Observation of Barr body in Human Buccal Epithelial Cells

 

Title: Observation of Barr body in Human Buccal Epithelial Cells 

Objective: 

To observe and identify the Barr body in buccal epithelial cells and understand its significance in  sex determination and X-chromosome inactivation. 

Theory: 

The Barr body is an inactivated X chromosome found in the nuclei of female cells. It appears as  a densely stained structure at the periphery of the nucleus. This phenomenon is a result of X chromosome inactivation, where one of the two X chromosomes in females becomes  transcriptionally inactive to balance the dosage of X-linked genes between males and females.  The Barr body can be used as a cytological marker for determining the sex of an individual. This darkly stained structure is named after Dr Murray Barr who was a Canadian physician who along with his student Dr Bertram way back in 1948 identified this structure.

Materials Required: 

∙ Sterile buccal swab/tooth pick 

∙ Microscope slides 

∙ Cover slips 

∙ Acetocarmine stain/Giemsa/Toluidine blue

∙ Distilled water 

∙ Dropper or pipette 

∙ Light microscope 

Procedure: 

1. Use a sterile buccal swab/tooth pick to gently scrape the inner lining of the cheek to collect  epithelial cells after washing mouth thoroughly with water. 

2. Smear the collected cells onto the centre of a clean microscope slide and allow the slide to air dry completely. 

4. Add a few drops of acetocarmine stain and allow it to stain for 5-10 minutes. 

7. Gently rinse off the excess stain with distilled water by keeping in a slanted position. 

8. Eventually, water can be blotted using tissue paper. 

9. Place a cover slip over the stained sample. 

10. Observe the slide under a light microscope at high magnification. 

11. Look for the Barr body, which appears as a small, darkly stained mass near the nuclear  membrane. 

Observations: 

∙ Barr Body Presence: Identify and note the presence of a small, round or oval-shaped,  darkly stained structure at the edge of the nucleus in some cells. 

∙ Barr Body Absence: In some cells, particularly in male samples, there will be no Barr  body present. 

Results: 

∙ The presence of a Barr body indicates a cell from a female, as it confirms the presence of  two X chromosomes with one being inactivated. 

∙ The absence of a Barr body indicates a male cell, which typically has only one X  chromosome. 

Fig: Barr body 


Conclusion: This experiment demonstrates the concept of X-chromosome inactivation and  allows for the identification of the Barr body as a marker of sex chromatin. The Barr body serves  as an important tool in cytogenetics for sex determination. 

Precautions: 

∙ Ensure the cells are spread evenly on the slide to avoid overlapping, which can obscure  the Barr body. 

∙ Handle stains and fixatives carefully as they are hazardous. 

∙ Properly focus the microscope to clearly identify the Barr body.

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