Quote:
Originally Posted by Shiari
A better example of codominance in a cat is actually a tortoiseshell. Orange and black are allelic and on the x chromosome. In order for a female cat to be orange, she must have two orange genes. In order to be black, she must have two black genes. If she has one orange and one black, she shows both colors in patches.
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Tortoiseshell
is not an example of codominance. The orange mutant is at the O locus on the X chromosome. The black mutant is at the a locus, which is not on either sex chromosome. The effect of the orange mutant masks the effect of the black mutant in areas where the orange-bearing X chromosome is active. The patchy coat color is an example of X chromosome inactivation, the Lyon hypothesis. See
http://cal.vet.upenn.edu/projects/ge...mple/page4.htm