REDUNDANT FUNCTIONS OF THE GENES KNIRPS AND KNIRPS-RELATED FOR THE ESTABLISHMENT OF ANTERIOR DROSOPHILA HEAD STRUCTURES

Developmental gene functions of Drosophila are typically characterized by a recognizable mutant phenotype. When molecular probes of such gen es were used to isolate homologues, distinct spatially and temporally restricted expression patterns were observed in vertebrates as well. H owever, corresponding ''gene knock-outs'' often revealed subtle or no scorable phenotypes, a phenomenon attributed to redundant gene functio ns. We found that the evolutionarily related genes knirps (kni) and kn irps-related (knrl) contribute to a similar phenomenon in Drosophila. The two closely situated genes show identical expression patterns in t he developing embryo, including the posterior and anterior expression domains in the blastoderm. Here we show that the two biochemically equ ivalent gene products are both functional in the head anlage and that the lack of one gene activity can be overcome by the activity of the o ther. Whereas kni is also required for abdominal segmentation, knrl is nonfunctional in its posterior expression domain. Thus, the kni/knrl pair of genes provides a region-specific buffering system, rather than a case of global functional redundancy.