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

Which banding technique is useful for observing chromosomal fluorescence?

1. Q-banding

2. R-banding

3. C-banding

4. G-banding

The correct answer is: Q-banding

Q-banding is particularly effective for observing chromosomal fluorescence because it utilizes a fluorochrome that binds selectively to specific DNA regions. This technique capitalizes on the differential fluorescent properties of the chromosomes under ultraviolet light, allowing for the visualization of unique banding patterns. Q-banding highlights both the dark-staining and the less-stained regions distinctly, which is particularly useful in identifying certain chromosomal abnormalities or specific chromosome regions that may not be as easily discernible with other banding techniques. In contrast, R-banding, C-banding, and G-banding employ different methodologies for chromosome staining. R-banding reverses the typical G-banding pattern and highlights the lighter bands, which can obscure some details under fluorescent conditions. C-banding focuses primarily on the centromeric regions, and while it can be helpful for specific types of evaluations, it does not provide the broad fluorescence analysis that Q-banding does. G-banding relies on the use of Giemsa stain, which does not utilize fluorescence and primarily distinguishes regions based on affinity for the dye rather than using fluorescent properties, making it less suitable for observing chromosomal fluorescence.