Molecular Basis of Inheritance: NEET PYQ, 2018–2026

Q1 · Botany · Molecular Basis of Inheritance

A tRNA has the anticodon 3′-UAC-5′. Written 5′ to 3′, which codon on the mRNA does it read?

• A5′-UAC-3′
• B5′-CAU-3′
• C5′-GUA-3′
• D5′-AUG-3′

Q2 · Botany · Molecular Basis of Inheritance

After hybridisation with a radioactive probe, the membrane is exposed to X-ray film to produce an autoradiograph. Why do the dark bands on the film mark the positions of the probe-bound DNA fragments?

• AThe radioactive label on the probe emits radiation that darkens the film wherever the probe has bound to a fragment on the membrane
• BThe film absorbs the DNA fragments themselves, and thicker fragments produce darker bands
• CThe probe changes colour when it binds, and the film records the colour change
• DThe X-rays cut the probe into small pieces that stick to the film, marking the fragment positions

Q3 · Botany · Molecular Basis of Inheritance

A wild-type E. coli culture is grown on glucose and lactose together. Glucose is consumed first, and lac gene transcription stays low until glucose is largely depleted, even though lactose is present throughout. Which explanation best accounts for the low transcription during the glucose phase?

• AGlucose inactivates the lac repressor by covalently modifying it, so the repressor cannot bind the operator even when no inducer is present.
• BLactose cannot enter the cell while glucose is present, so no allolactose is formed and the repressor stays bound to the operator.
• CWhen glucose is present, cAMP levels are low, so the cAMP-CAP complex does not form and RNA polymerase binds the lac promoter weakly, reducing transcription even though the operator is free.
• DGlucose stimulates the degradation of the lac structural gene DNA, so there is less template available for transcription while glucose is present.

Q4 · Botany · Molecular Basis of Inheritance

What does the abbreviation SNP stand for in the study of human genome variation, and what is one major use of SNPs?

• ASingle nucleotide polymorphism; used as markers to trace genes linked to diseases
• BSingle nucleotide protein; used to make new enzymes
• CShort nuclear polypeptide; used to measure chromosome length
• DSingle nucleus polymerase; used to replicate whole chromosomes

Q5 · Botany · Molecular Basis of Inheritance

In prokaryotes, which feature of the nascent RNA causes transcription to terminate without the help of the rho factor?

• AA GC-rich hairpin structure followed by a run of uracil residues
• BA binding site for rho on the RNA that unwinds the RNA-DNA hybrid
• CBinding of the sigma factor to the RNA transcript
• DA poly-A tail added to the 3′ end

Q6 · Botany · Molecular Basis of Inheritance

During DNA replication, the lagging strand is synthesised as short Okazaki fragments, while the leading strand is synthesised as one continuous chain. Which statement correctly explains this difference?

• ADNA polymerase can only add nucleotides in the 5'→3' direction, and the lagging-strand template runs such that the new strand must grow away from the fork, so it is made in short pieces, each primed separately; DNA ligase later seals the nicks between fragments after the primers are replaced.
• BThe lagging strand is synthesised continuously in one piece, but helicase cuts it into fragments as it unwinds the helix, and DNA ligase then unwinds the fragments back into a double helix.
• CBoth strands are synthesised in short fragments at the same rate, and the leading strand is later joined by topoisomerase, which removes the gaps between fragments.
• DOkazaki fragments form because the lagging strand template is read 3'→5' by polymerase, which lets it skip the template at the fork; the gaps are then filled by RNA polymerase without any ligase step.

Q7 · Botany · Molecular Basis of Inheritance

Which codon codes for methionine and also acts as the initiator codon?

• AUAA
• BUGA
• CGUG
• DAUG

Q8 · Botany · Molecular Basis of Inheritance

In the Southern-blot step of DNA fingerprinting, the radioactive probe used for hybridisation is a single-stranded DNA sequence that is complementary to the repeat unit. Why must the probe be single-stranded?

• ASingle-stranded probes can base-pair with the complementary single-stranded target DNA on the membrane, which is essential for hybridisation.
• BSingle-stranded probes are more radioactive per molecule, so they give stronger autoradiographic signals.
• CSingle-stranded probes resist digestion by the restriction enzymes used earlier in the procedure.
• DDouble-stranded probes cannot be labelled, so single strands are the only form that can be detected on the autoradiograph.

Q9 · Botany · Molecular Basis of Inheritance

A probe made from a short core repeat sequence of 16 base pairs is hybridised to a Southern blot of genomic DNA digested with a restriction enzyme, and many bands appear in each lane. Which property of the probe most directly explains this?

• AThe probe is double-stranded, so it binds non-specifically to all DNA fragments on the membrane
• BThe restriction enzyme cuts within the probe sequence, producing extra fragments that all hybridise
• CThe core sequence is present in tandem arrays at many different chromosomal loci, so the probe hybridises to fragments from several of them
• DThe probe is too long to enter the gel, so it smears and is read as many bands

Q10 · Botany · Molecular Basis of Inheritance

During processing of eukaryotic hnRNA to mature mRNA in the nucleus, which segments are removed by splicing?

• AIntrons
• BExons
• CThe 5′ cap
• DThe poly-A tail