When a person with blood type O and blood type B unite, the child’s blood type may be either O or B. People with blood type O have a gene for ii, and people with blood type B have two types of genes, BB and Bi. Half of the genes for the child’s blood type come from the mother, and half come from the father, so that the genes for the blood type can be expressed as either Bi or ii. Bi has a three-fourths chance and ii has a one-fourth chance. This means that the majority of the children’s blood type is B, and 25% are O.