UPPSC 2020 Prelims GS Paper-I · Question 89 of 150

Correct — A, Mutation. A gene is a stretch of DNA read as a sequence of bases (A, T, G, C). A mutation is a heritable change in that base sequence — a substitution, insertion or deletion of one or more bases. Such changes can alter the protein a gene codes for and are the ultimate source of new genetic variation.

• (b)Cloning — Cloning produces genetically identical copies of a gene, cell or organism; it copies the existing base sequence rather than changing it.
• (c)Fusion — Fusion refers to joining two cells, protoplasts or nuclei into one; it combines whole genomes but does not, by definition, alter the base sequence within a gene.
• (d)Breeding — Breeding is controlled reproduction to combine desirable traits across generations; it reshuffles existing genes rather than changing the base sequence of a single gene.

DNA stores information as an ordered sequence of four bases; a gene is a functional segment of this sequence. When that order is altered — by substitution, insertion or deletion of bases — the change is a mutation. Mutations may be silent, may change a protein, or may be harmful/beneficial, and they are the raw material on which natural selection acts.

The other options are all genetics/breeding terms, so the question checks the precise definition. Keep them distinct: mutation = a change in the sequence; cloning = identical copies; fusion = merging cells; breeding = controlled reproduction. Only 'mutation' describes an alteration of the base order itself.

• Mutation = a heritable change in the DNA base sequence (substitution, insertion or deletion).
• Mutations are the ultimate source of new genetic variation.
• The Mutation Theory of evolution was proposed by Hugo de Vries.
• Mutagens (e.g., UV/X-rays, certain chemicals) raise the mutation rate.

• Confusing mutation (change in sequence) with cloning (identical copies)
• Treating breeding/hybridisation as a change in the base sequence

UPPSC/UPSC ask for the exact term or its author (de Vries's Mutation Theory) — anchor 'change in DNA base sequence = mutation'.

• practice — not a real PYQ

  A mutation involving the addition or deletion of a single base, shifting the reading frame of a gene, is called a:

  • (a)Point mutation
  • (b)Frameshift mutation
  • (c)Silent mutation
  • (d)Chromosomal mutation

  Answer(b) Frameshift mutation — insertion/deletion shifts how all downstream codons are read.

• practice — not a real PYQ

  Which one of the following is a physical mutagen?

  • (a)Nitrous acid
  • (b)Ultraviolet radiation
  • (c)Ethyl methanesulfonate
  • (d)Acridine dye

  Answer(b) Ultraviolet radiation — a physical agent that damages DNA and raises the mutation rate.