Freemartin
female twin of a bull
A freemartin or free-martin (sometimes martin heifer) is an infertile cow with masculinized behavior and non-functioning ovaries. Such a cow is born as one of a pair of twins, with a male calf as the other twin. Phenotypically, the animal appears female, but various aspects of her female reproductive development were altered due to acquisition of anti-Müllerian hormone from the male twin. Genetically, the animal is chimeric: karyotypy as a sample of cells shows XX/XY chromosomes. The animal originates as a female (XX), but acquires the male (XY) component in utero by exchange of some cellular material from a male twin, via vascular connections between placentas. Such cows provide an example of microchimerism. The chimerism is mainly present in the hematopoietic stem cells.
History
The phenomenon of sterile cows being born as twins to bulls is known to have been described by the Roman writer Varro, who called these sterile females "taura".
The 18th century physician John Hunter discovered that a freemartin always has a male twin. Hunter's 1779 description of freemartins is the oldest known anatomical description of these animals.
The public source identifies “Freemartin” as female twin of a bull. This brief keeps that definition visible, then builds a research path around Freemartin, female and twin.
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This entry incorporates text from “Freemartin” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.