Test of Cre-mediated recombination at the chromosome level by breeding of Tg(zp3:cre, krt8:rfp) and Tg(mylz2:loxP-EGFP-loxP)gz3. A: The 48 hpf embryos with strong, weak, and nil green fluorescent protein (GFP) expression from a cross between female Tg(zp3:cre, krt8:rfp) and male Tg(mylz2:loxP-EGFP-loxP)gz3. Percentages of each type of embryos based on GFP expression are indicated. B: Polymerase chain reaction (PCR) detection of Cre-mediated recombination in offspring of female double transgenic fish Tg(zp3:cre, krt8:rfp)/Tg(mylz2:loxP-EGFP-loxP)gz3 and male wild-type fish. In both skin RFP-expressing (cre transgenic) and non-RFP-expressing (cre non-transgenic) embryos (4 days postfertilization), approximately half of them showed Cre-mediated recombination as anticipated from the female germline excision while the other half were loxP non-transgenic individuals. The expected PCR products are 2.1 kb and 1.2 kb, respectively, before and after the Cre-mediated recombination. P, positive PCR control with pMYLZ2-loxP-EGFP-loxP plasmid that is used to generate Tg(mylz2:loxP-EGFP-loxP)gz3; N, negative PCR control without a template DNA; M, 1-kb DNA ladder. Scale bar = 500 μm.