10 March 2013

Cats: Shaded Cameo Genetics

Since I'm getting my wonderful Peaches, I thought I would do a bit of research on the genetics behind the shaded cameo.  Her coat is wonderful and very intriguing to me.

First off, one must clearly understand what a shaded cameo is.  According to the Cat Fanciers' Association (CFA) website:
The Shaded and Smoke Division includes the shell and shaded cameos which have red tipping with a white undercoat....In repose, the smoke appears to be a solid color cat. In motion, the coat will break open, giving glimpses of a startling white undercoat. All should have the characteristic white ruff and ear tufts. The perfect balance of undercoat to overcoat is transitory and the perfection of color balance can usually only be seen six to eight weeks annually. Their brilliant copper eyes seem almost like burning embers within the smoke setting. CFA Persian Description
This description got me thinking of the silvers, which have white coats tipped in black. But that still didn't explain how you get colored tips on white hairs...  So, I looked up the genetics and gave myself a headache!  It seems the shaded cameo requires 3 different genes to produce their wonderful coat -- one gene off and no shaded cameo.  The genes are D-I-O.

The first gene, D, stands for Dense color.  The D works with the O to produce the red tipping, as opposed to a lighter cream tipping.  Having never seen a cream cameo, I have a hard time envisioning it.

The second gene, I, stands for Inhibitor.  The inhibitor gene I is dominant over the recessive i.  The I gives the hair the white shaft from the skin to the tip.  The amount of tipping varies from just a bit (shell cameos) to about half (shaded cameos) to most but not all (smoke cameos or red smokes).  With the i, the coat hairs would be solid (or agouti if carrying that gene).

The third gene, O, stands for Orange or red.

While it may sound 'easy' to produce a shaded cameo because all the genes are dominant, the problem is getting all 3 genes at one time without any other genes interfering, such as the gene for tabby markings.  

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