WKM was collected from adult wild-type, pgy/+ and sbn/+ fish on the gata1:gfp background. Samples were analyzed by flow cytometry for FSC, SSC and GFP; dead cells were gated out by PI staining. Two erythroid populations were quantified: proerythroblasts and polychromatophilic erythroblasts. For each genotype, the mean percent of progenitors within WKM was graphed for erythrocytes. For proerythroblasts and polychromatophilic erythroblasts the mean percent graphed, indicated by Gata1+ cells on the axis, refers to the percent GFP positive in the “precursor” or “lymphocyte” gate respectively, see Fig. 1 for details. P values were calculated by two-tailed student's T-test by comparing wild-type to smad5 mutants for each cell type. Sample numbers for each were: wild-type (n=8), pgy/+ (n=5), sbn/+ (n=3). *P<0.02.