Ultrastructural Evidence for Crossing Over in the XY Bivalent of the Turkish Hamster (Mesocricetus brandti).

A sequential electron microscopic study of XY synaptonemal complexes of male Turkish hamster sprematocytes by 2 methods was carried out. The results revealed that 1 or 2 chromatin fibril-like strands were commonly extending and connecting the XY axes either around the border of the differential and non-differential segments or near the attachment plaques. The existence of such strands between 2 axes, and the number and position they presented were found to be highly correlating to stages/sub-stages of the spermatocytes. A possibility of visual evidence for chiasma formation and terminalization in the sex bivalent in the present species is discussed.