What is a change in DNA sequence caused by radiation or chemicals?

• A. Mutation
• B. Gene expression
• C. Allele
• D. Chromosome duplication

Answer: (A)

Mutations are permanent changes in the DNA sequence. Radiation and chemicals can act as mutagens, causing a range of sequence alterations such as base substitutions, insertions, deletions, or more complex rearrangements. These changes can occur in germ cells, influencing inheritance, or in somatic cells, affecting only the individual. This exactly describes a change in DNA sequence caused by external agents, which is why it’s the right choice.

Gene expression refers to how genes are turned on or off and how their products are produced, not to a change in the DNA sequence itself. An allele is a variant form of a gene, which can arise from mutations but is not the process of mutagen-induced change itself. Chromosome duplication is a larger-scale change where extra copies of a chromosome segment or whole chromosome are present, not the specific sequence-level changes caused by mutagens.