[Bearshouse]

With only 9 blood donors it's a wonder this group hasn't already died out, unless it's a recurring mutation.

[SunkenCiv]

The possible history of it is indicated on the page, I just couldn’t fit it in the excerpt.

Chromosome 9, which carries our main blood type genes, has A and B — which differ by I think seven base pairs — and O, which is identical with A but is missing the leading base pair, making it non-functional, also carries the MN blood group, which is pretty small in terms of the world’s population, but somewhat common around the Bay of Bengal, if memory serves.

[gleeaikin]

Do they only die if they need a blood transfusion badly and don’t get it. Otherwise are there other drawbacks?