Booreana ENU mutant identification and heritability testing. Example of a variant embryo (mouse G3.8 from pedigree ENU11.28; A) identified by the FL screen as having atypical stem cell and progenitor FACS hematopoiesis (increased LT-HSC, MPP, CLP, and CMP; decreased GMP and MEP; B) at E14.5. The C57BL/6J G1 male founder was outcrossed to a C57BL/10SnJ female and then established as a true-breeding strain by intercrossing F1(B6 × B10) siblings and testing with the same screening protocol. Additional variant embryos (mutant F2.2, F2.3, F2.4, F2.12, and F2.19) showed an identical abnormal increase in KLS (cKit⁺Lin⁻Sca1⁺) and other stem cell subsets (C-D), and a perturbed fetal blood FACS profile (increased primitive RBC and platelets; decreased definitive RBC; E) at E14.5. Red dots represent putative recessive mutants; and black dots, phenotypic wild-type littermates.