Mutation - Classification of Mutation Types - By Effect On Function

By Effect On Function

  • Loss-of-function mutations are the result of gene product having less or no function. When the allele has a complete loss of function (null allele) it is often called an amorphic mutation. Phenotypes associated with such mutations are most often recessive. Exceptions are when the organism is haploid, or when the reduced dosage of a normal gene product is not enough for a normal phenotype (this is called haploinsufficiency).
  • Gain-of-function mutations change the gene product such that it gains a new and abnormal function. These mutations usually have dominant phenotypes. Often called a neomorphic mutation.
  • Dominant negative mutations (also called antimorphic mutations) have an altered gene product that acts antagonistically to the wild-type allele. These mutations usually result in an altered molecular function (often inactive) and are characterised by a dominant or semi-dominant phenotype. In humans, dominant negative mutations have been implicated in cancer (e.g. mutations in genes p53, ATM, CEBPA and PPARgamma. It was once thought that Marfan syndrome is an example of a dominant negative mutation occurring in an autosomal dominant disease where the defective glycoprotein product of the fibrillin gene (FBN1) antagonizes the product of the normal allele. However, this has since been deemed false and it has been shown that Marfan's is really a result of Haploinsufficiency because the absence of one normal allele causes the disease not the presence of an abnormal allele (i.e. Dominant negative).
  • Lethal mutations are mutations that lead to the death of the organisms which carry the mutations.
  • A back mutation or reversion is a point mutation that restores the original sequence and hence the original phenotype.

See also Behavior mutation.

Read more about this topic:  Mutation, Classification of Mutation Types

Famous quotes containing the words function and/or effect:

    The intension of a proposition comprises whatever the proposition entails: and it includes nothing else.... The connotation or intension of a function comprises all that attribution of this predicate to anything entails as also predicable to that thing.
    Clarence Lewis (1883–1964)

    Even a purely moral act that has no hope of any immediate and visible political effect can gradually and indirectly, over time, gain in political significance.
    Václav Havel (b. 1936)