Forelimb zeugopod skeletal elements are mispatterned in Hoxa11/d11 double mutants and Hoxa11eGFP expression is maintained in the zeugopod throughout forelimb development. (A,B) Alcian Blue- and Alizarin Red-stained skeletal preparations of E18.5 control (A) and Hoxa11/d11 double mutant (B) mouse forelimbs. (C-E,I-K) Whole-mount view of Hoxa11eGFP heterozygous embryo forelimb at E10.5 (C), E11.5 (D), E12.5 (E), E13.5 (I), E14.5 (J), and E18.5 (K). (F-H,L-N) Transverse sections through Hoxa11eGFP heterozygous forelimb co-stained with an antibody for the pre-chondrogenic marker Sox9 (red) at E10.5 (F), E11.5 (G), E12.5 (H), E13.5 (L), E14.5 (M), E18.5 (N). The initially broad and scattered expression of Hoxa11eGFP (C,F) becomes localized by E11.5 and is largely excluded from cartilage condensations from the earliest stages. Scale bars: 300 μm.