Fetal liver erythropoietic compartments. (A) Erythropoietic compartments defined by Ter119 and CD71 expression; maturation is shown by the progression from the least mature (R1) to most mature (R5) erythroid population. (B) Average proportion (±SD) of fetal liver cells in each compartment. Kit^Wv/Wv embryos have a reduced proportion of cells in R1, independent of the c-Mpl genotype.