An experimental analysis of bivalent interlocking in spermatocytes of the newt Triturus Vulgaris

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Abstract
Interlocked bivalents at 1st meiotic metaphase are relatively uncommon in spermatocytes of the newt Trituras vulgaris, but their frequency of occurrence can be significantly increased by subjecting newts to a 24-h heat shock. Newt spermatocytes are sensitive to a heat shock at any stage between the end of premeiotic S and mid to late pachytene. The heat shock does not cause evident desynapsis, nor does it significantly affect chiasma frequency; therefore the interlocked condition induced in spermatocytes which were subjected to a heat shock when they were in zygotene or pachytene is unlikely to be a consequence of synaptic trapping. By way of explanation it is suggested that a heat shock may cause telomeres to detach from the nuclear membrane, or from the synaptonemal complex where the latter is attached to the membrane, thus allowing non-homologous chromonemata to become intertwined before chiasmata have formed. If this explanation is valid, it is then further suggested that the recombination process which results in chiasma formation probably takes place in chromosomal regions lying outside the synaptonemal complex, rather than inside, between its 2 lateral elements.