If Adenine makes 30% of the DNA molecule, what will be the percentage of Thymine, Guanine and Cytosine in it ?

The correct answer/option is T : 30 ; G : 20 ; C : 20.

To determine the percentage of Thymine (T), Guanine (G), and Cytosine (C) in a DNA molecule where Adenine (A) makes up 30%, we use Chargaff's Rules of base pairing.

Chargaff's rules state that in a double-stranded DNA molecule:
1. Adenine (A) always pairs with Thymine (T). Therefore, the percentage of Adenine is equal to the percentage of Thymine:
$A=T$
2. Guanine (G) always pairs with Cytosine (C). Therefore, the percentage of Guanine is equal to the percentage of Cytosine:
$G=C$

Additionally, the sum of all four nitrogenous bases in a DNA molecule must equal 100%:
$A+T+G+C=100\%$

Let's calculate the percentages step-by-step:

Step 1: Find the percentage of Thymine (T)
Since Adenine (A) is given as 30%:
$T=A=30\%$

Step 2: Find the combined percentage of Guanine (G) and Cytosine (C)
Subtract the percentage of Adenine and Thymine from the total 100%:
$G+C=100\%-(A+T)$
$G+C=100\%-(30\%+30\%)$
$G+C=100\%-60\%=40\%$

Step 3: Find the individual percentages of Guanine (G) and Cytosine (C)
Since Guanine and Cytosine pair with each other, they are present in equal amounts:
$G=C=\frac{40\%}{2}=20\%$

Thus, the percentages are:
Thymine (T) = 30%
Guanine (G) = 20%
Cytosine (C) = 20%