Which procedure should be performed first if sequential banding techniques are required?

The correct choice of performing Q-banding first in sequential banding techniques is due to its specific application and method of detecting chromosome bands. Q-banding, or quinacrine banding, involves staining chromosomes with a fluorescent dye that emits bright fluorescence under ultraviolet light. This technique allows for the visualization of distinct banding patterns that help in identifying chromosomal abnormalities and structural features.

When performing sequential banding, the order of procedures is critical to ensure that the staining characteristics of the chromosomes are preserved. Q-banding is typically performed first because it provides a clear pattern that can guide further banding techniques. Once Q-banding is established, subsequent techniques like C-banding or NOR banding can be applied, allowing for additional identification of specific chromosomal regions without losing the initial banding pattern established by Q-banding.

C-banding, which highlights heterochromatin and can obscure some details, would not be performed first if one wishes to retain the clarity of the Q-banding results. NOR banding is specific for nucleolar organizer regions and typically does not take precedence in initial banding. FISH, while a powerful technique for detecting specific DNA sequences, also requires prior banding methods to provide a context for the signals obtained from fluorescent probes,