Sex Determination by PCR Analysis of the X-Y Amelogenin Gene

PCR-based sex determination was first accomplished by amplifying multiple-copy sequences in the Y-chromosomal DYZ1 locus (1 ,2 ). These methods are quite sensitive (amplifiable from trace samples) due to the multiplicity, but it is impossible to tell whether the template DNA is from a female or whether the analysis has ended in failure when no fragment is amplified by PCR. Simultaneous amplification of X- and Y-chromosomal genes is thus necessary for a reliable sex test, in which the X-specific product may act as an internal control for PCR. From this point of view, centromeric alphoid repeats on the X and Y chromosomes have been amplified separately (3 ) or in the same reaction mixture (4 ) using two pairs of primers. These methods are also sensitive. However, a difference in the copy numbers of the repeated sequences (i.e., 5000 and 100 copies in X and Y centromeres, respectively) is likely to cause a difference in the sensitivity of PCR amplification so that the X product does not act strictly as an internal control. Sex determination by PCR analysis of X-Y homologous genes is thus most trustworthy, because X and Y sequences are of equal (single) copy number and because they can be amplified using one set of primers.