Is there a gene for big breasts?

As you know, most of the time it is:

Big girl, big boobs and Skinny girls, zero to no boobs.

The reason for this being; big could be more fat or muscles, which is what breasts are made up of.



Now, I am a size 8 but most of the time my breasts will not fit (or the shirt will pop open or you can see the bra from the sides of the shirt).

So, is it possible to have genes which give you over or under the average size, or is it down to what you do and eat or is it both?



Ps I