Barr Bodies

Samford University -- Department of Biological and Environmental Sciences
Experimental Genetics -- Biol 334

NAME__________________________________________

Lab: Dosage Compensation: Observing Barr Bodies

In mammals, equalizing the dosage of X-linked genes (dosage compensation) occurs by the process dubbed lyonization. This is the inactivation of one of the two X chromosomes of the female that occurs during very early development. This inactivated chromosome can be see as a dark staining structure in various epithelial (and other) cell.

Observing Barr Bodies:
1) Add a very small drop of water to a very clean slide.
2) Gently scrap the inside of your cheek with a clean toothpick.
3) Dab the toothpick in the water and spread the drop out to a diameter of about 1 cm.
4) Let the slide air dry. (This can be sped up by placing the slide on a slide warmer.)
5) Add a drop of methylene blue stain to the spot.
6) Let stain for 5 min.
7) Gentle rinse the slide briefly under running distilled water.
8) Shake off excess water. (No coverslip necessary.)
9) Observe under a compound microscope. Note: Until the water all evaporates, use the 10X lens only. You may then move to 40X and 100X (oil immersion).

On the back of this sheet, sketch a typical epithelial cheek cell, including any Barr Bodies seen.

What is the general shape of these cells?

What does heterochromatinization have to do with Barr Bodies?

Why are Barr bodies not seen in normal males?