SYNAPTONEMAL COMPLEX-ANALYSIS IN SPERMATOCYTES OF WHITE STURGEON, ACIPENSER-TRANSMONTANUS RICHARDSON (PISCES, ACIPENSERIDAE), A FISH WITH AVERY HIGH CHROMOSOME-NUMBER

The surface-spreading synaptonemal complex (SC) technique was used to visualize the process of chromosome synapsis in white sturgeon spermat ocytes. Pachytene nuclei had various numbers of univalents (0-3) and s elf-paired foldback elements with no obvious centromeric region (1-7) that may represent accessory chromosomes. The total SC length was 482 (+/- 56) mu m and the average number of SC elements per nucleus was 13 9 (+/- 3.4). This SC number suggests a higher chromosome number than h ad been reported in previous mitotic studies (2n = 248 +/- 8). There w as variation in the SC count both within and between animals. A repres entative SC karyotype is presented and some differences between the mi totic and meiotic karyotypes for this species are discussed. There was no evidence of multivalent formation, suggesting that the process of diploidization has gone to completion in the males of this ancient pol yploid species. Each SC had lateral elements of equal length, and no b ivalent exhibited the atypical pairing behavior that is often characte ristically associated with heteromorphic sex chromosomes, suggesting t hat the male is not the heterogametic sex in white sturgeon.