A large portion of the Drosophila melanogaster genome is contained within heterochromatic regions of chromosomes, predominantly at centromeres and telomeres. The remaining euchromatic portions of the genome have been extensively characterized with respect to gene organization, function and regulation. However, it has been difficult to derive similar data for sequences within centromeric (centric) heterochromatin because these regions have not been as amenable to analysis by standard genetic and molecular tools. Here we present an updated genetic and molecular analysis of chromosome 3L centric heterochromatin (3L Het). We have generated and characterized a number of new, overlapping deficiencies (Dfs) which remove regions of 3L Het. These Dfs were critically important reagents in our subsequent genetic analysis for the isolation and characterization of lethal point mutations in the region. The assignment of these mutations to genetically-defined essential loci was followed by matching them to gene models derived from genome sequence data: this was done by using molecular mapping plus sequence analysis of mutant alleles, thereby aligning genetic and physical maps of the region. We also identified putative essential gene sequences in 3L Het by using RNA interference to target candidate gene sequences. We report that at least 25, or just under 2/3 of loci in 3L Het, are essential for viability and/or fertility. This work contributes to the functional annotation of centric heterochromatin in Drosophila , and the genetic and molecular tools generated should help to provide important insights into the organization and functions of gene sequences in 3L Het.

tised in a variety of settings. To exclude those who practise "less than" tertiary care medicine from our community is self-defeating. I believe that we will gain much more strength as a larger, more unified community.I would encourage CAEP and our EM community at large to engage in discussions about consolidated training, and wouldn't argue against "fellowships" and other recognitions of distinction in training. I believe that our EM colleagues from smaller centres will continue to be interested in educational opportunities and research initiatives designed by those with more training and with experience in high acuity/high volume centres. I propose that we look at a broader educational strategy to support our whole EM community rather than attempt to define a one-size-fits-all definition of an emergency physician that cleaves the majority from our ranks.

Sperm competition generates selection for male traits to prevent it. These traits remain unclear in species where males compete for a virgin who is briefly receptive. Males of the parasitoid wasp Ooencyrtus kuvanae Howard (Hymenoptera: Encyrtidae) compete over females following emergence from host egg masses. Males engage virgins in a precopulatory ritual, mate, and then immediately perform a postcopulatory ritual after which the female becomes unreceptive. Often, sneaker (M 2 ) males copulate with a female while she is engaged in the postcopulatory ritual, and they also perform the postcopulatory ritual. We investigated (i) paternity of M 1 and M 2 males using DNA microsatellite analysis, (ii) copulation and postcopulatory behaviour of both males, and (iii) morphological adaptations of the aedeagus for sperm removal. Eighty-eight percent of M 1 males sired all daughters when they were first to perform the precopulatory and postcopulatory ritual, suggesting a linked effect of both rituals on paternity. The number and length of copulations by both males did not affect paternity, and the shape of the aedeagus does not seem to facilitate sperm removal. Our results are consistent with the hypothesis that postcopulatory rituals represent forms of mate guarding that function to increase paternity in the context of sperm competition.Résumé-La compétition spermatique entraîne une sélection des traits mâles qui permettent de l'éviter. Ces traits restent obscurs chez les mâles qui font compétition pour une femelle vierge qui n'est réceptive que sur une courte période. Les mâles de la guêpe parasitoïde Ooencyrtus kuvanae Howard (Hymenoptera: Encyrtidae) se font compétition pour les femelles lors de leur émergence des masses d'oeufs de l'hôte. Les mâles entreprennent un rituel précopulatoire avec les femelles, s'accouplent et complètent immédiatement un rituel post-copulatoire à la suite duquel les femelles ne sont plus réceptives. Souvent, des mâles intrus (M 2 ) s'accouplent avec la femelle durant son rituel post-copulatoire et pratiquent aussi eux-mêmes le rituel postcopulatoire. Nous avons étudié i) la paternité chez les mâles M 1 et M 2 par analyse des microsatellites d'ADN, ii) la copulation et le comportement postcopulatoire chez les deux types de mâles et iii) les adaptations morphologiques de l'édéage pour le retrait du sperme. Quatre-vingt-huit pour cent des mâles M 1 engendrent toutes les guêpes filles lorsqu'ils sont les premiers à compléter les rituels copulatoire et postcopulatoire, ce qui laisse croire à un lien effectif entre ces deux rituels et la paternité. Le nombre et la durée des accouplements chez les deux types de mâles n'affectent pas la paternité et la forme de l'édéage ne semble pas faciliter le retrait du sperme. Nos résultats s'accordent avec l'hypothèse selon laquelle les rituels postcopulatoires représentent une forme de surveillance du partenaire dont la fonction est d'augmenter la paternité dans une situation de compétition spermatique.