Why are tortoiseshell cats usually females?

A Calico tabby cat that has solid black and tabby orange colors. Photo by Alecsander Alves on Unsplash

Where does this color pattern get its name from?

Tortoiseshell is a pricey material produced from the shells of large marine turtles like the Hawksbill Sea Turtle banned since the 1970s. The distinctive mottled pattern that it has is hard to imitate using semi-synthetic plastics like cellulose nitrate. The resemblance to this mottled pattern is the reason behind the name for this coat color.

A Tortoiseshell/ Tortie with solid colors. Photo by Andy Holmes on Unsplash

The Orange gene (Locus O) and it’s the connection to the Tortoiseshell coat.

The Orange gene is found on the X chromosome, a sex chromosome, and hence, is a sex-linked gene. When both the copies are the dominant alleles of the gene(O/O), the result is an ORANGE cat. A combination of the recessive alleles(o/o) produces a BLACK coat. When the dominant and recessive alleles are present together, they produce a tortoiseshell coat mix of yellow and black hairs. This happens only because of the codominance of the alleles.

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Leons Mathew Abraham

Leons Mathew Abraham

A Veterinary Microbiologist with a passion for birding.