mandatory fields

[bonsaiko]

Hello,

 

I'm trying to add the gender field as mandatory. 

So I went into the BO, in customers, and clicked on the plus sign: "define the require fields for this section", but there are only 2 require fields: optin and newsletter. 

I'd like to add gender.

How can I do ?

 

Or maybe I can edit some files, but which ones? 

 

Thanks for your help