On many occasions, gene-or locus-specific (other than the whole genome) copy number information is required. This is especially true in the cases of CYP2D6 and ERBB2 described above in which therapeutic decision needs to be made based upon the copy numbers of these genes. In addition to other conventional methods (Southern blot, long-range PCR and FISH), the possibility of using quantitative PCR in the CNV study of these two genes has been previously explored (61) (62) (63) (64) (65) .