Appropriate Selection of Tagging SNPs in Indirect Association Studies

While the human genome is 99.9% conserved the remaining 0.1% gives rise to a surprising amount of diversity. About 80% of this sequence divergence is in the form of single-nucleotide polymorphisms (SNPs) or single nucleotide substitutions that occur in at least 1% of the human population. The presence of such variants or alleles does not, in itself, provide a high degree of variability in the human population. However, recombination events that occur during gamete formation give rise to an enormous amount of diversity as segments of chromosomes are shuffled and resorted. This occurs before the first division when breaks in aligned chromatids rejoin to their homologous partner as illustrated in Fig.1a. After several generations, many recombination events occurring at different sites can result in a high degree of variability in a population as illustrated in Fig. 2a.