The sex chromatin body, also known as the Barr body, is an inactivated X chromosome found in female cells. To study the presence of Barr bodies, buccal mucosa cells are often used because they are easily accessible and can be collected non-invasively through a simple scraping of the inner cheek. Buccal epithelial cells are large and contain sufficient cytoplasm, making them suitable for microscopic examination. In contrast, blood cells (like lymphocytes) can also be used, but the collection process is more invasive and less convenient than obtaining buccal mucosa cells.