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FreemartinA '''freemartin''' or '''free-martin''' (sometimes '''martin heifer''') is a female bovinae|bovine or ovineHistory
The 18th-century physician John Hunter (surgeon)|John Hunter discovered that a freemartin always has a male twin. [jstor]
In 1916, several researchers independently discovered what happens when the chorion (the outer layer of the two membranes that completely envelop a fetus) of a male and the chorion of a female bovine fetus fuse in the uterus.
In rural areas folklore often claimed this condition was not just peculiar to cattle, but extended also to human twins; this belief perpetuated for generations, as was mentioned in the writings of Bede. [de Albuquerque, Martim ''Notes and Queries'' Volume 2. 1857 by Oxford University Press, p. 149]
Mechanism
In most cattle Twins#Dizygotic twins|twins, the blood vessels in the chorions become interconnected, allowing blood from each twin to flow around the other. If both fetuses are the same sex this is of no significance, but if they are different, male hormones pass from the male twin to the female twin. The male hormones then masculinize the female twin, and the result is a freemartin[
]. The degree of masculinization is greater if the fusion occurs earlier in the pregnancy – in about ten percent of cases no fusion takes place and the female remains fertile.
The male twin is largely unaffected by the fusion, although the size of the testicles may be slightly reduced. Testicle size is associated with fertility, so there may be some reduction in bull fertility.
Freemartins behave and grow in a similar way to Castration|castrated male cattle (steers).
Diagnosis
If suspected, a test can be done to detect the presence of the male Y-chromosomes in some circulating white blood cells of the subject. Genetic testing for the Y-chromosome can be performed within days of birth and can aid in the early identification of a sterile female bovine.
Examination of the animal may also reveal physical differences between a freemartin and fertile heifer.
Other animals
A freemartin is the normal outcome of mixed twins in all cattle species which have been studied. In most other mammals it does not normally occur.
Uses
Freemartins are occasionally used in stem cell and immunology research.[
Free full text in Stem Cells
]
During fetal development cells are exchanged between the fused circulations of the bovine twins. Up to 95% of the freemartin's blood cells can be derived from those of its twin brother. Male-derived cells and their progeny can be easily visualized in the freemartin tissues, as only they contain the male Y chromosome. Thus, by analyzing these tissues, one is able to investigate the capacity of hematopoietic stem cells or other circulating cells to produce other tissues in addition to blood. The freemartin model allows one to analyze perfectly healthy and unmanipulated animals, without resorting to Organ transplant|transplantation often used in stem cell research.
Fictional use
- In the Aldous Huxley novel ''Brave New World'', a "freemartin" (mentioned in chapters 1, 3, 11 and 17) is a woman who has been deliberately made sterile by exposure to hormones during fetal development; In the book government policy requires freemartins to form 70% of the female population.
- The Robert A. Heinlein novel ''Beyond This Horizon'' lists "the clever and repulsively beautiful pseudo-feminine freemartins" as one of the genetically-engineered specialist types of humans that were created in the "Empire of the Great Khans" (chapter 2).
- In the crime novel ''Freemartin'', by David Cohler, an transman|FtM transgender man is a murderer.
- In the fantasy book series ''Bazil Broketail'' by Christopher Rowley, "freemartin" is the name for a breed of sterile female dragons.
References
External links
- Mosaicism and Chimerism at colostate.edu
- Picture at agric.gov.ab.ca
Category:Sexual orientation and science
Category:Bovine health
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Sources: StartLearningNow, Wikipedia | Usage license: GNU FDL
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