do i have a male or just a female wanting to mate

Question
i just bought 6 white mice from petco and i have them in a really nice home and when i woke up this morning i heard these crazy squeeks coming from the cage, i have one mouse out of the six that keeps "mounting" the others, after "mounting" and being done with one mouse it goes to the wheel and runs for a bit and then goes on to another mouse, its been doing this for about 2 hours and is still pretty persistent on getting what it wants, it will stalk a mouse and then wait for the perfect moment. at petco i asked for all females but why is this one mouse acting like a male? there is no testicles present but i begining to wonder what is going on in there! can you help me?

Answer
Dear Melinda,

Although pet stores frequently make mistakes as to mouse sex, it is also normal for a female mouse establishing dominance to mount other females.  Mice need to decide who is the A-Mouse just like dogs establish who is the A-Dog.  This will be accompanied by chasing and squeaking.  This is all perfectly normal.  

Have fun with your girls!

squeaks n giggles,

Natasha