Important Questions Class 12 Biology Chapter 5 Molecular Basis of Inheritance

Important Questions Class 12 Biology Chapter 5 focuses on the Molecular Basis of Inheritance, a high-weightage chapter in the CBSE Class 12 Biology syllabus. As the 12th Biology board exam is scheduled for March 27, 2026, practicing these questions is important for effective revision and understanding key concepts.

This chapter covers DNA, RNA, replication, transcription, translation, and gene regulation, all of which are asked in board exams. By going through Molecular Basis of Inheritance Class 12 Important Questions and MCQs, students can identify the most expected questions, understand the exam pattern, and improve answer-writing skills under time pressure.

Important Questions Class 12 Biology Chapter 5

Questions from this chapter appear in both board exams and competitive exams. Students should practice MCQs, conceptual questions, and previous year board questions to ensure complete readiness. 

Here are some Molecular Basis of Inheritance Class 12 Biology MCQs as well as questions and answers for practice:

Question 1. A nucleoside differs from a nucleotide. It lacks the:

(1) base

(2) sugar

(3) phosphate group

(4) hydroxyl group

Ans. (2) sugar

2. The net electric charge on DNA and histones is:

(1) both positive

(2) both negative

(3) negative and positive, respectively

(4) zero

Ans. (3) negative and positive, respectively

3. Who amongst the following scientists had no contribution to the development of the double-helix model for the structure of DNA?

(1) Rosalind Franklin

(2) Maurice Wilkins

(3) Erwin Chargaff

(4) Meselson and Stahl

Ans. (4) Meselson and Stahl

4. What is the difference between heterochromatin and euchromatin?

Ans. Heterochromatin is a tightly packed DNA, which can be identified when stained in an extreme nuclear stain. Euchromatin is a lightly packed DNA, which can be identified when stained in a less nuclear stain.

5. What are the functions of the :

1. Methylated guanosine cap

2. Poly-A tail

Ans. 1. Methylated guanosine cap plays a primary role in the attachment of the mRNA to the smaller sub-units of the ribosome during translation initiation.

2. The Poly-A tail functions by increasing the length of the mRNA and also provides longevity to the mRNA.

6. Explain (in one or two lines) the function of the followings:

(a) Promoter

(b) tRNA

(c) Exons

Ans. (a) Promoter : The section of DNA which aids in initiating the transcription process and serving as a binding site for RNA polymerase is the promoter

(b) tRNA : The transfer RNA or tRNA is a small clover-shaped RNA that reads the genetic code that is located on mRNA. It conveys particular amino acids to the mRNA ribosome while proteins are translated. Specific tRNAs are present for specific amino acids.

(c) Exons : In eukaryotes, these are coding sequences of DNA which transcribe proteins. In between, exons comprise long non-coding sections of DNA known as introns.

7. Why is the Human Genome project called a mega project?

Ans. The Human Genome project was ought to be a mega project as the scale and the goals of the project were humongous. It had a goal to sequence every base pair located in the human genome, which took around 13 years to complete and was accomplished in 2003. This large-scale project intended to develop new technologies and produce new information in the stream of genomic studies. Subsequently, it unlocked the scope for several new areas and possibilities, such as in the stream of biotechnology, genetics, medical sciences etc., which hints at comprehending different aspects of human biology.

8. What is DNA fingerprinting? Mention its application.

Ans. The technique of DNA fingerprinting is helpful in identifying and analysing variations in different individuals at the DNA level. It is based on the principle of variability and polymorphism in DNA sequences. Its applications are as follows:

• To identify potential crime suspects in forensic science

• Helpful in establishing family and paternity relationships

• Useful in identifying and preserving the commercial varieties of livestock and crops

• Useful to discover and know more about the evolutionary history of an entity, thus tracing the linkages between different entities.

9. If a double-stranded DNA has 20 per cent of cytosine, calculate the per cent of adenine in the DNA.

Ans. As per Chargaff’s rule, DNA molecules are required to have an equal ratio of purine (adenine and guanine) and pyridine (cytosine and thymine). This is to say that the number of adenine molecules is equivalent to the cytosine molecule.

Percentage of adenosine = percentage of thymine

Percentage of guanine = percentage of cytosine

Hence, according to the law, if the double-stranded DNA has 20% of cytosine, it should have 20% of guanine. Therefore, the percentage of G + percentage of C = 40%

The other 60% indicates both A + T percentage molecules. As adenine and thymine are always found in equal numbers, the adenine content is 30 %.

10. List two essential roles of the ribosome during translation.

Ans. Two essential roles of the ribosome during translation are as given below:

• Ribosomes are sites where the synthesis of proteins occurs from individual amino acids. It consists of two subunits - the larger subunit serves as an amino acid binding site, whereas the smaller subunit attaches to the mRNA forming a protein-synthesising complex

• Since the large subunit of the ribosome has two different sites to attach to tRNA, it facilitates amino acids to come closer for peptide bond formation. Also, the ribosome behaves as a catalyst for the formation of the peptide bond. Example - 23s r-RNA acts as a ribozyme in bacteria

Last-Minute Revision Tips for Molecular Basis of Inheritance

As the Class 12 Biology board exam is scheduled on Feb 25, 2026, revising effectively is key. Here are some last-minute tips for Molecular Basis of Inheritance:

1. Focus on Key Concepts and Diagrams: Prioritize understanding DNA replication, transcription, translation, and the structure of nucleic acids. Diagrams like the DNA double helix or replication fork are often directly asked in exams.

2. Use Important Questions: Revise the short and long answer questions you’ve already practiced. Focus on frequently asked questions and high-weightage topics.

3. MCQ Practice: Go through Molecular Basis of Inheritance Class 12 Biology MCQs to improve speed and accuracy for objective sections.

4. Make Short Notes: Write definitions, formulas, and key points on a single sheet. Quick-glance notes are perfect for the last day before the exam.

5. Practice Question-Answer Pairs: Quickly go through Molecular Basis of Inheritance Question Answers you’ve prepared. Recall them aloud to strengthen memory.