Transgenesis in zebrafish. The synthetic transposase mRNA and a transposon donor plasmid containing a Tol2 construct with a promoter and the gene encoding green fluorescent protein (GFP) are co-injected into zebrafish fertilized eggs. The Tol2 construct is excised from the donor plasmid  and integrated into the genome. Tol2 insertions created in germ cells are transmitted to the F1 generation. Germ cells of the injected fish are mosaic, and, by crossing the injected fish (founder) with wild-type fish, nontransgenic fish and transgenic fish heterozygous for the Tol2 insertion are obtained . In this figure, the promoter is tentatively defined as a spinal cord specific enhancer/promoter and the spinal cord of the embryo is depicted in green.