Which nitrogenous base is $NOT$ present in $DNA$?

$A$ distinct mechanism that usually involves a short segment of $DNA$ with a remarkable capacity to move from one location in a chromosome to another is called:

Select the correct statement from the following.

How many nucleotides are present in one turn of $DNA$ helix (in $pairs$)?

Continuity of life from generation to generation in organisms is maintained by which of the following?

Which of the following ratios is generally not constant for all given species?