P25 is used to define the subclade R1b1 and it is a mutation from C to A. Noted that it has a reversion rate of ~2%, meaning that the SNP location is changed from A (positive/derived state) back to C (ie negative/ancestral state). P25 is not used alone for subclade determination. Our R subclade panel also test 20 other Y-SNP markers that are downstream of R1b1(P25+), and the mutation status of these downstream markers will be used for proper subclade determination.