II. Definitions

  1. Buccal Smear (or Sex Chromatin Test)
    1. Microscopy of cheek cell scraping
    2. Presence of barr bodies suggests 2 X-Chromosomes
  2. Barr Body
    1. Inactivated X-Chromosome in each cell of a female
    2. Seen as an intracellular dark spot on microscopy

III. History

  1. Barr Body first identified by Dr. Murray Barr in 1949
  2. Mary Lyon suggested etiology and named it Barr Body

IV. Physiology

  1. All cells in female, turn off 1 of 2 X-Chromosomes
  2. Occurs on day 16 of Embryonic development
  3. Each cell child inherits same inactivated X-Chromosome

V. Indications

  1. Replaced by karyotype for full chromosomal mapping
  2. Previously used to evaluate abnormal Sexual Development
    1. Delayed Menarche
    2. Delayed Puberty

VI. Procedure

  1. Gently scrape inside of cheek
    1. May use wooden Tongue blade or toothpick
  2. Spread sample onto slide into drop of saline
  3. Dry slide and stain with methylene blue 0.3%

VII. Interpretation

  1. Barr Body: Crumpled dark Chromosome seen in cell
    1. Suggests normal female karyotype 46XX

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