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    "headline": "Tortie Maine Coon kitten’s Halloween-candy coat wins fans online, and her X chromosomes explain it",
    "description": "Almost every tortoiseshell cat is female because the orange gene sits on the X chromosome; the rare males, about 1 in 3,000, usually carry an extra X.",
    "datePublished": "2026-10-18T02:50:00+01:00",
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    "articleSection": "Pets & Animals",
    "keywords": "cat genetics, kittens, Maine Coon, tortoiseshell cats",
    "articleBody": "A short video clip of a long-haired tortoiseshell Maine Coon kitten, her fur a scramble of near-black and golden orange, pulled in a run of naming suggestions this week after the account behind it asked viewers, “What would you name this perfect girl?” The clip was shared by the account @pawcache_coons. Commenters went straight to autumn food and art. “Biscotti,” “Butternut,” “Patches” and “Picasso” were among the offers, and one viewer made the case for “Autumn” because of her fall coloring. The kitten has bright orange flashes on her forehead and cheeks and the long ear tufts the breed is known for. We could not confirm her age or which name, if any, has stuck. The palette that makes her look like a Halloween candy bowl is not luck or grooming. It is a readable record of her sex chromosomes. Why a coat like this is almost always female Tortoiseshell is a coat pattern, not a breed, and it can turn up in pedigreed cats and in random-bred house cats alike. The switch between orange pigment and black-based pigment sits on the X chromosome and comes in two versions: one tells a pigment cell to make red or orange, the other leaves it making black, chocolate or, in diluted coats, blue-gray. A female carries two X chromosomes, so she can inherit one of each. Very early in the embryo, every one of her cells silences one X at random, a process called X-inactivation, and that cell’s descendants keep the same choice. Patches that trace back to cells where the orange X stayed active grow orange fur; the rest grow dark fur. When pigment cells mix early, as they did in this kitten, the result is the fine brindled blend torties are known for. In calico cats, a separate white-spotting gene slows the pigment cells down, so the colors settle into larger, sharper blocks. A typical male has one X and one Y, which leaves room for only one version of the gene: he is either all orange or all dark. To be tortoiseshell he needs a second X. One widely cited estimate puts male torties at about 1 in 3,000, and most carry an XXY set of sex chromosomes, the feline counterpart of Klinefelter syndrome in people. In a 2022 review in the Journal of Feline Medicine and Surgery, Robert A. Foster wrote that any male cat with three coat colors must have at least two X chromosomes and that these cats are rarely fertile. A smaller group are chimeras, built from two early embryos that fused, or mosaics in which the extra X appeared after conception. The geneticist Leonard Doncaster first showed the pattern was sex-linked and noticed that tortie males were often sterile. The orange switch was only identified in 2025 For about a hundred years, researchers knew roughly where the orange variant sat without knowing what it was. In May 2025 a Stanford Medicine team led by Christopher Kaelin, with Greg Barsh as senior author, reported the answer in the journal Current Biology. Comparing male orange cats, they found 51 candidate variants on the X chromosome, threw out 48 that also showed up in non-orange cats, and settled on a small deletion that ramps up a nearby gene called Arhgap36. That gene is not switched on in the pigment cells of mice, humans or non-orange cats. “This is something that arose in the domestic cat, probably early on in the domestication process,” Kaelin said, pointing to 12th-century paintings that already show calico cats. The team found no difference in Arhgap36 activity between orange and non-orange cats in kidney, heart, brain or adrenal tissue. That fits the wider evidence on so-called “tortitude”: plenty of owners believe in it, but there is little scientific support, and one study found no link between coat color and tameness. A Maine Coon kitten has years of growing ahead The breed brings its own features. Maine Coons, named Maine’s official state cat in 1985, can carry nearly any color other cats show, tortoiseshell included. Their coat runs shorter on the head and shoulders and longer on the belly and flanks, and the oversized paws, tufts between the toes and heavily furred ears are traits tied to surviving hard New England winters. They are the largest cat breed that is not a wild-cat hybrid, and the breed is prone to a heart-muscle disease, hypertrophic cardiomyopathy: at Washington State University’s veterinary cardiac genetics lab, about one in three Maine Coons tested carried a mutation linked to it. They also mature slowly. Most cats reach adult size at about a year, but a Maine Coon usually keeps filling out until age 3 to 5. Adult males average 18 to 22 pounds (8 to 10 kg). If this kitten tracks the female average, the candy bowl will weigh 12 to 15 pounds (5 to 7 kg) by the time she is fully grown, somewhere between her third and fifth birthdays.",
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