# Identical Twins marry identical twins

**URL:** <https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088>\
**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:** 4\
**Page:** 2

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**Author:** ![AKAmame](https://avatars.discourse-cdn.com/v4/letter/a/aca169/32.png) [@AKAmame](https://boards.straightdope.com/u/AKAmame)\
**Post date:** [December 19, 2000, 11:57am UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/21 "2000-12-19T11:57:21Z")

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Frogstein:

XY gives usual male.  
XX gives usual female.  
X gives Turner’s (syndrome).  
XXY gives Klinefelter’s (syndrome).  
XYY gives “XYY male”.  
(syndrome) is in brackets, as apparently not every individual with the genotype will go on to manifest the syndrome.

The latter three genetic variations will not necessarily cause miscarriage, nor, at least for XXY, sterility. XXY seems to be a functional variant, and given the rates, there may be well be a couple of individuals with that genotype on the SDMB.

For introductory info, try [http://www.nichd.nih.gov/publications/pubs/klinefelter.htm#xwhat](http://www.nichd.nih.gov/publications/pubs/klinefelter.htm#xwhat).

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**Author:** ![wevets](https://avatars.discourse-cdn.com/v4/letter/w/e9a140/32.png) [@wevets](https://boards.straightdope.com/u/wevets)\
**Post date:** [February 10, 2001, 1:23am UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/22 "2001-02-10T01:23:23Z")

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Frogstein and AKAmame:  
It is important to note that fertilization of one egg by two sperm would not just cause trisomy of the sex chromosomes (Kleinfelter’s, “supermale”, et al.), but would cause _Triploidy_, having three copies of every chromosome. This is possible, but does not bode well for the fetus:

> [@](#):
>
> Human Triploids – 2 paternal +1 maternal -\> large cystic placenta (partial mole) +/- fetus with triploidy, 2 maternal + 1 paternal -\> small underdeveloped placenta

(from [This genetics site](http://www.umanitoba.ca/faculties/medicine/biochem/coursenotes/pedigreeanalysis.htm))

In addition:

> [@](#):
>
> Any ploidy (extra copies of all chromosomes, i.e., triploidy, tertaploidy, etc.) higher than diploid results in  
> early death in utero.

(from [A Univ. of Illinois site](http://www.uic.edu/classes/bms/bms655/lesson9.html)

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<div class="post-metadata">

**Author:** ![Gaspode](https://avatars.discourse-cdn.com/v4/letter/g/aeb1de/32.png) [@Gaspode](https://boards.straightdope.com/u/Gaspode)\
**Post date:** [February 10, 2001, 1:54am UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/23 "2001-02-10T01:54:18Z")

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> [@](#):
>
> **Javaman**  
> 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?

Yes twins do often display this symmetry (about 25% IIRC). Trouble is it’s caused by environmental factors, not genetics and can’t be used to determine paternity and won’t have any effect on the baby.

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**Author:** ![AKAmame](https://avatars.discourse-cdn.com/v4/letter/a/aca169/32.png) [@AKAmame](https://boards.straightdope.com/u/AKAmame)\
**Post date:** [February 11, 2001, 6:02am UTC](https://boards.straightdope.com/t/identical-twins-marry-identical-twins/46088/24 "2001-02-11T06:02:50Z")

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**wevets** , you are correct about the triploidy. On re-reading **frogstein** ’s post, I discovered that I had mentally removed the ‘one egg, two sperm’ bit, and just processed the ‘one X two Y bit’ and replied accordingly. An interesting example of selective reading, but embarassing to have made the error nonetheless.

I suspect I also owe a mental apology to **frogstein** for my comment of

> [@](#):
>
> given the rates, there may be well be a couple of individuals with that genotype on the SDMB

.

Maybe I should give up posting so late at night.

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