SYNAPTIC ABNORMALITIES IN SPREAD NUCLEI OF SECALE .2. SECALE VAVILOVII

Secale vavilovii PMCs have more univalents and a lower frequency of bo und arms at metaphase I than other diploid Secale species. The spreadi ng technique applied at prophase I showed that the nuclei were able to complete synapsis at pachytene. However, 25% of the nuclei that the n uclei were able to complete synapsis at pachytene. However, 25% of the nuclei analyzed, which had more than 90% of their total length paired , showed two abnormalities: long fold-back loops, which were located m ainly on the nucleolar organizer bivalent, and pairing-partner switche s, probably involving all the chromosome complement. These synaptic ab normalities are unusual in diploid species and give rise to a high fre quency of nonhomologous pairing regions and, therefore, could produce desynapsis, which could explain the data obtained from metaphase I. Th e possible origin of the unusual synaptic abnormalities of S. vavilovi i is discussed.