Cecil attempts to explain why Trivial Pursuit would say there are five types of twins. However, there seems to be something missing.
I understand the bit about the DiDi, DiMo, and MoMo types for identical twins - but then he says the two types of fraternal (all are DiDi) differ in how they are attached to the uterine wall:
What I don’t get is if you distinguish the fraternal DiDi based on their uterine join - then wouldn’t you distinguish the identical DiDi twins based on uterine join? There is no reason identical DiDi’s wouldn’t have both types of attachment schemes.
Maybe the difference that the Trivial Pursuit editors were thinking of is that you can have same sex or opposite sex fraternal twins - I’m pretty sure there are names for both of these, does anyone know what they are? Otherwise, it seems like they’d have to go with 6 types.
I remember reading a few years ago that there was a possibility of a third type of twin, aside from fraternal and identical. The third type was half-identicals, that occured when a barr body was big enough to be fertilized and develop, so you had twins that had identical maternal genes, and different fraternal genes. Has anybody else heard of this, and does anybody know if any further research has been done to see if this does happen?
There is actually another type of twin besides the ones metioned about them being identical and the gender. You can have identical twins of a different gender. In other words, identical B-G.
Justin, you seem to be confused about what ‘identical’ means. It does not mean they look a lot like each other when they are both 2 years old and dressed in the same sailor outfit. It means they have identical genes - like clones. Obviously two people with the same genetic code will be the same sex, just like they will have same hair color and eye color (assuming they don’t grow up in environments that are about the same and don’t have sex change operations or dye their hair).
Lucretia: what is a barr body? Could you explain this a little more? It sounds interesting.
As I understand it, after the egg is released, it undergoes several division processes (I forget the name… meiosis?) that further shuffle the chromosomes. After each division, the chromosomes that aren’t included in the egg are divided off into a small body next to the egg, called a Barr body (I assume after the scientist that first described them) that contains chromosomes and not much else.
The half-identical twin theory is that rarely a Barr body will contain chromosomes plus enough of the nourishing material in the egg to be fertilized, and grow. When I read about it, it was just a theory, though.
I’m not an obstetrician, so maybe I’m wrong here, but I thought identical twins always share a single placenta and thus a single uterine attachment, even if they are DiDi.
Lucrecia is on the right track. There is a half identical twin. The egg splits before fertilization and then is insemenated by two different sperm from the father. This results in half of the chromasomes (sorry about the spelling) being exavtly the same but the other half are pot luck. I had a friend with a set of twins like this.
I also have heard of twins that were conceived in seperate ovulation cycles. One egg is released and fertilized, then anothe is released on the next cycle and fertilized resulting in twins that were concieved roughly one month apart. I understand that this is very rare but does happen occasionally.
No one knows how rare the half-identical twins might be, as most twins that are presumed to be fraternal (and can be male and female) don’t get tested to see if this occurred. I think it was only recently discovered that it could happen.
An early SD column described a set of fraternal twins in which two eggs were released and two different fathers inseminated them… one black and one white. Sorry I don’t have a link… I think it was in the first book.
Revedge, I’d be interested to know how your friend knew her twins were half-identical, instead of fraternal. Was there some sort of testing done on them, and why?
I had friends in Junior High school (actually they were children of my mother’s friend). Anyway, I obviously have no proof of this, but according to this woman (and I gota say I believed it) her children were from different fathers. Two girls, they were twins, one standing (at age 14) about 5’10" with long, straight blond hair and obviously white. The other standing about 5’1", with a completely different build, dark, curly hair, and obviously black (or part black). It was the strangest thing to see. Not in a million years would you think these girls were sisters, let alone twins. (My mother was kind of a trash-magnet, a wonderful woman, she just always felt the need to let some really weird people into her life.- The woman claimed she had gotten drunk approximately around the time she believed she had conceived and slept with 2 men at once, one white, one black. She also had 3 other children, all different fathers (and different ages) as far as I can recall.) True story, I swear. All I can tell ya is that this was in central jersey. Just thought I’d share.
so you found a girl who thinks really deep thoughts. what’s so amazing about really deep thoughts? Tori Amos
Back to the topic of twins. Since the questions first appeared in Trivial Pursuit, I think the answers provided and debated here have been overly complex. DiDi, DiMO and MoMo are not exactly in common–or even uncommon–parlance; it would be like asking anyone other than a Volvo Mechanic to name the original factory part number on the front left fender of a 1963 P1800. I submit that what the question-writers probably had in mind were:
As simple as that. I could be wrong, but I suspect that this is what the docents at Trivial Pursuit were thinking when they penned the question.
As an addendum: my wife has a twin brother. On occasions in which she has mentioned “I have a twin brother” in mixed company, a surprising number of people who otherwise look intelligent have proceeded to ask “Oh really? Identical?”
Brian
Brian Maffitt
Chief Software Architect
Atomic Power Corporation
Trivial Pursuit notwithstanding, there are four (substantially different) types of twins:
identical twins
fraternal twins
half-identical twins
half-fraternal twins
Half-identical twins result when the ovum splits prior to fertilization and both halves are independently fertilized.
Half-fraternal twins result when fraternal twins have different fathers. Heteropaternal superfecundation, as it is known, obviously
requires a certain amount of hanky panky on the part of the mother at the critical time.
Until the advent of genetic testing, known cases of heteropaternal superfecundation were rare, since they required fathers of patently
different ethnic backgrounds, as in the 1980 case of a German prostitute who managed to conceived two children by two different
American servicemen – one black, one white – in a single afternoon.
A fifth case – heteropaternal half-identical twins, where two halves of a prematurely split ovum are fertilized by different fathers – is possible, but my research didn’t turn up any actual cases.
BTW, the five types of twins that Trivial Pursuit was probably thinking of are identical boys, identical girls, fraternal boys, fraternal girls, and fraternal boy/girl siblings.
Depends on what you mean by “space”. From low earth orbit, i.e. 150 - 250 nautical miles or the levels the shuttle orbits, there are lots of human-made objects visible. Cities stand out pretty well. The Great Wall is visible. Often, boundaries between fields and plots of land stand out. The Great Pyramids are visible. Etc.
From the trip to the moon, get far enough away and you cannot see those objects. Great Wall included.
Oh, there is one other important thing you can see from space. Look at the ground at night and you see all the human settlements lighting up the ground.
Further comment on the semi-identical twin syndrome. I think my twins may be a set of those. There is a geneticist in North Carolina (either UNC-Charlotte or one of the NC States; not at UNC-Chapel Hill) who is researching it. I found his name in the appendix of a book on twins, but it escapes me now.
He will do DNA testing to determine the twin type. He requires a blood sample from each parent and each twin. I’ve never followed through on it.
My girlfriend is an identical twin. One placenta at birth. But, she doesnt look exactly like her sister. Her sister has a stronger chin and is noticably different, although I could not tell them apart in a picture of the two of them at 3 years old. So, presuming they are identical twins, one confused egg and one sperm, why dont they look exactly alike?