SYNAPTONEMAL COMPLEX-ANALYSIS IN SPERMATOCYTES AND OOCYTES OF RAINBOW-TROUT, ONCORHYNCHUS-MYKISS (PISCES, SALMONIDAE) - THE PROCESS OF AUTOSOME AND SEX-CHROMOSOME SYNAPSIS

The surface-spreading synaptonemal complex (SC) technique was employed to analyze spermatocytes and oocytes of rainbow trout in order to vis ualize the process of autosome and sex chromosome synapsis in this spe cies. The structure of lateral elements (LEs) of the SC and the chromo some synapsis process at the stages of leptotene, zygotene and pachyte ne are described. Comparative analysis of SCs of spermatocytes and ooc ytes showed a difference in the synaptic process, i.e. in spermatocyte s all LEs were synapsed before the appearance of centromeric regions i n the biarmed elements, while in the oocytes some fully synapsed LEs, including the centromeric region of the biarmed elements, were found t ogether with fully or partially unsynapsed LEs. In males the sex chrom osome synapsis starts only after all autosomes have synapsed. Irregula r synapses involving three or four LEs were found in 3.4% of the cells analyzed in mid or late zygotene. Multivalents were found in males an d females. Some aspects of initial meiotic development and their impli cations in rainbow trout cytogenetics, genetics and evolution are disc ussed.