Fig. 1

Schematic representation of testicular structure and spermatogenesis in adult mice (A), adult Drosophila (B), and in the various nymph stages of Nasonia vitripennis (C). Above: The spatial distribution of germ cells during these various stages is taxon specific: seminiferous tubule structure in mice (with the spermatogonia at the base of tubules and the spermatids in the luminal pole; see the red arrow) and cyst structure in the two insects. In N. vitripennis, each stage occurs consecutively during pupal development, whereas, in Drosophila, the stages occur simultaneously in the testis. Below: the main events occurring during meiosis, from the formation of spermatogonia to the formation of spermatids. The colors correspond to the four differentiation stages of spermatogenesis as follows: pink—spermatogonia (undifferentiated cells); blue—primary spermatocytes (after DNA duplication); green—secondary spermatocytes (after meiosis I); and yellow—spermatids (after meiosis II). In contrast to what occurs in the mouse, there is no recombination between homologous chromosomes in Drosophila (diploid) during meiosis. In N. vitripennis, males are haploid. Drawing of organisms © Eric Imbert/IRBI CNRS/Université de Tours