In a book I’m currently reading, the protagonist is an identical twin. She is a mirror twin - same genes, but where her twin has a beauty mark on her left cheek, the protagonist has it on her right cheek, one twin is left-handed while the other is right-, etc.
Is this a literary device invented by the author, or are there such a things as mirror twins?
Sua
I have heard of this-- it was brought up in a couple of threads about identical twins. I can’t explain it any more, though.
I just saw some mirror twins on America’s Most Talented Kid (or one of those talent shows). I think it’s a real thing. Spooky, eh?
The whole twin thing in general is fascinating. I love to watch programs on it. I get a little weirded out when I’m amongst identicals, though. It’s just so…freaky.
Ha! At a restaurant the I frequent, mirror twins work. Indeed, one of them has a birthmark on the left side of her neck. The other on the right. One of them is left handed. The other right-handed. Don’t know of any other examples, but they do have those.
And, it could just be coincidence.
i know that mirror twins exist…read about it in National Geographic long years ago.
what i want to know is, does being “mirror” mean that one has the heart on the right side?
No right sided hearts for mirror twins. IIRC, the origin has to do with how late the balstocist (or whatever it is at the time) splits into two distinct cell clusters. Later = mirror. I could be wrong about that, but that is what I’ve read.
cowers in ignorance
a balstocist? sounds like some kind of bizarre doctor who specialises in testicles and toes.
stops cowering and marches off to google-land
:smack:
you meant blastocyst!!
but yup, you’re right. mirror-twinning evidently has something to do with splitting in the blastocyst phase. no mention of topsy-turvy hearts, though.
Mirror twins definitely exist – I should know, I am one! I’m right-handed, my brother’s left-handed. Our hair whirls start on opposite sides of our heads. And as kids, we lost our teeth on opposite sides of the mouth. He likes absurdly skinny girls, while I don’t – I don’t think that last one has anything to do with the mirror thing, though. 
Back Lot Brawl-- welcome to the list from another (albeit standard-issue) identical twin. Ok, so a first person report-- can you tell us much more about this? How did your development differ from standard-issue twins-- was it that the egg split late or what?
definetly. My two younger brothers are mirror twins and this has been explained by our doctor. Its not just made up.
Hope I helped xxx 
Twins can have different characteristics even though they have the same DNA. When a baby develops in the womb, somethings develop randomly like birthmarks, sexual orientation (there are cases of identical twins having different sexual orientations), etc . This can happen because of stress on the mother or what she is eating at the time, or other factors.
I remember a study of woman who were pregnant during the bombing of England during WWII having a higher percentage of homosexual babies due to hormone fluctuations caused by the stress.
I also saw a kitten on TV that was cloned from an adult cat which had a different fur pattern than its “mother” even thought they should have the same DNA. Evidently some characteristics express themselves in a random matter even though their basic structures is still guided by genes. The two cats had black and white fur, just the shape of the spots were different.
matter = manner :smack:
Thanks for the first hand report. I’m somewhat suspicious of the left/right handedness of mirror twins. Does anyone know how much of handedness is determined by genetics? Hair swirls, yes, definitely 99.99% genetic. Anyway, I’m guessing there are some mirror twins out there who are both right or left handed. Anyone know?
I was unclear, above. I would expect handedness to be **largely[/] genetic, but not of the same order as hair color or nose shape.
Jodocus the pattern differences are due to the fact that most (maybe all, my memory on the cat issue is fuzzy) cats have genetic mosaics. This means that different chromosomes/genes are active in different cells. There is a tendancy for cells near eachother to have the same genes active, this creates the fur patterns of certain breeds of cats.
As a factual tidbit women also have genetic mosaics, as in any given cell only one of the X chromosomes are active and this varies from cell to cell. Female identical twins can have different patterns of which chromosome is active. However since my knowledge of genetics comes primarily through behavioral genetics I’m not entirely sure what sort of superficial impact, if any, these differences would have.
It seems to me the blastocysts has to “decide” that this half of itself will develope into the right side of the body and the other half will develope into the left side of the body.
In identical twins the blastocyst divides into two distinct intities.
In most twins the same sides develope into the right side and other sides develop into the left sides of the twins. But occasionally one blastocyst goes one way and the other goes another way!
Drachillix’s twin sons have mirror-image moles on their otherwise identical backs, the heir on his left and the spare on his right.
actually, The Tim, what you said about cats is still only true in female (XX) cats or male cats with an extra X chromosome (XXY).
As in human females, this has to do with the random (virtual) inactivation of one of the X chromosomes in each of the female’s cells–if the X chromosome from dad has the brown allele and the X chromosome from mom has the white allele, and the one from mom gets inactivated in a certain group of cells, the cells in that group will produce the brown pigment and that area of the cat will be brown, whereas another group of cells could have the dad’s X chromosome inactivated, causing another area of the cat to be white. So, even if mom & daughter had the same set of alleles (which they definitely would in the case of clones), they can look different because their cells made different decisions as to which X to inactivate.
What you probably remember hearing about cats is that mosaicism is what causes calico coloration. Hence, you rarely see a male calico, and if you do, he is most certainly XXY. A girly-man!!