:38pm UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/9 "2000-12-18T13:38:36Z")
> [@](#): > > \*Originally posted by beatle \* > \*\* > > > [@](#): > > > > For example, one is 2 inches shorter than his “identical” twin brother. > > Are you sure they’re not fraternal twins? \*\* They could be fraternal twins who look very much alike. They could also be “half-twins”. In general terms, fraternal twins are the result of 2 eggs, each fertilized by a different sperm. Identical twins are the result of 1 egg and 1 sperm, so you have identical DNA. It sometimes happens that one egg will be fertilized by 2 sperm, resulting in twins that have all the same DNA from the mother. They might look more alike than regular fraternals, but are not actually identical. I read about this in a book several years ago that also dealt with the various anomalies that can occur with regards to the proper distribution of X and Y chromosomes. It was quite fascinating, all the variations that are possible. ---
**Author:** ![Gravity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gravity/32/14322_2.png) [@Gravity](https://boards.straightdope.com/u/Gravity)\ **Post date:** [December 18, 2000, 1:40pm UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/10 "2000-12-18T13:40:33Z")
according to [this](http://exn.ca/Forensics/Fingerprints.cfm)article on fingerprints, identical twins have different fingerprints. In part: > [@](#): > > Recent studies comparing the fingerprints of cloned monkeys show that they, just like identical twin humans, have completely different fingerprints from each other. > > Copyright © 2953285 Canada Inc. cob Discovery Channel Canada 2000. So clones have different fingerprints, too! That was something that I didn’t know! Very cool. K. ---
**Author:** ![Arjuna34](https://avatars.discourse-cdn.com/v4/letter/a/eb8c5e/32.png) [@Arjuna34](https://boards.straightdope.com/u/Arjuna34)\ **Post date:** [December 18, 2000, 3:07pm UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/11 "2000-12-18T15:07:56Z")
Here’s Cecil on identical twin fingerprints: [http://www.straightdope.com/columns/980821.html](http://www.straightdope.com/columns/980821.html) Arjuna34 ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [December 18, 2000, 4:22pm UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/12 "2000-12-18T16:22:29Z")
Since it is statistically likely that an average person has one or two point mutations, it might be possible to tell some identical twins apart by their DNA. But you would have to sequence their entire genome in the hopes of discovering the one or two base pairs that were different. And I’m sure that our techniques are not accurate enough that we could say that the differences couldn’t be attributed to error. After all, you’d have to transcribe 9 billion base pairs twice without making a mistake…which is something our cellular machinery can’t even do, which is why we have these base pair substitution mutations in the first place. ---
**Author:** ![Spectre\_of\_Pithecanthropus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spectre_of_pithecanthropus/32/12343_2.png) [@Spectre\_of\_Pithecanthropus](https://boards.straightdope.com/u/Spectre_of_Pithecanthropus)\ **Post date:** [December 18, 2000, 4:43pm UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/13 "2000-12-18T16:43:24Z")
Sometimes, doesn’t the embryo split after symmetry appears, so that the resulting twins are mirror images of one another? In that case if the wife cheats with her brother-in-law (or vice versa), then couldn’t the sidedness of the baby be a giveaway? ---
**Author:** ![Running\_with\_Scissors](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Running\_with\_Scissors](https://boards.straightdope.com/u/Running_with_Scissors)\ **Post date:** [December 18, 2000, 6:02pm UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/14 "2000-12-18T18:02:41Z")
> [@](#): > > _Originally posted by **robinh** _: > It sometimes happens that one egg will be fertilized by 2 sperm, resulting in twins that have all the same DNA from the mother. They might look more alike than regular fraternals, but are not actually identical. I believe this is incorrect. One egg being fertilized by two sperm would be considered a birth defect, giving two sets of Y chromosomes for every X chromosome. I do not know if any fetus conceived this way would be able to be brought to term; I would think (or at least hope) instead that this would cause a miscarriage. For half twins, I believe the scenario is that the egg splits **before** fertilization, then each new egg is fertilized by a different sperm. Identical eggs+different sperm = half twins. ---
**Author:** ![robinh](https://avatars.discourse-cdn.com/v4/letter/r/b77776/32.png) [@robinh](https://boards.straightdope.com/u/robinh)\ **Post date:** [December 18, 2000, 7:46pm UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/15 "2000-12-18T19:46:58Z")
I think you’re probably correct, **frogstein** ; it has been 6 or 7 years since I read about this and the details are a bit fuzzy. IIRC there was at least one other way in which twins could be considered “half-identical” but I cannot remember what it was. ---
**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:** [December 18, 2000, 8:08pm UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/16 "2000-12-18T20:08:19Z")
> [@](#): > > \*Originally posted by heraldgwena \* > \*\*Heraldgwena steps up to the plate. Ahhh, finally something I know about. As a multiple I can tell you right now that identical twins have identical DNA. There is no way to tell which one is the father. There are no difference. If the DNA is different the the twins are not identical. They are fraternal. Their DNA is no more similar then that of regular siblings. This doesn’t mean they can’t look almost totally identical. While my sisters and I are not identical, many people think that we are. \*\* Sorry Heraldgwena, if you get to the plate at all, you do so on a balk. Identical twins start out with identical dna, but random new mutations occur even before the twins have separated. by birth, their DNA may differ by as much as 0.00000001%, maybe more! So if you read out each twin’s entire genetic structure and document the exact differences, you should be able to figure out who the father was. Of course it would take years and cost millions of dollars to sequence the genes that thoroughly. But it is theoretically possible. Alternatively, just find a few mutations where the twins differ, and see if the kid has these. At least you won’t have to analyze the kid’s entire sequence. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [December 18, 2000, 8:20pm UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/17 "2000-12-18T20:20:52Z")
BTW, the women being identical twins is immaterial to the problem stated by the OP, which boils down to assigning paternity based on DNA in the case of identical twin prospective fathers. The answer, for all practical purposes, is “no”. To use the full “identical twins marry identical twins” scenario: Suppose both couples had babies at the same time, and they mix up the kids at the hospital. Could you tell through DNA which baby went with which couple? The answer is still “no”. ---
**Author:** ![Markxxx](https://avatars.discourse-cdn.com/v4/letter/m/5daacb/32.png) [@Markxxx](https://boards.straightdope.com/u/Markxxx)\ **Post date:** [December 19, 2000, 3:21am UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/18 "2000-12-19T03:21:15Z")
Let me ask another question using the same premise. Supposing Identical Twins marry Identical Twins and NO cheating occurs. Now would the babies, who would be first cousins to each other be genetically the same as siblings? ---
**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:** [December 19, 2000, 4:18am UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/19 "2000-12-19T04:18:55Z")
> [@](#): > > \*Originally posted by Markxxx \* > \*\*Let me ask another question using the same premise. Supposing Identical Twins marry Identical Twins and NO cheating occurs. Now would the babies, who would be first cousins to each other be genetically the same as siblings? > > \*\* Genetically speaking, they’d be the same as full siblings. Legally they’d only be cousins. Let’s hope they don’t move to California and get married to each other! Qadgop, MD ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [December 19, 2000, 8:26am UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/20 "2000-12-19T08:26:53Z")
> [@](#): > > \*Originally posted by Lemur866 \* > \*\*Since it is statistically likely that an average person has one or two point mutations, it might be possible to tell some identical twins apart by their DNA. But you would have to sequence their entire genome in the hopes of discovering the one or two base pairs that were different. And I’m sure that our techniques are not accurate enough that we could say that the differences couldn’t be attributed to error. After all, you’d have to transcribe 9 billion base pairs twice without making a mistake…which is something our cellular machinery can’t even do, which is why we have these base pair substitution mutations in the first place. \*\* Not to mention that if you did all this and found some differences (which you would, without question), you would then have to figure out when those differences arose. If they were in the father early enough to be present in most of his cells, you could probably establish paternity. If you were lucky. But, a mutation could have occurred just in the germ line leading to his sperm, in which case the sperm would have been different than the rest of his body. Or the mutation could have arisen during development of the twin’s child. It’s not very cut and dry. [Next page](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088.md?page=2)