Question

a mutagen is
o a living thing that has undergone a mutation.
o an agent that causes a mutation in dna.
o a mutation that has affected one gene.
o any chemical that can poison living cells.

Explanation:

A mutagen is defined as an agent that can induce changes (mutations) in the DNA sequence. Let's analyze each option:

• A living thing that has undergone a mutation is called a mutant, not a mutagen.
• A mutation that has affected one gene is just a description of a type of mutation (a point mutation perhaps), not what a mutagen is.
• Any chemical that can poison living cells is a general toxic chemical. While some mutagens can be toxic, this is not the specific definition of a mutagen.

Answer:

an agent that causes a mutation in DNA.