The feline orange gene sits on the X chromosome, with orange and non-orange as versions of one locus, and a single X expresses only one.
Females carry two Xs, and random X-inactivation in embryonic cells creates a mosaic of orange and black patches, which plus white-spotting genes makes a calico.
Males usually have one X and cannot carry both colors; the rare male calico comes from anomalies like XXY and is typically sterile.
The same logic explains why tortoiseshells are nearly all female; coat color has no proven link to personality or health despite folklore.
