Question

if 35% of an organisms dna is thymine, what is the percentage of guanine?
a. 15%

b. 35%

c. 70%

d. 50%

Explanation:

Step1: Apply Chargaff's base pairing rule

In DNA, thymine (T) pairs with adenine (A), so %T = %A. Given %T = 35%, thus %A = 35%.

Step2: Calculate total of T and A

$\%T + \%A = 35\% + 35\% = 70\%$

Step3: Find remaining base percentage

Total DNA bases = 100%, so remaining percentage for guanine (G) and cytosine (C) is $100\% - 70\% = 30\%$.

Step4: Calculate guanine percentage

G pairs with C, so %G = %C. $\%G = \frac{30\%}{2} = 15\%$

Answer:

A. 15%