(genetics) A type of mutation wherein the change in gene leads to an increase in normal (wild-type) gene function
The effects of mutations in organisms vary. There are instances wherein the mutation in the gene structure leads to no detectable normal function of the gene. This form of mutation, i.e. “loss-of-function” mutation, may be categorized as amorphic mutation (where mutation leads to a complete loss of gene function) or hypomorphic mutation (where mutation results in the reduced function of the gene). In other instances, the effects lead to the so-called “gain-of-function”. In the latter, the mutation causes the gene to increase the gene function or to gain an atypically new function. There are three categories under the “gain-of-function” mutation: hypermorphic mutation, antimorphic mutation, and neomorphic mutation. In hypermorphic mutation, the mutation results in an increase in gene activity, such as the expression of mRNA or protein, with respect to the wild-type allele. An example of hypermorphic mutation is that in the dominant alleles of the C. elegans gene lin-12 involved in cell-fate determination. Increased gene dose of lin-12 results in more cells transforming to another cell type.