CBSE Important Questions Class 12 Biology Chapter 6

Important Questions Class 12 Biology Chapter 6

Important Questions for CBSE Class 12 Biology Chapter 6 – Molecular Basis of Inheritance

The study of genes in the body, including DNA and its various processes such as replication, transcription, translation, genetic code, regulation, and others, is known as molecular inheritance. This concept explains why offspring resemble their parents.

The concept of molecular inheritance is covered in Chapter 6 of Class 12 Biology. This section is included in the Extramarks Important Questions Class 12 Chapter 6 which is compiled by subject matter experts from NCERT books. These questions are written in the most straightforward manner possible so that students can easily understand and learn during exams.

CBSE Class 12 Biology Chapter-6 Important Questions

Study Important Questions for Class 12 Biology Chapter 6 – Molecular basis of Inheritance

A sample of the important questions for Class 12 Biology Chapter 6 is given below. For the set of questionnaires, access the link given below. 

Very Short Answer Questions(One Mark)

Q1. RNA viruses mutate and evolve more quickly than other types of viruses. Why?

  1. Because the -OH group on RNA is reactive, it is unstable and mutates more quickly.

Q2. What exactly does aminoacyl tRNA synthetase do?

  1. Aminoacyl tRNA synthetase catalyses the activation of amino acids and their attachment to the 3-end of specific tRNA molecules.

Q3. What exactly is point mutation?

  1. Ans: A point mutation occurs when a single base pair in a DNA sequence changes.
  2. What exactly is a codon?
  3. A codon is a triplet sequence of bases that codes for a single amino acid.

Short Answer Questions (2 Marks)

Q1. Why is it so important for tRNA to bind to both amino acids and mRNA codons during protein synthesis?

  1. It is critical that tRNA binds to both amino acids and mRNA codons because tRNA functions as an adapter molecule that picks up a specifically activated amino acid from the cytoplasm and transports it to the ribosomal within the cytoplasm where proteins are synthesised. It binds to the ribosome in the sequence specified by mRNA and then transfers its amino acid to a new polypeptide chain.

Q2. Mention any four significant features of the genetic code.

  1. A genetic codon has the following important characteristics:
  • Each codon is a triplet with three bases.
  • Each codon encodes only one amino acid, making it unambiguous.
  • Some amino acids are coded, and it is said that more than one codon is degenerative.
  • Codons are read in a continuous direction with no punctuation.

Q3. Why can transcription and translation be coupled in prokaryotic cells but not eukaryotic cells?

  1. In prokaryotes, the mRNA synthesised does not require any processing to become active; both transcription and translation occur in the same cytosol; however, in eukaryotes, the primary transcript contains both exons and introns and is subjected to a process known as splicing, in which introns are removed or exons are joined in a specific order to form mRNA.

Short Answer Questions (2 Marks)

Q1. Two claimant fathers sued a woman who claimed to be the father of her only daughter. How could identifying the true biological father resolve this case?

  1. The DNA – fingerprinting technique could have resolved this case to identify the true biological father. In this method:-
  • First and foremost, the DNA of the two claimants who must be tested is isolated.
  • Isolated DNA is then digested with a restriction enzyme and the digest is run through gel electrophoresis.
  • Alkali treatment denatures ds DNA fragments, resulting in ss DNA.
  • The electrophoresed DNA is then transferred into a nitrocellulose filter paper and fixed.
  • A known sequence of DNA is prepared and labelled with the radioactive isotope 32p before being added to nitrocellulose paper.
  • Autoradiography is used to photograph nitrocellulose paper on X-ray film. The film is examined for the presence of hybrid nucleic acid.
  • The DNA fingerprints of the two claimants are then compared with the DNA fingerprints of the lady and her daughter, and whoever matches is declared to be the biological father of her daughter.

Q2. What are the three types of RNA and what role do they play in protein synthesis?

  1. There are three kinds of RNA:
  • Messenger RNA (mRNA): It is a single-stranded RNA that transports the genetic information from DNA transcribed on it to the cell for protein synthesis.
  • Transfer RNA (tRNA): A molecule with a “anticodon loop” on one end that reads the code and an amino acid acceptor end that binds to the specific amino acid on the other.
  • Ribosomal RNA (rRNA): Ribosomes serve as a site for protein synthesis and catalyse the formation of peptide bonds.

Long Answer Questions (3 Marks)

Q1. What do you mean by DNA replication’s semi-conservative nature? Who and how did they prove it?

  1. The semiconservative nature of DNA replication suggested that during replication, two strands separate and each acts as a template for the synthesis of a new complementary strand, so that after complete replication, each DNA molecule would have one parental strand and one newly synthesised strand, preserving half of the information over a generation. Mathew Messselson and Franklin Stahl used Escherichia coli to demonstrate that DNA replication is semiconservative. They grew E.coli in a medium containing 15NH4Cl until 15N was incorporated into the two strands of newly synthesised DNA. Heavy DNA can be separated from normal DNA by centrifugation in a CsCl density gradient. 

The cells were then placed in a medium containing normal X14NH4Cl, samples were taken at various time intervals, DNA was extracted, and the cells were centrifuged to determine their densities. After one generation, the DNA is extracted from the cells in order to transfer from X15N medium to X14N medium.

Important Questions Class 12 Biology Chapter 6

Molecular Basis of Inheritance Important Questions

Extramarks Class 12 Chapter 6 Important Questions are highly recommended and preferred for making preparation easy for the board examinations and competitive exams. 

Subject matter experts have compiled all the extra questions of Chapter 6 Biology Class 12 so that no important topic is skipped while studying. These important questions come with solutions, so students can improve their answers and aim for the highest possible score.

Molecular Basis of Inheritance Class 12 Questions – Summary

DNA (Deoxyribonucleic Acid) (Deoxyribonucleic Acid)

Except for certain viruses, which have an RNA genome, most species’ genetic material is DNA. TMV is a good example of this (Tobacco mosaic virus).

RNA is primarily a messenger, an adaptor, and a catalytic agent. The nucleotide or base pair count of DNA is specified by its length (bp).

Structure of a Polynucleotide Chain

The polynucleotide chain structure is made up of three fundamental components:

Nitrogenous Substance:

  • Purines – Adenine (A) and Guanine (G) can be found in both DNA and RNA.
  • Pyrimidines are RNA’s cytosine and uracil, and DNA’s cytosine (C) and thymine (T). Thymine, also known as 5-methyl uracil, is responsible for increased DNA molecule stability.


  • Pentose sugar- As the name implies, ribose is found in RNA (ribonucleic acid) and deoxyribose is found in DNA.

Phosphate Group:

  • Nucleoside:  A nitrogen base linked to the hydroxyl group of 1 ‘C pentose sugar via an N-glycosidic bond.
  • Nucleotide: A phospho-ester bond connects the phosphate group to the hydroxyl group at 5 ‘C of the nucleoside.

In this way, each strand of DNA has a “backbone” of phosphate-sugar-phosphate-sugar-phosphate.

Double Helix Model Given for the DNA Structure

Watson and Crick proposed the DNA double-helix structure in 1953.

  • The adenine and thymine to guanine and cytosine ratio is one and tends to remain constant. Ervin Chargaff stated as much.
  • DNA is made up of two polynucleotide chains with sugar-phosphate backbones and bases within.
  • There is the polarity between the two chains, namely one with 3′-5′ polarity and the other with 5′-3′ polarity.
  • The base pair (bp) is formed by hydrogen bonding between the nitrogen bases found on two of the polypeptide chains.
  • A purine base from one nucleotide chain is frequently connected to a pyrimidine base from another nucleotide chain to form a base pair.
  • Adenine and Thymine (or Uracil in RNA) are linked by two hydrogen bonds (A=T), while Guanine and Cytosine are linked by three hydrogen bonds (A=T) (G).


According to Watson and Crick, DNA replication is semi-conservative in nature. Meselson and Stahl demonstrated it experimentally in 1958. The replication of DNA begins at the origin of replication and ends with the formation of a replication fork. It results in the formation of two strands, leading and lagging. Furthermore, the formation of some fragments known as the Okazaki fragments occurs.


Transcription is the first step in gene expression. To make an RNA molecule, the DNA sequence of a gene must be copied. This is accomplished by the enzyme RNA polymerase, which attaches nucleotides to form an RNA chain, which is then transcribed (using a DNA strand as a template). Transcription occurs at three stages: initiation, elongation, and termination.

Genetic Code

  • Amino acids are the sequences of bases found in mRNA that are responsible for coding for a specific amino acid.
  • Each code is made up of three nucleotides and is known as a triplet. Codons are almost universal, with the exception of some protozoan and mitochondrial codons.
  • Because more than one triplet can code for the same amino acid, the code is said to have degenerated.
  • There are 64 codons in total, 61 of which code for amino acids.
  • There are three different stop codons that do not code for any amino acids: UAA, UAG, and UGA.
  • AUG, in addition to being a starting codon, also codes for methionine.


Point Mutation: A single base pair shift, for example, causes a point mutation. Sickle cell anaemia is caused by a single point mutation in the gene that codes for the -globin chain. As a result, glutamate in the regular protein is converted to valine in the sickle cell.

Frameshift mutation occurs when one or two base pairs are lost or gained, causing the reading frame to shift at the point of insertion or deletion.


The translation is the process of converting a messenger RNA (mRNA) molecule sequence during protein synthesis into an amino acid chain. The translation process is completed in four steps: activation, initiation, elongation, and termination. These words describe the progression of the amino acid chain (polypeptide). Amino acids are transferred to ribosomes and combined to form proteins.

Human Genome Project

In 1990, the Human Genome Project (HGP) was launched in order to decode the entire DNA sequence of the human genome.

Using genetic engineering techniques, the DNA section was separated and cloned in order to determine the DNA sequence.

The project was completed in 2003, and the sequence of chromosome 1 was completed in May 2006.

DNA Fingerprinting

DNA fingerprinting is a type of test that represents an individual’s or any other living thing’s genetic makeup. It is the technique used to establish a link between a suspect and biological evidence in a criminal investigation. A DNA sample from a crime scene is compared to a DNA sample from a suspect. If the two DNA profiles match, then the evidence comes from that perpetrator.


The Molecular Basis of Inheritance Class 12 Important Questions are crucial in terms of exam preparation. Students will learn about DNA (Deoxyribonucleic acid), the structure of a polynucleotide chain, the Double Helix Model for DNA Structure, replication, transcription, genetic code, mutation, translation, the human genome project, and DNA fingerprinting in this chapter. Students can access the set of important questions available on the website at their convenience.

FAQs (Frequently Asked Questions)

1. What is DNA polymorphism?

DNA polymorphism is a process of variation in DNA caused by mutations occurring at non-coding sequences, i.e., DNA Polymorphism refers to the various DNA sequences found in living organisms. There are numerous variations occurring at the DNA level, such as base pair changes, repeated sequences, and so on.

2. Why both strands of DNA are not copied during DNA transcription? Explain.

Both strands of DNA are not copied during transcription because of the following reasons: 

I)If both strands code for RNA, two different RNA molecules and two different proteins are formed, making genetic machinery more complicated.


  1. II) Because the two RNA molecules are complementary, they will wind together to form dsRNA without undergoing translation, implying that transcription is pointless.