Single nucleotide polymorphism is way too many syllables, so you can understand why we just say "snip". And this is really a simple concept. These are the places in the genome where people differ. In about one out of every 1,000 letters of the code you'll run into one of these where I might have a C and you might have a T, and we'd call that a SNP. Most SNPs don't do very much, 'cause they're in a part of the genome that doesn't have a critical function. But some of them confer a risk of disease like diabetes or heart disease, and those are of intense current interest because of what they teach us about why those diseases happen.Francis S. Collins, M.D., Ph.D.