Question of genetics and twins

[triskellian]

Possible spoiler for White Teeth. I say 'possible' because while it's definitely a spoiler for the TV adaptation (which I think is rather good, by the way), I can't remember enough of the ending of the book to know if the TV ending was a made-up one.

OK. We have a woman who is pregnant with twins. I believe it's possible to be pregnant with twins by two different men, if you had sex with them close enough together, and if so, it's possible she's pregnant by two different men. These men are themselves identical twins, so if they are indeed each responsible for one of the babies, are the babies genetically full siblings or halves?

Comments

[onebyone.livejournal.com]

Identical twins have identical chromosomal DNA.

Thus, the twins will have as much genetic material in common as would normally be expected for non-identical twins. In that sense, they're like full siblings.

Note that the same is true if this bizarre twinney-thing hadn't happened, and they were born consecutively to the same mother with identical twin fathers.

Must have been quite a night.

[lathany.livejournal.com]

I believe it's possible to be pregnant with twins by two different men

There was a case in this country in the eighties of a woman giving birth to a black twin and a white twin (not through a fertility clinic, I should add).

(So that would be a yes.)

[dr-bob.livejournal.com]

Only problem is, it would be impossible to tell which child came from which parent. Indeed it's impossible to tell if both had the same father or if there were one from each. So I can't see any plotline that works except the 'we don't know who the father is' one.
Actually, sequencing the entire genome of both possible fathers, looking for (very rare) mutations could enable the parents to be told apart genetically. However, the first human genome sequence (the only one we've got) cost several billion quid and took 10 years, although it could probably be done in three now. Unlikely for a paternity case.

[triskellian]

Ooh, that's interesting - I hadn't thought of that aspect.

From a plot pov it doesn't matter, btw, cos it's the end of the story, not the beginning, but the impossible-to-tell aspect sheds a slightly different light on the resolution of the story, which is pretty interesting - thanks!

[arralethe.livejournal.com]

My probably useless tuppence....

Twins happen by either a) the egg dividing into two once fertilised (identical twins)
or b) 2 eggs being available and being fertilised by two different sperm.

Not sure on the genetic split, as each egg might have marginally different genetic material, but I'll leave that bit to biologists.