Female sperm storage

Female sperm storage is a biological process and often a type of sexual selection in which sperm cells transferred to a female during mating are temporarily retained within a specific part of the reproductive tract before the oocyte, or egg, is fertilized. The site of storage is variable among different animal taxa and ranges from structures that appear to function solely for sperm retention, such as insect spermatheca and bird sperm storage tubules (bird anatomy), to more general regions of the reproductive tract enriched with receptors to which sperm associate before fertilization, such as the caudal portion of the cow oviduct containing sperm-associating annexins. Female sperm storage is an integral stage in the reproductive process for many animals with internal fertilization. It has several documented biological functions including:

Female sperm

Female sperm can be either:

This article focuses on the second definition.

Since the late 1980s, scientists have explored how to produce sperm where all of the chromosomes come from a female donor. In the late 1990s, this concept became a partial reality when scientists in Japan developed chicken female sperm by injecting bone marrow stem cells from a female chicken into a rooster's testicles. This technique proved to fall below expectations, however, and has not yet been successfully adapted for use on humans.

Female sperm production

Creating female sperm was first raised as a possibility in a patent filed in 1991 by injecting a woman's cells into a man's testicles, though the patent focused mostly on injecting altered male cells into a man's testes (to correct genetic diseases). In 1997, Japanese scientists partially confirmed such techniques by creating chicken female sperm in a similar manner. "However, the ratio of produced W chromosome-bearing (W-bearing) spermatozoa fell substantially below expectations. It is therefore concluded that most of the W-bearing PGC could not differentiate into spermatozoa because of restricted spermatogenesis." These simple transplantation methods follow from earlier observations by developmental biologists that germ stem cells are autonomous in the sense that they can begin the processes to become both sperm and eggs.