The hypotonic pretreatment in mammalian cytology: its function and effect on the aspect of meiotic chromosomes.

Abstract

The hypotonic pretreatment has become a part of the preparation technique of mammalian chromosomes, where it is used in order to reach a good spreading of the chromosomes. Our results strongly indicate that the hypotonic treatment causes a spreading of the chromosomes by loosening the interchromosomal connections, which otherwise hold the chromosomes tightly together into a clump. But this treatment also releases the tight folding of the chromatin fibres. Some chromatin fibres from the surface of chromosomes become free and look like an irregular network of interchromosomal connections. These connections on the other hand are artefacts, and a large part of the observed and discussed “interconnections” is of this origin. In meiotic cells of amphibians, invertebrates and plants, the metaphase chromosomes are not interconnected. The hypotonic pretreatment is unnecessary and, in fact, is never used in the preparation of chromosomes from these phylogenetical groups. © 1979 Mendelian Society of Lund