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Rextiles
at Wed Nov 17 19:40:32 2010 [ Email Message ] [ Show All Posts by Rextiles ]
Nomenclature is a construct of man. It is way for humans to categorize things so they are easier to understand. In genetics, I am not aware of a single term specifically created to represent a doubly homozygous recessive genotype.
While I too am currently unaware of a term that defines the unique phenotype of 2 or more combined Recessive traits resulting in a homozygous animal, the two closest terms, but yet differently defined would be dihybrid and polygenic (otherwise known as linebred traits).
Dihybrids are often explained using the model of a Dominant trait mixed with a Recessive non-related type of trait. When I say non-related, I mean that the traits are different in terms of physical characteristics such as one trait being blond hair while the other is blue eyes. Obviously, would not apply because what we are talking about with Snows are all color related traits. I would ponder though whether it would apply to something like an Albino Anaconda/Superconda as the Albino is one type of trait (color) while the Anaconda/Superconda is another type (pattern reduction), I believe it would.
Polygenic traits are something entirely far more complex being traits that are expressed from multiple genes residing at different loci on different chromosomes. Polygenic traits are far more complex than the simple Recessive traits that we are discussing such as a Snow but Polygenic traits are generally attributed to phenotypes such as the red coloration in an Extreme Red Albino and all of the variations that these consist of.
The reason why I mention that a Double Recessive Homozygous animal, like a Snow, is kind of like an Incomplete Dominance type of condition is because of the blending condition that appears to be happening. For those that didn't read my previous indepth post on Dodominance and Incomplete Dominance, please read this: Codominance & Incomplete Dominance. Also be sure to read the references I cite at the bottom of my post if you in fact question what I said in that post.
The phenotype however can be called whatever we want, for example "Snow" or "Ghost". Realistically the genotype is what is important, not the phenotype.
While I do agree with you in general, the one time that the genotype isn't necessarily important is when epistasis occurs. Of course this typically only happens with animals such as Leucistics, so it will be interesting when the Leucistic Hognose emerge how, or if, they can be implemented with other morphs. And while you state "Realistically the genotype is what is important, not the phenotype.", it's the phenotype that commands the price, which is why hets are usually 50-75% cheaper than the phenotypic animals. 
Now, it is worth noting that NOT all phenotypic characters come from single-gene interacts like the examples follow. Human eye color for instance is control by multiple genes, also known as multiple gene interactions (check out google for more info.). Line-bred traits are traits that are likely control by multiple gene interacts, that for now, are too complicated for breeders to predict.
Agreed, these are generally termed as Polygenic traits, meaning many genes.
A good entry-level (college) genetics book I have is:
Brooker, Robert. 2008. Genetics: Analysis and Principles. 3rd Edition. McGraw-Hill Science. p864..
Thanks for the recommendation. I was actually looking at purchasing that book a few weeks ago to better supplement these two books I've been reading from to gain my knowledge:
Biology: Concepts & Connections
Genetics For Herpers
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Troy Rexroth
Rextiles
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RE: Rextiles and others... - Rextiles, Wed Nov 17 19:40:32 2010
