MEIOTIC MUTANTS OF RYE SECALE-CEREALE L .2. THE NONHOMOLOGOUS SYNAPSIS IN DESYNAPTIC MUTANTS SY7 AND SY10

We studied the expression and inheritance of two spontaneous mutations found in different populations of rye Secale cereale L. that cause hi gh univalent frequency in meiosis and low fertility. Both mutations we re inherited as monogenic recessives. For each of the mutations the co rresponding gene symbols (sy7 and sy10) were suggested although their allelism has not been studied. These mutants differ in chiasma frequen cy and in the number of univalents per meiocyte. Electron microscopy o f the wholemount surface-spread synaptonemal complexes (SCs) from micr osporocytes of both mutants revealed that during meiotic prophase I ra ndom synapsis began and progressed that involved not only homologous b ut also nonhomologous chromosomes. SCs were formed with frequent chang es of pairing partners (switches) and intrachromosomal foldbacks of un paired axial elements. As a result, incompletely synapsed, non-homolog ous and multivalent SCs were formed in mutants by the stage analogous to pachytene in normal plants. In sy7 a maximum in the number of switc hes and foldbacks were observed at zygotene, whereas in sy10 this occu rred at pachytene. We suggest that it is the process of recognition of homology that is impaired in both mutants. This leads to indiscrimina te synapsis and prevents chiasma formation. Both mutants may be classi fied as desynaptic.