Homozygotes of both sexes had small gonads (Figure 2C; see below) and were invariably sterile. Ovaries of adult Trip13Gt/Gt females were severely dysmorphic and had few or no follicles (Figure 3A and 3B). The majority of oocyte loss occurred in late embryogenesis or early in postnatal development, since 2 d postpartum ovaries were markedly smaller than those of control littermates, and were lacking oocytes or newly forming follicles (Figure 3C and 3D). Thus, oocytes failed to progress to the dictyate (resting) phase. Since we observed oocytes with pachytene stage chromosomes in 17.5 d Trip13Gt/Gt embryonic ovaries (unpublished data), this indicates that oocytes were eliminated somewhere between pachynema and dictyate.