These could be major or minor climbs (6)
I believe the answer is:
scales
This clue is a double definition.
'these could be major or minor' is the first definition.
(musical scales)
'climbs' is the second definition.
(scaling is a kind of climbing)
(Other definitions for scales that I've seen before include "Balance - climbs" , "Set of musical notes - balanced on a fish?" , "Flakes of fish skin" , "Climbs the weight measuring device" , "Sequences of musical notes" .)