Change in the base sequence within the gene is called

The correct answer is C) mutation. A mutation is a heritable change in the nucleotide sequence of DNA. It can be a substitution, insertion, deletion or frameshift. The classic example is sickle cell anaemia, where a single base substitution (A to T) in the beta-globin gene changes codon 6 from GAG to GTG, so glutamic acid is replaced by valine.

• A) Breeding is selective crossing of organisms with desirable traits. It recombines existing variation and does not alter the base sequence of a gene. Hybridisation is a rearrangement, not a sequence change.
• B) Cloning means producing genetically identical copies, either of an organism (as with Dolly the sheep) or of a DNA fragment in a vector. The sequence is copied faithfully, not changed.
• D) Fusion refers to joining two cells (protoplast or hybridoma fusion) or joining two genes or DNA segments. It concerns the combination of material, not a change in base order within a gene.

Conceptually, this links to the central dogma and to the source of genetic variation that drives evolution. For Mains, it connects to genetic disorders, mutagens, and the biosafety debates around genome editing such as CRISPR.

Trap: aspirants often pick breeding or fusion because they sound like genetic changes. Ask whether the base sequence itself has changed. Only mutation does that.