In Mutations : 1. Morphological Level (Including Lethal Mutations)
and Mutations : 2. Biochemical Level (Biochemical and Microbial Genetics)
, we discussed mutations (both spontaneous and induced) either at the phenotypic level in terms of their ultimate effect on morphology or in terms of changes in enzymes, which are the
immediate products of gene activity and are responsible for the ultimate phenotype to which the mutant is assigned. Therefore, any heritable change in phenotype can be traced back, first to a change in a protein or enzyme and then to a change in concerned gene. The gene, as we know, is a segment of nucleic acid, usually DNA, but rarely RNA as in some plant and animal viruses (consult Chemistry of the Gene 1. Nucleic Acids and Their Structure
). Therefore, one would like to understand the changes in the gene at the level of nucleic acid molecules during induction of a mutation and the mechanism involved in bringing about these alterations. One may also study the changes due to mutations in proteins or enzymes, at the molecular level, particularly in terms of sequences, of amino acids. These aspects of mutations will be discussed in this section.