Molecular Basis of InheritanceNEET MCQs with solutions

Not quite — the answer is B.

The active repressor binds the operator and physically blocks RNA polymerase from transcribing the structural genes. The promoter is the RNA polymerase binding site; the regulatory gene produces the repressor but is not the repressor binding target.

Not quite — the answer is A.

Ribosomes are the molecular machines where mRNA codons are decoded and polypeptides are assembled. They are found free in cytoplasm or bound to rough ER, but translation always occurs on ribosomes.

Not quite — the answer is C.

In the Meselson-Stahl experiment, after one generation in 14N medium, each daughter DNA molecule contains the original 15N parental strand and a newly synthesised 14N strand. All molecules are therefore hybrid and appear at a single intermediate density band on caesium chloride density gradient centrifugation. This is the definitive evidence for semiconservative replication.

Not quite — the answer is C.

DNA ligase joins adjacent DNA fragments by sealing nicks in the phosphodiester backbone. Restriction endonucleases cut DNA at specific sequences, helicase unwinds the double helix and primase synthesises RNA primers during replication.

Not quite — the answer is A.

Degeneracy means several codons can specify the same amino acid. For example, leucine is coded by six codons. This reduces the mutational impact on protein sequence.

Not quite — the answer is A.

Sigma factor confers promoter specificity to the core RNA polymerase holoenzyme, enabling initiation at the correct site. Rho factor is involved in termination, not initiation.

Not quite — the answer is C.

Mice died when living R bacteria mixed with heat-killed S bacteria because DNA from dead S cells transformed R cells into virulent S type. Option D fails because heat-killed S alone cannot infect.

Not quite — the answer is B.

Chargaff found that in DNA, adenine content equals thymine and guanine equals cytosine — this complementarity became the chemical foundation of Watson-Crick base pairing. Option D uses uracil, which is RNA-specific.

Not quite — the answer is A.

DNA wraps around histone proteins forming nucleosomes, enabling compaction of eukaryotic DNA inside the nucleus.

Not quite — the answer is A.

In semiconservative replication, each daughter DNA contains one parental strand and one new strand; conservative would keep both parental strands together — a common distractor.

Not quite — the answer is A.

Lac operon encodes enzymes specifically for lactose uptake and hydrolysis. Glucose is the preferred sugar but is not regulated by the lac operon.

Not quite — the answer is A.

Alec Jeffreys developed DNA fingerprinting in 1985 using polymorphism in minisatellite DNA sequences. Watson and Crick elucidated DNA structure; Sanger developed DNA sequencing.

Not quite — the answer is A.

The Human Genome Project (HGP) had sequencing and mapping of the entire human genome as its primary goal. The Human Proteome Project deals with proteins, not DNA sequences.

Not quite — the answer is A.

Bioinformatics combines biology, computer science, and mathematics to manage and interpret large biological datasets such as genome sequences. Biophysics and biochemistry do not involve computational sequence analysis.

Not quite — the answer is A.

The polysaccharide capsule gives S strain colonies a smooth appearance and protects bacteria from host immune destruction. R strain lacks this capsule and is non-virulent.

Not quite — the answer is B.

Recovery of living S bacteria from dead mice proved genetic material passed from heat-killed S to R cells, converting them permanently. Griffith did not identify the molecule — that was Avery et al.

Not quite — the answer is D.

Recovery of living virulent S bacteria from dead mice proved R bacteria were genetically transformed — not just transiently altered — by material from dead S cells.

Not quite — the answer is B.

Avery, MacLeod, and McCarty purified DNA, RNA, and protein separately from S strain and showed only DNA transformed R cells into S type.

Not quite — the answer is C.

DNase specifically degrades DNA; its addition destroyed transforming activity while protease and RNase treatments had no effect — proving DNA is the transforming principle.

Not quite — the answer is A.

Protease digests proteins completely; if protein were the transforming principle, transformation would stop. Since it continued, protein is ruled out. DNase result confirms DNA is the molecule.

Not quite — the answer is B.

DNA contains phosphorus (in phosphate backbone) but no sulfur, so ³²P labels DNA. Proteins contain sulfur in amino acids cysteine and methionine, so ³⁵S labels protein.

Not quite — the answer is D.

³²P-labelled DNA was injected into bacterial cells during infection; centrifugation sediments bacteria into the pellet, carrying the ³²P DNA with them.

Not quite — the answer is B.

Faithful semi-conservative replication ensures each daughter cell receives an identical copy of genetic information — this is the foundational replication criterion for genetic material.

Not quite — the answer is C.

Viruses like TMV and retroviruses have RNA genomes; RNA carries heritable sequence information and can be replicated by RNA-dependent RNA polymerase or reverse transcriptase in host cells.