What is a mutation?

A mutation is best understood as a change in the DNA sequence that can affect genetic information. This definition encompasses various types of alterations that can occur within an organism's genome, leading to potential changes in the phenotype or biological characteristics of that organism.

When the DNA sequence of a gene is altered, it may impact how that gene is expressed or how the protein that it encodes functions. Such changes can arise from various processes, including spontaneous errors during DNA replication or as a result of external factors such as radiation or chemicals.

The options provided explore different aspects of genetic changes. A change in the RNA sequence pertains specifically to transcription and does not encompass all forms of mutations, as the initial mutation occurs at the DNA level before any RNA transcription. A duplication of a gene segment refers to a specific kind of mutation but doesn't account for the broader scope of mutations, which can also involve deletions or substitutions. Meanwhile, a replacement of one nucleotide with another is a type of mutation known as a point mutation, but it is more specific than what is generally defined as a mutation. Overall, the definition of a mutation as a change in the DNA sequence that can affect genetic information is the most inclusive and accurate.