An alteration in the base sequence of a nucleic acid molecule is called:

The reason for the double helical structure of $DNA$ is the operation of

The $AT/GC$ ratio in human beings is (where $A = \text{adenine}$,$T = \text{thymine}$,$G = \text{guanine}$,$C = \text{cytosine}$)

Which of the following nitrogen bases,either of purine or pyrimidine,does $NOT$ contain an $-NH_2$ group attached to its ring?

The type of bond connecting two nucleotides is

Which of the following is $NOT$ a salient feature of the Watson and Crick model for $DNA$?