This type of signal is kept under tight control, since unregulated cell division leads to tumor formation. Cells containing this type of mutant allele would divide constantly, resulting in tumor growth. The effect of a neomorphic allele cannot be rescued by adding back normal copies of the gene. Whether or not normal copies are added, the products of the mutant genes are still present and still convey inappropriate signals. Since this types of allele causes a mutant phenotype even when present in a single copy, it is dominant .
Antimorphic alleles make gene products that antagonize the normal gene product.
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.