Question

Which among the following is the exact ratio of guanine to cytosine in a DNA double helical structure?

(a) 3:2

(b) 2:1

(c) 1:3

(d) 1:1

The question was asked by my college professor while I was bunking the class.

Query is from Structure of a Polynucleotide Chain in division Molecular Basis of Inheritance of Biology – Class 12

Answer 1

Correct choice is (d) 1:1

For explanation I would say: The ratio of the purines (adenine and guanine) to the pyrimidine (thymine and cytosine) should always be equal to 1:1. This is in accordance to the Chargaff’s rule. The ratio of 1:1 is also based on the base pair rule.