Mechanisms by which mutations can alter cellular function
Loss-of-function mutations cause a reduction or absence of normal function in the product of a gene.
When the mutant allele has a complete loss of function it is often called a null allele or an amorphic allele . Often, the phenotypes associated with loss-of-function mutations are recessive.
However, in haploinsufficiency, a heterozygous loss-of-function mutation is sufficient to cause a phenotypic abnormality or disease. Gain-of-function mutations alter the gene in such a way that its product gains either a new or abnormal function.
These mutations are usually associated with dominant phenotypes and are also called neomorphic mutations .
Dominant negative mutations modify a gene in such a way that its product antagonizes the function of the normal wild-type allele.
These mutations are also called antimorphic and cause alterations of molecular function, which generally lead to inactivation or gene function and are associated with dominant or semidominant phenotypes.
