what are snps in dna
What are single nucleotide polymorphisms (SNPs)? Single nucleotide polymorphisms, frequently called SNPs (pronounced âsnipsâ), are the most common type of genetic variation among people. Each SNP represents a difference in a single DNA building block, called a nucleotide. For example, a SNP may replace the nucleotide cytosine (C) with the nucleotide thymine (T) in a certain stretch of DNA. SNPs occur normally throughout a personâs DNA. They occur once in every 300 nucleotides on average, which means there are roughly 10 million SNPs in the human genome.