Imprecise excision of a P-element insertion, resulting in a 1.1kb deletion that encompasses the miRNA cluster containing mir-310, mir-311, mir-312 and mir-313.

Homozygotes are viable. Eggs deposited by homozygous females mated to wild-type males hatch at only a slightly lower rate than wild-type controls. In contrast, very few eggs laid by wild-type females mated to homozygous males hatch, with the majority of the eggs appearing to be unfertilised.

Testes of homozygous males contain abnormal accumulations of large cysts of overproliferating, undifferentiated spermatogonia/germ cell clusters. These clusters are found far from the hub and the number of germ cells within each cluster far exceeds those found within normally differentiating wild-type cysts. The germ cells in the cluster show synchronous cell division and are connected by a shared cytoplasm (large branched fusomes are present). There is also a marked increase in the number of somatic cyst cells.