Gata1-GFP homozygous transgenic fish were used to identify clo^–/– mutants at the 15-somite stage. (A) Wild-type embryo; (B) clo^–/– embryo. Note that GFP fluorescence in hematopoietic precursor cells (arrows) is absent in the clo^–/– embryo, while nonspecific GFP expression in the anterior region is not affected (arrowheads).