Cytological identification of sex in pig embryos at indifferent gonadal stages.

A reliable method of sex identification in pig embryos at sexually indifferent and early differentiated gonadal stages (age 21-26 days) was developed in association with ultrastructural studies on gonadal development and differentiation. The routine carbolfuchsin staining for the sex chromatin and the quinacrine mustard dihydrochloride staining for the fluorescent Y chromosome were not successful when applied to interphase cells. Therefore, it was necessary to develop a method for complete chromosome preparations. Head, heart and liver proved to have a sufficiently high spontaneous mitotic rate without any mitogenic stimulation. The tissues were suspended in the culture medium. Optimal conditions for colchicine treatment and hypotonization were tested and the details of the procedure are reported. This direct method yielded adequate metaphase plates for chromosome analyses in pig embryos. Because no culturing is used, the method is rapid and artefactual changes in the chromosomes during stimulated cell divisions in vitro are avoided.