Genetic problem

It be really cool if my fry are a cross of a molly and a guppy. But only one looks like a guppy so far.
 
Chances are you just bought a pregnant female just after she spawned. Inter-breeding is difficult to do not only in that the fry tend not to survive, but you have to coax two parents of different species to mate. =/
 
AquariaCentral.com