Freemartin
Encyclopedia
A freemartin or free-martin (sometimes martin heifer) is an infertile
female mammal
which has masculinized
behavior and non-functioning ovaries. Genetically and externally the animal is female, but it is sterilized
in the womb
by hormone
s from a male twin
, becoming an infertile partial intersex
. Freemartinism is the normal outcome of mixed-sex twins in all cattle
species that have been studied, and it also occurs occasionally in other mammals including sheep, goats and pigs.
discovered that a freemartin always has a male twin.
It was hypothesized early in the 20th century that masculinizing factors travel from the male twin to the female twin through the vascular connections of the placenta because of the vascular fusion and affect the internal anatomy of the female.
Several researchers made the discovery that a freemartin results when a female fetus has its chorion
fuse in the uterus
with that of a male twin. The result was published in 1916 by Tandler and Keller. The discovery was made independently by American biologist Frank R. Lillie, who published it in Science
in 1916. Both teams are now credited with the discovery.
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
.
s 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 castrated
male cattle (steers).
Physical examination of the calf may also reveal differences: many (but not all) freemartins have a short vagina
compared with that of a fertile heifer.
s.
and immunology
research.
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 transplantation
often used in stem cell research.
Infertility
Infertility primarily refers to the biological inability of a person to contribute to conception. Infertility may also refer to the state of a woman who is unable to carry a pregnancy to full term...
female mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
which has masculinized
Virilization
In biology and medicine, virilization refers to the biological development of sex differences, changes that make a male body different from a female body. Most of the changes of virilization are produced by androgens...
behavior and non-functioning ovaries. Genetically and externally the animal is female, but it is sterilized
Neutering
Neutering, from the Latin neuter , is the removal of an animal's reproductive organ, either all of it or a considerably large part. The process is often used in reference to males whereas spaying is often reserved for females. Colloquially, both terms are often referred to as fixing...
in the womb
In utero
In utero is a Latin term literally meaning "in the womb". In biology, the phrase describes the state of an embryo or fetus. In legal contexts, the phrase is used to refer to unborn children. Under common law, unborn children are still considered to exist for property transfer purposes.-See also:*...
by hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
s from a male twin
Twin
A twin is one of two offspring produced in the same pregnancy. Twins can either be monozygotic , meaning that they develop from one zygote that splits and forms two embryos, or dizygotic because they develop from two separate eggs that are fertilized by two separate sperm.In contrast, a fetus...
, becoming an infertile partial intersex
Intersex
Intersex, in humans and other animals, is the presence of intermediate or atypical combinations of physical features that usually distinguish female from male...
. Freemartinism is the normal outcome of mixed-sex twins in all cattle
Bovinae
The biological subfamily Bovinae includes a diverse group of 10 genera of medium to large sized ungulates, including domestic cattle, the bison, African buffalo, the water buffalo, the yak, and the four-horned and spiral-horned antelopes...
species that have been studied, and it also occurs occasionally in other mammals including sheep, goats and pigs.
History
The 18th-century physician John HunterJohn Hunter (surgeon)
John Hunter FRS was a Scottish surgeon regarded as one of the most distinguished scientists and surgeons of his day. He was an early advocate of careful observation and scientific method in medicine. The Hunterian Society of London was named in his honour...
discovered that a freemartin always has a male twin.
It was hypothesized early in the 20th century that masculinizing factors travel from the male twin to the female twin through the vascular connections of the placenta because of the vascular fusion and affect the internal anatomy of the female.
Several researchers made the discovery that a freemartin results when a female fetus has its chorion
Chorion
The chorion is one of the membranes that exist during pregnancy between the developing fetus and mother. It is formed by extraembryonic mesoderm and the two layers of trophoblast and surrounds the embryo and other membranes...
fuse in the uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
with that of a male twin. The result was published in 1916 by Tandler and Keller. The discovery was made independently by American biologist Frank R. Lillie, who published it in Science
Science (journal)
Science is the academic journal of the American Association for the Advancement of Science and is one of the world's top scientific journals....
in 1916. Both teams are now credited with the discovery.
In rural areas folklore
Folklore
Folklore consists of legends, music, oral history, proverbs, jokes, popular beliefs, fairy tales and customs that are the traditions of a culture, subculture, or group. It is also the set of practices through which those expressive genres are shared. The study of folklore is sometimes called...
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
Bede
Bede , also referred to as Saint Bede or the Venerable Bede , was a monk at the Northumbrian monastery of Saint Peter at Monkwearmouth, today part of Sunderland, England, and of its companion monastery, Saint Paul's, in modern Jarrow , both in the Kingdom of Northumbria...
.
Mechanism
In most cattle 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 hormoneHormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
s 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 castrated
Castration
Castration is any action, surgical, chemical, or otherwise, by which a male loses the functions of the testicles or a female loses the functions of the ovaries.-Humans:...
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.Physical examination of the calf may also reveal differences: many (but not all) freemartins have a short vagina
Vagina
The vagina is a fibromuscular tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. Female insects and other invertebrates also have a vagina, which is the terminal part of the...
compared with that of a fertile heifer.
Other animals
A freemartin is the normal outcome of mixed twins in all cattle species which have been studied. It does not normally occur in most other mammals, though it has been recorded in sheep, goats, and pigPig
A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...
s.
Uses
Freemartins are occasionally used in stem cellStem cell
This article is about the cell type. For the medical therapy, see Stem Cell TreatmentsStem cells are biological cells found in all multicellular organisms, that can divide and differentiate into diverse specialized cell types and can self-renew to produce more stem cells...
and immunology
Immunology
Immunology is a broad branch of biomedical science that covers the study of all aspects of the immune system in all organisms. It deals with the physiological functioning of the immune system in states of both health and diseases; malfunctions of the immune system in immunological disorders ; the...
research.
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
Y chromosome
The Y chromosome is one of the two sex-determining chromosomes in most mammals, including humans. In mammals, it contains the gene SRY, which triggers testis development if present. The human Y chromosome is composed of about 60 million base pairs...
. 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 transplantation
Organ transplant
Organ transplantation is the moving of an organ from one body to another or from a donor site on the patient's own body, for the purpose of replacing the recipient's damaged or absent organ. The emerging field of regenerative medicine is allowing scientists and engineers to create organs to be...
often used in stem cell research.
Fictional use
- In the Aldous HuxleyAldous HuxleyAldous Leonard Huxley was an English writer and one of the most prominent members of the famous Huxley family. Best known for his novels including Brave New World and a wide-ranging output of essays, Huxley also edited the magazine Oxford Poetry, and published short stories, poetry, travel...
novel Brave New WorldBrave New WorldBrave New World is Aldous Huxley's fifth novel, written in 1931 and published in 1932. Set in London of AD 2540 , the novel anticipates developments in reproductive technology and sleep-learning that combine to change society. The future society is an embodiment of the ideals that form the basis of...
, 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. HeinleinRobert A. HeinleinRobert Anson Heinlein was an American science fiction writer. Often called the "dean of science fiction writers", he was one of the most influential and controversial authors of the genre. He set a standard for science and engineering plausibility and helped to raise the genre's standards of...
novel Beyond This HorizonBeyond This HorizonBeyond This Horizon is a science fiction novel by Robert A. Heinlein. It was originally published as a two-part serial in Astounding Science Fiction and then eventually as a single volume by Fantasy Press in 1948.-Overview:The novel depicts a world where genetic selection for increased health,...
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 Robert Heinlein novel Farnham's FreeholdFarnham's FreeholdFarnham's Freehold is a science fiction novel set in the near future by Robert A. Heinlein. A serialised version, edited by Frederik Pohl, appeared in Worlds of If magazine . The complete version was published in novel form by G.P...
, the protagonist, Hugh Farnham, is given a companion (bedwarmer) that is described as a natural freemartin. - In the crime novel Freemartin, by David Cohler, an FtM transgenderTransgenderTransgender is a general term applied to a variety of individuals, behaviors, and groups involving tendencies to vary from culturally conventional gender roles....
man is a murderer. - In the Avram DavidsonAvram DavidsonAvram Davidson was an American writer of fantasy fiction, science fiction, and crime fiction, as well as the author of many stories that do not fit into a genre niche...
story "The House the Blakeneys Built", the cattle are freemartins. - In the fantasy book series Bazil BroketailBazil BroketailBazil Broketail is a 1992 fantasy novel by author Christopher Rowley, the name of its main character, and the name of the further series of books featuring him...
by Christopher RowleyChristopher RowleyChristopher Rowley is an American writer of both science fiction and fantasy novels.Rowley was born in 1948 in Lynn, Massachusetts to an American mother and an English father. Educated for the most part at Brentwood School, Essex, England, he became a London-based journalist in the 1970s...
, "freemartin" is the name for a breed of sterile female dragons. - In the novel "FootfallFootfallFootfall is a 1985 science fiction novel written by Larry Niven and Jerry Pournelle. It was nominated for the both the Hugo and Locus Awards in 1986, and was a No...
" by Larry NivenLarry NivenLaurence van Cott Niven / ˈlæri ˈnɪvən/ is an American science fiction author. His best-known work is Ringworld , which received Hugo, Locus, Ditmar, and Nebula awards. His work is primarily hard science fiction, using big science concepts and theoretical physics...
and Jerry PournelleJerry PournelleJerry Eugene Pournelle is an American science fiction writer, essayist and journalist who contributed for many years to the computer magazine Byte and has since 1998 been maintaining his own website/blog....
, a female character refers to herself as a freemartin.