SOX2 and anemia: Global recombination of our Hba1 conditional allele (Hba1fl/fl; Sox2-Cre19), hereafter referred to as global Hba1Δ/Δ, (Supplementary Fig. 7a–c) produced an anemia phenotype that mirrors the global loss of Hba1 through the insertion of a neomycin resistance cassette20 (Supplementary Fig. 7d–f) with significant defects in blood hemoglobin and hematocrit but with no statistically significant change in total RBCs.