Two species of frogs belonging to the same genus occasionally mate, but the embryos stop developing after a day and then die. these two frog species separate by two species of frogs belonging to the same genus occasionally mate, but the embryos stop developing after a day and then die. these two frog species separate by reduced hybrid viability reduced hybrid fertility hybrid breakdown gametic isolation

These two frog species separate by reduced hybrid viability. In reduced hybrid viability gene of different parent species may interact and impair the hybrid's development while in a reduced hybrid fertility a viable individual is sterile often due to the inability to produce normal gametes in meiosis. Hybrid breakdown; the first generation are viable and fertile, but when they mate the offspring are feeble and sterile.