Think about a wall made of both good and bad quality bricks. Even though the good bricks are strong, the presence of the bad bricks in the wall may cause the whole wall to fail. In this situation, adding more good bricks may not be enough to rescue the wall. Even adding another normal copy of the gene might not fix the problem. Antimorphic alleles also are observed in signalling processes.
Signals sent between cells are necessary for large multicellular organisms to exist.
Frequently, proteins that act in pairs, called dimers, to convey signals. If one protein in a dimer is mutant and the other is normal, poisoned dimers can result. Even though normal protein is present, too few dimers containing only normal protein may be formed to execute the normal protein function. Just one copy of an antimorphic allele can do significant damage to the cell. Therefore, antimorphic alleles tend to be dominant to the normal alleles.