Adaptive Mutations and Genotrophs

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
Earlier in Maternal Effects and Cytoplasmic Inheritance, we discussed induction of streptomycin resistant (sr)and streptomycin dependent (sd)mutants in Chlamydomonas. Similar mutations are induced in bacteria in culture media. However, in the beginning these observations led some workers to believe that the medium selectively induced these adaptive (or described as postadaptive)mutations. However, with the help of several studies in bacteriophages conducted by S.E. Luria and M. Delbruck (Luria won Nobel Prize for medicine in the year 1975, with A.D. Hershey and R. Dulbecco), it could be demonstrated that the mutations were already present and that these adaptive mutations were only selected in culture medium (consult next main topic for more details). If these mutations were to be post-adaptive, i.e. if these were selectively induced due to culture medium, this concept will be aLamarckian concept and we may have to accept inheritance of acquired characters.
However, in United Kingdom, Durrant in 1963 reported heritable changes in flax, induced due to different fertilizer regimes in which plants were grown. He obtained lines, which had large (L) and small (S) plants, which bred true to type, independent of fertilizer treatment, in subsequent generations. These were called genotrophs by him. It was shown that L plants had 16% more nuclear DNA than S plants, which suggested that these heritable changes giving rise to genotrophs were not true gene mutations but were due to a change leading to gene amplification.