SPREADING SYNAPTONEMAL COMPLEXES FROM THE GRASSHOPPER CHORTHIPPUS-JACOBSI - PACHYTENE AND ZYGOTENE OBSERVATIONS

Pachytene and zygotene stages have been analysed on silver stained spr eads of synaptonemal complexes (SCs) from Chorthippus jacobsi spermato cytes. SC lengths are compared to those obtained from C-banded mitotic metaphases. The pattern of meiotic pairing initiation and progression is described. In the submetacentric bivalents it is initiated from bo th chromosomal ends whereas in acrocentric bivalents two potential pai ring initiation points arc located in the long arms, the short arms re maining as late pairing regions. In addition. some interstitial pairin g initiation points also occur, particularly in the L and M4-M5 bivale nt groups. Shorter chromosomes commence and finish pairing relatively early. Interlockings form and are mostly resolved throughout zygotene. The estimated mean number of interlockings is 1.6 at zygotene as oppo sed to 0.17 at early-mid pachytene.