[Visualization of elementary structures in polytene chromosomes of Drosophila melanogaster]

Abstract

Electron microscopic study of total polytene chromosome preparations makes it possible to reveal elementary structures of polytene chromosomes. Elementary chromosomes are detected which contain chromomeric and interchromomeric regions. Transcription is seen in puffs and in many bands. Chromatin spreading shows that both chromomeric and interchromomeric regions of elementary chromosomes consist of nucleosomes. A ribbon-like model of polytene chromosome structure is suggested and discussed. In the ribbon-like chromosome each elementary chromosome gels conjugated only with the two adjacent sister chromosomes. Conjugation occurs only in the chromomeric regions, interchromomeric regions do not conjugate. Both chromomeric and interchromomeric regions are duplicated during polytenization which ensure proportional replication of all the bands and interbands in the course of polytenization.