Question
Biology Question on the molecular basis of inheritance
In sea urchin DNA, which is double stranded, 17% of the bases were shown to be cytosine. The percentages of the other three bases expected to be present in this DNA are
A
G 17%, A 33%, T 33%
B
G 8.5%, A 50%, T24.5%
C
G 34%, A 24.5%, T24.5%
D
G 17%, A 16.5%, T 32.5%.
Answer
G 17%, A 33%, T 33%
Explanation
Solution
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. 374 i.e.y 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 17% cytosine and hence guanine will be also 17%. So, A + T must be 66% Therefore, percentage of adenine or thymine would be 66/2 = 33%.