Centromeric Behaviour of the Univalents in Two Phalaris Hybrids

Abstract

The hybrid between Phalaris coerulescens (2n = 14) and P. minor (2n = 28) usually forms seven bivalents and seven univalents at the first metaphase of meiosis. The univalents are derived from P. minor. The centromeres of the seven univalents do not divide at the first anaphase, but neocentromeres in distal parts of the chromosomes assume control of their movement. These neocentromeres move towards opposite poles, between which the univalents become stretched. Formation of the cell wall causes breakage of the univalent bridges. Fusions may occur between fragments or between broken ends of sister chromatids in a fragment. Neocentric activity occurs only infrequently at the second anaphase.