Tr4 heterozygous mutant mice are anemic. (A) The number of total bone marrow cells was quantified in WT (closed circles) and Tr4^+/− (open circles) femurs. Peripheral blood was collected from 6- to 8-week-old WT (Tr4^+/+; closed circles) or heterozygous mutant (Tr4^+/−; open circles) B6 congenic mice and then stained with o-thiazole orange to determine the percentage of (B) reticulocytes and CBCs to analyze the (C) concentration (RBC), (D) Hb, and (E) hematocrit in triplicate samples. *P ≤ .05 as determined by Student t test comparing Tr4^+/− with WT.