Almost every calico cat is female, and the reason is a coin flip happening in every cell of her body during development. Barr and Bertram found part of it in 1949. A 2025 paper finally named the gene.
Why Are Almost All Calico Cats Female? The Genetics of Tortoiseshell CoatsCalico cat genetics, explained: X-inactivation, the ARHGAP36 orange gene cracked in 2025, why male calicos carry an extra X, and the folklore behind them.pudgycat.io