Why only female cats are tortoiseshell or calico


Carolyn Brown’s lab at the University of British Columbia in Vancouver studies X chromosome inactivation, which prevents females (XX) from getting an overdose of the proteins produced by the X chromosome, compared to males (XY). This phenomenon explains why (with rare exceptions) only female cats are bi- or tricolor.

Go to the link to see the slideshow gallery of tortie and calico kitties. Crucially, THE CATS IN THESE PHOTOS ARE NOT LAB CATS. Brown’s lab doesn’t study cats. These are shelter cats photographed while awaiting adoption. Aren’t they beautiful?!

This doesn’t explain the “dilute” gene that makes some cats pink and blue instead of orange and blackā€”or the white-spotting gene that turns a tortie into a tricolor calico. Lovers of science + cats, follow the links! And as a bonus, here’s Lumi, who somehow manages to be “all of the above”: tabby, Siamese, dilute (see the pale orange patches on her face and paw), and white-spotted.