The following information accompanied stocks donated to the Bloomington Stock Center by Tom Cline, University of California at Berkeley.
SxlfP7bo is currently listed as a single-gene deletion, but microarray analysis of mRNA in male heads by Sha Sun indicated that the proximal breakpoint likely extends at least 10 kb past Sxl to eliminate fz4. 
Since viability is unaffected in hemizygous males, the distal breakpoint must not extend as far as nullo (~25 kb away), an essential zygotic gene.