Identical twins of opposite sex? Wha???

So…I just got the latest issue of Discover magazine in the mail and was reading the article “Study the Clones First” when this sentence, differentiating fraternal and identical twins, stopped me cold:

Um…?? What circumstances? For lack of a better description, could there be a sort of hormonal programming dysfunction where one twin fails to ever get the signal to develop as a male and remains female? Although…wouldn’t that just produce a hermaphrodite, or androgen insensitive genetic male?

I’m fascinated to know how on Earth this happens.

Apaprently, it’s extrememly rare, resulting in a normal male and a phenotypic female with Turner’s Syndrome:

From here.

Wow. Who would’ve thunk it?

To steer away from the OP just a little ways… is there any consensus as to whether ‘half-identical’ twins really exist?

The way that I’ve generally heard this explained is that an egg splits into two viable halves before conception, and each split egg is fertilized by different sperm.

Therefore, you have twins who are considerably closer genetically than any ordinary brother and sister, since fully half of their genetic pattern, the half from the mother, is identical. But the genetic material from the father can differ somewhat, including gender, since that basically depends on whether the sperm is carrying an X chromosome or a Y chromosome.


You mean polar body twinning? I don’t believe it’s been documented to have happened in humans. Doesn’t mean it hasn’t happened, though

google “polar body twinning” for lots of hypotheses with a few actual reputable articles.

I’ve read that the Olsen twins are polar body twins…no reason to believe it’s true though.

It’s just conjecture, as far as I can ascertain.

However, with the advent of modern DNA identification, it’s just a matter of time until we actually get documentation of some hypothesized genetic conditions.

A recent People magazine article (hey, need some fluffy reading for the airport, lemme alone)–actually, I think it’s still on the stands–describes Ashley and Mary Kate as being fraternal twins.

I summarily dismissed it because, well, LOOK at them. Their appearance is identical (of course, now one is sickly-skinny, and they have different hair color, but you follow) and fercryingoutloud, they were hired to play the SAME PERSON.

So, uh, maybe they are polar body twins. That, at least, is more plausible IMHO than fraternal.

I disagree. Seeing as how some siblings who are not identical resemble each other very very strongly, I’d say this is the far more likely reason the Olsen twins resemble each other. After all, human polar twins have never actually been demonstrated.


On the other hand, as far as I can see from the links, there really isn’t any possible way of differentiating fraternal twins and polar body twins. (You might argue that traditional fraternal twins have never been ‘demonstrated’ either, though I think that’s a bit of a leap too far.)

Once genetic testing becomes accurate enough and cheap enough to be applied to a question like this, we’ll find out what’s what… until then, it will probably remain entirely theoretical.

I know of at least three pairs of brothers who look so much alike that I can only distinguish them when they’re standing next to each other. And even there, I can only tell based on their ages. And for that matter, I’ve also known a pair of twin sisters who really were “identical” (same genome), but who were easily distinguished (mostly by things like hair style and mannerism, admittedly).

Ironically, one of the afore-mentioned brothers is a fraternal triplet, but not with his brother. But that’s irrelevant.

Okay, I give. Having perused more fan websites about the Olsen twins than I ever care to see again, I have to accept what was repeated over and over:

That really is an amazing resemblence, though.

And yes, Qadgop, I should have given my morning reply the teensiest bit more thought before I started jabbing at the keyboard. I remember (now) reading in the thread that there are no demonstrated cases of polar body twins, and therefore, it is FAR more likely they are lookalike fraternal twins. Der.

In some cases identical twins grow to look less and less alike as they age. Here is a picture ofmy father and his identical twin brother at about age 60. And no, they were not about to be executed, or made to go to church.

You know in the Simpsons, when Homer wants Mel Gibson to put a dog in his movie, which you can tell is the bad guy because he shifts his eyes suspiciously?

Dude on the right’s doing that. Was he the evil one?

Absolutely. If he hadn’t been evil he wouldn’t have been saddled with me as punishment.

Actually they were a couple of Yankee Doodle Dandys, Born on The Fourth of July. And it just occurred to me that event was 115 years ago today.

[off topic]

Anya Christina Emmanuella Jenkins. Twenty years old. Born on the fourth of July, and don’t think there weren’t jokes about that my whole life, mister, 'cause there were. “Who’s our little patriot?” they’d say when I was younger and therefore smaller and shorter than I am now. And when I was seven, I had a pet dachshund that died from chocking on a wiener, which I find ironic.

So… you spell it A-N-Y-A, then?


Fine. Now we can get to the questions.

[/off topic]

Ah, but what I want to know is: how do we end up with identical cousins???

I kept thinking to myself: “If he’s not a triplet with his brother, then who is he a triplet with?”

I had to read the quoted sentence four times before the “fraternal” qualifier sunk in, so, duh, the other two triplets would be sisters. Do I get a cookie?

I don’t really think it’s that uncommon to have similar looking siblings, especially if the age difference is small (as it obviously would be for fraternal twins). Heck, one of my brothers is two years younger than me, and we got a lot of “are you twins” questions until we hit our late teens. We still look enough alike that we’re obviously related, but can easily be told apart.

And getting back to the OP…

There’s a genetic disorder where the child gets XXY chromosomes (I think this came up in the “Jamie Lee Curtis: hermaphrodite?” thread), does that allow the fetus to develop as either male or female? Depending on how sensitive that “triggering” would be, identical twins with that genetic makeup might come out one male one female.

Sorry to bring back a thread that died a couple weeks ago, but I was about to ask a similar question.

See, my fiance went to high school with a set of twins who claimed to be identical. They were opposite sexed.

So, my question is this: Is it possible the girl is intersexed?

People with XXY have Klinefelter’s Syndrome, and develop as males.