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Semi-Identical Twins Discovered

kdawson posted about 7 years ago | from the my-brother's-a-keeper dept.

Biotech 224

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.

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224 comments

hmm... (0, Redundant)

nothing now (1062628) | about 7 years ago | (#18509717)

...interesting.

God I Luv the News that Matters here at SlashDot (-1, Troll)

Anonymous Coward | about 7 years ago | (#18510317)

God I Luv the News that Matters here at SlashDot, because this is what matters to me.

Sounds like mom was a busy girl. (5, Funny)

alcmaeon (684971) | about 7 years ago | (#18509735)

Subject says it all.

Re:Sounds like mom was a busy girl. (5, Funny)

maxume (22995) | about 7 years ago | (#18509753)

Problems with your sperm count? (lots of guys have more than, ya know, one. Harr).

Re:Sounds like mom was a busy girl. (5, Funny)

Anonymous Coward | about 7 years ago | (#18510059)

Inconceivable!

Re:Sounds like mom was a busy girl. (1)

robyannetta (820243) | about 7 years ago | (#18510135)

Both children are chimeras

I'm still waiting for someone to make a Full Metal Alchemist reference...

Re:Sounds like mom was a busy girl. (4, Interesting)

countach (534280) | about 7 years ago | (#18510243)

One wonders what would happen with child support payments if the two sperms came from a different father. I doubt the rules and regulations know how to deal with that one.

Re:Sounds like mom was a busy girl. (4, Interesting)

iamacat (583406) | about 7 years ago | (#18510637)

This is the least of these kids problems. One of the kids has genitals which are in between penis and vagina. Both have inconsistent genetic makeup which is bound to cause health or at least fertility issues. Imagine living a life where you are called "a very special and wonderful person", but no personal life or even ability to enter either public restroom without people looking at you dubiously.

doesn't sound like a big deal (2, Insightful)

Anonymous Coward | about 7 years ago | (#18511395)

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.

Re:Sounds like mom was a busy girl. (1)

Brad1138 (590148) | about 7 years ago | (#18510875)

the two sperms came from a different father.

Probably the different father would pay.

Robert Leeshock (0)

Anonymous Coward | about 7 years ago | (#18510315)

I always envisioned a chimera as an alien hybrid with glowing hands, but on another note I wonder if this would be anything like Fry being his own grandfather...;)

Discovery Health "I'm my own twin" (5, Interesting)

Marxist Hacker 42 (638312) | about 7 years ago | (#18509737)

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.

Re:Discovery Health "I'm my own twin" (5, Interesting)

Anonymous Coward | about 7 years ago | (#18509929)

Could a similar event lead to a virgin giving birth? News of such an event could be of Biblical proportions.

Re:Discovery Health "I'm my own twin" (5, Funny)

Starburnt (860851) | about 7 years ago | (#18510127)

More importantly, Slashdotters may now be able to reproduce.

That could be of Biblical proportions.

Re:Discovery Health "I'm my own twin" (0)

Anonymous Coward | about 7 years ago | (#18510811)

Could a similar event lead to a virgin giving birth? News of such an event could be of Biblical proportions.\

Are you suggesting that Jesus may have been inbred? I mean, that would certainly explain a lot of things about the Deep South....

Re:Discovery Health "I'm my own twin" (4, Informative)

kestasjk (933987) | about 7 years ago | (#18511127)

Are you calling the virgin Mary a hermaphrodite?! Blasphemy!

As we probably all know 'virgin' was indisputably a mistranslation; the Hebrew for 'young woman' (almah) was translated into the Greek for 'virgin' (parthenos). I wonder why we all still refer to her as the virgin Mary, now that we know she wasn't (necessarily, to be absolutely pedantic) a virgin.

Re:Discovery Health "I'm my own twin" (2)

Rolgar (556636) | about 7 years ago | (#18511501)

Christianity teaches that Jesus is the God-man. That is, his mother was human, his conception caused by the Holy Spirit, so that the mix of his divinity (Godness) and humanity has cured our humanity from some of its brokenness, and his death was the death of sin, and his rising from the third day was the defeat of our mortality that gives us a chance at eternal life. If he had a human father, that's not the case, Jesus wasn't God, and his death would not be sufficient to redeem humanity from sin. Some individuals who claim to be Christian would disagree, but probably 1.5 billion of the 1.6 billion Christians would agree. The Muslims and Jews disagree.

Re:Discovery Health "I'm my own twin" (2, Interesting)

Boronx (228853) | about 7 years ago | (#18511565)

The new testament wasn't translated from Hebrew, was it?

Link? That sounds pretty incredible. (2, Insightful)

gcnaddict (841664) | about 7 years ago | (#18509935)

Hate to be the party pooper, but do you have a link?

Re:Link? That sounds pretty incredible. (1)

Marxist Hacker 42 (638312) | about 7 years ago | (#18509967)

I searched for one. All I got was bloggers to the show. Perhaps you'll find something at Discovery Channel [discoverychannel.com], but as I can't see that from work, perhaps you'll do better than I did....

Re:Link? That sounds pretty incredible. (2, Informative)

brunes69 (86786) | about 7 years ago | (#18510343)

I'll vouch for the parent, I saw the same show. But I think it was on TLC.

Re:Link? That sounds pretty incredible. (1)

Schemat1c (464768) | about 7 years ago | (#18510579)

Hate to be the party pooper, but do you have a link?
I don't know if it's the same story but here's a link to a New Scientist [katewerk.com] story about Chimera's.

Re:Link? That sounds pretty incredible. (1)

porcupine8 (816071) | about 7 years ago | (#18511367)

I saw this show too, about a year ago - it was the first thing that came to mind when I saw this article.

Some of these women nearly lost their kids because they couldn't prove via DNA tests that the kids were theirs - child services thought they'd switched them at the hospital or something, even though the father was the father.

Re:Discovery Health "I'm my own twin" (4, Informative)

good soldier svejk (571730) | about 7 years ago | (#18509953)

Chimerism is also a source of the exceedingly rare brindle coat pattern in horses. [aol.com] In such cases the different color hairs will have different DNA. In one case this caused two consecutive DNA sample sent to a lab for pedigree verification to return negative parentage for both the sire and dam, [209.85.165.104] even though the owner had personally witnessed both the fertilization and the birth and hence knew for sure who the foal's parents were. DNA from the stallion's blood samples also showed no evidence of a Y chromosome.

Re:Discovery Health "I'm my own twin" (1)

BobPaul (710574) | about 7 years ago | (#18510025)

Your description sounded really "out there" so I did some looking. There's a paragraph on wikipedia that gives a good summary: Chimerism [wikipedia.org]. The rest of the page is about intersex (hermaphrodite).

Re:Discovery Health "I'm my own twin" (4, Informative)

NIckGorton (974753) | about 7 years ago | (#18511041)

Intersex is not the same thing as a hermaphrodite. All hermaphrodites are intersex, but the vast majority of intersex people are not hermaphrodites. To be a human hermaphrodite, you have to have ovarian and testicular tissue in the same person. Most people who are intersex have only ovarian OR testicular tissue. Instead of having both types of gonads there is some problem with sexual development in the womb that results in a person with physical characteristics somewhere on the spectrum between the poles of male and female bodies. (Hence the newer term for intersex conditions: DSD or disorder of sex development.)

More importantly, if you call a person who is intersex a hermaphrodite many will likely be quite unhappy with you. Its akin to calling a Native American an 'Indian' - not only generally disliked by the people you are labeling but also factually incorrect because of a misunderstanding of what the term means (or on what continent you are located.)

Nick

Re:Discovery Health "I'm my own twin" (0)

Anonymous Coward | about 7 years ago | (#18510085)

a fraternal twin that had been absorbed early in the gestation process.

Wonder if she grew up to be a Maneater [sing365.com]?

Re:Discovery Health "I'm my own twin" (1)

spielermacher (856042) | about 7 years ago | (#18510631)

This is interesting. Tyler Hamilton, the American who won the Cycling Gold Medal at the Athens Olympics (and a stage at the Tour de France) tested postive for blood doping - where atheletes get infusions of other people's more oxygen rich blood. I saw an interview with him a bit later on HBO Sports where he claimed that he was innocent, and that he tested positive because he was a chimera, and had two different types of blood, which is what led to the appearance of having an infusion. He was basically laughed out of the sport because of this; maybe it's not so farfetched and there may be some truth to his story?

Re:Discovery Health "I'm my own twin" (2, Interesting)

boingo82 (932244) | about 7 years ago | (#18510801)

Your description of the show is VERY inaccurate - the main person featured in the show, Lydia, was not a hermaphrodite. She did not have male eggs. She did not have male cells.

When she was DNA tested to receive welfare, the DNA indicated that her children weren't hers - but the mother would've been someone with similar DNA *like a brother* of hers.

Somehow you took that to mean that she had hermaphroditism, which would have made her infertile. That's pretty illogical - how the hell does a person have male eggs? And how would they think that her kids had been fathered by two males? They didn't.

A more accurate summary of the show is here. [go.com]

DUP!! (5, Funny)

dustball23 (309393) | about 7 years ago | (#18509739)

This story was already posted!! Oh, no, wait...

Re: DUP!! (5, Funny)

Black Parrot (19622) | about 7 years ago | (#18509815)

We don't get dupes, we get semi-identical posts.

Re: DUP!! (1, Funny)

Anonymous Coward | about 7 years ago | (#18510033)

We don't get duplicates, we get semi-identical posts.

Re: DUP!! (-1, Offtopic)

Anonymous Coward | about 7 years ago | (#18510181)

This post is not funny. But it is offtopic.

DUPE!! (0)

Anonymous Coward | about 7 years ago | (#18510299)

We don't get bupes, we get semi-identical posts.

(Damn! It mutated on me.)

They need a different term besides "Chimera" (5, Funny)

The-Bus (138060) | about 7 years ago | (#18509767)

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.

Solidarity (1)

attemptedgoalie (634133) | about 7 years ago | (#18510157)

I'm with you.

One of these days, something from the Monster Manual is going to happen.

I don't know if that's good or not.

While it would be cool to see a Mind Flayer wandering about, it's probably not a good start to the day if you run into him.

Re:They need a different term besides "Chimera" (0)

Anonymous Coward | about 7 years ago | (#18510225)

Interesting. I always envisioned a chimera as an alien hybrid with glowing hands, but on another note I wonder if this would be anything like Fry being his own grandfather..;)

Re:They need a different term besides "Chimera" (1)

darkreaper00 (978543) | about 7 years ago | (#18510607)

Continue to keep your eyes open: science continues to make unnatural chimeras at a blinding speed. Check out that story a few down about growing teeth, for example. The bioengineering we're up to these days is heavy stuff.

Re:They need a different term besides "Chimera" (1)

ozmanjusri (601766) | about 7 years ago | (#18510621)

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

I see you've met my wife, then.

Serious question (3, Insightful)

Anonymous Coward | about 7 years ago | (#18509781)

How is this interesting? What are the implications?

(I'm sure it is, it just seems.. moot to me).

Re:Serious question (1)

maxume (22995) | about 7 years ago | (#18509923)

No one understands the process by which it happened. (That's pretty interesting to me, the implications, who knows.)

Re:Serious question (1)

khallow (566160) | about 7 years ago | (#18509979)

I see several things. First, it's another indication of the extraordinary stability of the reproduction process and is yet another route for evolutionary speciation (by shuffling around the chromosomes both in location and number). And it's an incredibly rare event. First, identical twins occur in 3 of 1000 births. Second, fertilization by two sperm (as occured here) is a 1% event. Assuming that they are independent of each other in frequency, then you have a 3 in 100,000 births event that probably is almost aways unviable.

Re:Serious question (4, Interesting)

tloh (451585) | about 7 years ago | (#18509991)

talk about deja vu!

Some time ago, I wondered about the exact situation this article raises.

http://science.slashdot.org/comments.pl?sid=130374 &cid=10879347 [slashdot.org]

At the time, it fascinated me because it occured to me that you could have twins which share a maternal set of chromosomes but have one sex chromosome from the father be an X for one of the siblings and the other be a Y.

In other words, almost identical twin brother/sister pair! One wonders how much of gender is actually in our genes. Well, to have a pair of individuals share so much with the exception of the sex chromosomes - it becomes more reasonable to do an actual comparison. (I am aware there is still lots of room for genetic variation from the rest of the father's somatic set) I don't know how scientific it would be, but as a thought experiment, I wasn't to concerned about it at the time I posted it.

Re:Serious question (5, Informative)

reverseengineer (580922) | about 7 years ago | (#18510185)

Well, this case is primarily interesting in the sense of "this thing that very rarely happens, it just happened." The main scientific benefit is that further light is shed on the mechanisms of human reproduction. Obviously, the outlines of that process are well-known, but there's still a lot of uncharted territory when it comes to the non-normal functioning on this process. Reproductive biology is an area where animal models (even in other primates) tend to translate rather poorly to human beings, and is of course also an area with ethical limits on human experimentation. Conceivably, learning about cases like this can advance knowledge about things like infertility and birth defects.

There's actually an interesting story, almost the flip side of this rare case in humans, running now in the New York Times about marmosets [nytimes.com], in which a form of chimerism is quite widespread:

One of the most surprising results of the study is that over half of male marmosets have chimeric sperm. Dr. Ross and her colleagues discovered cases in which the DNA of male marmosets turned up in babies supposedly fathered by their fraternal twins. In other words, the sperm came from one male, but it had the DNA of the male's brother. A paternity test would show that the baby's genetic father was actually its uncle. The scientists were not able to isolate DNA from marmoset eggs, but they did find that 2 out of 21 marmoset ovaries were chimeric. It's possible that a female marmoset can give birth to nephews and nieces.

Re:Serious question (0)

Anonymous Coward | about 7 years ago | (#18510507)

The main scientific benefit is that further light is shed on the mechanisms of human reproduction. Obviously, the outlines of that process are well-known, but there's still a lot of uncharted territory when it comes to the non-normal functioning on this process.

Remember, this is Slashdot, so it is not obvious that the mechanisms of human reproduction are well known the average reader. Shashdot readers are not very likely to have first had experience with human reproduction, except for the being born part.

Or... (1)

WK2 (1072560) | about 7 years ago | (#18510523)

A paternity test would show that the baby's genetic father was actually its uncle.

That usually means something else.

Re:Serious question (0)

Anonymous Coward | about 7 years ago | (#18511491)

A paternity test would show that the baby's genetic father was actually its uncle.

Man... that's really going to fuck with the marmoset Montel Jordan.

wow, that must be embarassing (0)

Anonymous Coward | about 7 years ago | (#18509795)

having it all over the news that their mom was into double penetration i mean jesus maybe she was in college

Re:wow, that must be embarassing (2, Interesting)

Grishnakh (216268) | about 7 years ago | (#18509911)

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...

Re:wow, that must be embarassing (1)

TekPolitik (147802) | about 7 years ago | (#18510013)

Maybe some women should try for this to achieve notoriety and advance the cause of science...

Does Freddy Krueger count?

Re:wow, that must be embarassing (1)

BobPaul (710574) | about 7 years ago | (#18510095)

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.


Umm, no they wouldn't. They're semi-identical because they're from the same egg but different sperm. If there was a double-penetration act each semi-twin would still have a distinct father, but share since they shared the same egg, would share the same placenta and traits inherited from the mother.

To the casual observer, the two would appear no different than fraternal twins.

Re:wow, that must be embarassing (2, Informative)

Grishnakh (216268) | about 7 years ago | (#18510233)

This is incorrect. From TFA:

The 'semi-identical' twins are the result of two sperm cells fusing with a single egg -- a previously unreported way for twins to come about, say the team that made the finding. The twins are chimaeras, meaning that their cells are not genetically uniform. Each sperm has contributed genes to each child.


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.

Re:wow, that must be embarassing (1)

dazilla (647166) | about 7 years ago | (#18510423)

From TFA:

The twins are chimaeras, meaning that their cells are not genetically uniform. Each sperm has contributed genes to each child.
So they would be "identical" from the mother's DNA (which depending on the genes that activate from the mother's side, can increase or decrease the closeness of appearance between the twins). However each sperm would contribute a different set of DNA (but since the twins are chimeras, they get both sets in different areas).

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.

Re:wow, that must be embarassing (3, Informative)

DavidTC (10147) | about 7 years ago | (#18510617)

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.

Re:wow, that must be embarassing (5, Funny)

The One and Only (691315) | about 7 years ago | (#18510329)

Maybe some women should try for this to achieve notoriety and advance the cause of science...

And the plot for the next gang-bang porno suddenly comes into view.

No more jokes (2, Funny)

Anonymous Coward | about 7 years ago | (#18509821)

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.

This isn't new... (4, Interesting)

7Prime (871679) | about 7 years ago | (#18509883)

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.

Re:This isn't new... (1)

0100010001010011 (652467) | about 7 years ago | (#18510023)

Furthermore, they really looked the part, being much closer in appearance than fraternal twins, but being subtley different from identical twins.
The Olsen Twins?

Re:This isn't new... (1)

jd (1658) | about 7 years ago | (#18510501)

It should be possible to determine, provided the genetic material shared is not 100%. What will matter is how the genetic material is distributed. For example, in the story being described, the twins both have two sets of DNA. The presence of some gene G in both twins tells us relatively little. The presence of some gene G in the same subset of DNA on both twins would tell you much more, as would it occurring on one subset of DNA on one twin but in both subsets of DNA on the other.

I'm not so sure about "polar body twins", but it would seem to me that exactly one of them should be chimerical and the other should just have the normal set of DNA, because of the mechanics. This would mean that if you tested two twins and looked for matches in the genetic material, the mismatches would be asymmetric. (2 sets of genes - 1 set != one set - two sets.) This could also happen in the case of non-identical triplets where two of them ARE identical, and the non-identical one merges into one of the identical twins to form a single body. Basically, merging of twins is supposed to be how most chimeras arise, so this is just a variant of that with triplets instead. I guess for something like that, you'd say "polar body twins" is good enough until the technology exists to make greater differentiation meaningful.

Whether or not polar body twins exist, whether or not my musings are even roughly on the mark, I think this goes to show that the field of genetics is a very complicated one. It's no longer a simple case of "map the sequences", because we're discovering lots of new ways in which multiple sequences can simultaneously exist. Of course, it's unlikely a real geneticist has ever seriously believed simple mapping would be sufficient, but given that we now use genetics in everything from modifying food to identifying suspects in a criminal case, it seems apparent that general knowledge could do with improving a whole lot.

(I wonder what will happen if Anna Nicole Smith's baby is found to be a chimera, and all three claimants for father are matches for different DNA. That could pose an interesting problem for the courts. Hell, if the technology existed to safely turn a person into a chimera, this would be the perfect scenario.)

Re:This isn't new... (2, Interesting)

DavidTC (10147) | about 7 years ago | (#18510805)

While in theory siblings can share 0% genetic code (At least, 0% of the genetic code that actually differs among humans.), male siblings must share at least a little. There's only one possibly source for the Y chromosome.

Incidentally, this article is talking about polar body twins, but ones that 'merged' and then 'unmerged', or, more technically, separated incorrectly. Instead of splitting when first fertilized, they split later, along non-genetic lines.

This resulted in two people who had both sets of genetic codes, in fairly random cells. This is called a chimera, or, rather, two chimeras, and usually results in death....it's like doing random transplants between people on the street with no regard to the immune system or blood types. Usually part of the body ends up attacking another part.

When they do live, they usually have odd 'banding' where their skin changes color and their eyes can be different colors. (Note: Eyes can be different colors for other reasons.) If they are a mix of XX and XY, they not only can be intersexed, they can be fully functional hermaphrodites, with both ovaries and testicles, and all the genitalia that goes with both of them. (Although thanks to weird hormones they are unlikely to produce children either way.)

These kids are 'half-chimeras', in that the genetic code they got from their mother is the same throughout, so only half of the code differs. I seem to recall that most chimeras who live are 'half-chimeras', which makes sense. These two are just odd in that they split into twins, which is mildly ironic in that they 'should' have been polar body twins in the first place, but didn't become twins at that time, and then, later on, they did split up randomly.

Required Filthy Comment (no vulgarity) (0)

Anonymous Coward | about 7 years ago | (#18509931)

Well, at least the father was the donor of BOTH sperm cells! Would have been interesting had there been 'something else' going on!

"semi-identical" makes as much sense as... (1)

3on3 (1007539) | about 7 years ago | (#18509995)

"Almost never".They're either identical or not, theres no in-between.

Re:"semi-identical" makes as much sense as... (1)

darkhitman (939662) | about 7 years ago | (#18510073)

Identical twins are formed by a single fertilized egg dividing and forming two embryos. Fraternal twins, on the other hand, are formed by two eggs being fertilized by two separate sperm. What supposedly happened here is that two separate sperm fertilized one egg, which the divided. So they'll look identical (unless I'm misinterpreting TFA), but two sperm were involved in the process (the fraternal part). Meaning, the label of "semi-identical" applies genetically, if not quite literally.

On a side note, my brother and I are fraternal twins. However, we look identical. Reasoning? I have no clue; apparently the doctors were vague. For all I know, it could be due to a situation like this, or it could just be random chance.

Re:"semi-identical" makes as much sense as... (1)

miskate (730309) | about 7 years ago | (#18510409)

No, they wouldn't necessarily look identical - as in this case, one twin was male and the other was a "true hermaphrodite" with ambiguous genitalia, which is what led to their being genetically tested in the first place. The following isn't necessarily correct as I'm not a geneticist or whatever you'd need to be to be authoritative on this, but that never stops anyone on slashdot, so I'll have a go: Once the double fertilised embryo splits and the cells start to differentiate (from stem cells into cells with specific functions), some cells will have the genes from one of the sperm and some cells will have the genes from the other sperm. It doesn't follow that in each child the pattern of differentiation for which gene-set's stem cells turn into which types of differentiated cells will necessarily be the same. In this case it would appear that one of the sperm had an X chromosone and one had a Y chromosone (ie one was male and one was female, as gender is determined by the sperm not the ova). Both kids would have parts of their body which contain male genes and parts which contain female genes. In one child, all the genetalia apparently developed with the Y chromosone gene set and in the other the genetalia developed from a mix, leading to it have both testicular and ovarian tissue. If I'm right, then there was probably about an even chance that one of them could have had all femal genetalia. Chimeras often have a strange (but generally barely visible) stripey pattern on their skin as there are bands of flesh from each gene-set (same as with the horses mentioned in a post above). I suspect such twins would not necessarily have the same pattern. If the ova's set of genes had the recessive gene for blue eyes and one sperm had the dominant brown-eyed gene and the other sperm had the recessive blue eyed gene, then the two babies could either both have blue eyes (if the blue-eyed sperm got to do eye colour on both), brown eyes (if the brown eyed sperm got to do eye colour on both) or one could be blue and the other brown (if each got a different sperm's set in the cells that turned into their eyes). Anyway, that's my hokum for the day.

Re:"semi-identical" makes as much sense as... (1)

stratjakt (596332) | about 7 years ago | (#18510081)

I remember hearing about this as soon as it was announced the mother was sort-of pregnant.

Re:"semi-identical" makes as much sense as... (1)

NIckGorton (974753) | about 7 years ago | (#18511123)

It makes perfect sense if you realize that identical in the colloquial sense means something different from the scientific sense.

Its like the word normal with regards to statistics or common usage: Being a lefty, red-headed, or type AB- blood may be on the tail end of the bell curve, but they are not 'abnormal' in the colloquial sense.

Nick

Tommo and Hawk (1)

hansamurai (907719) | about 7 years ago | (#18510129)

There's a great book series by Bryce Courtenay where the first book's (The Potato Factory) last story arc tells about the birth and childhood of a unique pair of semi-identical twins. The mother was a white woman who gave both a black man and an American Indian the right to have sex with her on the same night (long story, read it if you're interested) and had a pair of twins where one was black and the other white. The next book (Tommo and Hawk) was all about the boys and their teenage years living in Australia and New Zealand in the early 20th century. Great series but the really interesting part are the boys, who are technically twins, but are very different in both looks and personality.

Actually now that I think about it they might not have been semi-identical but just fraternal...

A child of two fathers? (0)

Anonymous Coward | about 7 years ago | (#18510197)

So, does it mean that if a woman has sex with 2 guys, she could (theoretically) have 1 child from 2 men. Does she get to collect a child support from both of them?

Why this is notable: Cortical reaction (5, Informative)

wile_e_wonka (934864) | about 7 years ago | (#18510207)

I thought I would note why this doesn't happen all the time in humans (in some mammals it is common for an egg to be able to be penetrated by more than one sperm).

According to my anatomy textbook, after the spem digests its way through the zona pellucida:

The plasma membranes of the sperm and oocyte then fuse, and the sperm nucleus is engulfed by the oocyte's cytoplasm. This fusion induces the cortical reaction, wherin granules in the oocyte secrete enzymes into the extracellular space beneath the zona pellucida. These enzymes destroy the sperm receptors on the zona pellucida, preventing any other sperm from binding to and entering the egg.

Re:Why this is notable: Cortical reaction (1)

xLittleP (987772) | about 7 years ago | (#18511145)

I think you're missing the point. While a single egg being penetrated by more than one sperm is rare for humans, it has been known to happen. The big deal here is that the two sperm (sperms?) came from DIFFERENT people.

Honestly I don't know why this article hasn't been tagged with an "lol" or a "haha" yet -- it's flipping hilarious.

Re:Why this is notable: Cortical reaction (1)

chrisb33 (964639) | about 7 years ago | (#18511667)

I think you're missing the point. While a single egg being penetrated by more than one sperm is rare for humans, it has been known to happen. The big deal here is that the two sperm (sperms?) came from DIFFERENT people.
No, that's not what happened. The sperm are both from the same person, they are just different since every sperm contains a (different) random half of your genes. This is quite rare, as the parent post pointed out.

far left (1)

moremojo (904902) | about 7 years ago | (#18510335)

This is just another example of the far left trying to discredit intelligent design

Re:far left (0)

syphax (189065) | about 7 years ago | (#18510555)


It's cool, though- this is just another curveball that God throws in now and again to test our faith.

Obligatory Stephen Colbert (1, Insightful)

Anonymous Coward | about 7 years ago | (#18510821)

> This is just another example of the far left trying to discredit intelligent design

Reality has a well-known liberal bias!

Just a Sibling? (0)

Anonymous Coward | about 7 years ago | (#18510339)

Or can I now claim ( in mixed company ) to be a semi-identical non-twin?

So let me get this straight . . . (1)

mmell (832646) | about 7 years ago | (#18510565)

These two are almost, but not quite completely unlike identical twins?

First Ever? Bullshit! (1)

throatmonster (147275) | about 7 years ago | (#18510717)

I heard about this over a year ago, and the explosion of DNA testing has led scientists and researchers to realize this is far more common that once thought. Hermaphrodites are probably the most common noticeable result of this; spontaneous abortions are by far the most common (but not commonly linked to this cause) result, but many apparently 'normal' people also have more than one set of DNA that can be traced back to this. When a sperm penetrates an egg, the chemistry that blocks out other sperms is *almost* immediate, but not quite. There is a window of opportunity for this to happen. Go sperms go!

Talk about your race conditions (0)

Anonymous Coward | about 7 years ago | (#18511553)

laugh, it's funny
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