Gene Cloning Class 12 Biotechnology Chapter 3 NCERT Book PDF

Gene Cloning is the chapter where Class 12 Biotechnology moves from theory into the actual lab workflow. The NCERT Book Class 12 Biotechnology Chapter 3 Gene Cloning file on this page is the official chapter for the 2026-27 session. Download it to read every section from identifying a candidate gene to building a DNA library.

• 40 pages, printed pages 27 to 66, the complete official chapter with 8 numbered sections
• Covers candidate gene identification, nucleic acid isolation, DNA transfer, screening, blotting and PCR
• Includes assertion-reason and case-based questions in the exercise set, matching the CBSE 2026-27 pattern

This is the official NCERT chapter file for the 2026-27 session, hosted by Collegedunia with no pages removed.

How the Gene Cloning Chapter Is Laid Out

The chapter opens by explaining why gene cloning matters in biotechnology, then works through eight sections in the order a real cloning experiment would follow. Each section hands over the next step, from finding the gene to storing the clones in a library.

Gene Cloning Explained by Khan Academy

Source: Khan Academy India - English on YouTube

What the Gene Cloning Chapter PDF Contains

The PDF holds the whole chapter exactly as NCERT printed it, with nothing trimmed from either end.

• All eight numbered sections, from candidate gene identification to DNA libraries
• Figure 3.1 on DNA isolation and Figure 3.2 on RNA isolation, both as flowcharts
• Four boxed inserts, including a box on separating plasmid DNA from genomic DNA and a box on the eastern blot
• Diagrams of restriction enzyme cutting, blue-white selection and the PCR cycle
• The full exercise set at the end, including assertion-reason and case-based questions

Identifying the Candidate Gene for Cloning

Section 3.1 opens with what the chapter calls the first and most formidable problem in gene cloning: finding the right gene in the genome. A gene becomes a candidate for cloning based on its role in health, the economy or evolution, so the chapter lists examples such as the insulin gene linked to diabetes, iron-deficiency genes linked to chlorosis in plants, and salinity-tolerance genes.

• A haploid human genome holds about 3.2 billion base pairs, while a target gene is often only 3,000 to 3,500 bp
• The chapter compares this search to finding a needle in a haystack
• One method deduces the gene's DNA sequence from the amino acid sequence of its protein
• Another method isolates mRNA from a tissue and converts it into cDNA using reverse transcriptase

Once a candidate gene is identified, the chapter explains that it still has to be explored in new sources and then cloned through the steps covered in the rest of the chapter.

Isolating Nucleic Acids and the Enzymes Used in Gene Cloning

Section 3.2 walks through DNA and RNA extraction step by step, and Section 3.3 covers the enzymes that cut and join DNA once it is isolated. Both sections explain why the same four extraction steps apply across bacteria, plants and animals, even though each cell type needs a different way to break its outer layer open.

The chapter also separates plasmid DNA from genomic DNA in a dedicated box. Boiling a bacterial lysate denatures the long chromosomal DNA irreversibly, while the smaller circular plasmid DNA renatures and stays soluble, which is exactly why plasmids can be recovered and used as cloning vectors.

Modes of DNA Transfer Into a Host Cell

Section 3.4 explains how a foreign DNA molecule actually gets inside a host cell, prokaryotic or eukaryotic. In nature, bacteria pick up foreign DNA in three ways, and the chapter uses all three as the basis for the transfer methods used in the lab.

• Transformation: a cell directly takes up exogenous DNA through its membrane; the recipient is called a transformant
• Transduction: a bacteriophage carries bacterial DNA between cells during its lytic or lysogenic cycle
• Conjugation: DNA passes directly between two bacterial cells in contact

This section connects back to the host-vector systems covered earlier in the book, since the transfer method decides which vector and which host cell a cloning experiment can use.

Screening and Selection of Recombinant Clones

Section 3.5 solves a practical problem: after transformation, only a tiny fraction of cells actually carry the recombinant plasmid. The chapter calls this the most essential step for a successful cloning experiment, since sorting a handful of true recombinants out of a huge bacterial population is not simple.

• Recombinants are told apart from non-recombinants by a trait such as antibiotic resistance or a marker protein
• Blue-white selection uses the lacZ gene and the substrate X-gal; unbroken lacZ turns colonies blue, an insert in lacZ leaves them white
• Colonies are grown on ampicillin plus X-gal-IPTG media so untransformed cells are eliminated first
• Selection can also use dependence on a nutrient, such as the amino acid leucine

Blotting Techniques and the Polymerase Chain Reaction

Sections 3.6 and 3.7 cover how scientists confirm that a gene, its RNA transcript or its protein product is actually present, and how they multiply a tiny DNA sample into millions of copies.

The chapter calls PCR "molecular photocopying" and explains the thermocycler, the machine that cycles a reaction through denaturation, annealing and extension temperatures. It also covers real-time quantitative PCR, where a fluorescent dye such as SYBR green lets the amount of product be measured after every cycle, skipping the gel electrophoresis step used in conventional PCR.

DNA Libraries and What Collegedunia Adds to This Chapter PDF

Section 3.8 closes the chapter with two kinds of DNA libraries, the storage step that keeps cloned fragments available for later use.

• Genomic library: a collection of clones covering an organism's entire genome, used for full genome sequencing and comparing healthy versus diseased tissue
• cDNA library: built from the mRNA expressed in one specific tissue, since genes such as insulin or albumin switch on only in particular cells

Collegedunia hosts the exact NCERT file plus a way to read it before downloading.

• Official file: the exact NCERT chapter PDF, no pages removed
• Read in the browser: page through all 40 pages before downloading
• Chapter list: jump to any other Biotechnology chapter from one table

Also Check: the related Class 12 Biology chapter that covers the same rDNA technology basics from a different subject's lens.

Class 12 Biotechnology NCERT Book PDF: All Chapters

Every chapter of the book gets its own page. The 2026-27 Class 12 Biotechnology textbook has 13 chapters, and Chapter 3 sits right after the host-vector system that a cloning experiment depends on.

Gene Cloning Class 12 NCERT Book PDF FAQs