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The synaptonemal complex (SC) is a prominent and evolutionaly well conserved structure which is strictly meiotic. Several evidences from mutant phenotypes support the hypothesis that recombination and SC formation are mutually interdependent processes. Moreover, the SC recombination nodules correspond in number and location to the crossing-over events. However, recent data confirm that SC formation does not require initiation of recombination, and several observations indicate that full synapsis is not required for recombination. The potential roles played by the SC will be discussed in the following framework: First, although not required for homology recognition, the SC could promote interhomolog interactions in situations where the normal processes have failed (interlocking, heterologous pairing, etc.); Second, polymerization of the SC components might permit the recombination process to progress by modulating the number and localisation of reciprocal versus nonreciprocal exchanges (i.e. interference) and; Third, the SC may play an important role in meiotic chromosome structure and especially in inter-sister interactions.

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Summary - A new Robertsonian translocation was found in 7 animals of the Grey Ukrainian breed. The translocated chromosome, analyzed by GTG- and RBG-banding, resulted from the fusion of chromosomes 8 and 23. C-banding suggested that the translocated chromosome has a double heterochromatic block. Synaptonemal complex analysis was performed using electron microscopy. cattle / chromosome / Robertsonian translocation

Summary - Analysis of synaptonemal complexes from a bull homozygous carrier for the 1;29 Robertsonian translocation showed the presence of 28 autosomal bivalent figures including one with subtelocentrically located kinetochores. No association with the sex vesicle was detected. In the X — Y bivalent, a pairing segment existed between the extremity of the X and Y chromosomes throughout pachytene. A gap separating that complex from the rest of the Y chromosome was apparent, regardless of the stain used. The results of this study confirm that there is no meiotic impairment when this homozygous translocation is present.