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MUTATION

Mutation is a phenomenon which results in alteration of DNA sequencesand consequently results in changes in the genotype and the phenotypeof an organism. In addition to recombination, mutation is another phenomenon that leads to variation in DNA. One DNA helix runs continuously fromone end to the other in each chromatid, in a highly supercoiled form. Therefore loss (deletions) or gain (insertion/duplication) of a segment of DNA, result in alteration in chromosomes. Since genes are known to belocated on chromosomes, alteration in chromosomes results inabnormalities or aberrations. Chromosomal aberrations are commonly observed in cancer cells.In addition to the above, mutation also arise due to change in a single base pair of DNA. This is known as point mutation. A classical example of such a mutation is sickle cell anemia. Deletions and insertions of basepairs of DNA, causes frame-shift mutations (see Chapter 6). The mechanism of mutation is beyond the scope of this discussion, at this level. However, there are many chemical and physical factors that induce mutations. These are referred to as mutagens. UV radiations cancause mutations in organisms – it is a mutagen
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