If a double stranded DNA has 20% of cytosine, what will be the percentage of adenine in it ?

Options

A. 0.2
B. 0.4
C. 0.3
D. 0.6

Answer

C

Explanation

(c) : According to Chargaff' s rule, the amount of adenine is always equal to that of thymine and the amount of guanine is always equal to that of cytosine, i.e., A=T and G=C. Also, the purines and pyrimidines are always in equal amounts,i.e.,A+G=T+C. Now , given dsDNA has 20% cytosine and hence guanine will be also 20% .
So, A+T must be 60% . Therefore, percentage of adenine would be `60//2=30%`