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Background  Thousands of parthenogenetic animal species have been described and cytogenetic manifestations of this reproductive mode are well known. However, little is understood about the molecular determinants of parthenogenesis. The  Daphnia pulex  genome must contain the molecular machinery for different reproductive modes: sexual (both male and female meiosis) and parthenogenetic (which is either cyclical or obligate). This feature makes  D. pulex  an ideal model to investigate the genetic basis of parthenogenesis and its consequences for gene and genome evolution. Here we describe the inventory of meiotic genes and their expression patterns during meiotic and parthenogenetic reproduction to help address whether parthenogenesis uses existing meiotic and mitotic machinery, or whether novel processes may be involved.    Results  We report an inventory of 130 homologs representing over 40 genes encoding proteins with diverse roles in meiotic processes in the genome of  D. pulex . Many genes involved in cell cycle regulation and sister chromatid cohesion are characterized by expansions in copy number. In contrast, most genes involved in DNA replication and homologous recombination are present as single copies. Notably,  RECQ2  (which suppresses homologous recombination) is present in multiple copies while  DMC1  is the only gene in our inventory that is absent in the  Daphnia  genome. Expression patterns for 44 gene copies were similar during meiosis  versus  parthenogenesis, although several genes displayed marked differences in expression level in germline and somatic tissues.    Conclusion  We propose that expansions in meiotic gene families in  D. pulex  may be associated with parthenogenesis. Taking into account our findings, we provide a mechanistic model of parthenogenesis, highlighting steps that must differ from meiosis including sister chromatid cohesion and kinetochore attachment.

Meiosis genes in Daphnia pulexand the role of parthenogenesis in genome evolution