In disputed parentage, blood group analysis of mother, alleged father and child can

The correct option is "only prove that he cannot be the father".

Under the ABO blood group system, the inheritance of blood types is determined by three alleles: I^A, I^B, and i. Since alleles are inherited from biological parents, a child's blood group must be a combination of alleles received from the biological mother and the biological father.

In cases of disputed parentage, blood group analysis works through the principle of exclusion. While it can conclusively prove that an alleged father could not have contributed the necessary allele to the child (thereby ruling him out as the father), it cannot uniquely prove that he is the father. This is because many other individuals in the general population share the same blood type and alleles, meaning a match only indicates compatibility, not definitive proof of paternity.