Fig. 6. Using unc-36 to identify specific classes of mosaics. (A) The phenotypes of the progeny of unc-36(–); Ex100[unc-36(+) sur-5::gfp] hermaphrodites, as shown in Fig. 5. The upper two classes of progeny are the most frequent. The non-mutant (fully coordinated), non-mosaic worms have the same genotype as the mother and can be used to propagate the strain. The uncoordinated, non-mosaic progeny derive from zygotes that failed to inherit the array owing to meiotic segregation. (B) The segregation pattern for let-a, a hypothetical gene that is essential for viability (let – lethal when mutant). Homozygosity for a recessive mutation in the gene, designated as let-a(–), results in death soon after hatching. The segregants are from mothers with the genotype unc-36(–); let-a(–); Ex101[unc-36(+) let-a(+) sur-5::gfp]. Ex101 is an extrachromosomal array that has wild-type copies of the unc-36 gene, wild-type copies of the let-a gene and a marker gene that expresses GFP. The segregation of mosaic worms that are fully viable but uncoordinated indicates that the focus of the lethal mutation is not in ABp, because loss of the array in ABp, which affects coordination, has no effect on viability. (C) The segregation pattern for a different lethal gene, let-b. Mutation of this gene also causes death soon after hatching. The segregants derive from mothers with the genotype unc-36(–); let-b(–); Ex102[unc-36(+) let-b(+) sur-5::gfp]. The failure to see older larvae and adults that are uncoordinated indicates that the focus of let-b includes the same part of the cell lineage as the focus of unc-36.