What mutation affects the number or structure of whole chromosomes?

• A. Point mutation
• B. Chromosomal mutation
• C. Gene mutation
• D. Frameshift mutation

Answer: (B)

Mutations that affect the number or arrangement of whole chromosomes are chromosomal mutations. These changes involve the structure or the number of chromosomes rather than just a single DNA base. For example, having an extra copy of a chromosome (such as trisomy 21) changes the overall chromosome count and can disrupt development. Structural rearrangements—like deletions (loss of a chromosome segment), duplications (extra copies of a segment), inversions (a segment flipped in orientation), and translocations (segments moved to another chromosome)—alter how genetic material is organized on the chromosomes.

This is different from point mutations, which are single-base changes; gene mutations, which affect a single gene rather than whole chromosomes; and frameshift mutations, which are insertions or deletions that shift the reading frame within a gene. Those latter changes involve individual genes or small blocks of DNA rather than the entire chromosome’s number or structure.

So the mutation that changes the number or structure of whole chromosomes is chromosomal mutation.