Movie S1.

S18 (untreated) ES-cell derived embryo. Whole embryos derived from F1 hybrid S18 nonrecombinant ES cells. Embryos with almost exclusively ES cell contribution could be generated in the founder generation via laser-assisted morula injection. This allowed phenotyping of organismal traits by circumvention of hybrid sterility. Embryos were dissected in midgestation stage (∼14.5 d postcoitus or E14.5), contrast-stained, and scanned by using X-ray microCT at 9.4-µm resolution. The use of contrast staining allowed identification and precise measurements of individual organs (colorized here for clarity).