<prompt> One of the following forms the basis for sex chromatin testing:Barr bodyTestosterone receptorsHormone levelsPhenotypic features  <response>: Ans. a, i.e. Barr bodyRef: Gamong 24thed, p392-393Barr body forms the basis for sex chromatin testing.Barr BodyWhen two X chromosomes are present in a cell as in a normal female one of them becomes inactivated and condensed on the nuclear membrane and is called the Barr body. This process is termed as X chromosome lyonization inactivationPresence or absence of Barr bodies helps in ascertaining the sex of an individuals Absence of Barr body indicates that the patient has only one X chromosome e.g. Normal male XY or Turners syndrome XO Nuclei of cells in females XX contain a darkly staining Barr body that is not present in the nuclei of cells in males. Barr bodies are most easily seen in a smear of squamous epithelial cells obtained by scraping the buccal mucosaQ Barr bodies react differently to histological stains and are best seen as dark staining bodies within the nucleus of non- dividing interphase cells. 