Meiotic chromosome pairing in maize is associated with a novel chromatin organization.

Three-dimensional light microscopy and the excellent cytological features of maize meiotic chromosomes are used to analyze the early events of chromosome synapsis. We demonstrate that the chromosomes undergo a dramatic structural reorganization prior to synapsis in zygotene. The unique features of prezygotene chromosomes are a partial separation of sister chromatids, an elongation of knob heterochromatin, an increase in surface complexity, a 50% increase in total chromosome volume, and a peripheral localization and alignment of telomeric, but not proximal, loci. At zygotene, chromosome volume decreases and chromosomes appear as single fibers. The specialized prezygotene chromosome morphology may facilitate homology recognition once the homologs have been brought together.