Change in the base sequence within a gene is called

1. A

   Mutation

   (a) Mutation. A change in the base sequence within a gene is a mutation (point mutation if one base; indel if insertion/deletion). That is the official key.

2. B

   Cloning

   (b) Cloning. Cloning copies an organism or gene; it is not itself a base-sequence change.

3. C

   Fusion

   (c) Fusion. Cell or protoplast fusion is a biotechnological joining, not a gene-sequence change.

4. D

   Breeding

   (d) Breeding. Breeding selects and crosses organisms; mutation may feed it but is not the definition of a base change.

Summary. Official key is (a). Change in a gene’s base sequence is mutation. Cloning, fusion and breeding are different operations.