Centromere sizes, positions, and movements in the interphase nucleus

Abstract

Each microspore of the onion Allium fistulosum (n=8) has 8 chromosomes. It is shown that in the microspore the 8 centromeres aggregate to form 2 or 3 centromeric structures. Subsequently, at early mitotic prophase, these aggregates are resolved into 8 separate centromeres and each becomes structurally double. After mitosis the pollen grain contains 2 nuclei, each with 8 separate and distinct centromeres, clustered at the nuclear envelope. As interphase progresses the centromeres of the vegetative nucleus are no longer at the nuclear envelope and they aggregate into 3 or 4 centromeric masses. In the generative nucleus there is less movement. The interphase centromere movements occur in the absence of microtubules. The centromeres range in size from about 0.10 to 0.17 μm³ with an average of 0.14 μm³ per centromere.