Deletion of otu transcription unit of more than 6.5kb.

Deletion of approximately 10kb removing the entire coding region of otu, starting in the upstream inverted repeat of the P-element of the parental allele, and extending into the neighbouring chorion gene cluster.

Mutant females form either small tumourous egg chambers, or chamberless (quiescent) ovarioles. Although appearing agametic, virtually all quiescent ovarioles contain germ cell clusters in their germarial regions. Most mutant XX germ cells survive and proliferate in adult ovaries. In each case mutant cells initiate gametogenic differentiation, producing either spectrosomes or short linear fusomes. Mutant fusomes are limited to 2-cell clusters and have variable amount of f-actin associated with them. This phenotype is similar to the most aberrant class of otu⁺ XY pseudofemale germ cells (produced by tra^hs.PB), however unlike in pseudofemales multi-branched fusomes are never detected nor are truncated fusomes associated with ring canals containing f-actin.

Homozygous viable and female sterile. Homozygous females produce either agametic ovarioles or tumorous egg chambers. Germarial region I is enlarged compared to wild-type, due to an increased number of germ cells arrested at stages prior to when they would normally interact with follicle cells. Ring canals lack inner rims, outer rims are in opposite orientation, and they are associated with fusomes. Fusomes contain substantial levels of actin filaments, in contrast to wild-type.

Homozygous female embryos and larvae contain the wild-type number of germ cells, indicating that XX germ cells do not require otu function for survival before pupariation. Homozygous adult ovaries often lack germ cells or have a variable number of ovarioles which contain small, dividing tumorous cells.

Homozygous females lack egg chambers. XY pseudofemales contain gonads that are similarly agametic. 90% of pseudoovaries lack egg cysts with the rest containing fewer than five chambers.

Agametic phenotype. otu¹/Df(1)otu-PΔ1 transheterozygotes carrying P{hs-otu.98} have relatively large ovaries containing many tumourous egg chambers.

Necessarily a null mutation for otu, the female sterility phenotype is predominantly of tumorous egg cysts, a phenotype that is less severe than for other otu alleles, e.g. otu^PΔ4.