Fig. 4.

Accessing developmental phenotypes in recombinants between evolutionarily divergent species. Embryos at midgestation (14.5 d after fertilization) were derived from nonrecombinant F1 S18 ES cells (A) and IVR lines 1 (B) and 2 (C; see Methods for details). Embryos were dissected, contrast-stained, and scanned by using X-ray microCT at 9.4-µm resolution. The high scanning resolution allowed identification and precise measurements of individual organs (colorized here). Major developmental craniofacial and neural tube closure defects were observed in the IVR lines (B; caudal view with arrowhead indicates neural tube lesion). (Scale bars: 200 µm.)