SYNAPTONEMAL COMPLEX-ANALYSIS IN SPERMATOCYTES OF TILAPIA, OREOCHROMIS-NILOTICUS (PISCES, CICHLIDAE)

Some adaptations of the synaptonemal complex (SC) whole-mounting techn ique first used in plants permitted its application to meiotic studies in tilapia, Oreochromis niloticus. Direct observation of the chromoso me pairing process and bivalent structure during the meiotic prophase of this fish species by light and electron microscopy permitted the an alysis of SCs in autosomes and the possible identification of sex chro mosomes. The analysis of SCs in spermatocytes of 0. niloticus revealed that all 22 bivalent chromosomes completely paired, except for the oc currence of a size heteromorphism in the terminal region of the larges t bivalent associated with the presence of an incompletely paired segm ent during the synapsis process, which may be the cytological visualiz ation of an XX/XY sex chromosome system in this species.