任何有潜在性的会导致一个或更多基因的功能变化的DNA的改变。突变可以是DNA的单个碱基变化（点突变）或一个基因中的一对碱基对丢失（缺失突变），或染色体的一段移位从而影响很多基因。突变可以是由辐射、化学作用、外部病原体（如：病毒）或细胞分裂时基因组复制错误造成。突变会影响基因调节和表达或造成蛋白质本身变化从而产生无功能蛋白或异常蛋白。有些DNA的变化是自然发生的不会产生有害影响；这些在一个群体中的变化被称为多态性。

Any alteration to DNA that can potentially result in a change in the function of one or more genes. Mutations can be a change in a single base of DNA (point mutation) or a loss of base pairs (deletion) affecting a single gene, or a movement of chromosomal regions (translocation) affecting many genes. Mutations can be induced by radiation, chemical treatment, foreign pathogens (e.g. viruses), or due to errors that occur during replication of the genome each time a cell divides. Mutations can affect gene regulation and expression or can cause a change in the protein itself that results in a non-functional protein (e.g. the CFTR protein defective in cystic fibrosis) or one with abnormal activity (e.g. the p53 cancer-causing protein). Some changes in DNA occur naturally and lead to no harmful effects; these changes in a population are called polymorphisms.