Preparation and orcein staining of mitotic chromosomes from Drosophila larval brain

In this protocol, larval brains from Drosophila are incubated in vitro with colchicine, treated with hypotonic solution, fixed, and squashed in aceto-orcein. This procedure provides a large number of well-spread metaphase figures (200-400 per brain) that can be analyzed for chromosome morphology, the presence of chromosome aberrations, and the degree of ploidy.