PCR amplification products were visualized under UV light after electrophoresis on 1% agarose gels in Tris-acetate-EDTA buffer pH 8.5 (30 min at 10 V/cm) and staining with ethidium bromide (0.5 mg⁄ l; Sigma, Bornem, Belgium). The size of the amplified products was assessed by comparison with a commercial weight marker, Smart Ladder (Eurogentec, Liege, Belgium).