Spontaneous Vs Induced Mutations

Mutations : 1.  Morphological Level (Including Lethal Mutations)
Brief History
Range of Mutations
Stages of Which Mutations Occur
Types of Mutations
Spontaneous Vs Induced Mutations
Mutation Rates and Frequencies
Induced Mutations 
Detection of Mutations in Drosophila 
Detection of Mutations in Plants
Use of Microbial Systems to Assess Potency of Mutagens
Practical Applications of Mutations
Effect of Genotypes on Induction of Mutations (Mutator Gene and Paramutations)
Adaptive Mutations and Genotrophs
Mutations are rare events in nature and are then described as spontaneous mutations. Due to their rare occurrence, sometimes, it is difficult to identify and score them. This difficulty has been overcome by two methods : (i) Selective systems have been designed, which facilitate the selection of mutants against normal wild type, as in case of biochemical, resistance and conditional mutations, where under certain conditions only mutants will grow permitting selection of one mutant among even a million individuals. Most of the selective systems are used in microorganisms and are discussed in the next main topic, (ii) Induced mutations are used, when selective systems are not available and therefore, frequency of mutations need to be increased artificially, to allow convenient identification and scoring of mutations.