Different predefined list based on selector choice

I'm trying to implement a system with which you can choose a general occupation field (like doctor) by a selector when creating a profile, and based off of the choice you picked, a different predefined list with specific job titles within the field will be displayed to further specify your job. This is a step to a system which we want to implement, which puts you into groups right after joining, based on your occupation so you can connect to colleagues or other people of your field easily.

Is there a mod for this or something similar? Also, which files would be the prime candidate if one would want to code such a functionality himself? (Im still fairly new to this and getting overwhelmed by the amount of php files).

Thanks in advance 

The Dependent Fields module by AntonLV should work for this.