Fig. 4. Expression of sur-5::gfp in nuclei. (A) Fluorescent image of a non-mosaic worm. Arrowheads indicate three intestinal nuclei that have inherited an extrachromosomal array that expresses sur-5::gfp. (B) The corresponding Nomarski image. (C,D) Lack of fluorescence of three intestinal nuclei is indicated with arrowheads in a mosaic worm that lost the array in the embryonic cell E, the progenitor of the gut. (E,F) Patchy mosaicism in the gut. Two positive clones can be seen within an otherwise dark intestine, indicating consecutive losses of the array within the gut cell lineage. Consecutive losses occur more frequently for extrachromosomal arrays than for free duplications. Scale bars: in A, 50 µm for A-D; in F, 150 µm for E,F.