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A Western blot detects selected proteins after their separation and transfer to a membrane, using antibodies. In the yeast cross-species complementation experiment, detection helps distinguish failed protein production from failure of an expressed protein to restore growth.

The useful idea is to preserve where proteins migrated in gel electrophoresis, then ask which positions retain an antibody. Western blot separation, Western blot transfer and Western blot antibody detection answer different questions. A band is evidence of retained label at a position; Western blot band interpretation requires Western blot controls before assigning identity or comparing abundance.

Western blot loading controls ask how much sample entered each lane; Western blot transfer controls ask what reached the receiving sheet; Western blot antibody specificity controls ask what the antibodies recognized. Each closes a different gap in Western blot band interpretation.