depends on what it is

Il est assez fréquent de voir des pièces musicales entières se développer à partir de petites cellules très simples de quelques notes.

*First answer here, please be kind :)*

If it has to do with an opera, you could even use the word leitmotif, which would even be more accurate (depending on context and target audience, too). E.g.: leitmotif de l'aveu, leitmotif du désir in Wagner's Tristan und Isolde.

I feel like choosing notes instead of tons would sound a bit more natural, but that is from my experience as a music student in college and university here in Quebec. Maybe it would not be the best match, culturally speaking.

Hope this was helpful.