F1 and F2 refer to the first and second filial generations of a pairing. Whether they are hybrids or not is a separate question. If the two original parents were from the same population, they would not be considered hybrids, but the result might not be interesting, either. If, however, one parent had a genetic disorder, then the F1 and F2 generations would be very interesting: that is, would the disorder be displayed in the F1 generation, and to what extent would it be displayed in the F2 generation, etc. If on the other hand, the two parents were taken from non-interbreeding populations, then the F1 generation (if it survived) could be called a hybrid. Some people, however, might insist that they may be called hybrids only if the original parents were not conspecific. David E.