The Chromomeres of Pre-pachytene Chromosomes

Abstract

The arrangement of the chromomeres in relation to the chromosome axis in pre-pachytene chromosomes was studied with the light microscope in these plants: Vagaria parviflora, Fritillaria lanceolata, the garden tulip Mad. Lefeber and the hybrid lily Formobel. The fine structure of the leptotene chromosomes of some of these was also studied with the electron microscope.Evidence in support of the premise that chromomeres are formed eccentric to the axis of leptotene chromosomes, in order to segregate non-recombinational DNA from a pairing face, was obtained with the light microscope.The uncoiling of condensed parts of chromosomes, seen in pre-meiotic interphases and somatic nuclei of a lily, coincided with the onset of leptotene.Because of the alternation of chromomeres around the axis of the leptotene chromosomes, as a consequence of rotation, their eccentric alignment was difficult to confirm in thin sections with the electron microscope. The dense axial cores and less opaque chromomeral chromatin of leptotene chromosomes showed an equivalent staining behaviour with uranyl/lead ions and ethanolic phosphotungstic acid, thought to be largely specific for basic protein. No evidence was found of a close association of cores, indicative of pre-alignment of homologous chromosomes in pairs.