For the candidate gene approach, the pharmacokinetic and pharmacodynamic pathways of the drug are used to identify a gene (or a small group of genes) that is potentially important. The single gene is then studied in order to determine if variants in the gene contribute to variation in susceptibility to the cytotoxic effects of the drug. By contrast, with the whole-genome approach, the entire genome is studied, either by association analyses or linkage analyses or both, in order to identify candidate genes.