🔬 Biology · Class 12 · NEET
Molecular Basis of Inheritance - Practice Questions with Answers 75 free MCQs on Molecular Basis of Inheritance, each with its own worked answer and explanation. DNA structure, replication, transcription, translation, the genetic code, and gene regulation (lac operon). The single most important chapter for NEET molecular biology.
Take the timed Molecular Basis of Inheritance chapterwise test → 75 practice questions on Molecular Basis of Inheritance , sorted Easy → Hard. Try each one first, then open its answer page for the worked explanation. Want the full theory first? Read the Molecular Basis of Inheritance notes .
The Replication Fork helicase (unwinds fork) leading strand (continuous, 5'→3') lagging strand: Okazaki fragments (discontinuous) Helicase unwinds the double helix at the replication fork; one new strand (leading) is synthesised continuously toward the fork, while the other (lagging) must be made in short, separate Okazaki fragments because DNA polymerase only adds nucleotides 5'→3'.
Easy - 25 questions Q2.
Griffith performed his transformation experiments using the bacterium:
A Streptococcus pneumoniaeB Escherichia coli strain KC Salmonella typhimuriumD Bacillus subtilis strainShow answer & explanation →
Q4.
A nucleoside is formed by joining a nitrogenous base with:
A a phosphate group onlyB two phosphate groupsC a base and a phosphateD a pentose sugarShow answer & explanation →
Q6.
Who proposed the double helix model of DNA?
A Meselson and StahlB Watson and CrickC Jacob and MonodD Hershey and ChaseShow answer & explanation →
Q8.
The two strands of the DNA double helix are arranged:
A Parallel to each otherB Antiparallel to each otherC Perpendicular to each otherD Randomly orientedShow answer & explanation →
Q9.
Histone proteins are rich in which type of amino acids?
A Acidic amino acidsB Basic amino acidsC Sulphur-containing amino acidsD Aromatic amino acidsShow answer & explanation →
Q10.
DNA replication is described as semiconservative because:
A Both resulting daughter molecules consist largely of newly synthesized strandsB Each daughter molecule retains one parental strand and gains one new strandC Half of the nitrogenous bases are conserved while the other half are replacedD Mainly one of the two daughter molecules contains any original parental DNAShow answer & explanation →
Q11.
Which experiment provided direct evidence for semiconservative DNA replication?
A Griffith's transformation experimentB Hershey-Chase experimentC Meselson-Stahl experimentD Avery-MacLeod-McCarty experimentShow answer & explanation →
Q12.
Which enzyme unwinds the DNA double helix at the replication fork?
A DNA polymeraseB HelicaseC LigaseD PrimaseShow answer & explanation →
Q13.
Which enzyme joins Okazaki fragments to form a continuous DNA strand?
A DNA polymeraseB RNA polymeraseC DNA ligaseD TopoisomeraseShow answer & explanation →
Q14.
According to the central dogma of molecular biology, genetic information flows:
A Protein to RNA to DNAB RNA to DNA to ProteinC DNA to RNA to ProteinD DNA to Protein to RNAShow answer & explanation →
Q15.
Which enzyme catalyses transcription?
A DNA polymeraseB RNA polymeraseC Reverse transcriptaseD DNA ligaseShow answer & explanation →
Q16.
The DNA strand that is actually copied during transcription is called the:
A Coding strandB Template strandC Leading strandD Sense strandShow answer & explanation →
Q19.
Which molecule acts as the adaptor between mRNA codons and amino acids during translation?
A rRNAB tRNAC hnRNAD snRNAShow answer & explanation →
Q20.
In the lac operon, which gene codes for beta-galactosidase?
A The i geneB The z geneC The y geneD The a geneShow answer & explanation →
Q21.
DNA fingerprinting relies mainly on variation in which type of DNA sequence?
A Coding exonsB Satellite DNA (VNTRs)C Promoter sequencesD tRNA genesShow answer & explanation →
Q22.
The molecule that carries the hereditary information in most organisms is:
A DNAB proteinC carbohydrateD fatShow answer & explanation →
Q23.
The abbreviation DNA stands for:
A deoxyribonucleic acidB dinucleic acidC diribose acidD double nucleic acidShow answer & explanation →
Q24.
The repeating monomer units that make up DNA are called:
A nucleotidesB amino acidsC fatty acidsD simple sugarsShow answer & explanation →
Medium - 25 questions Q26.
Griffith's transforming principle was later shown to be DNA by:
A Hershey and Martha ChaseB Avery, MacLeod and McCartyC Watson, Crick and WilkinsD Meselson and F. StahlShow answer & explanation →
Q27.
The histone octamer of a nucleosome is made up of:
A two molecules of histone H1 onlyB four different histones, one eachC two each of H2A, H2B, H3 and H4D eight molecules of a single histoneShow answer & explanation →
Q28.
In a typical nucleosome, the length of DNA wrapped around the histone core is about:
A 50 base pairsB 100 base pairsC 1000 base pairsD 200 base pairsShow answer & explanation →
Q29.
The 5 prime cap added during processing of eukaryotic mRNA is:
A methyl guanosine triphosphateB a long poly-adenine tailC a single uracil residueD a methylated thymine baseShow answer & explanation →
Q30.
The enzyme that attaches the correct amino acid to its tRNA is:
A peptidyl transferase enzymeB aminoacyl-tRNA synthetaseC an RNA-dependent polymeraseD reverse transcriptase enzymeShow answer & explanation →
Q31.
Why is a primer required to start DNA replication?
A DNA polymerase is unable to unwind the double helix without a primer presentB DNA polymerase can only add nucleotides to an existing 3 prime OH endC Primers are required to supply the chemical energy needed for replicationD Primers function to protect newly synthesized DNA strands from nucleasesShow answer & explanation →
Q32.
Which enzyme synthesises the short RNA primer needed for DNA replication?
A HelicaseB PrimaseC LigaseD TopoisomeraseShow answer & explanation →
Q33.
On the lagging strand, DNA synthesis proceeds:
A Continuously in the same direction as the replication fork movementB Discontinuously, away from the replication fork, in short fragmentsC Without any RNA primerD In the 3 prime to 5 prime direction by DNA polymeraseShow answer & explanation →
Q34.
Which RNA polymerase in eukaryotes transcribes the precursor of mRNA (hnRNA)?
A RNA polymerase IB RNA polymerase IIC RNA polymerase IIID RNA polymerase IVShow answer & explanation →
Q35.
Splicing during mRNA processing refers to:
A Addition of a poly-A tail at the 3 prime endB Addition of a methyl guanosine cap at the 5 prime endC Removal of introns and joining of exonsD Conversion of mRNA back into DNAShow answer & explanation →
Q36.
The genetic code is described as degenerate because:
A Some codons fail to correspond to any specific amino acid residueB Most amino acids are specified by more than one codonC The genetic code differs noticeably between different organism lineagesD Codons physically overlap with each other along the mRNA strandShow answer & explanation →
Q37.
The wobble hypothesis explains how:
A How ribosomes physically move stepwise along the mRNA strandB A single tRNA can recognise more than one codon for the same amino acidC How RNA polymerase correctly selects the appropriate gene promoterD How spliceosomes remove introns from precursor hnRNA transcriptsShow answer & explanation →
Q38.
In the lac operon, what is the role of the inducer (allolactose)?
A It binds directly to RNA polymerase to switch on its activityB It binds to the repressor protein, preventing it from binding the operatorC It binds directly to the operator sequence itself to block transcriptionD It enzymatically degrades the repressor protein into inactive fragmentsShow answer & explanation →
Q39.
In the absence of lactose, the lac operon remains switched off because:
A RNA polymerase is degraded before it can bind the promoter regionB The repressor protein binds the operator and blocks transcriptionC The promoter sequence has been permanently deleted from the operonD The structural genes z, y, and a are entirely absent from the operonShow answer & explanation →
Q40.
The Human Genome Project revealed that the human genome contains roughly:
A Fewer than 30,000 to 25,000 genesB About 100,000 genesC About 250,000 genesD Exactly 46 genes, one per chromosomeShow answer & explanation →
Q41.
What proportion of the human genome consists of non-coding sequences?
A About 10%B About 50%C Over 90%D Almost 0%Show answer & explanation →
Q42.
Which scientist is closely associated with developing DNA fingerprinting techniques in India?
A Har Gobind KhoranaB Lalji SinghC Marshall NirenbergD G.N. RamachandranShow answer & explanation →
Q43.
Which feature of the genetic code means that a given codon always specifies the same amino acid?
A DegeneracyB UniversalityC Unambiguous natureD WobbleShow answer & explanation →
Q47.
The process by which a DNA molecule makes an exact copy of itself is:
A replicationB translationC transcriptionD mutationShow answer & explanation →
Q48.
The process of synthesising an RNA molecule from a DNA template is called:
A transcriptionB replicationC translationD mutationShow answer & explanation →
Q49.
The process of building a protein from the information in mRNA is called:
A translationB transcriptionC replicationD mutationShow answer & explanation →
Hard - 25 questions Q51.
The total length of DNA present in a typical human diploid cell is approximately:
A 0.22 millimetresB 22 centimetresC 2.2 metresD 22 metres longShow answer & explanation →
Q52.
Which observation provided evidence that RNA can serve as genetic material?
A Griffith's mouse transformationB the Meselson-Stahl experimentC the Hershey-Chase blender studyD reconstituted TMV infectivityShow answer & explanation →
Q53.
The genetic code is said to be comma-less, which means that:
A codons are read with no gaps between themB one codon can code for many amino acidsC a codon overlaps with the next codonD each codon needs a spacer base after itShow answer & explanation →
Q54.
In the poly-U experiment, Nirenberg and Matthaei found that UUU codes for:
A the amino acid prolineB the amino acid phenylalanineC a chain-terminating signalD the amino acid methionineShow answer & explanation →
Q55.
In eukaryotes, RNA polymerase III is responsible for transcribing:
A the precursor of mRNA (hnRNA)B ribosomal 28S and 18S rRNAC tRNA, 5S rRNA and snRNAsD all three classes of RNAShow answer & explanation →
Q56.
DNA polymerase synthesises new DNA strands in which direction relative to the template?
A It adds nucleotides only in the 5 prime to 3 prime direction on the new strandB It adds nucleotides only in the 3 prime to 5 prime direction on the new strandC It synthesises both strands in the 3 prime to 5 prime directionD Direction depends on which strand is being copiedShow answer & explanation →
Q57.
In the Meselson-Stahl experiment, after one round of replication in 14N medium, bacteria initially grown in 15N medium produced DNA that was:
A Largely light (14N-14N)B Largely heavy (15N-15N)C Hybrid density (15N-14N)D A mixture of light and heavy, with little hybridShow answer & explanation →
Q58.
Which statement about RNA polymerase in bacteria is correct?
A Three largely separate RNA polymerase enzymes transcribe rRNA, tRNA, and mRNA respectively in bacterial cellsB A single RNA polymerase, with the help of factors like sigma and rho, catalyses transcription of all RNA typesC RNA polymerase in bacteria highly requires a short RNA or DNA primer in order to begin transcriptionD RNA polymerase in bacterial cells is understood to synthesise new RNA strands in the 3 prime to 5 prime directionShow answer & explanation →
Q59.
Why does eukaryotic mRNA require extensive processing before translation, while bacterial mRNA generally does not?
A Bacterial cells are understood to largely lack ribosomes needed for translating any mRNA transcriptB Bacterial genes do not have introns and transcription/translation are not separated by a nuclear membraneC Eukaryotic mRNA transcripts are understood to rarely require any start codon before translation beginsD Bacterial RNA polymerase is understood to synthesise mainly tRNA molecules, rarely any mRNA transcriptsShow answer & explanation →
Q60.
If a region of the coding strand of DNA reads 5 prime-ATGCCG-3 prime, what is the sequence of the corresponding template strand and mRNA?
A Template: 3 prime-TACGGC-5 prime; mRNA: 5 prime-AUGCCG-3 primeB Template: 5 prime-TACGGC-3 prime; mRNA: 5 prime-UACGGC-3 primeC Template: 3 prime-ATGCCG-5 prime; mRNA: 5 prime-ATGCCG-3 primeD Template: 3 prime-TACGGC-5 prime; mRNA: 3 prime-AUGCCG-5 primeShow answer & explanation →
Q61.
Which of the following best explains why far fewer than 61 distinct tRNAs are sufficient to translate all sense codons?
A Many of the sixty-one possible sense codons are rarely actually used within real protein-coding genes under usual circumstancesB The wobble hypothesis allows flexible pairing at the third codon position, letting one tRNA read multiple synonymous codonsC Ribosomes are understood to be able to read certain codons directly without requiring any matching tRNA molecule according to most researchersD Stop codons are understood to be read and recognized by special dedicated tRNA molecules that get reused repeatedly in the majority of cases studiedShow answer & explanation →
Q62.
A mutation that converts the lac operon's operator sequence so the repressor can never bind would most likely result in:
A The operon would become largely switched off, even when lactose is present in the cellB Constitutive (continuous) expression of the z, y, and a genes regardless of lactose presenceC Complete and total loss of RNA polymerase's ability to bind to the operon's promoter regionD No change would occur, since the operator sequence does not affect transcription ratesShow answer & explanation →
Q63.
Which statement correctly distinguishes euchromatin from heterochromatin?
A Euchromatin is densely packed and transcriptionally active, while heterochromatin is loosely packed and transcriptionally inactive instead under typical conditionsB Euchromatin is loosely packed, stains light, and is transcriptionally active; heterochromatin is densely packed, stains dark, and is transcriptionally inactiveC Both forms of chromatin are equally condensed throughout, differing from one another mainly in their underlying base composition according to standard textbooksD Heterochromatin is understood to contain mainly RNA molecules within its structure, and no DNA whatsoever in general practice as commonly described in most textbook accountsShow answer & explanation →
Q64.
What is the key structural distinction between the coding strand and the template strand of a gene during transcription?
A The coding strand has the same base sequence as the mRNA (with T instead of U) and is not transcribed; the template strand is read by RNA polymeraseB The template strand is understood to usually contain more guanine bases overall than the corresponding coding strand according to conventional understandingC Mainly the coding strand of a gene is understood to be found and present specifically within eukaryotic genomes in routine practice overall in most casesD The coding strand of a gene is understood to be synthesised first chemically, before the template strand forms under typical conditions according to standard textbooksShow answer & explanation →
Q65.
Why is DNA replication confined largely to the S-phase of the cell cycle rather than continuing throughout interphase?
A DNA polymerase is only active during S-phase due to availability of dNTPs and coordinated licensing of replication originsB DNA molecules are understood to be physically incapable of being replicated anywhere outside the cell nucleus during normal conditionsC Histone proteins are understood to be largely absent from chromatin during every other phase of the cycle as generally observedD RNA polymerase is understood to actively block DNA polymerase activity during all other phases of the cell cycle in typical laboratory settingsShow answer & explanation →
Q66.
During DNA fingerprinting, why is a probe complementary to VNTR sequences used in the hybridisation step?
A VNTR regions are understood to be largely identical in sequence and length across all individuals, providing a control band under usual circumstances according to most researchersB VNTR regions vary in repeat number between individuals, so the probe binds to fragments whose size differs from person to person, producing a unique patternC VNTR sequences are understood to be located mainly within protein-coding exons of the genome, rarely elsewhere in the majority of cases studied as widely reportedD The hybridisation probe is understood to chemically destroy all non-VNTR DNA fragments before electrophoresis runs in standard practice under most conditions encounteredShow answer & explanation →
Q67.
Which of the following correctly orders the size relationship of repeating units along the chromatin fibre, from smallest to largest packaging level?
A Chromosome, then nucleosome, then chromatin fibre, then finally the DNA double helix itselfB DNA double helix, nucleosome, chromatin fibre (beads on string and higher coiling), chromosomeC Nucleosome, then chromosome, then the DNA double helix, then finally the chromatin fibre itselfD Chromatin fibre, then chromosome, then nucleosome, then finally the DNA double helix itselfShow answer & explanation →
Q68.
The sequence of three bases on mRNA that codes for one amino acid is called a:
A codonB whole geneC anticodonD operonShow answer & explanation →
Q69.
The double-helix model of DNA was proposed by:
A Watson and CrickB Gregor MendelC Charles DarwinD Jean LamarckShow answer & explanation →
Q70.
The two strands of a DNA molecule are held together by ___ bonds between the bases:
A hydrogenB peptideC ionicD strong covalentShow answer & explanation →
Q71.
The complete set of genetic material in an organism is called its:
A genomeB ribosomeC chromosomeD enzymeShow answer & explanation →
Q72.
The central dogma of molecular biology describes the flow of information from DNA to RNA to:
A proteinB fatC carbohydrateD waterShow answer & explanation →
Q73.
By Chargaff’s rule, in a DNA sample the amount of adenine equals the amount of:
A thymineB guanineC cytosineD uracilShow answer & explanation →
Q74.
The enzyme that builds an RNA strand during transcription is:
A RNA polymeraseB DNA ligaseC simple amylaseD stomach pepsinShow answer & explanation →
Q75.
A permanent change in the base sequence of DNA is called a:
A mutationB translationC transcriptionD replicationShow answer & explanation →