Barr, Murray Llewellyn (1908-1995)

Canadian anatomist and geneticist. Barr carried out research into defects of the human reproductive system, and simplified diagnostic tests for chromosomal defects.

Barr was born in Belmont, Ontario, and attended the University of Western Ontario, where he spent his entire academic career.

In 1949 Barr noticed that the nuclei of nerve cells in females have a mass of chromatin (the nucleoprotein of chromosomes, which stains strongly with basic dyes), whereas those in males do not. He found that this sex difference occurs in the cells of most mammals. From his investigations, the sex chromatin (called the Barr body) is now known to be one of the two X-chromosomes in the cells of females; it is more condensed than the other chromosomes and is genetically inactive. The other X-chromosome in females is attenuated and genetically active in resting cells. Stained sex chromatin offered a much needed investigative and diagnostic procedure for patients with developmental anomalies of the reproductive system.

Barr and his colleagues also devised a buccal smear test by rubbing the lining of the patient's mouth (the buccal cavity) and examining the cells obtained for chromosomal defects. This test is now used extensively to screen patients, including newborn babies.