MUTATIONS

A mutation may be defined as a change in the genetic constitution from one stable state to another, and strictly speaking, can be either a chromosomal alteration or a point mutation (alteration in DNA). In a point mutation, the altered DNA produces a changed messenger RNA, and a corresponding change in the amino acid sequence in the polypeptide. It is in this sense that it is commonly used.

Mutations provide genetic variation which help evolution and are usually beneficial. However most mutations are random changes in a system which has already incorporated possible improvements, and are harmful. Any harmful mutation causing a deformity or disease, thereby reducing fertility will have a lesser chance of being passed to the next generation than its normal allele. It will be then selected against. Selection can be expressed mathematically as the probability of the mutant gene being passed on to the next generation, relative to that of the normal allele. On the other hand some mutations confer on the individual a distinct advantage. An example is the heterozygote advantage seen among sickle cell carriers (traits) who are resistant to falciparum malaria infections unlike its normal genotype. Unfortunately this mechanism provides a better chance of transmitting the sickle cell gene to the next generation.