Effects of acetic glycol fixation on chromosomes

Abstract

After fixation with ethylene glycol, acetic acid and water, 1:1:1, the kinetochore can be studied with the light microscope. In unstained material, when phase contrast optics is used, the kinetochores stand out as dense granules against the more transparent chromosome bodies. Comparative experiments with different kinds of fixation show that the chromosomes swell more in acetic glycol than in conventional types of fixative, such as acetic alcohol. Although the acetic glycol‐treated chromosomes to some extent contract again, when subjected to various post‐treatments, they remain more transparent than after other fixations. Kinetochores, as well as chromosome arms, show a normal Feulgen reaction for DNA after treatment with acetic glycol. Histones were extracted from the chromosomes during the fixation, however, as indicated by reduced fluorescence with 7‐chloro‐4‐nitrobenzo‐2‐oxa‐1,3‐diazole. To facilitate the separation of histories from DNA, a modified fixative with magnesium salt added was tested. This was very successful for the differential staining with crystal violet of kinetochores in smeared microspores. The conclusions are that the changed density relations within the chromosome after acetic glycol fixation are due to swelling of chromatin and extraction of histones. The kinetochore is more resistant towards swelling and extraction. The experimental material was Tradescantia. © 1978 Mendelian Society of Lund