Synaptonemal Complex and Male Crossing-over in Drosophila ananassae

抄録

Although it has been known that crossing-over does not take place in the male of Drosophila species, D. ananassae is a notable exception in which spontaneous crossing-over occurs in the male. The results of a study of crossing-over in the males of a Tonga strain (T_15-4) of D. ananassae are described. Whether the synaptonemal complex is formed in pro-spermatocytes from testes of the T_15-4 strain was examined by electron microscopy. The synaptonemal complex with typical tripartite structure which was seen in pro-oocytes could not be found. However, in leptotene and early zygotene cells, the axial filament which makes up the center of each chromosome was clearly observed. Furthermore, in zygotene cells, homologous chromosomes formed incomplete synapses with the aid of an imperfectly developed synaptonemal complex. It is considered, therefore, that male crossingover takes place between these imperfectly synapsed homologues, although its frequency is much lower than that seen in females.