In genetics and bioinformatics, SNP stands for Single-nucleotide polymorphism. It is a germline substitution of a single nucleotide at a specific position in the genome that is present in a sufficiently large fraction of the considered population. SNPs are the most common type of genetic variation among people, and they occur almost once in every 1,000 nucleotides on average, which means there are roughly 4 to 5 million SNPs in a persons genome. SNPs can act as biological markers, helping scientists locate genes that are associated with disease. When SNPs occur within a gene or in a regulatory region near a gene, they may play a more direct role in disease by affecting the gene’s function. Most SNPs have no effect on health or development, but some of these genetic differences have proven to be very important in the study of human health. SNPs help predict an individual’s response to certain drugs, susceptibility to environmental factors such as toxins, and risk of developing diseases. SNPs can also be used to track the inheritance of disease-associated genetic variants within families.