The internal mechanics of the chromosomes - IV—Pairing and coiling in salivary gland nuclei of drosophila

Abstract

The banded chromosomes of the salivary glands of Diptera show relic coiling before pairing and both relic and relational coiling after pairing. The direction of this coiling is characteristic of the particular chromosome arms. The torsion which determines the relational coiling also leads to reflex relational coiling within chromosomes, especially in redundant segments, opposite deletions. The pairing of inverted segments is promoted by the development of relational coiling between them. Occasionally the type of coiling of one arm is redistributed to another arm of the X-chromosome which has a characteristically opposite direction of coiling. These properties of coiling are analogous with those found in the prophases of mitosis and meiosis, and are presumably due to analogous changes in the molecular spiral, whose coiling determines the spiralization of metaphase chromosomes.