With the near-completion of the human genome project, we
are entering the exciting era in which one can begin to elucidate
the relationship between DNA sequence variation and susceptibility
to disease, as modified by environmental factors. Single nucleotide
polymorphisms (SNPs) are by far the most prevalent of all DNA
sequence variations. Although the vast majority of the SNPs are
found in noncoding regions of the genome, and most of the SNPs
found in coding regions do not change the gene products in
deleterious ways, SNPs are thought to be the basis for much of the
genetic variation found in humans. As explained eloquently by Lisa
Brooks in Chapter 1 of Single Nucleotide Polymorphisms: Methods
and Protocols, SNPs are the markers of choice in complex disease
mapping and will be the focus of the next phase of the human
genome project. Besides the obvious applications in human disease
studies, SNPs are also extremely useful in genetic studies of all
organisms, from model organisms to commercially important plants
and animals.