One of the following is used for sex chromatin testing :

Chromosomal sex can be determined by the study of the leucocytes or by simply taking a smear from the buccal mucosa The nuclei of the female chromosome contains a stainable body called the sex chromatin, hence female cells are termed as chromatin positive. In epithelial cell nuclei this small peripherally situated darkly staining nodule is called Barr body. Male cell nuclei lack this body and termed chromatin negative. Ref: SHAW'S TEXTBOOK OF GYNAECOLOGY; 15th edition; Pg no:108