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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