Discovered sex chromatin
Barr’s main interest was cytological research as it applies to sex anomalies and mental retardation. He is author of numerous publications in the field of cytology (the structure and function of cells), principally the cytology of the nervous system and human cytogenetics. His popular textbook on neuroanatomy, The Human Nervous System: An Anatomical Viewpoint is now in its 9th edition.
In 1949, Barr discovered sex chromatin, a substance made of DNA and protein, a discovery which made it possible to determine the cellular sex of an individual. Barr and his colleagues also devised the buccal smear test, whereby cells from the patient’s mouth are taken and examined for chromosomal defects. This test is now used extensively to screen patients, including newborn babies.