Functional redundancy: the respective roles of the two sloppy paired genes in Drosophila segmentation.

The sloppy paired (slp) locus consists of two genes, slp1 and slp2, both of which encode proteins containing a forkhead domain (a DNA-binding motif). Previous work has shown that a severe segmentation phenotype is obtained only when both slp genes are deleted. Here we examine the functional redundancy of the locus in more detail. The phenotypes of embryos containing various combinations of functional slp genes suggest that for early slp function, until gastrulation, only slp1 is required. At later times, there is still a greater requirement for slp1, but in many respects the two slp genes are completely redundant. Both slp genes produce similar phenotypes when ubiquitously expressed via a heat shock promoter. We propose that the slp proteins are biochemically equivalent and that the greater requirement for slp1 in some functions can be explained in large part by its earlier expression.