This document discusses Barr bodies, which are condensed inactivated X chromosomes visible under a microscope in female cells but not male cells. The document presents the process of examining cheek cells under a microscope to identify Barr bodies and determine sex. It notes some limitations of using Barr body testing for gender verification, as some conditions like Turner's syndrome or Klinefelter's syndrome may produce results that contradict the person's biological sex. The assumptions of Barr body testing may be incorrect in cases of mosaicism or rare chromosomal combinations.

1. KENYATTA UNIVERSITY
SCHOOL OF MEDICINE.
DEPARTMENT OF MEDICAL BIOCHEMESTRY
NAME: LANDO ELVIS OTIENO
REG NO: P29S/16344/2015.
COURSE: MBCHB
LECTURER: Dr RUNO STEPHEN
HANDING DATE: /11/2016
SUBJECT: PRACTICAL REPPORT ON BARR BODIES.
ELVIS L
©

2. INTRODUCTION:
In human being the sex can be identified by observing the nucleus of their resting
cells (the interphase nucleus) in the cells of female. A darkly stained chromatin matrix is
observed on the slide in the interphase nucleus. This is known as sex chromatin or Barr
body after the name of its discoverer Murray Barr in 1940.
Barr body testing is a test to determine the presence of multiple X chromosomes in a cell.
When more than one X chromosome is present in a cell, only one X is allowed to remain
active, and any excess X chromosomes are randomly inactivated and condensed. The
condensed, inactivated X chromosome is called a Barr Body. In this method of testing,
cells are frozen in interphase, when the Barr body is condensed, and stained to allow
viewing under a microscope.
PRINCIPLE:
Buccal epithelial cells especially have Barr body structure, which are considered
to play a major role for sex determination. This small round Barr body is located either in
the border of nuclear membrane or sometimes inside of nucleus. This Barr body may be
single or more in number in some cases. These structures are present only in the female
sex.
MATERIALS
Light microscope Beaker Paper towel
Glass slide Dropper pipette Lens paper
Cover slip Water
Flat toothpick Methylene blue (0.3%)
PROCEDURE
1. Obtain a clean glass microscope slide.
2. Place a drop of water in the center of the slide.
3. Gently scrape the inside of your cheek with the flat edge of a toothpick.
4. Spread cells in the drop of water.
5. Place cover slip on top of specimen. Use correct technique to prevent air
bubbles.
6. Observe, diagram, label, and record magnification.
7. Apply one drop of methylene blue along one side of the cover slip.
8. Along the opposite edge of the cover slip, gently touch with a piece of
paper towel. This will draw the methylene blue under the cover slip to
stain the cells.

3. 9. Observe, diagram, label, and record magnification.
10. Switch slide with someone of the opposite sex.
11. Observe, diagram, label, and record magnification.
Analysis
12. Describe the shape of the cheek cells.
13. Compare and contrast male and female cheek cells.
14. What structure is visible in a female that is not present in a male cheek
cell?
15. Describe the location of this structure.
16. A woman undergoes amniocentesis. She is informed by the physician that
the karyotype indicates the fetus has 47 chromosomes. Chromosome #23
has a pattern of XXY. What is the sex of the fetus? How many Barr
bodies will the fetus have? What condition does the fetus have?
Further Investigation Assignments
17. Investigate a sex-linked genetic disorder.
18. Determine the history and role Barr body testing has had in athletic
competitions. (Olympics)
19. Determine the history and roles medical and criminal forensics have had
in determining and legally defining the sex of an individual.

4. OBSERVATION AND RESULTS:
In female epithelial cells dark stained heterochromatin (Barr body) is observed
On the periphery of the nucleus, clearly under high power microscope.
DISCURSION
Any cell with more than one X chromosome will exhibit (n – 1) Barr bodies during
interphase. Each excess X chromosome will form one Barr body. This means that 46,XX
women will have cells that exhibit one Barr body, while the cells from a 46, XY male
will not exhibit any Barr bodies.
Barr body testing defines a woman as an individual whose cells display the presence of
one Barr body. If an athlete underwent gender verification via this method, but no Barr
body was observed in her cells, then she would be disqualified from further competition.
Barr Body testing was used by both the IOC and the IAAF beginning in 1968. Unlike the
nude parades they replaced, Barr Body testing was much more objective, and less
demeaning to women, as only a blood sample was needed to obtain a cell sample that
could be tested, instead of forcing women to strip off their clothes and undergo a physical
examination. Another advantage of Barr Body testing is that there is a much greater
potential for protecting the privacy of the athletes as compared to the previous method of
using nude parades
Assumptions:Barr body gender verification testing is based on the assumption that all
women have two X chromosomes and therefore display one Barr body, while men, who
have one X and one Y chromosome, display no Barr bodies. Furthermore, testing is based

5. on the assumption that every cell in an individual contains the same genetic material. In
other words, Barr body testing assumes that mosaicism does not exist, when in fact there
are multiple documented cases of mosaic individuals.
Special Cases:
-barr body testing incorrectly excludes some women from competing who do not have an
advantage.
 Women with Turner’s Syndrome (45, XO) will not have a Barr body, so they will
not pass a Barr body test. However, they are considered female and the syndrome
does not confer a competitive athletic advantage.
-barr body testing could incorrectly allow some men to compete.
 Men with Klinefelter’s Syndrome (47,XXY) are phenotypically male, but would
pass the test because their cells will exhibit one Barr Body.
 There are some individuals who are 46,XX but phenotypically completely male
due to recombination: according to the Barr Body test, they would be allowed to
compete as women.
-barr body testing can categorize the same individual as a man or a woman.
 Some individuals have mosaicism, meaning that some of their cells are XX while
others are XY. Depending on the proportion of the cells that are XX, the
individual may appear completely phenotypically female. However, depending on
the cells taken, the same individual can be classified as either a man or a woman
at different instances.
REFERENCES
Qinjie, Tian, He Fangfang, Zhou Yuanzheng, and Ge Qinsheng. “Gender Verification in
Athletes with Disorders of Sex Development.” Gynecological Endocrinology 25.2
(2009): 117-21. Print.
Ritchie, R., J. Reynard, and T. Lewis. “Intersex and the Olympic Games.” Journal of the
Royal Society of Medicine 101.8 (2008): 395-99. Print.