In the last post, I wrote about the agouti fur pattern that marks the background pattern between the stripes on a tabby. The image to the right shows a single agouti hair, with the bands of black pigment alternating with the orangeish rufousing pigment. The agouti gene comes in two variants – A which expresses agouti normally, and a, which stops the agouti pattern, making the agouti hairs solidly colored.
The a/a combination thus allows a cat that is all one color, or almost so. The tabby pattern is still there under it all, it’s just black stripes on a black background. At times you can see the ghost pattern on a solid cat, especially when young. Both Calla and Gus have the a/a setup, whereas Julius has at least one A to express his tabby stripes.
There’s one wrinkle in the a/a ‘solid’ or non-agouti chromosome. It only works on the black pigments. If the cat is orange, the tabby stripes will show through regardless of the presence of A/- or a/a. On a tortie cat, the orange parts will show stripes while the black areas will follow suit if the cat s an A, and won’t if she is an a/a.
Breeders who want their solid orange to look solid manipulate the color of the rufousing to match the intensity of the stripes as closely as they can to mute them, but they can not hide them all. The stripes on the face especially will show.
Note: I’ve put this and some additional genetic information in a separate page for easy reference. I hope you find it useful.