The desynaptic mutant of maize as a combined defect of synaptonemal complex and chiasma maintenance

The phenotype of the desynaptic (dy) mutant of maize in microsporocytes at meiotic prophase was compared with normal microsporocytes of a closely related strain and with microsporocytes of a maize inbred line (KYS) assumed to be normal. Strikingly more univalents and open arms of bivalents were found in the mutant cells than in normal cells at diakinesis, and where there was heterozygosity for a distal knob (heterochromatic region), separation was usually equational, indicating the occurrence of normal crossing-over followed by failure of chiasma maintenance in the mutant. Differences found in the mutant by electron microscopy were a statistically significant wider dimension of the synaptonemal complex central region and also less twisting of synapsed configurations at pachytene. It is suggested that these are side-effect symptoms of a defect in the synaptonemal complex (or associated substance), which is expressed later as sporadic loss of chiasma maintenance.