Genetics - A. V. Sivolob 2008

Variability of Genetic Material
Molecular Mechanisms of Mutational Variability

Mutational changes stem from rearrangements in the DNA nucleotide sequence caused by chemical modifications of the molecule, tautomerization of nitrogenous bases, transposition of mobile elements (see Chapter 6), Integration of Foreign (e.g., viral) DNA, and errors during Replication and Repair. DNA damage itself does not constitute a mutation, but rather represents pre-mutational changes that are either corrected by repair systems or fixed in the DNA as Mutations. In other words, a mutation is a DNA sequence alteration that persists after repair and subsequent rounds of replication.

DNA damage can result from the byproducts of normal cellular METABOLISM as well as from external environmental factors. Endogenous and exogenous agents capable of damaging DNA are termed mutagens, and the process by which mutations arise is known as mutagenesis. Mutagenesis that occurs under natural conditions, where specific causes are generally difficult to identify, is referred to as spontaneous mutagenesis. When mutations are artificially induced (through the experimental application of Mutagenic Factors), it is called induced mutagenesis. The molecular mechanisms underlying DNA damage and its fixation as mutations are fundamentally similar for both types of mutagenesis.