Electropherograms of QF-PCR products using 4 different microsatellite markers. The x-axis displays the lengths of the PCR products in base pairs, determined by the use of an internal size standard. The y-axis displays the fluorescence activity in arbitrary units. Row 1, ALL sample; row 2, remission sample; row 3, maternal sample; row 4, paternal sample. (A) Patient 9, marker D8S347, showing duplication of the paternal allele (ratio 1.8). (B) Patient 10, marker D9S1679, showing LOH with retention of the maternal allele. (C) Patient 5, marker D14S139, showing duplication of the maternal allele (ratio 1.6). (D) Patient 10, marker Penta D, showing tetrasomy 21, visible as equal allele dosage (ratio 1.0).