UC Riverside

For normal transition through meiosis, chromosomes rely on pairing with their homologues. Chromosomes which fail to pair, univalents, behave irregularly and may undergo various types of breakage across their centromeres. Here, we analyzed the meiotic behavior of misdivision products themselves: isochromosomes and telocentrics in wheat. Both types of chromosomes behaved in the same fashion as standard 2-armed chromosomes. The 2 most frequent scenarios were separation of sister chromatids in anaphase I or monopolar/bipolar attachment of the univalent to the spindle apparatus with unseparated chromatids. Misdivision was rare, and its frequency appeared directly related to the size of the centromere. The previously deduced relationship between misdivision frequency and chromosome size was likely erroneous and can be explained by a general relationship between chromosome length and the size of its centromere. Pairing of identical arms in isochromosomes did not protect them from misdivision. It is not chiasmate pairing that protects from misdivision but mechanistic issues that arise through that pairing.