Introduction

Genes may be transformed by spontaneous mutations, which occur at a low frequency in the range of 1 in every 2 × 10-4 to 4 × 10-10 meiotic divisions. Agents such as UV light, X-rays and certain chemicals known as mutagens increase the frequency of mutation. Mutations involve changes in the structure of DNA and hence the information coded in the DNA sequences. Different types of changes can occur such as the removal or addition of a base, or the inversion or transposition of a segment of DNA. Mutation is generally thought of as a random process, although certain positions in DNA may be more sensitive to change. Because of the random nature of any change most mutations are detrimental to the organism concerned. It is somewhat analogous to making a random replacement of a component in a computer; it is much more likely that the computer will perform less well, than that it will show additional capabilities. Very occasionally mutants may produce an improved genotype that will have a selective advantage in the environment. This is of great importance in the process of evolution.

Many mutations are pleiotropic, that is, they are wide ranging in their effects on the phenotype, and it is in most cases difficult to establish the nature of the primary effect.