NEET BIOLOGY

GENETICS AND EVOLUTION

MOLECULAR BASIS OF INHERITANCE

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
Thymine makes up 42% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be cytosine?
A
42%
B
31%
C
16%
D
8%
Explanation: 

Detailed explanation-1: -Cytosine makes up 42% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine? 8% (In this example cytosine makes up 42%, which means that guanine also makes up 42%. So 84% of the DNA is a G-C base pair.

Detailed explanation-2: -Thymine (T) makes up 28% of the nucleotides in a sample of DNA from an organism.

Detailed explanation-3: -Therefore, Guanine would be 20% and total of G+C = 40% and hence A+T would be 60% that is 30% each. Hence, option C is correct answer.

Detailed explanation-4: -Chargaff’s rules explained that adenine always pairs with thymine and cytosine always pairs with guanine in a DNA molecule. Since adenine pairs with thymine, for every adenine base there will also be one thymine base. Thus, a sample with 15% adenine must also have 15% thymine.

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