In the larval eye discs of csw1 mutants only a few photoreceptors develop along the morphogenetic furrow. The residual photoreceptors are mostly R8 cells.
csw1/Y third larval instar eye discs show an increase in the number of apoptotic cells compared to wild type. There is also a zone of apoptotic cells anterior to the morphogenetic furrow, which is not seen in wild-type discs.
Has no "Enhancer of sev" activity. Clones of mutant cells induced during the first larval instar only rarely develop photoreceptors.
csw1 germline clone mosaics cause maternal effect lethality. There is slight paternal rescue of the germline clone phenotype; 74% embryos progress further through embryogenesis, complete germband shortening, often complete head involution and exhibit the corkscrew shape. Embryos that do not receive a wild type copy from their father (26%) die in the shape of a 'U' when the germband is fully extended or as it is shortening, often do not complete head involution.
Abnormal development of terminal internal structures. Syncytial and cellular blastoderm embryos show reduced posterior tll domain. hb remains as a posterior cap and the seventh ftz stripe expands posteriorly, both due to lack of hkb repressing activity.
Lethality occurs during larval and pupal stages. Phenotype of homozygous germ line clones is maternal effect lethal.