It isn't really a 3rd phenotype but rather the 2 phenotypes occurring at the same time. A snow is an albino axanthic individual, but instead of calling it an albino axanthic, we call it 'snow' for short.

Chris, I couldn't disagree more, especially based on the actual scientific definitions of what a phenotype is.

Let us first read what Wikipedia's definition is: Wikipedia: Phenotype - "A phenotype is any observable characteristic or trait of an organism: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior (such as a bird's nest). Phenotypes result from the expression of an organism's genes as well as the influence of environmental factors and the interactions between the two."

I could recite all other references online, but they all basically say the same thing. I think the main part that truly defines it is "the expression of an organism's genes". If you notice, the word genes is plural, not singular, which dictates that it's not just always one gene that defines a phenotype.

Let's use a different example for now instead of using an expressed Double Recessive type, like a regular Albino versus an Extreme Red Albino. No one would argue that these are not expressing the same compatible Albino gene, but these types of Albinos are totally discernible from each other. That's a phenotype! How about an Anaconda versus a Superconda, both carry the exact same gene(s) (albeit a different genotype) but yet are completely different in appearance. That's a phenotype! It's no different when you combine multiple genetic traits such as two Recessive traits unless you start getting into the realm of epistasis where one trait surpresses, or masks, the other trait "invisible" but still has the genotype of two different homozygous traits.

Let us look a little more closely at the example of the Anaconda and Superconda types. While the gene involved is the same gene, it is not only expressed differently but it's genotype is different as well due to the Superconda being the homozygous form and the Anaconda being the heterozygous form. Let's refer to the Superconda genotype as 'ss'. With this genotype, we will always get a Superconda, even hypothetically should other color traits be included. Let us use for example that a Normal (Wild Type) genotype would be 'SS'. Now, we can easily distinguish between the two phenotypes, Superconda vs. a Normal. Obviously, when you breed a Superconda to a Normal, you get all Anacondas of which the genotype would be 'Ss' and it's phenotype would be completely different from it's parents thus creating a completely new phenotype. So, from the expression of the mixing of this single gene, we get 3 different phenotypes which, again, is defined as "any observable characteristic or trait of an organism".

In regards to a Snow, if a Snow was found in the wild, how would anybody know that it was the product of 2 separate genes at first glance? You wouldn't! If you bred a Snow to a Normal, you would get all Normals that would be Double Het for both Albino and Axanthic, but you still wouldn't know the specifics of the genotype until you did testcross breeding trials. In fact, after the first breeding, with the F1's, you would first assert at that point that the Snow is just a simple Recessive because all you would get are Normals that are hypothetically het for "Snow". Only upon inbreeding the F1's and producing the F2's would you then start to realize that the Snow is a culmination of at least 2 traits by producing 4 entirely different phenotypes, Normals, Albinos, Axanthics and Snows. All are very different phenotypes and definitely many more genotypes when you start to get into the het aspects of some of the Normals, Albinos and Axanthics being possible het for any of the other traits.

Again, I want to reiterate that the definition of a phenotype "is any observable characteristic or trait of an organism". If a Snow is different looking than an Albino or an Axanthic, then that is it's phenotype, Snow. If an Albino is also het for Axanthic (or vice versa), then it's phenotype is still that of an Albino but it's genotype will be totally different than that of a non-het Albino. So for the 2 Albinos, one het, one non-het, there would be 2 completely different genotypes but still only one phenotype.

And thanks Chris for the invitation on discussing this further on a personal level. I will have to take you upon that.
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Troy Rexroth
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