What is a mutation and how do point mutations differ from chromosomal mutations?

• A. Mutations can only occur during replication in somatic cells.
• B. Mutations always result in disease.
• C. Mutations are reversible.
• D. A mutation is a change in DNA; a point mutation affects a single nucleotide, while a chromosomal mutation involves larger changes to chromosome structure or number.

Answer: (D)

Mutations are changes in the DNA sequence, and they can arise in many ways, not just during DNA replication in body cells. A single nucleotide change is called a point mutation, which can alter a codon and potentially change the amino acid, create a premature stop, or have no effect at all. A chromosomal mutation, on the other hand, involves larger changes to the structure or number of chromosomes—such as deletions, duplications, inversions, translocations, or aneuploidy—which can affect many genes at once and have more dramatic phenotypic consequences.

So the best description is that a mutation is a change in DNA; a point mutation affects a single nucleotide, while a chromosomal mutation involves larger changes to chromosome structure or number. This distinction explains why point mutations tend to have localized effects, whereas chromosomal mutations can impact many genes and inheritance patterns.

Mutations can occur outside replication and in germ cells, so they are not limited to somatic cells. They do not always cause disease—many are neutral or even beneficial. And they are not generally reversible; back mutations are rare and not guaranteed.