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Semi-Identical Twins Discovered
daftna writes in with a story from Nature about a pair of twins who are neither identical nor fraternal: they are semi-identical. Researchers discovered twins who share all of their mother's DNA but only half of their father's. Both children are chimeras — their cells are not genetically uniform, but include a mix of genes from two separate sperm cells that fertilized a single egg. This is, apparently, not as rare as one might think; but the resulting fetus is rarely viable. This report marks the first known incidence of two half-identical twins resulting from a double fertilization.
Subject says it all.
We're finding new chimeras every day, now that DNA testing is becoming more common. Discovery Health even had a program where genetic testing showed a mother's children to be the product of her BROTHER and her husband; though she had no brother. Turned out she was a hermaphrodite- some of her cells, including her EGGS, were male- a fraternal twin that had been absorbed early in the gestation process.
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This story was already posted!! Oh, no, wait...
I understand it's mythologically correct to use the term "chimera" but whenever I hear it I always envision something else: a ghastly soulless beast with an iron heart, breathing fire out of a cavernous tooth-lined maw, crushing entire houses under gigantic feathered elephant legs; a scaled, whiplike tail kicks up ashy dust clouds as its dragged for miles behind this monstrocity.
No matter how many times I hear the biological equivalent of the term (which is never as exciting) I'm always let down. I always think some giant monster has been discovered, or someone turned into this monster, or geneticists have new clues as to the cause of this monster.
It's a bit annoying once I'm letdown but for a precious few seconds I'm always aghast in wonder.
Small potatoes make the steak look bigger.
How is this interesting? What are the implications?
(I'm sure it is, it just seems.. moot to me).
Well that should cock up the old joke about the blonde who gave birth to twins and wanted to know who the father of the other one was.
No I can count up to five, even with one hand busy!
Engineering is the art of compromise.
Maybe this was slightly different, but I knew two guys back in high school who were genetically half-identical twins. I guess the condition was caused by the polar body (which normally disentigrates) containing enough cytoplasm to sustain itself, and thus allowing it to be fertilized by a sperm other than its pair. They refered to this as "Polar Body Twins". It is extremely rare, but not unheard of. Furthermore, they really looked the part, being much closer in appearance than fraternal twins, but being subtley different from identical twins.
There seems to be a hot debate over the possibility of this happening. Some scientists fully support the notion that this happens, while some have rejected the notion altogether, citing that polar body's don't "normally" contain enough cytoplasm to sustain themselves. But this sounds like a rediculous arguement, to me, since the exact amount of cytoplasm that is both required for fertilization, and the exact amount that a polar body usually contain, very wildly.
Unfortunately, it's very difficult to confirm whether or not this occurs, since percentage of difference in genetics between both fraternal twins and polar body twins is not exact. Polar Body twins will always contain between 50% to 100% of the same genentics (averaging at 75%0, where-as fraternal twins could be anywhere between 0% to 100% similarity. So, my friends will never actually know whether they developed from identical zygotes, but their genetic makeup was similar enough, that many doctors speculated that this was the case.
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This is the second comment along these lines. I don't see anything in TFA indicating that the two sperm cells are from different men; they're just different sperm cells (which all are different, even from the same man, since they only contain half the man's genetic code).
However, I have heard of women having fraternal twins by two different men. So "semi-identical" twins by two different men would be an extremely rare and interesting bit of news, since the twins would each have genetic material from both fathers.
Maybe some women should try for this to achieve notoriety and advance the cause of science...
Hate to be the party pooper, but do you have a link?
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According to my anatomy textbook, after the spem digests its way through the zona pellucida:
According to this, in these chimaera-twins, each sperm contributes genes to each child. So if the sperm were from different fathers, the resulting twins would each really have two fathers, sharing traits from both (and the mother). It'd be interesting if some twins were created this way, with the three parents all of different races.
And the plot for the next gang-bang porno suddenly comes into view.
In Repressive Burma, it's not just your connection that dies. slashdot.org/comments.pl?sid=314547&cid=20819199
I don't even want to imagine the scenario that would be required to get two sperm from two different fathers to fertilize one egg at the same time.
From what I remember from biology, almost all fertilization often happens when the egg drops into place, and the sperm is just hanging around already there. The 'sperm swims to the egg' is a fairly large over-simplification of the process.
This is how the morning after pill works, it stops the release of the egg so it won't hit the sperm waiting for it, or at least screws the release up long enough that the sperm dies. (Sperm lasts like 24 hours inside a woman, IIRC.)
So one egg being fertilized from two fathers is not that amazing, timewise. The egg (Or two eggs, or three, or whatever) shows up, and there are two men's sperm waiting for it. Considering the low amount of two sperm fertilizing one egg, the odds of them every happening with two fathers is improbable, but plenty of fraternal twins have different fathers. (Well, 'plenty' is probably overstating it, but it's happened enough that it's not even that neat a trick.)
Incidentally, there's some study out that that demonstrated that men can sometimes produce sperm that is a good deal less viable, and the main purpose of it appears to be entangling other men's sperm, stopping it from reaching any eggs. And that men who are suspicious of affairs, or just know their lover has other lovers, are more likely to produce said combatant sperm.
The real amazing trick here is two chimera twins. Human chimeras are fairly unlikely to be healthy, as the two parts often react in bad ways. Although, now that I think about it, if one survived, that logically means the combination 'worked', and thus the other surviving is not that impressive.
I'm confused as to why they're calling these 'semi-identical' twins, though. They'd be semi-identical if each of them contained a single genetic code that considered of the same part from the mother but with each having a different part from the father. However, they both contain the same genetic codes, so they are, indeed, identical twins. They just have 1.5 times the genetic code of anyone else, with cells in their body randomly containing one code or another.
What they really are are two semi-chimeras. Parts of their body have half the genetic code differing, instead of all their genetic code differing like normal chimeras. Which is, I guess, why they managed to live. But I seem to recall that a lot of the surviving human chimeras are like this. So they're just unique in being a pair.
I guess they're 'semi-identical' in the sense that different parts of their bodies might contain different genetic codes. One twin's heart might contain code A, and the other code B, whereas they both have code A eyes and code B hair color.
If corporations are people, aren't stockholders guilty of slavery?
It just hasn't happened in humans yet.
. stm
http://news.bbc.co.uk/2/hi/science/nature/6196225
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but no personal life or even ability to enter either public restroom without people looking at you dubiously.
I dunno about you, but when I go to the restroom, people usually don't see my weenie. And there's always the stalls to do your business, you know. Furthermore, if people really want this sort of thing "corrected", there are surgical procedures and drugs to make anyone clearly male or clearly female. As for medical risks, most people who are chimeras never seem to find out anyway.
Is that also the gene for compulsive goatee growing?
Here's one thought for you: Splash Conception. A.k.a., anal sex is not 100% reliable as birth control. It only takes one drop of sperm on reaching the vulva, and the spermatozoa's mobility takes it from there.
Then there are things like an elastic hymen, and various other fun ways to end up pregnant while technically a virgin.
And to make it even more fun, think this: they later had to invent an explanation for exactly this kind of thing, namely the succubi and incubi. Virgin virtuous girls (yeah right) were supposedly impregnated by incubi. You don't invent a whole explanation for something that never happened ever since. So basically they knew it happened more than once, and in fact it happened again and again.
So here's what _really_ makes me wonder: why is everyone pretending that something happening all the time is a one-time divine miracle? I mean, hello? It's like proclaiming that there is only one Car made by God himself, and steadfastly refusing to acknowledge all the other cars around you. They can't exist, because God said they don't exist.
I don't know, it's basically fascinating how people can basically force themselves in a thoroughly schizophrenic frame of mind where they believe two completely opposite things at the same time. E.g., simultaneously that (1) Mary's virgin conception was such a unique and inexplicable thing that can only possibly be explained by divine intervention, yet at the same time (2) thousands of other virgin girls got pregnant too, e.g., via incubi. Hello? How can one have unyielding faith that something is unique and non-unique at the same time? Or that it could have been possible only by divine intervention, yet at the same time the same happens without divine intervention all the time? (E.g., via demons.) Mind boggles.
Or maybe that's the ticket. The more absurd and illogical a religion is, the more people will rabidly fight against anyone saying otherwise, because it trips their own insecurity and doubt. Better burn the heretic before he manages to make you think more about that.
A polar bear is a cartesian bear after a coordinate transform.
Do you really think that this is the biggest problem intersexual people will ever face in their life? If yes, you seriously need to read up on these things a bit.
First of all, as a disclaimer, I'm not intersexual myself, but I'm interested in inter- and transsexuality and know a couple of people who are. Most of the intersexuals I know had a gender surgically assigned to them after birth, too (female, FWIW; as doctors say, "it's easier to dig a hole than build a pole"). But you know what? Neither of them is happy.
In fact, the *exact opposite* is true. *Every single* intersexual I've talked to or heard about has said the same thing so far - that doing so is, essentially, butchering, a traumatic experience that will haunt you for your entire life. Even in these times where sexual reassignmet surgery is not impossible anymore, the results are far inferior to anything that nature came up with (if you can even afford the whole procedure!), and the psychological problems associated with having your body mutilated after birth are just as serious.
What really needs to be done when an intersexual child is born is really easy: bloody leave them alone. The child will eventually grow up and be able to make their own decisions; if they decide then that they really belong to one gender, it's not too late to do surgery etc.. What's more, it might well be that the child decides that they're really male - contrary to popular opinion, "intersexual" and "transsexual" do not mean "a guy who wants to become a chick".
But there's also a decent chance that the child will say "I'm happy the way I am", and who's to say that that's not within their rights? If the only reason you can come up with is that there might be confusion over which restroom is appropriate, well... I'm sorry, but that isn't quite enough.
What's more, when you're talking about things like restroom usage, you make a very fundamental mistake: you look at what other people and society in general will see the child as, rather than what the child themselves thinks. But it's the child who will have to live with their body; the idea that society has a right to say "you don't fit into our binary system, so we'll cut up your body and then pretend that you do (even though you really still don't)" is outrageous.
FWIW, BTW, another fundamental mistake that's often being made is the assumption that it's even possible to reassign gender - that is, the actual gender that someone identifies as, as opposed to their physical sex. One of the reasons why intersexual people were mutilated in the past and raised as girls is that doctors (wrongly) believed that if you just cut off everything that was non-girly and if you just put the child into a dress and told them they were female, they'd really believe it and grow up as a normal, well-adjusted *woman* - but in reality, it doesn't work, and never has.
Of course, I do understand that there are no ulterior motives - doctors, parents etc. really are trying to help intersexual children. But it's also important to realise that it's not working and that the only thing you're doing is CAUSING harm, not preventing it.
So, although this has little do to anymore with the original TFA, just let me say this: leave intersexual children alone, and let them make their own decisions when they're old enough. Until then, be tolerant, be honest, explain to them why they're different, and explain that it doesn't make them worth less or anything like that. That's the ONLY way you can actually help them.
butter the donkey