20-50% of homozygotes die during the embryonic stages. Female fertility is unaffected. Mutants testes are smaller than wild type and do not contain elongated spermatids. Primary spermatocytes enter the growth phase, giving rise to morphologically mature primary spermatocytes with normal large nuclei, prominent nucleoli and decondensed chromosomes. They then degenerate without initiating the meiotic chromosome condensation that normally occurs after growth phase. Neither meiotic figures nor spermatids are observed in mutant testes. The basal region of mutant testes is filled with the debris of degenerating primary spermatocytes.