e, recombination-based mechanisms also help maintain chromosome termini. Nevertheless, in Drosophila males, there is no recombination, and thus the higher mre11 expression levels in males than in females might have been anticipated. Two functional polo gene duplicates are observed in D. persimilis/ D. pseudoobscura. polo-dup1 and 
polo-dup2 are apparently exclusively expressed in males. It can thus be predicted that in the obscura group of Drosophila nuclear envelope breakdown and entry into prometaphase occurs earlier in males from these species when compared with what happens in D. melanogaster. The D. melanogaster Mtrm protein is a meiosis-specific 1:1 stoichiometric inhibitor of the Polo kinase protein. Two independent duplications of this gene were found, one in D. willistoni and the other in D. virilis. The D. willistoni mtrm-dup gene seems to be a recent pseudogene, whereas strong evidence is here presented supporting the fact that the D. 1353550-13-6 cost virilis mtrm-dup is an old functional gene duplication. It is unlikely that mtrm-dup is a meiotic drive element that was duplicated just by chance. It can thus be predicted that in D. virilis nuclear envelope breakdown and entry into prometaphase occurs later than in D. melanogaster. It should be noted that the D. virilis mtrm-dup is expressed in females only. There are functional gene duplicates of meiS332 in D. mojavensis and D. virilis. If there is more MeiS332 protein to be removed from centromeres by Polo, then meiosis would be delayed, since removal of MeiS332 from centromeres is a step required for proper chromosome segregation at the metaphase II/anaphase II transition. Interestingly, in D. virilis females the mtrm gene is also duplicated. As noted above, an increase in Mtrm protein levels is also predicted to result in a delay in meiosis. A delayed meiosis could result in more time available to deal with large genomes such as that of D. virilis. It is, however, unclear whether the high heterochromatin content found in D. virilis is the consequence of an historically advantageous long meiosis duration that allowed the accumulation of high amounts of 2187993 heterochromatin without deleterious consequences, or whether the long meiosis duration is an adaptive response aiming at handling the large amount of heterochromatin found in this species, that may have accumulated due to other reasons. In conclusion, in this work we find that, contrary to theoretical expectations, meiosis-related genes are duplicated and retained at the same rate as the average for all genes. The duplicated genes were, a priori, unlikely to be found duplicated, and may represent examples of neofunctionalization. Detailed cellular and biochemical experiments must be performed in order to address this issue. Nevertheless, given the nature of the genes that were found duplicated, it is here speculated that the duplicated genes may affect meiosis duration. D. melanogaster is the only Drosophila species where meiosis duration has been recorded. The results here presented suggest that in the obscura group of species, male meiosis duration may be shorter than in D. melanogaster, while in D. virilis, where three meiosis genes are duplicated, meiosis duration may be much longer than in D. melanogaster. Interestingly, D. virilis is among the Drosophila species the one with highest nuclear DNA content, and Bennett has shown a linear correlation in insects between nuclear DNA content and the duration of meiosis. If the correlation derive
