Molecular Basis of Inheritance
23 solved NEET Biology previous year questions on Molecular Basis of Inheritance, each with the correct answer and a full explanation.
Q1
A segment of DNA has 120 adenine and 120 cytosine bases. The total number of nucleotides present in the segment is:
✓ Correct answer: d) 480
ExplanationAccording to Chargaff's rules, the amount of adenine is always equal to that of thymine, and the amount of guanine is always equal to that of cytosine, i.e., (120) and , therefore, the total number of nucleotides would be .
Q2
The process of translation is
✓ Correct answer: b) protein synthesis
ExplanationTranslation is the process where the information in messenger RNA (mRNA) is used to synthesize proteins.This process occurs in the ribosome, where transfer RNA (tRNA) reads the mRNA code and assembles amino acids in the correct sequence to form a protein.
Q3
Which one of the following is the genetic material of prokaryotic cell?
✓ Correct answer: a) Non-histonic double stranded DNA
ExplanationThe genetic material of a prokaryotic cell is: Option A: Non-histonic double stranded DNA Explanation: Prokaryotic cells contain double-stranded DNA that is not associated with histones.Unlike eukaryotic cells, prokaryotic DNA is circular and lacks histone proteins, which are present in eukaryotic chromosomes to help in DNA packaging.
Q4
Transformation experiment was first performed on which bacteria?
✓ Correct answer: b) Diplococcus pneumoniae
ExplanationCorrect Answer: B. Diplococcus pneumoniae Explanation: The transformation experiment was first performed by Frederick Griffith in 1928. He worked with two strains of Diplococcus pneumoniae (now known as Streptococcus pneumoniae): S strain (smooth, virulent) R strain (rough, non-virulent) Griffith discovered that the heat-killed S strain could transfer genetic material to the R strain, transforming it into a virulent form.This experiment was the first evidence of the transfer of genetic information (later identified as DNA).Incorrect Options: A. E. coli – Used in later experiments (e.g., Hershey-Chase), not Griffith’s.C. Salmonella – Not involved in the transformation experiment.D. Pasteurella pestis – Old name for Yersinia pestis (plague bacterium); unrelated. ✅ Final Answer: B. Diplococcus pneumoniae
Q5
Semi-conservative replication of DNA was first demonstrated in;
✓ Correct answer: a) Escherichia coli.
ExplanationThe classic Meselson–Stahl experiment (1958) proved semi-conservative DNA replication using heavy nitrogen (¹⁵N) in E. coli cultures.Hence, the first demonstration was in Escherichia coli.Other options: Streptococcus pneumoniae → Griffith & Avery (transformation) Salmonella typhimurium → Lederberg’s recombination studies Drosophila melanogaster → Morgan’s genetics work
Q6
Which one of the following is not a part of a transcription unit in DNA?
✓ Correct answer: a) The inducer
ExplanationA transcription unit in DNA consists of three main parts:1. Promoter – initiation site for RNA polymerase2. Structural gene – the region that is transcribed3. Terminator – signals the end of transcription The inducer is not a part of the DNA transcription unit.It is usually a small molecule (like lactose in lac operon) that regulates gene expression, not a DNA sequence.So, the correct answer is A.
Q7
Transformation was discovered by;
✓ Correct answer: c) Griffith.
ExplanationFrederick Griffith discovered the phenomenon of transformation in 1928 while working with Streptococcus pneumoniae bacteria.He showed that harmless bacteria could acquire virulence (ability to cause disease) by taking up genetic material from dead, virulent bacteria.This process is known as transformation.
Q8
Identify the correct order of organisation of genetic material from largest to smallest:
✓ Correct answer: b) Genome, chromosome, gene, nucleotide
ExplanationThe genome is described as the genetic information repository of an organism.The genetic material, i.e., DNA is packaged into thread-like structures called chromosomes.Gene is the segment of DNA that codes for the protein.Nucleotide is the building block of genetic material.Therefore, the correct order of organisation is: Genome - Chromosome - Gene - Nucleotide [New NCERT Class 12th Page No. 83]
Q9
Taylor conducted the experiments to prove semiconservative mode of chromosome replication on;
✓ Correct answer: b) Vicia faba.
ExplanationTaylor and his colleagues conducted experiments on root tip cells of Vicia faba (broad bean) to demonstrate the semiconservative mode of chromosome replication in eukaryotes.They used radioactive thymidine (^3H-thymidine) to label newly synthesized DNA and tracked it through successive cell divisions using autoradiography.The results showed that after one replication cycle, only one chromatid was labeled, and after two cycles, only half the chromatids were labeled — supporting semiconservative replication, where each new DNA molecule consists of one parental and one newly synthesized strand.In contrast, E. coli was used in Meselson and Stahl’s famous DNA replication experiment.
Q10
A molecule that can act as a genetic material must fulfill the traits given below, except;
✓ Correct answer: c) it should be unstable structurally and chemically.
ExplanationA genetic material must be structurally and chemically stable to preserve the integrity of genetic information across generations.It must also be capable of replication, expression (producing traits), and allowing slow, heritable variations for evolution.DNA fulfills all these criteria.An unstable molecule would degrade or mutate rapidly, disrupting genetic continuity.Therefore, instability is not a desirable trait for genetic material, making option C the correct answer as the exception among the listed traits.
Q11
The association of histone H1 with a nucleosome indicates that
✓ Correct answer: b) the DNA is condensed into a chromatin fibre
ExplanationNucleosomes are the structural units of chromatin, consisting of DNA wrapped around histone proteins.Histone H1 is a linker histone that binds to the DNA between nucleosomes, helping pack the chromatin into a more condensed form.Its association indicates a more compact form of DNA.Hence, the correct answer is option B.
Q12
E. coli has only base pairs and completes the process of replication within 18 minutes; then the average rate of polymerisation is approximately-
✓ Correct answer: d) 2000 base pairs/second
ExplanationE. coli that has only completes the process of replication within 18 minutes; that means the average rate of polymerisation has to be approximately 2000 bp per second.
Q13
The term 'Nuclein' for the genetic material was used by: [Re-NEET 2020]
✓ Correct answer: a) Miescher
ExplanationThe term "Nuclein" for the genetic material was first used by Friedrich Miescher in 1869 when he discovered the substance in the nucleus of white blood cells.This term was later changed to nucleic acid as the molecular structure of DNA was understood.
Q14
The first phase of translation is:
✓ Correct answer: b) Aminoacylation of tRNA
ExplanationIn the first phase of translation, amino acids are activated in the presence of ATP and linked to their cognate tRNA – a process commonly called as charging of tRNA or aminoacylation of tRNA.
Q15
Which of the following statements is correct?
✓ Correct answer: a) Adenine pairs with thymine through two H- bonds.
ExplanationIn the DNA double helix, base pairing occurs via hydrogen bonds: Adenine (A) pairs with Thymine (T) through two hydrogen bonds.Cytosine (C) pairs with Guanine (G) through three hydrogen bonds. [New NCERT Class 12th Page No. 81]
Q16
Ten E.coli with - dsDNA are incubated in medium containing nucleotide. After 60 minutes, how many E.coli cells will have DNA totally free from ?
✓ Correct answer: d) 60 cells
ExplanationThe bacterium E. coli can divide in every .In other words, after every 20 minutes, the number of cells becomes doubled.When -dsDNA is incubated in medium containing nucleotide, the first generation has intermediates only .Second generation (after 20 minutes) will produce two hybrid strands, i.e., in equal proportion, so the ratio is 1:1. Third generation (after 20 minutes) will produce 2 hybrid strands and 2 light strands containing only.Fourth generation (after 20 minutes) will produce 2 hybrid strands and 6 light strands.So, after 60 minutes there will be 6 light strands totally free from .Total number of E.coli cells cells cells.
Q17
Given below are two statements: Statement I : In prokaryotes, the positively charged DNA is held with some negatively charged proteins in a region called nucleoid. Statement II : In eukaryotes, the negatively charged DNA is wrapped around the positively charged histone octamer to form nucleosome. In the light of the above statements, choose the correct answer from the options given below : [NEET 2023]
✓ Correct answer: c) Statement I incorrect but Statement II is true.
ExplanationIn prokaryotes, such as, E. coli, though they do not have a defined nucleus, the DNA is not scattered throughout the cell.DNA (being negatively charged) is held with some proteins (that have positive charges) in a region termed as ‘nucleoid’.The DNA in nucleoid is organised in large loops held by proteins.In eukaryotes, this organisation is much more complex.There is a set of positively charged, basic proteins called histones.A protein acquires charge depending upon the abundance of amino acids residues with charged side chains.Histones are rich in the basic amino acid residues lysine and arginine.Both the amino acid residues carry positive charges in their side chains.Histones are organised to form a unit of eight molecules called histone octamer.The negatively charged DNA is wrapped around the positively charged histone octamer to form a structure called nucleosome.
Q18
Statement I: RNA mutates at a faster rate. Statement II: Viruses having RNA genome and shorter life span mutate and evolve faster. In the light of the above statements, choose the correct answer from the options given below.
✓ Correct answer: b) Both Statement I and Statement II are true.
ExplanationRNA mutates at a faster rate because it is unstable.Therefore, viruses having RNA genome and shorter life span allow them to mutate and evolve at faster rates.
Q19
What is the role of RNA polymerase III in the process of transcription in Eukaryotes?
✓ Correct answer: a) Transcription of tRNA, 5 srRNA and snRNA
ExplanationRNA polymerase III in eukaryotes is responsible for transcribing tRNA, 5S rRNA, and small nuclear RNAs (snRNA).It does not transcribe precursor mRNA or rRNA subunits like 28S, 18S, and 5.8S, which are transcribed by RNA polymerase I. RNA polymerase II is responsible for transcribing precursor mRNA.RNA polymerase I transcribes the major rRNAs (28S, 18S, and 5.8S).
Q20
How many different proteins does the ribosome consist of?
✓ Correct answer: d) 80
ExplanationThe ribosome is composed of approximately 80 different proteins, along with rRNA.These proteins are part of the large and small subunits of the ribosome, which work together during protein synthesis (translation).The small subunit contains about 30 proteins, while the large subunit contains around 50 proteins, contributing to the total of approximately 80 proteins.
Q21
Which of the following statement is correct regarding the process of replication in E.coli ? [NEET 2024]
✓ Correct answer: a) The DNA dependent DNA polymerase catalyses polymerization in 5' ' direction.
ExplanationDuring DNA replication in E. coli, the enzyme DNA-dependent DNA polymerase catalyzes the polymerization of deoxynucleotides in the 5′→3′ direction.This means that nucleotides are added to the 3′-OH end of the growing DNA strand.The leading strand is synthesized continuously in this direction, while the lagging strand is synthesized discontinuously, forming Okazaki fragments, which are later joined by DNA ligase.Thus, the correct option is A.
Q22
The lactose present in the growth medium of bacteria is transported to the cell by the action of: [NEET 2024]
✓ Correct answer: d) permease.
ExplanationIn the lac operon of bacteria, permease is responsible for transporting lactose into the bacterial cell.Beta-galactosidase (option B) is the enzyme that breaks down lactose into glucose and galactose once it has entered the cell, but it does not transport lactose.Permease specifically facilitates the transport of lactose across the cell membrane.
Q23
A transcription unit in DNA is defined primarily by the three regions in DNA and these are with respect to upstream and down stream end; [NEET 2024]
✓ Correct answer: a) Promotor, Structural gene, Terminator
ExplanationA transcription unit in DNA consists of three primary regions:1. Promoter: The region where RNA polymerase binds to initiate transcription.2. Structural gene: The region that codes for the RNA molecule to be transcribed.3. Terminator: The region that signals the end of transcription.These elements define the transcription unit and help regulate the process of transcription in both prokaryotes and eukaryotes.
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