Speciation
Factors which prevent mating being successful, such as genetic incompatibility, hybrid inviability or sterility.Zygotic mortality: The egg is fertilized, but the zygote does not develop.Hybrid inviability: Hybrid embryo forms, but is not viable.Hybrid sterility: Hybrid is viable, but the resulting adult is sterile. Hybrid breakdown: First generation (F1) hybrids are viable and fertile, but further hybrid generations (F2 and backcrosses) are inviable or sterile.