Early stages of male germ cell differentiation proceed normally in mutant testes. However, mature spermatocytes are all arrested at the G2/M transition of meiosis I and fail to initiate spermatid differentiation.

The first defects observed in mutant male germ cells are abnormalities in chromatin condensation during the spermatocyte growth stages: autosomal bivalents are subtley disorganized at immature stages and these defects become more apparent as the spermatocytes grow and mature; in mature mutant spermatocytes, chromatin is less condensed and forms variable structures lacking clear boundaries.

Instead of entering the first meiotic division, mutant spermatocytes arrest with partially fragmented nucleoli and incompletely condensed chromatin forming abnormal structures. No signs of spermatid differentiation are observed; instead, arrested spermatocytes accumulate throughout the basal end of the mutant testis and eventually degenerate.