XamBaaz
Log in

Molecular Basis of Inheritance — Class 12 MCQs with Answers

Class 12 CBSE Biology · Chapter 5

90 practice questions · 30 Easy · 30 Medium · 30 Hard · Updated

Jump to the 6 solved questions

Practise the most important Class 12 CBSE Biology questions from Chapter 5, "Molecular Basis of Inheritance". You get 9 timed quizzes made from 90 NCERT-based MCQs, with answers and explanations. The questions are split into 30 Easy, 30 Medium and 30 Hard. Warm up on the basics, then move on to the exam-level questions that top scorers in CBSE & Maharashtra HSC Board exams, MHT-CET and NEET UG get right.

To score well in "Molecular Basis of Inheritance", focus on diagrams, key terms and knowing NCERT line by line. Each MCQ here is timed and uses exam-style marking (+4 correct, −1 wrong, 0 skipped). This helps you stay accurate when time is short, just as real papers need. Every question has a short explanation, so a wrong answer becomes a quick lesson. It is the fastest way to fix gaps before a test.

Use this chapter for focused revision. Start with the Easy set to check your basics on Molecular Basis of Inheritance, then move to Medium and Hard to practise applying them. Your accuracy, streaks and XP save automatically. This chapter also adds to your overall Class 12 Biology mastery score. Try the 6 sample questions below: tap an option to see the answer and a worked explanation. Sign in free to start practising.

Molecular Basis of Inheritance — important questions & MCQs with answers (Class 12 Biology)

6 solved questions from this chapter's difficulty levels, each with its answer and explanation. Tap an option to check yourself.

0 of 6 answered

  1. Q1 of 6Easy

    DNA double helix model proposed by:

    Show answer

    Answer: Watson and Crick

    Explanation: Watson and Crick built the double-helix model in 1953 using Rosalind Franklin's X-ray diffraction photo 51; Franklin generated the key data but is often left out of this answer.

  2. Q2 of 6Easy

    Central dogma:

    Show answer

    Answer: DNA → RNA → Protein

    Explanation: The central dogma states DNA to RNA to Protein: transcription copies DNA into RNA, translation reads RNA into protein. Information never flows from protein back into DNA or RNA.

  3. Q3 of 6Medium

    DNA replication is:

    Show answer

    Answer: Semiconservative

    Explanation: Meselson and Stahl showed replication is semiconservative: each daughter duplex keeps one parental strand and gains one newly synthesised strand, ruling out conservative or dispersive models.

  4. Q4 of 6Medium

    Codon is:

    Show answer

    Answer: Triplet of bases coding for one amino acid

    Explanation: A codon is a triplet of three consecutive mRNA bases specifying one amino acid or a stop signal; with 4 bases at each of 3 positions, 4³ = 64 codons exist, not one base per amino acid.

  5. Q5 of 6Hard

    PCR is used to:

    Show answer

    Answer: Amplify DNA in vitro

    Explanation: PCR (polymerase chain reaction) amplifies a specific DNA segment exponentially in vitro using heat-stable Taq polymerase and repeated denature-anneal-extend cycles; it does not sequence or cut DNA.

  6. Q6 of 6Hard

    Lac operon model proposed by:

    Show answer

    Answer: Jacob and Monod

    Explanation: Jacob and Monod proposed the lac operon model in 1961 to explain inducible gene regulation in E. coli, where lactose switches on the structural genes z, y and a.

Molecular Basis of Inheritance notes: key concepts (Class 12 Biology)

Molecular basis of inheritance: DNA as the genetic material (Griffith, Hershey-Chase), the Watson-Crick double helix and Chargaff's rule, DNA packaging into nucleosomes, semiconservative replication, transcription, the genetic code, translation, the lac operon, and the Human Genome Project and DNA fingerprinting.

DNA double helix
Two antiparallel strands in a right-handed helix; sugar-phosphate backbone outside, base pairs (A=T, G≡C) inside. B-DNA has ~10 bp per 3.4 nm turn.
The DNA double helix drawn lying on its side: two strands twisting round a common axis, with base pairs as rungs between them. The strands are antiparallel: one runs 5′ on the left to 3′ on the right, the other 3′ on the left to 5′ on the right. The sugar-phosphate backbones are outside, the base pairs inside: A pairs with T by two hydrogen bonds (A=T) and G with C by three (G≡C). One full turn, the pitch, is 3.4 nm and holds about 10 base pairs, 0.34 nm apart.
Chargaff's rule
In any double-stranded DNA, adenine equals thymine and guanine equals cytosine (A=T, G=C), so purines equal pyrimidines (A+G = T+C).
Nucleosome
Repeating unit of chromatin — about 200 bp of DNA wrapped around a histone octamer; histones are positively charged (rich in lysine, arginine).
Transforming principle
Griffith showed a heat-killed virulent strain could transform a live avirulent one; Avery, MacLeod and McCarty identified the transforming agent as DNA.
Hershey-Chase experiment
Using radiolabelled phages (³²P DNA, ³⁵S protein), showed only DNA (³²P) entered bacteria — confirming DNA is the genetic material.
Semiconservative replication
Each daughter DNA keeps one old and one new strand; proved by Meselson-Stahl with ¹⁵N/¹⁴N density-gradient centrifugation. DNA polymerase builds new strands.
Semiconservative replication. A parent DNA molecule of two old strands, both drawn dark blue, separates, and each old strand serves as the template for a new strand, drawn light amber. The result is two daughter DNA molecules, and each one keeps one old (parental) strand and one newly made strand.
Transcription
Synthesis of RNA from a DNA template strand (read 3′→5′) by RNA polymerase; eukaryotic hnRNA is capped, tailed and spliced to remove introns.
A transcription unit in DNA: a promoter at the start, the structural gene in the middle and a terminator at the end. The coding strand runs 5′→3′ and the template strand runs 3′→5′. RNA polymerase sits on the gene and moves along the template strand, making mRNA in the 5′→3′ direction; the mRNA trails behind it from its 5′ end and has the same sequence as the coding strand (with U for T).
Genetic code
Triplet codons on mRNA specify amino acids; 61 sense + 3 stop codons. It is degenerate, non-overlapping, universal and comma-less; AUG is the start codon.
Translation
Assembly of a polypeptide on the ribosome; tRNA (the adapter) brings amino acids by codon-anticodon pairing; rRNA is the peptidyl transferase (a ribozyme).
lac operon
Jacob-Monod model of an inducible operon; lactose (inducer) inactivates the repressor so RNA polymerase transcribes the z, y, a genes (β-galactosidase etc.).
The lac operon in two states. DNA carries the regulator gene i, then the promoter p, the operator o and the structural genes z, y and a. Top, no lactose: the i gene makes the repressor, which binds the operator, so RNA polymerase at the promoter cannot transcribe and the operon is off. Bottom, lactose present: lactose, the inducer, binds the repressor and inactivates it, so it leaves the operator and RNA polymerase transcribes z, y and a into mRNA (for β-galactosidase, permease and transacetylase).
Central dogma
Flow of information DNA → RNA → protein. Reverse transcription (RNA → DNA) by reverse transcriptase in retroviruses is an exception.
Human Genome Project
1990-2003 project that sequenced the human genome of 3164.7 million bp; the total number of genes is estimated at about 30,000, and less than 2% of the genome codes for proteins.
DNA fingerprinting
Identifies individuals from variation in repetitive VNTR sequences; developed by Alec Jeffreys. Used in paternity and forensic testing.
Okazaki fragments
Short DNA pieces made discontinuously on the lagging strand (synthesis is 5′→3′ only) and later joined by DNA ligase; the leading strand is continuous.
A replication fork. The parent DNA on the right unwinds and its two old strands, drawn blue, separate. New DNA, drawn amber, is made only in the 5′→3′ direction by DNA polymerase. On the upper template (3′→5′) the leading strand is made continuously towards the fork. On the lower template (5′→3′) the lagging strand is made away from the fork in short pieces, the Okazaki fragments, whose arrows point away from the fork; DNA ligase joins the fragments.
6 formulas and exam tips — free with sign-in.

Start this chapter free

You have 6 to try above. Sign in with Google (no card needed). You get 1 Easy + 1 Medium quiz on every chapter, free for good (up to 6 quizzes a day) — plus a free Hard quiz when you score 70%+ on a Medium quiz (1 per subject), and the formulas & exam tips.

This chapter has 90 questions (30 Easy · 30 Medium · 30 Hard), with timed scoring and instant feedback. The rest unlock with the ₹1,999/year plan.

Start with the questions above. The full quiz opens here after.

Molecular Basis of Inheritance — FAQs

What are the key concepts in Class 12 Biology Molecular Basis of Inheritance?+

Molecular basis of inheritance: DNA as the genetic material (Griffith, Hershey-Chase), the Watson-Crick double helix and Chargaff's rule, DNA packaging into nucleosomes, semiconservative replication, transcription, the genetic code, translation, the lac operon, and the Human Genome Project and DNA fingerprinting. Key ideas include DNA double helix, Chargaff's rule, Nucleosome, Transforming principle, Hershey-Chase experiment, Semiconservative replication.

What does Class 12 Biology Chapter 5 (Molecular Basis of Inheritance) cover on XamBaaz?+

It has 90 NCERT-based MCQs on "Molecular Basis of Inheritance": 30 Easy, 30 Medium and 30 Hard. Together they make 9 timed quizzes, and you never get the same set twice. Every question has an instant explanation. They help you prepare for CBSE & Maharashtra HSC Board exams, MHT-CET and NEET UG.

Are these "Molecular Basis of Inheritance" questions free to practise?+

Yes. Sign in with Google to practise "Molecular Basis of Inheritance" free. Full unlimited access is ₹1,999/year. One year from the day you pay. Class 12 is your last school year, so your class stays as it is. No chapter is charged separately.

How should I revise "Molecular Basis of Inheritance" for the exam?+

Start with the Easy quiz to check your basics, then try Medium and Hard to practise applying them. There are 9 timed quizzes on this chapter, so you can come back for a fresh set instead of one you have seen. Read each explanation, retry the questions you miss, and track your accuracy until it stays high.

Are these "Molecular Basis of Inheritance" MCQs available with answers?+

Yes. 6 sample questions are on this page with answers: tap an option, or "Show answer", to see the correct option and a step-by-step explanation. Sign in free with Google to start practising, with instant scoring.

Is there negative marking in the "Molecular Basis of Inheritance" quizzes?+

Yes. The timed quizzes use exam-style marking: +4 for a right answer, −1 for a wrong one and 0 for a skip, the same negative marking as NEET UG. MHT-CET and CBSE board papers have no negative marking. Our mocks for those are scored their way.

What are the important questions from Molecular Basis of Inheritance (Class 12 Biology)?+

The questions that matter most test DNA double helix, Chargaff's rule, Nucleosome, Transforming principle, Hershey-Chase experiment, Semiconservative replication. This page shows 6 solved important MCQs with answers and explanations. Sign in to practise all 90 questions on the chapter as timed quizzes.

Is there an online quiz for Molecular Basis of Inheritance?+

Yes — Class 12 Biology Molecular Basis of Inheritance has timed online quizzes at Easy, Medium and Hard levels, with instant scoring and a worked explanation on every question. The first quiz on the chapter is free.

Are there question answers and extra questions for Molecular Basis of Inheritance (Class 12 Biology)?+

Yes. This page has 6 solved questions on Molecular Basis of Inheritance, each with the correct answer and a short explanation. Sign in to practise all 90 questions on the chapter as timed quizzes.

More Class 12 Biology chapters

Class 12 — other subjects

← All Class 12 Biology chapters
🦅 One new exam question every day on Instagram — Follow @xambaaz