Sterility (physiology)

Hybrid sterility can be caused by different closely related species breeding and producing offspring. These animals are usually sterile due to different numbers of chromosomes from the two parents. The imbalance results in offspring that is viable but not fertile, as is the case with the mule.

Sterility can also be caused by selective breeding, where a selected trait is closely linked to genes involved in sex determination or fertility. For example goats breed to be polled (hornless). This results in a high number of intersex individuals among the offspring, which are typically sterile.[1]

Sterility can also be caused by chromosomal differences within an individual. These individuals tend to be known as a genetic mosaics. Loss of part of a chromosome can also cause sterility due to nondisjunction.

XX male syndrome is another cause of sterility, wherein the sexual determining factor on the Y chromosome (SRY) is transferred to the X chromosome due to an unequal crossing over. This gene triggers the development of testes, causing the individual to be phenotypically male but genotypically female.

Economic uses of sterility include:

• the production of certain kinds of seedless fruit, such as seedless tomato[2] or watermelon (though sterility is not the only available route to fruit seedlessness);
• terminator technology, methods for restricting the use of genetically modified plants by causing second generation seeds to be sterile;
• biological control; for example, trap-neuter-return programs for cats; and the sterile insect technique, in which large numbers of sterile insects are released, which compete with fertile insects for food and mates, thus reducing the population size of subsequent generations, which can be used to fight diseases spread by insect vectors such as malaria in mosquitoes.
• some animals which can produce sterile offspring because of mating with closely related species like mule, jenny, liger and tigon.