EVIDENCE FROM A MAIZE DESYNAPTIC MUTANT POINTS TO A PROBABLE ROLE OF SYNAPTONEMAL COMPLEX CENTRAL REGION COMPONENTS IN PROVISION FOR SUBSEQUENT CHIASMA MAINTENANCE

Homozygotes for the dsy1 desynaptic mutant of maize show massive failu re of chiasma maintenance during diplotene and diakinesis. Although so me chiasmata persist until anaphase I in most microsporocytes expressi ng this mutant, homozygotes are completely or nearly, completely steri le, owing apparently to disjunctive irregularities. Pachytene synaptic errors and some synaptic failure also are found, but recombination no dules are common in homologously synapsed regions, and equational sepa ration of a heterozygous knob into univalents or open arms at diakines is clearly demonstrates that chiasma failure occurs following crossing -over. A wider than normal synaptonemal complex central region and uni form apparent weakness of central region cross connections to spreadin g procedures strongly suggest the presence of a genetic lesion in a sy naptonemal complex central region component. The dsy1 mutant may provi de an especially important source of material for molecular studies on the nature of chiasma maintenance mechanism.