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Molecular Basis of Inheritance — NEET Biology MCQs

30 questions written by hand against the NCERT chapter. Every wrong option is explained, not just the right one.

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Sample questions from this chapter

Which components must be joined to make a DNA nucleotide?
  1. Nitrogenous base, deoxyribose and phosphate ✓
  2. Amino acid, ribose and phosphate
  3. Base and sugar only
  4. Deoxyribose and peptide
Answer: A. A base attaches to 1′ carbon of deoxyribose and phosphate to 5′ carbon, forming a deoxyribonucleotide. Polynucleotides then use 3′–5′ phosphodiester bonds.
Why not B: An amino acid belongs to proteins, and ribose would identify RNA rather than DNA.
Why not C: Base plus sugar is a nucleoside; phosphate converts it to a nucleotide.
Why not D: Peptide bonds join amino acids and are absent from the nucleotide backbone.
Heavy-nitrogen bacteria are shifted to light medium. After one division, DNA forms one intermediate-density band. Which model is supported?
  1. Conservative replication with separate heavy and light bands
  2. Random mutation of nitrogen atoms
  3. Semiconservative replication producing hybrid duplexes ✓
  4. Dispersive protein synthesis
Answer: C. Every first-generation duplex contains one ¹⁵N parental strand and one ¹⁴N new strand, giving uniform intermediate density. The second generation adds a light band.
Why not A: Conservative copying predicts an intact heavy parental duplex plus a fully light daughter after one generation.
Why not B: Isotope distribution follows templated synthesis, not chemical conversion of nitrogen.
Why not D: The density measurement concerns extracted DNA, and later generations distinguish replication models.
A double-stranded DNA sample contains 20% cytosine. What percentages of guanine and adenine should it contain?
  1. G equals C, while A and T divide the remaining 60% equally ✓
  2. Guanine exceeds cytosine by 10 percentage points, leaving adenine at 20%
  3. Guanine matches cytosine at 20%, while adenine is also 20% and thymine takes the remainder
  4. The two purines, adenine and guanine, each account for 30%
Answer: A. C=G=20%, leaving 60% for A+T; therefore A=T=30%. Complementarity converts one base measurement into the full composition.
Why not B: Chargaff pairing requires G to equal C, not A.
Why not C: After 40% G+C, the remaining 60% must be shared equally by A and T.
Why not D: Purines do not equal one another individually; A pairs with T and G with C.

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Questions

How many NEET questions are there on Molecular Basis of Inheritance?

This chapter test has 30 questions — 10 easy, 14 medium and 6 hard — all written against the NCERT Class 12 chapter.

Is this NEET Biology chapter test free?

Yes. Every chapter test is free with no login. The only paid thing on the site is the full-length 90-question Biology mock and its all-India rank.

Do the questions explain the wrong options?

Yes — every distractor carries its own explanation naming the specific misconception that makes a student pick it. That is the part most question banks skip, and it is the part that changes your next attempt.