You can use Blood type to “Disprove” paternity, not to prove Paternity.
The main Blood group is the A-B-O blood Group
O is recessive and A-B is dominant.
In the following example the Husband cannot be the father. If the Mother has O type and the Father has A Type and the Baby has B Type, Since neither the Mother or the “Husband” had B type it had to come from somewhere else