Molecular Basis of Inheritance Question 9
9. 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 $17 %, A 16.5 %$, T $32.5 %$
(b) G $17 %, A 33 %$, T $33 %$
(c) G $8.5 %$, A $50 %$, T $24.5 %$
(d) G $34 %$, A $24.5 %$, T $24.5 %$
Show Answer
Answer : b
Hints & Solution
(b) Chargaff’s rule states that $A=T$ and $G$ $\equiv C$. The molar amount of adenine $=$ molar amount of thymine. The molar amount of guanine $=$ molar amount of cytosine. Hence, $G$ is $17 %, \quad$ so, $C=17 %$ $ A=33 %, \quad \text{ so, } T=33 % $
