Detection of loxP fragment excision by PCR. Genomic DNA samples from the putative marker-free T1 plants L10-T1-10 and L10-T1-18 were amplified by PCR for detection of Cre/loxP-mediated loxP fragment excision using primer pairs P1/P2, P3/P4 and P1/P4 . The presence or absence of the Hpt and Cry1Ab/1Ac genes were also detected by PCR. Plasmid DNA of pCCreloxPBt and genomic DNA from MD44 were used as the controls. Primers are listed in Table 4.