how to add validation in user fields ?

Question

Hi there,

I'm trying to add some extra fields in the user profile.

Let's say I want to add "Gender" for example.

so I managed to create the field using the admin console.

However,if I want the user to only have the choice to select Male or Female(dropdown) when he fill up his profile, how would you make changes in the core or as a pluggin to handle that ?

 

Thanks a lot for your support