What is defined as a spontaneous change in a DNA sequence?

A mutation is defined as a spontaneous change in a DNA sequence. Mutations can occur due to various factors such as environmental influences, replication errors, or simply as a natural part of cellular processes. They can involve changes to single nucleotides—like substitutions, insertions, or deletions—or larger-scale alterations affecting larger segments of DNA. These changes can affect the function of genes, leading to variations in traits among organisms.

The other options reference different biological processes: gene expression involves the process by which information from a gene is used to synthesize functional gene products like proteins, chromosomal rearrangement refers to larger-scale structural changes in chromosomes that can impact gene function or inheritance, and replication errors are mistakes that occur during DNA replication, which can lead to mutations but do not define all mutations.