Sudha Bansode*
In most organisms genes are segments of DNA molecules. In the broad sense the term ‘Mutation' refers to all or any the heritable changes within the genome, excluding those resulting from incorporation of genetic material from other organisms. A mutation is an abrupt qualitative or quantitative change within the genetic material of an organism. Mutations may be intragenic or intergenic. Intragenic mutations or point mutations include alterations within the structure of the DNA molecule within a gene. In a point mutation there is a change in the normal base sequence of the DNA molecule. This change results in a modification of the structural characteristics or enzymatic capacities of the individual. The unit of gene mutation is the muton. This may consist of one or many nucleotide pairs. Intergenic mulations, of which chromosomal changes in structure are examples, involve long regions of DNA, i.e. many genes. These include deletion or addition of segments of chromosomes, resulting in deficiency and duplication respectively. In large deletions a base sequence corresponding to an entire polypeptide chain is sometimes lost. Such mutations are very useful in genetic mapping.