Asked by: Michelle Gatt, Malta
Blood type A involves having a particular antigen (type of protein) on the membrane of your red blood cells. Type B blood has a different antigen on the membrane of its red cells, while type O has neither.
The gene for type O is ‘recessive’, because if you have one gene for O and one for A, then you still end up with A antigens on your cell membranes, and the same goes for O and B. In order to be group O, you need both parent cells to be O. But group O is still more common simply because it is the ancestral form.
The A and B mutations appeared in the last 20,000 years and haven’t spread through the population yet.