sexing gebils

[Sharon Fazi]

When sexing gerbils at pet stores, I have noticed shape differences with the testicles of the males.  Some are nice smooth and oval.  Some are pointy toward the anal opening and the tails are bare of hair underneath at the base.  Is this an age thing or a genetic thing?  My first impression of the pointy kind was unattractive and poor quality.  Would someone please elaborate on testicle shapes/appearance for me and what is good or bad?  What effects does this have on breeding if any?