Histological sections of mutant testes revealed a lack of postmeiotic cell types that are characteristic of wild-type seminiferous tubules (Figure 3E). The most developmentally advanced seminiferous tubules contained adluminal spermatocytes with condensed chromatin characteristic of pachynema (Figure 3F). The absence of coordinated spermatogenic progression beyond this stage is indicative of a pachytene arrest. This was revealed more clearly by chromosome analysis (see below). Some sections of adult seminiferous tubules contained postmeiotic spermatids (Figure 3G), although we saw no motile epididymal sperm. These drastic meiotic defects stand in contrast to yeast and C. elegans, in which deletion of Pch2 alone has minor effects on spore/gamete development [2,8].