pet dander and allergies?

[daized_rain]

Is cat and dog dander the same or different? My son is allergic to dogs but the doc told me that my son was allergic to cats and that dogs were fine. I asked another doctor about this and he told me that cats just have 7x more stronger dander than dogs. So that sounds like it's just a pet dander allergy and has nothing to do with weather its a cat or dog. But then why do you get tested for cat and dog allergies instead of just dander. Can anyone help me out with explaining this?
Thanks for the help. My son shows symptoms of dog allergies not cat allergies. The allergist told me the complete oposite though. That he was allergic to cats and not dogs. I was trying to find out how he got these results or if the test is just wrong.