What do relative major and minor scales share?

Relative major and minor scales share the same key signature, which is a defining characteristic of these scales. For example, the C major scale and the A minor scale are relative to each other; they both have no sharps or flats in their key signature. This relationship allows them to utilize the same set of notes while creating different moods and tonalities.

Different key signatures pertain to major and minor scales that are not relative. If they shared different key signatures, they would not be considered relative at all. Similar melodic patterns can occur, but they are not a defining feature of relative scales since the characteristics of melodies can vary widely depending on the context in which they are used. Lastly, opposite tonalities suggest a stark contrast between major and minor, which does not account for the shared foundational notes of relative scales. Thus, the shared key signature is the fundamental connection between relative major and minor scales.