Definition: A gene dosage effect that occurs when a diploid requires both functional copies of a gene for a wild-type phenotype. An organism that is heterozygous for a haploinsufficient locus does not have a wild-type phenotype.

Thus, it cam be considered as a phenotypic state that results from loss of one functional allele of any given gene in diploid cells. Sometimes also called allelic insufficiency.

See also

 mutations

• genic mutations