Definition of single nucleotide polymorphism

single nucleotide polymorphism (SING-gul NOO-klee-oh-tide PAH-lee-MOR-fih-zum): A DNA sequence variation that occurs when a single nucleotide (adenine, thymine, cytosine, or guanine) is different from the reference sequence. Single nucleotide polymorphisms are usually present in at least 1% of the population and are the most common type of genetic variation among people. Single nucleotide polymorphisms may increase the risk of developing certain diseases, act as biomarkers to help predict the risk of developing certain diseases or how a person may respond to certain drugs, or be used to track the inheritance of disease-causing variants within families. Also called SNP.