THE RELATIONSHIP OF HOMOLOGOUS SYNAPSIS AND CROSSING-OVER IN A MAIZE INVERSION

Frequency of homologous synapsis at pachytene for a relatively short h eterozygous inversion was compared to the frequency of crossover occur rence within the inversion and to the frequency of the presence of a r ecombination nodule within the homologously synapsed inverted region. Crossover frequencies were estimated from bridge-fragment frequencies at anaphase I and anaphase II. Recombination nodules (RNs) were observ ed in electron micrographs. Results show very similar frequencies of h omologous synapsis and the occurrence of reciprocal recombination with in the inverted region, consistent with the interpretation that establ ishment of homologous synapsis in this case is related to at least com mitment to the form of resolution of crossover intermediates which giv es rise to reciprocal recombination, not conversion only, events. An R N was generally found at pachytene in homologously synapsed inverted r egions.