Meiotic crossing-over and disjunction: Overt and hidden layers of description and control

Abstract

Sexual reproduction is observed in the vast majority of eukaryotic organisms. Foremost, this includes animals, plants, and fungi. In the course of sexually propagated generations, the regularities of Mendelian genetics and the segregation of partly recombined chromosomes at meiosis are two complementary faces of one and the same coin. This chapter opens the first book of two in a series, both volumes being dedicated to the complex process of meiotic recombination. This editorial synopsis focuses on the various facets of meiosis from a descriptional perspective, before the specific chapters discuss the details of molecular mechanisms. Meiosis and mitosis are viewed as alternative schemes of eukaryotic chromosome segregation, which supposedly have coevolved from a very early start. The structure and kinetics of meiotic bivalents depend on the formation of chiasmata between non-sister chromatids and the different stability of sister-chromatid cohesion along the chromosome arms and at the centromeres. The relevance of spindle dynamics for bivalent segregation and potential nondisjunction is discussed. Telomere clustering plays an assisting role during the intermediate phase of the bouquet arrangement. At the heart of meiotic prophase, pairing and synapsis of homologous chromosomes is accompanied by genetic crossing-over and chiasma formation. The what, where, and how of DNA exchange proceed from site facilitation via partner choice and homology search to the formation and resolution of heteroduplex intermediates. The nonrandom distribution of crossovers and chiasmata is subject to interference mechanisms at various levels. Finally, the segregation of chromosomes during meiosis I and II is accomplished by an interplay of basically mitotic proteins with meiosis-specific components. © 2007 Springer-Verlag Berlin Heidelberg.