<u>Codominance.</u> This is shown by the calico cats, who have both black and orange phenotypic expression; the black and orange are not mixed like incomplete dominance, and one is not entirely dominant over the other. (A common example is the roan cow, whose fur is a bit red, a bit white.)
<u>Sex-linked inheritance.</u> Since calico cats are said to always be female (which actually isn't entirely accurate, by the way) this means that the coat color is sex-linked. It's found on the X chromosome, so a female cat can have one X black and one X orange chromosome. This is only possible in males when they are nondisjunct and inherit two Xs along with their Y... but that's a completely different story. :)
1. They are easy to raise. 2. Have many offspring during per mating. 3. It can fertilize itself. 4. It has varieties in genotype that is easy observable. 5. It has phenotype that is also easy observable.
