II. Definitions
- Buccal Smear (or Sex Chromatin Test)
- Microscopy of cheek cell scraping
- Presence of barr bodies suggests 2 X-Chromosomes
- Barr Body
- Inactivated X-Chromosome in each cell of a female
- Seen as an intracellular dark spot on microscopy
III. History
- Barr Body first identified by Dr. Murray Barr in 1949
- Mary Lyon suggested etiology and named it Barr Body
IV. Physiology
- All cells in female, turn off 1 of 2 X-Chromosomes
- Occurs on day 16 of Embryonic development
- Each cell child inherits same inactivated X-Chromosome
V. Indications
- Replaced by karyotype for full chromosomal mapping
- Previously used to evaluate abnormal Sexual Development
VI. Procedure
- Gently scrape inside of cheek
- May use wooden Tongue blade or toothpick
- Spread sample onto slide into drop of saline
- Dry slide and stain with methylene blue 0.3%
VII. Interpretation
- Barr Body: Crumpled dark Chromosome seen in cell
- Suggests normal female karyotype 46XX