The father has blood type O and the mother has blood type A. The child may have blood type A or O. There are 4 types of blood types, in order, blood type A, blood type B, blood type O, and blood type AB. If the father is blood type O and the mother is blood type A, then the child should have blood type A or O. There will be no cases of blood type AB or blood type B. Blood type is mainly related to the chromosomes in the cells. Humans have a total of 23 pairs of chromosomes, and each pair of chromosomes is formed by two chromosomes. One chromosome comes from the father and the other from the mother. The chromosomes contain DNA, also known as deoxyribonucleic acid, which determines inherited traits as well as functions.