Twinquiry

This is a vintage silly discussion that came up in my old lab one coffee break but I thought was worth sharing again (Filler material and the blog isn't even a week old!). Identical twins are a topic of discussion that geneticists like to bring up a lot.
They are the perfect "controls" and I think it's something that everyone who doesn't have one would be curious to have. It's also nature's clone, you don't need a lock of hair (you need a bloody root) and a vat if you have an identical twin.

For those who don't know, identical twins are when a single egg is fertilised only for it to split into two embryos. This means both individuals will be genetically identical. Not to be confused with fraternal twins which occur from two separate egg/fertilisation events which are essentially the same as siblings but are born at the same time.

The usual stuff was cropping up like how can identical twins brought up in the same home have different personalities (we figure it's because they aren't treat exactly the same - one might be a favourite or initially submissive to the other one) and the ethically dubious question of spare parts in the sense it would be nice to know you have a donor match if you ever need a spare kidney or bone marrow transplant.  Although we also wondered whether it would only be a short-term fix if the reason your kidney packed in was due to an underlying genetic problem. Could your twin ask for it back if their remaining kidney then went wrong?

We then got onto sillier things like the possibility of male twins marrying female twins living together. Would it be possible to accidentally sleep with the wrong twin? This led me to a curious thought.

If identical twins married other identical twins and had kids would those children be siblings?

Genetically they'd be the equivalent of siblings - depending on recombination some of these "cousins" could be more alike than their actual siblings which would be rather odd and a pitfall for communities that like to marry their cousins. Chances are such an example really exists. I guess legally they are still cousins but you'd hope they'd have the sense to avoid those marriages.
This then made one of colleagues, say that scenario would be handy in that she could just let her twin have a baby for her so she wouldn't have to take time off work. Maybe the future is in having identical twins (or getting our own clones)