A Combined Hcl-Acetic-Alcohol Fixation and Hydrolysis Followed by Cresyl Violet Staining for Mosquito Chromosome Spreads

Abstract

Mosquito tissues of cytogenetical importance were dissected out on a slide in 0.65% NaCl, under a dissecting microscope, and treated about 30 sec in a drop of 1:3 Carnoy's fixative diluted 1:19 with distilled water. Fixing and hydrolysis was done by a single step in a mixture consisting of: glacial acetic acid, 1; ethanol 96%, 3; HCl conc., 2; and distilled water, 2 (v/v) for 2–6 min at 20–25 C. The specimen was then rinsed with the acetic-alcohol fixative and covered in a drop of 1% cresyl violet in 50% acetic acid under a coverslip coated with Mayer's albumen. Washing was performed immediately by adding water dropwise to one side of the coverslip and drawing the fluid from the other side with absorbent paper. The preparation could be used either as a temporary slide or made into a durable mount. The DNA-containing bands of the giant polytenic chromosomes stained dark violet; interband regions, weakly stained or colourless against a clear background. Mitotic and meiotic figures in gonadal cells stained selectively dark violet or violet with a practically unstained cytoplasm.