Decreased efficiency of erythroid body formation in Rps19 mutant cell line. Primary differentiation was performed on Rps19- haploinsufficient and parental ES cell lines. Cultures were scored for total embryoid body (EB) number on day 6 and for hematopoietic percentage on day 13. The Rps19- haploinsufficient line (YHC074) showed a marked reduction in efficiency of EB formation compared with the parental line (E14). This difference was most pronounced in the hematopoietic EB population.