Class I fu allele, affects the catalytic domain but does not change the open reading frame.
weak wing phenotype - veins L3 and L4 fused only proximally; strong viability phenotype - ratio of the number of fused flies to wild type in fu/+ X fu/Y is 0.25-0.5; weak fecundity phenotype - ratio of eggs laid by fu/fu versus fu/+ sisters is 0.5-1.0; strong maternal effect on segmentation - percent of embryos with all segments entirely duplicated is 70-100%.
