Sterility (physiology)

Sterility is the physiological inability to effect sexual reproduction in a living thing, members of whose kind have been produced sexually. Sterility has a wide range of causes. 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.

Mechanisms of sterility

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, causing an imbalance in the resulting offspring making it viable but not fertile, this is the case with the mule. Sterility can also be caused by chromosomal differences within the patient, these individuals tend to be known as a genetic mosaics. Loss of part of a chromosome can also cause sterility due to nondisjunction. Sterility can also be caused by selective breeding, where the trait you are selecting for 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. XX male syndrome is another cause of sterility, this is where the sexual determining factor on the Y chromosome (SRY) is transferred to the X chromosome due to an unequal crossing over, this gene indicated what gender the individual should be and causes the development of testes, causing the individual to be phenotypically male but genotypically female, the resulting individual is (information needed).

Economic uses of sterility

Economic uses of sterility include:

• the production of certain kinds of seedless fruit, such as seedless tomato 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 a malaria in mosquitoes.