the presence of each transgene by PCR amplification of genomic DNA extracted from a 5-mm tail biopsy. Tails were heated to 95 °C for 45 min in 250 μl of 50 mM NaOH, vortexed, then neutralized with an equal volume of 0.5 M Tris-HCl (pH 5.5). Debris was sedimented by centrifugation,