It may be an inherited trait, as in the mule; or it may be acquired from the environment, for example through physical injury or disease, or by exposure to radiation.
Hybrid sterility can be caused by different closely related species breeding and producing offspring.
The imbalance results in offspring that is viable but not fertile, as is the case with the mule.
This results in a high number of intersex individuals among the offspring, which are typically sterile.
This gene triggers the development of testes, causing the individual to be phenotypically male but genotypically female.