Calico cats are almost all female
#0042 Animals & plants
Fact rank
A
The mechanism and the breakdown of chromosomes were confirmed in primary sources (paper abstracts). Not S because there is no reliable source for how rare male calicos are (one in how many)
Wow rank
S
The colour of a familiar cat's coat depends on its sex, and the males are all exceptions
Usefulness
—
A fact worth knowing for its own sake
Verification: Supported by evidence
AI verification reports the evidence it found; it does not guarantee that a claim is true.
Calico cats are almost all female, and males are rarely born. Almost every male calico is an exception whose combination of sex chromosomes is unusual.
Why
The gene that decides whether a cat's fur is orange or black sits on the X chromosome (identified in 2025 by a team including Kyushu University). A calico needs both orange and black, which means two X chromosomes, but a male is normally XY with only one X, so he comes out either orange or black.Evidence
Primary Abstract of the paper by Kyushu University and others (2025, Current Biology). A deletion of about 5.1 kb in the ARHGAP36 gene on the X chromosome is associated exclusively with orange coat colour link
Secondary Explainer by the Japan Science and Technology Agency (2025). A male is XY, so his single X chromosome makes him either orange or black. The male calico in the study had two X chromosomes (XXY) link
Primary Abstract of a survey of UK vets (1999, Veterinary Record). Of 4,598 males, 20 were recorded as tortoiseshell or calico. Of the 11 whose chromosomes were examined, 6 were XX/XY chimeras, 2 were XXY, 2 were XX and 1 was XY link
Primary Danish case report (2013, Cytogenetic and Genome Research). An XXY male tortoiseshell cat had no germ cells in the testes: a classic sterile case link
Primary Abstract of a Polish case report (2026, Sexual Development). An XX/XY chimeric male tortoiseshell Maine Coon mated and five kittens were born. Chimeric males can be fertile link
Primary Exhibition material from the National Institute of Polar Research. Just before the first expedition sailed, a kitten was handed over with the words "a male calico brings good luck, take him as a charm for the voyage". He became Takeshi, the only cat to winter with the expedition link
Primary Exhibition material from the National Institute of Polar Research. The first expedition's ship Soya left Harumi port on 8 November 1956 link
Secondary Article in the Kumamoto Nichinichi Shimbun. Male calicos are "said to be one in 30,000" link
Notes and limits
Male calicos are born not only as XXY, with one extra X chromosome, but also as chimeras (XX/XY), where two fertilised eggs merged into one. In the UK survey, chimeras outnumbered XXY among the males whose chromosomes were examined. XXY males are normally sterile, but chimeric males have fathered kittens. Their rarity is often given as "one in 3,000" or "one in 30,000", but the original survey behind either figure was not found. In Japan they were prized as guardians of ships, and the first Japanese Antarctic Research Expedition, which sailed in 1956, took along a male calico named Takeshi, handed over as a charm for the voyage; he wintered at Syowa Station. Japanese Wikipedia's "Calico cat" (三毛猫) article also covers the mechanism and Takeshi.
Derivations
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