emacs not creating backup ~ files to file under git control. Why not?

[emacs+git-user]

I was working on a file and it created backups as usual. However I noticed that 
when i decided to put it under git countrol and created a git directory, then 
emacs stops to create a backup file~ ever since then.

So to test, i created a new directory and edited a file in it and it creates a 
backup in the directory.

Then I deleted the file~ then I did 

git int 
in the directory and then did 
git add file
then i edited the file and now it does not create then file~.
Why not and what code controls this to shut it off?

Mitchell