Fig. 3. The Ncl phenotype. (A) Nomarski image of normal nucleoli (arrows) in the nuclei of three neurons that have the genotype ncl-1(e1865)/ncl-1(e1865); sDp3[ncl-1(+)]. Although the endogenous copies of the ncl-1 gene carry e1865, a loss-of-function mutation that is completely recessive to the wild-type gene, each neuron inherited a free duplication (sDp3) that has a wild-type (+) copy of ncl-1, which fully complements the e1865 mutation. (B) Neurons that fail to inherit sDp3 have the genotype ncl-1(e1865)/ncl-1(e1865). They show the Ncl phenotype, a cell-autonomous enlargement of nucleoli (arrowheads). (C) The three nuclei are mosaic for the duplication. The two nuclei on the left have enlarged nucleoli, indicating that they failed to inherit sDp3; the nucleus on the right has a normal nucleolus, indicating its inheritance of the duplication. (D) The opposite pattern of mosaicism results when the two nuclei on the left, but not the nucleus on the right, inherit the duplication. (A'-D') The boundaries of the nuclei (gray) and of the nucleoli (white circles) are indicated for each of the upper panels. Scale bar: 10 µm.