No. The "letter" of one's blood type is determined by a gene with three possible genes, A, B, and O. Having an A gene guarantees the presence of a characteristic on the outside of one's blood cells....
No, because type O people have the genotype of OO. A person's ABO phenotype (how a person appears) is a general description of a blood type. The person may be type A for example but more specifically...
Yes, in fact that is all they can have.
O is recessive, so each parent must have had an O gene from their mother and an O gene from their father. All they can pass on is O genes. They are O-O and...