Definitive blood lineages are absent in cbfb^del4/del4 embryos. Expression of markers for definitive hematopoietic lineages in WT control siblings (A,C,E,G) and cbfb^del4/del4 embryos (B,D,F,H) by WISH. At 3 dpf, the myeloid marker l-plastin was expressed in the CHT of WT embryos (A, black arrow), but not in cbfb^del4/del4 embryos (B). hbae1 expression in the erythroid progenitors within the CHT (C, black arrow) was completely abrogated in cbfb^del4/del4 embryos (D) at 6 dpf. Expression of the T-lymphocyte markers ikaros and rag1 within the thymus (E,G black arrowheads) was also abrogated in cbfb^del4/del4 embryos (F,H) at 5 dpf.