mutants defective in meiotic cytokinesis can be easily identified by their multinucleate spermatids. Moreover, the large
size of meiotic spindles allows characterization of mutant phenotypes with exquisite cytological resolution. We have
screened a collection of 1955 homozygous mutant male sterile lines for those with multinucleate spermatids, and thereby
identified mutations in 19 genes required for cytokinesis. These include 16 novel loci and three genes, diaphanous, four
wheel drive, and pebble, already known to be involved in Drosophila cytokinesis. To define the primary defects leading
to failure of cytokinesis, we analyzed meiotic divisions in male mutants for each of these 19 genes. Examination of
preparations stained for tubulin, anillin, KLP3A, and F-actin revealed discrete defects in the components of the cytokinetic
apparatus, suggesting that these genes act at four major points in a stepwise pathway for cytokinesis. Our results also
indicated that the central spindle and the contractile ring are interdependent structures that interact throughout cytokinesis.
Moreover, our genetic and cytological analyses provide further evidence for a cell type-specific control of Drosophila
cytokinesis, suggesting that several genes required for meiotic cytokinesis in males are not required for mitotic
cytokinesis