Index >> Mutation

Mutation
In a species variations may be caused by changes in the environment, by changes in the heredity constitution or more commonly by a combination of both. If a variation appears only when the environment is changed and disappears when it is restored, it is not heritable and as it is not built into the genotype, it does not provide a permanent step on which evolutionary changes can be based. These are phenotypic variations and are known as modifications. They are defined as phenotypic differences between organisms of similar genotype. If, however, changes occur which are independent of the environment and heritable, they are liable to provide a permanent step on which evolutionary changes may be built. Such changes occur in the genome of an individual and may be caused by recombination or crossing over and mutation. Recombination usually causes no remarked variation because it merely redistributes existing genetic material among different individuals.