I am confused and I believe that you are too--F1 is not a strain. When we are talking genetics, F1, F2, F3, etc, are representations of different generations in genetic crosses. F1 represents the original cross between two parent species. F2 represents the cross between 2 members of the F1 generation. F3 represents the cross between 2 members of the F2 generation...they can be any strain.