Many thanks Valentijn. The information overload of that dbSNP page has blown a fuse in my feeble brain,... but very interesting! I am a bit confused as to why in the dbSNP page population data table, in the "Genotype Details" columns, there is not only AA, AG and GG, but also A, G and N. Why these single values of A and G? And what does N mean? Don't people always have two versions of the SNP, maternal and paternal?