The definition of X- and Y-chromatin is often called the method of express diagnostics of sex. Explore the cells of the mucosa of the mouth, vaginal epithelium or hair bulb. In the nuclei of cells of women in a diploid set, there are two chromosomes X, one of which is completely inactivated (spiralized, tightly packed) already in the early stages of embryonic development and is visible as a heterochromatin block attached to the core shell.