What defines a mutation?

A mutation is defined as a random change in the DNA sequence that can lead to variations in traits among organisms. This definition highlights the inherent randomness of mutations, which can arise spontaneously due to errors during DNA replication, damage from environmental factors, or other biological processes.

These random changes in the genetic code can result in alterations to proteins, potentially affecting an organism's phenotype. Such variations are crucial for the process of evolution, as they provide the raw material upon which natural selection can act. Therefore, while mutations are indeed crucial for evolution, they are not necessarily deliberate or required for it to occur; they are simply changes that arise randomly within populations.

In contrast to this, deliberate changes in DNA (as in the first choice) typically refer to genetic engineering rather than mutations. The third option incorrectly emphasizes RNA structure changes rather than direct DNA alterations, and the last choice suggests that mutations are necessary for evolution, which, while they do contribute, does not encompass the full definition of a mutation itself. Thus, the second choice accurately captures the essence of what a mutation is.