Chromosome Preparations from the Avian Allantoic Sac

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Abstract
An abundance of mitotic cells, a rapid and uniform response of cells to mitotic inhibition, ease in obtaining a monolayer of cells, clear and well-spread chromosomes make the allantois an ideal tissue for squash preparations. After a 45 min incubation of each embryo, still in the shell, with 0.02 ml of 0.05% Colcemid, 4-day avian embryos were treated in distilled water for 15 min or in 0.9% sodium citrate for 30–60 min and then fixed for at least 1 hr in 1:3 acetic-alcohol. Squash preparations were made after immersion of the allantois in 45% acetic acid for 5–10 mm. Phase contrast microscopy could be used, or permanent preparations made by freezing, air-drying and staining. Staining with Gram's iodine for 4 min followed by 1% crystal violet in 95% ethanol for 3 min is recommended. The allantois is well suited for use in biology laboratories to demonstrate avian chromosomes in different stages of mitosis.