Schematic of mutant library construction and screening. F₁larvae of chemically mutagenized P₀ animals are cultured in microtiter arrays to produce F₂ larvae, constituting the worm library. An aliquot of worms from each well is removed and processed into a corresponding genomic DNA array; simultaneously, the 96 samples from each plate are pooled and processed to produce genomic DNA plate pools. The DNA plate pools are screened by nested PCR in 96-well plates for deletion amplicons, which identify a positive worm library plate Y. After confirmation by quadruplicate PCR (not illustrated), the genomic DNA array for that specific library plate is similarly screened to identify the specific well. The corresponding well is then retrieved from the frozen mutant worm library and thawed. Individual live worms are allowed to have self-progeny in microtiter wells, and aliquots of each well are tested by PCR to determine which of the thawed worms contain the deletion (see Methods for details).