American Society for Clinical Pathology (ASCP) Technologist in Cytogenetics certification (ASCP CG) Practice Test

Which type of chromatin can be identified using a C-band staining technique?

1. Gene-rich chromatin

2. Constitutive heterochromatin

3. Facultative heterochromatin

4. Telomeric regions

The correct answer is: Constitutive heterochromatin

C-band staining is a specialized technique used to specifically identify and visualize constitutive heterochromatin. This type of chromatin is typically located in the centromeric regions of chromosomes and is characterized by being densely packed and transcriptionally inactive. The C-band technique exploits the differences in chromatin composition, allowing for clear visualization of these dense regions, often appearing as darkly stained bands in comparison to the lighter-staining gene-rich regions. Constitutive heterochromatin is defined by its stable presence in the genome, being essential for maintaining chromosome structure and function during cell division. This contrasts with facultative heterochromatin, which can vary in its expression or packaging status depending on the cell type and developmental stage. Likewise, gene-rich chromatin refers to areas on the chromosome that contain active genes, which are usually less dense and do not retain C-band staining effectively, resulting in a lighter appearance. Telomeric regions, while critical to chromosome stability, are not primarily identified through C-banding but rather through other staining methods that highlight repeat DNA sequences. In summary, C-band staining effectively highlights constitutive heterochromatin predominately found at centromeres, making this type of chromatin the best identified using this technique.