Adaptation and Mutation

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Chapter: Pharmaceutical Microbiology : Microbial Genetics and Variations

Adaptation refers to the adjustment of an organism, to change in internal or external conditions or circumstances.


Adaptation and Mutation

 

Adaptation refers to the adjustment of an organism, to change in internal or external conditions or circumstances.

 

Mutation means a permanent variation in genetic structure with offspring differing from parents in its characteristics and is, thus, differentiated from gradual variation through several generations.

 

In fact, the above two absolutely distinct and remarkable observations adequately gained cogni-zance even much before the emergence of ‘genetics’ as a highly prominent discipline in ‘molecular biology’, which evidently explained ‘adaptation’ as — ‘such environmental factors that may affect the bacterial behaviour’ ; and ‘mutation’ as — ‘such organism which give rise to bacteria’.

 

Examples : Various examples are as given under :

 

(a) For Adaptation. A particular bacterium which first failed to grow on a certain culture medium would do so after a certain lapse of time. This kind of adaptation was usually observed to take place with any slightest alteration in the genetic material.

 

(b) For Mutation. A particular ‘bacterial strain’ that initially had the ability to grow on lactose, but finally lost this ability altogether.

 

Eventually, it has been widely accepted that such mutations are invariably caused due to a definite change in either of the two following means, namely :

 

(i) alteration in the nucleotide sequence, and

 

(ii) loss of nucleotides in the DNA.

 

The above two modalities with regard to the nucleotides quite often lead to either absolute non-occurrence of synthesis, or synthesis of exclusively non-functional peptides. Interestingly, this ulti-mately gives rise to an observable change in the ‘phenotype’ of the organism.

 

One may define the ‘rate of mutation’ as — ‘the probability which a specific gene shall mutate each time a cell undergoes the phenomenon of ‘division’, and is usually, expressed as the negative exponent per cell division’.

 

Thus, mutation takes place almost spontaneously but the rate of spontaneous mutation is always found to be extremely small viz., 10– 6 to 10– 9 per cell division.

 

Example : In case, there exists only ‘one possible change’ in a million that a gene shall un-dergo mutation when a cell divides then the determined ‘rate of mutation’ will be 10– 6 per cell division.

 

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