Thank you Sqad, I hoped you's be around. Mt eldest brother is so unlike me an my other brother that have always thought he could not be a full brother. But, if you say it's possible then I guess he's just 'different'.
Yes, everyone has two genes for blood group. Ia and Ib are dominant and Io is recessive.
If for example your father had IaIo and you mother had IbIo, taking one gene each from your parents there are 4 possibilities:
IaIb = group AB
IaIo = Group A
IoIb = Group B
IoIo = Group O
Ellipsis my sought after blood was rejected as I have very low blood pressure and they can get 3 people on the table by the time it takes for me to part with my pint. My eldest bother never gives blood at a normal session but they do send a police escort for him when his is needed. Nice to know he's good for something