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We do a typical class exercise of aceto-orsein staining of buccal epithelial cells from female students to visualize Barr bodies under the light microscope. All the illustrations and pictures in the books depict a Barr body located on the edge of the nucleus, but that is not always the case in the students' samples. Given that the cell is a 3D structure, I couldn't explain why the Barr body would localize itself to the edge of the nucleus with respect to the viewer's 2D perspective. In this article's introduction, a statement is found saying:

"In interphase, the inactive X chromosome (Xi) is found as a condensed heterochromatic Barr body, usually positioned at the nuclear or nucleolar periphery (1-4)."

By "usually", does it mean that it is pure luck? Is there any explanation as to why we would have a tendency to see it localized to the edge from our perspective, exactly on the rim of the nucleus, and not just somewhere random?

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