 It is a well-known fact that everyone’s genome is different. There are, however, several ways in which genomes of individuals can vary from each other, ranging from the deletion, insertion or rearrangement of longer stretches of DNA to differences in single nucleotides at specific locations on a chromosome. The latter form of variation was the focus of the HapMap project. If we align the DNA sequence of two individuals they will be identical for hundreds of nucleotides; the DNA of two human beings typically displays about 99.9% sequence identity (Li &amp; Sadler 1991; Wang et al. 1998; Cargill et al. 1999). But the 0.1% difference means that approximately every 1000 nucleotides there will be a difference in a single nucleotide between any two individuals.