The phenomenon of sudden, heritable mutations that occur. At the molecular level, a mutation is a change in the structure of a gene in terms of the composition or order of arrangement of base pairs. Although genes are very stable and can replicate themselves precisely during cell division, this stability is relative. Under certain conditions a gene can also suddenly change from its original form of existence to another new form of existence, that is, a new gene suddenly appears at a locus, replacing the original gene, and this gene is called a mutant gene. This gene is called a mutant gene, and the offspring suddenly exhibit new traits that the ancestor never had. Gene mutations usually occur during DNA replication, i.e., interphase, including mitosis and meiosis; they are also related to DNA replication, DNA damage repair, carcinogenesis and aging, and are an important factor in biological evolution, low frequency and reversibility.