Barr bodies are inactive X chromosomes that appear as darkly stained masses within the nuclei of female somatic cells. They were first observed in 1943 by Murray Barr in the nerve cells of female cats. A Barr body test examines buccal smear cells scraped from the inner cheek to identify Barr bodies, which appear as dark disks attached to the nuclear membrane in female cells but are absent in males. This test can determine the sex of an individual by observing the presence or absence of Barr bodies in their buccal epithelial cells under a microscope.

1. Barr body
Barr bodies can be defined as an inactive X chromosome in a female’s somatic cell.
What is chromosome and X chromosome?
Structure of Chromosomes
Chromosomes can be defined as an organized structure, which consists of a single, long piece of
DNA and its size varies from 1 to 30µm in length and 0.2 to 2µm in diameter. They are
composed of proteins, which includes protamines and histones and nucleic acids mainly DNA
(deoxyribonucleic acid).
XX Chromosomes
In a normal individual, there are about 23 pairs of chromosomes and every chromosome in a cell
contains a single strand of DNA (deoxyribonucleic acid).These DNA plays a vital role in
carrying the genetic codes for a couple of thousand genes. Chromosomes are also responsible for
determining our sex (male or female).All living organism carry definite number of
chromosomes. In 23 pairs of chromosomes, there are 22 autosomes and one pair of sex
chromosome (X and Y are sex chromosome).In female there is 2 copies of “X” chromosomes
(xx chromosomes), among which one is active and other one is inactive. In case of males, they
have one “X “and one “Y” chromosome and both are active.

2. Barr Body Definition
A Barr body can be defined as a small dark stained mass of X chromosome, which is inactive
and are found only in the female cells. It is present in the nuclei of all cells except the germ cells.
It is also called as sex chromatin as it indicates the presence of sex hormone.
Structure and formation of Barr body
A Barr body represents an inactive X chromosome in a female’s somatic cell. Barr bodies are
small, dark stained mass of inactive X-chromosomes in females within the nucleus. Mc.Barr”
and “Bertram were the two scientists to observe the deeply stained chromatin body in the nerve
cell of female cat in the year 1943. Later they came to know that the chromatin body was found
absent in male cat. This chromatin body is called as a sex chromatin or Barr body, which is
named after the name of its discoverer “Dr. Murray Llewellyn Barr”.
The Barr bodies are present in other parts of body cells. For example: skin cells, epithelium cells,
nerve cells, etc. In a normal female, the number of Barr bodies present is comparatively less than
the total number of X-chromosomes. Barr bodies are present in the nucleus and if the Barr body
are present in the nucleus of the cell, then it is referred to as positive and in case if they are
present in other cell like skin cells, nerve cells, blood cells, then it is referred to as negative . Barr
bodies are only present in female somatic cells and are absent in case of male somatic cells.
X Chromosome Female

3. In female cells, Barr bodies or sex chromatin can be observed in 4 positions:
 They will be attached to the nucleus in nerve cells.
 They will be attached to the nuclear membrane.
 They are found freely in the nucleoplasm.
 They can also be found in nuclear expansions.
A small biological test was performed previously to identify the sex determinants with the help
of these Barr bodies. In this test of buccal smear, Barr bodies appear as a circular, disk shaped
attached to their nuclear membrane. They play a vital role in representing the presence of
inactive X-chromosome, which are present in the vegetative or the somatic cells.
Barr Body Test
Barr bodies can be easily and clearly observed in the buccal smear of females. It appears as a
round, disk attached to the nuclear membrane. A buccal smear is a test, where cells are taken
from the inner lining of mouth. Cells are collected by scraping the deeper layer cheeks or tongue
with a spatula.
The main objective of Barr body testing is to recognize the cell structures, observes the inactive
X-chromosome present in the vegetative cells, examine their shape and to compare the presence
of Barr bodies in male and female cells.
Materials Required:
 Buccal epithelial cells.(Cells are collected from inner lining of mouth-tongue or cheeks)
 Spatula.
 Distilled water.
 Glass slide.
 Microscope.
 95% Alcohol
 Carbol fuchsin (It is a dye or stain mainly used for identifying the microscopic organisms
or objects which cannot be seen through our naked eye. Carbol fuchsin is the mixture of
aqueous solution of phenol and alcoholic solution of fuchsin, mainly used in different
smear culture of organisms.)
Procedure:
 Rinse your mouth thoroughly with tap water and followed with distilled water.
 Scrap the mucosa gently from the deeper layer of your mouth with the help of cleanly
washed spoon or spatula.
 Spread the sample over a small area on a clean dry slide and allow it for air drying.

4.  Add 95% Alcohol and allow it to settle for 5-6 min.
 Stain the slide with Carbol fuchsin and allow it to settle for 15-20 min.
 Wash the slide with distilled water and immediately observe the slide under the
microscope.
Observation and result:
 Buccal smear of female shows one dark stained Barr bodies which are attached to nuclear
membrane within the cell.
 Buccal smear of male shows nuclear membrane within the cell, which represents the
absence of Barr bodies.
The below image shows the presences of Barr bodies in Buccal smear of female epithelial
cells.
The buccal smear test is mainly performed to check the presence of sex hormone and to identify
whether the given sample belongs to male or female.
Note:
In humanswithmore thanone X chromosome,the numberof Barr bodiesvisible at interphase isalways
one fewerthanthe total numberof X chromosomes.Forexample,menwith Klinefeltersyndrome
(47,XXY karyotype) have asingle Barrbody,whereaswomenwitha47,XXXkaryotype have twoBarr
bodies.Barrbodiescanbe seenonthe nucleusof neutrophils.