Characteristic yeast cell phenotypes observed on arrays. DIC images from cell chips were collected automatically at 60× magnification with DAPI-stained nuclei superimposed in blue pseudocolor. Each gene name indicates the corresponding deletion strain (for example, dse2 ΔKanMX4 ). (a) Six phenotypic classes observed among the haploid yeast deletion strains. YIL141W overlaps the AXL2 gene, whose disruption in the deletion strain probably provides the observed morphology. (b) Changes in cell morphology observed after treating the deletion collection with mating pheromone. Many mutants, such as the mrps5 ΔKanMX4 deletion strain (left), form 'wild-type'-like mating projections upon adding alpha factor, while cells lacking STE7 (middle) fail to form mating projections, and cells lacking KEL1 (right) form mating projections of unusual morphology.