### Neet Solved Paper 2015 Question 79

##### Question: 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

#### Options:

A) G/34%, A/24.5%, T/24.5%

B) G/17%, A/16.5%, T/32.5%

C) G/17%, A/33%, T/33%

D) G/8.5%, A/50%, T/24.5%

## Show Answer

#### Answer:

Correct Answer: C

#### Solution:

Chargaffs rule states that purine and pyrimidine base paires are present in equal amount, i.e. A = T, G = C. (A + T) = (G + C)

$ \therefore $ $ \frac{A+T}{G+C}=1 $ Cytosine = 17% If $ A+G+C+T=100 $ and $ G=C,,A=T $ Then $ A+17+7+T=100 $

$ \therefore $ $ G=17 $% $ A+T+34=100 $ $ A+T=100-34 $ $ A+T=66 $ $ A=T=33=66 $%

Hence, if cytosine is 17%, then G = 17% A and T will be 33% each.