Do identical twins also have identical navels? The reason I ask is that I had the impression that whether you have an ‘innie’ or and ‘outie’ are at least sometimes effected by environmental factors, i.e. what happens with the stump of the umbilical cord as it decays.
Could someone give me the Straight Dope?
Thanks for all replies,
AllFree
No. The navel is basically a scar and as such is environmental, not genetic. In fact, differences in navels can be used to distinguish between identical twins.
A definitive answer, thank you Colibri. If anyone has anything fun/interesting to add feel free.
AllFree
In case you’re thinking about ways in which ‘identical’ twins are actually different from one another, there are at least two more: their fingerprints and their “repertoire” of antibodies.
I can’t find it yet, but I’m sure I heard a story recently about a court case that was dismissed because a pair of twins had the same fingerprints.
And I don’t think it was April the first when I heard it.
I’ll keep looking.
I’ve got a pair of hot identical twins coming round to my house on Sunday. I think I might ask to see their navels.
identical twins arenLt identical genetically. IIRC, they are a 90%-ish match. Environmental factors in the womb and during birth can also reduce the identicalness
Would you care to elaborate on that? Because unless you’re talking about something I’ve never heard of, that’s completely wrong.
Identical twins are clones, and while there may be some differences due to mutations or other anomalies they are very close to genetically identical. The 90% match doesn’t conform to anything I have ever heard either. Please clarify what kind of genetic differences you are talking about and the source of the 90% figures.
Identical twins are the result of the fertilized egg splitting in two during early development. Each part goes on to develop into a separate person, but with identical chromosomes. Fraternal twins are the result of two eggs separately fertilized, and are no more related than any other two siblings - may even have separate fathers under the right(?) scenario.
I’m not that up on my biology - the process of cell division creates (virtually) identical copies of the chormosomes. I don’t know if the split guarantees that evey cell gets a copy of all the mitochrondrial(?) DNA, those little rings of DNA fragments that are in the egg and inherited from the mother. So there could be a difference there.
DNA does change over time due to replication accidents, etc. However, it’s nowhere near 10%; heck, the amount we differ in DNA from chimps and apes is, IIRC, close to zero. (less than 5%?)
I have also read that identical twins have different fingerprints, since this is a developmental accident of which cells replicate how fast during gestation. If there was even the remte possibility that they were the same, you would have seen some use of that in CSI or Law & Order. God knows the twin-DNA thing has happened often enough.
FWIW, I know a pair of identical twins where one is gay and the other has 4 children.
(bolding mine)
So what? The two states are not mutually exclusive, y’know.
Retinal scans and iris recognition supposedly would reveal differences, too.
I agree. The condition is likely developmentally rather than genetically determined. An interesting factoid.
I couldn’t find that recent news story, but I did find this. The Myth Of Fingerprints
Does anyone want to contest what is wrote in that article?
The Fox brothers were a pair of identical twins in 19th c. England who were partners in crime. One would make himself prominent in a town far off while the other committed crimes. If arrested each would blame the other and as no one could say which was which the prosecution failed. They were identified by fingerprints, possibly the first case in England where this was admitted as evidence.
The Shirley McKie case in Scotland was one which turned solely on fingerprint identification, and was essentially about whether a police officer was telling the truth or not, and whether fingerprint identification was incontrovertible or not.
Anecdotally, my two oldest nieces are identical twins, and both are without doubt, lesbians. Their three younger siblings are quite straight.
All five siblings have Masters Degrees and/or are working on their doctorates. This has nothing to do with anything, of course, but I’m very proud of them and like to mention what good kids they are whenever possible. 
So you make an outlandish assertion, can’t back it up, come up with an unrelated article on fingerprints, and then dare us to challenge that? Better get back to your Jew baiting; you seem to do better at that.
[Moderator Note]
Dragging in some unrelated matter to attack another poster is not appropriate for GQ. No warning issued, but don’t do this again.
Colibri
General Questions Moderator
And, of course, other mostly-environmental marks like birthmarks and moles. News reporters apparently used a mole on the late Polish President Kazcynski’s cheek to distinguish him from his identical twin brother (who is the Prime Minister and therefore also often in the spotlight). Coincidentally that’s also how I distinguish two of my younger son’s best friends, who are identical twins: one has a mole on his cheek and the other doesn’t.
While MZ (monozygotic) twins have identical DNA, epigenetic factors (ie external chemical modifiers that attach to DNA influencing gene expression) can cause differences in development over time. These sorts of changes are more likely to diverge significantly when twins experience environmental variation or illness. Cite. I doubt that this adds up to a 10% difference in expression, though.
Si