Question

In one polynucleotide strand of a DNA molecule the ratio of A + T/G + C is 0.3, What is the A + G/T + C ratio of the entire DNA molecule?

• A. $0.6$
• B. $0.3$
• C. $1$
• D. $1.2$

Answer 1

The correct option is C $1$

According to Chargaff’s rules (1950), purine and pyrimidine base pairs are present in equal amounts in a DNA molecule
i.e., $[A+G]=[T+C]\text{or}\left[\frac{A+G}{T+C}\right]=1$.

A + T/G + C ratio is species specific and here mentioned to be 0.3.

While A + G/T + C is the ratio which is constant for all double-stranded DNA and its value is 1 because in a ds-DNA Adenine will always bind to Thymine so A=T while Guanine will always bind to Cytosine so G=C and Purine will always be equal to pyrimidines according to Chargaff rule.
So, the correct answer to the question is '1'.