Chromosome Segregation in Maize Translocations in Relation to Crossing Over in Interstitial Segments

Abstract

In maize, the second meiotic division in the microsporocytes results in a quartet of four microspores in which it is possible to distinguish the two division planes. In normal material, the prominent feature of these spores, as revealed by acetocarmine smears, is the single nucleolus. In translocations involving chromosome 6 which carries a nucleolar organizer region, non-disjunction may result in spores with two nucleolar organizers (potentially two nucleoli), or with no organizer (nucleolar material remains scattered or diffuse) in the same quartet. By this method, McClintock [4] established the fact that the chromosomes which crossover in an interstitial segment (between the centromere and the translocation break) pass to opposite poles. A further relation between chromosome segregation in such maize translocations and the frequency of crossing over in an interstitial segment has been reported in abstracts [1,2]. This is a report of additional studies of chromosome segregation in maize translocations involving chromosome 6, the detailed data to be published elsewhere. The ultimate objective is to determine why chromosome segregation is directed (i.e., largely alternate) in certain species and not in others.