Meiotic genes annotated in the D. pulex genome (shown in boxes) and a schematic of a possible model for parthenogenesis. Arrows indicate their roles in meiosis, and potentially in parthenogenesis. Proteins in bold are encoded by multiple gene copies in D. pulex (some non-annotated genes are italicized; see text for details). A timeline (top) for three stages of meiosis (meiosis entry, recombination, and segregation) is indicated at the top. Meiosis I events from germline stem cell (GSC) division (1) through DSB formation, synapsis and recombination (2–9), kinetochore attachment (10) and anaphase (11) occur during canonical meiosis I. Meiosis II follows (12), with the loss of centromeric cohesion and segregation of sister chromatids resulting in the final haploid gamete. In our model for parthenogenesis (bottom), sister chromatid cohesion somehow differs from meiosis while altered heterochromatin and centromere formation may be important for homolog pairing and segregation. Reciprocal recombination is suppressed and syntelic rather than amphitelic kinetochore attachment is also posited (grey ovals). Our model for parthenogenesis predicts the expulsion of a single diploid polar body after a mitotic cell division accompanies production of the diploid "gamete" which gives rise to the next generation. See text for a more detailed description of the stages of meiosis and explanation of our model for parthenogenesis.