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Thanks. Here's a semi-relevant sidebar.

The human blood type genes are on chromosome nine. Type A seems to be the fountainhead, as the codominant B sequence is similar to A, and is about 15 per cent of the world population, while A is approximately 40 per cent. Type O is otherwise identical with the sequence for A, just missing the first base pair. Also there is something called (I think) Bombay syndrome, which is nearly the same as A, and tests positive for A using common blood tests, but isn't quite compatible, so an A transfusion will kill someone with Bombay syndrome.

Kind of a "gotcha".

There is also the MN family, which resides in the same chromosome, but isn't part of the ABO family. Not a huge percentage of the world population has it. M and N are codominant within that system, and I'm not sure what happens with the (probably rare) intermarriages with ABO people.