Postmating isolation prevents successful fertilization and
development, even though mating may have occurred. For example,
conditions in the reproductive tract of a female may not support
the sperm of another individual, which prevents successful
fertilization. Postmating isolation also occurs because hybrids are
usually sterile (e.g., the mule produced from a mating of a male
donkey and a mare is a sterile hybrid). Mismatched chromosomes
cannot synapse properly during meiosis, and any gametes produced
are not viable. Other kinds of postmating isolation include
developmental failures of the fertilized egg or embryo.
