Genome-wide P values for warfarin dose association in the index population. All P values shown are for univariate effects using an additive genetic model. Chromosomes are numbered on the x-axis. Polymorphisms within 500 kb of VKORC1 and CYP2C9 are shown in red and blue, respectively. Genome-wide significance was set at the P value 10⁻⁷ (black line), and polymorphisms with P values less than 10⁻⁴ (brown line) were selected for replication, among others (see “Statistical analysis”).