Synaptonemal complex karyotyping in spermatocytes of the Chinese hamster (Cricetulus griseus). I. Morphology of the autosomal complement in spread preparations.

Using the Counce-Meyer spreading technique, in over 70 spermatocytes it was possible consistently to obtain whole, flattened nuclei containing complete sets of pachytene SCs. The SCs are visible in both the phase and electron microscopes. Each SC is morphologically intact, preferentially stained, and attached to the nuclear envelope by a dense, terminal plaque. It is thus possible to trace each SC for its entire length. Also, a structure representing the kinetochore is clearly visible in each autosomal SC. Karyotypes comparable to the somatic karyotype can be constructed by arranging SCs according to length and kinetochore position. The observed regularity of SC morphology implies structural stability sufficient to withstand the stresses imposed by the procedure.--A coarse network of closely packed nuclear annuli connecting SC attachment plaques often provides end-to-end associations and may tend to immobilize SCs during processing.--Three kinds of perturbation of SC structure are encountered. Twists in the SC frequently occur, but no regular pattern or correspondence with chiasma distribution is observed. SCs occasionally hook around each other without disruption, but in two instances the unpaired axis of the X apparently was interlocked within an autosomal SC. Streching of the SC is infrequent; it is conspicous when it occurs and is usaully associated with other obvious distortions of the nucleus.--Distinctive morphologies of the X and Y chromosomes facilitate their identification inall preparations.--During zygotene, autosomal synapsis, i.e., the formation of SCs from the pairing of single axial elements, initiates at distal ends and terminates at the kinetochore region; neither initiation nor termination is synchronous among all autosomes.