Haploinsufficiency is the phenomenon where a diploid organism has only a single functional copy of a gene (with the other copy inactivated by mutation) and the single functional copy of the gene does not produce enough gene product (typically a protein) to bring about a wild-type condition, leading to an abnormal or diseased state. It is responsible for some but not all autosomal dominant disorders. Haploinsufficiency is therefore an example of incomplete or partial dominance, as a heterozygote (with one mutant and one normal allele) displays a phenotypic effect. It can be contrasted with haplosufficiency, where the single, unmutated allele can produce enough gene product to maintain the wild-type phenotype without the other allele.