Single nucleotide polymorphism
A Single Nucleotide Polymorphism or SNP (pronounced snip) is a DNA sequence variation, occurring when a single nucleotide: adenine (A), thymine (T), cytosine (C) or guanine (G) – in the genome is altered. A variation must occur in at least 1% of the population to be considered a SNP.
SNPs make up 90% of all human genetic variations, and occur every 100 to 300 bases along the human genome. Two of every three SNPs substitute Cytosine (C) with Thymine (T). Variations in the DNA sequences of humans can affect how humans handle diseases, bacteria, viruses, chemicals, drugs, etc.
SNPs are of great value to biomedical research and in developing pharmacy products. Because SNPs do not change much from generation to generation, following them during population studies is straighforward.
SNPs are generally considered to a form of point mutation that has been evolutionarily successful enough to recur in a significant proportion of a species' population.