How can I tell?

Question
I've had my gerbil for one year, and I can't tell it's gender. My mom says it's male, but I insist it's female. How can I tell? What if it won't let me? Thanks for listening.
                          Signed, Lin

Answer
Hi, sorry for the delay in response, was having some internet difficulties.

There is a good article on how to sex gerbils on this site:
http://www.gerbils.co.uk/gerbils/gender.htm

Gerbils are usually pretty easy to sex.  Males have a bulge at the base of their tail, under neither them, which is the scrotum.  The spacing between the anus and urinary areas are also different, on a female the 2 holes are close together, on a male his penis will be further away from his anal opening.