The previously reported sterility of Mst77F¹/Df(3L)ri-79c males (FBrf0188104, FBrf0210142) is probably unrelated to Mst77F function (although analysis of other alleles of Mst77F establishes that this gene is required for male fertility): Df(3L)ri-79c does not uncover the Mst77F gene and does not affect its expression (shown by genomic DNA sequencing and Western blotting) and Df(3L)ri-79c fully complements the male sterility phenotype of the Mst77F^Δ1 allele (a mutation within the Mst77F coding sequence that results in a frameshift and premature stop codon and whose sterility phenotype is rescued by the Mst77F^+tg transgene). The Mst77F¹ line does contain a S149T mutation within the Mst77F coding sequence (FBrf0188104). This lesion was identified on a chromosome originally isolated as the unmapped 'ms(3)nc3' male sterile mutation. The Mst77F¹ line is probably no longer available.

Spermatid nuclei of Mst77F¹/Df(3L)ri-79c males are often not aligned in parallel but are scattered within a cyst.

Mst77F¹/Df(3L)ri-79c males show defective spermatid nuclei. At early stages, the spermatid nuclei appear normal but at later stages the nuclei are scattered instead of clustered and are round or ellipsoid instead of elongated. Some spermatid nuclei begin to elongate but at a far lesser rate than wild type. Chromatin condensation fails to occur properly and spermatids do not develop into individualized sperm. Mst77F¹/Mst77F^c06969 males show a slightly less severe phenotype with fewer small nuclei being produced but still no sperm individualization.

Mst77F¹/+ males, although fertile, show a few aberrant tiny nuclei in scattered and individualized mature sperm.

Male fertility of homozygotes not determined. ms(3)nc3¹/+ males fertile.