At this point it's probably safe to assume everyone knows Mendel's laws. I won't state them, but I'll give a couple examples then move on to my main ideas.

First, some terms, in case the reader does not know them.

Genotype is the actual genetic coding for a trait. You can't see it without specialized equipment. There is no electrophoresis for Meeroos so we have to work it out Old School .. by deduction.

Locus (plural: loci) is a single genetic factor.

Alleles are the bits which make up a locus.

Phenotype is what we can see. This includes any factor one can see in the Edit box in-world .. mainly textures and sizes. It also includes the text associated with those factors whether in-world or on the web site in the Tome, spreadsheet or on the Details page. It also includes the Treasures found as well as behaviors (notably the effects of Personality upon breeding).

A "mapping" is the relationship between Genotype and the Phenotype. I know, mapping means something different in genetics but, hey, I'm a mathematician and that's the word we use to describe the process of showing the relationships and processes between the production set (the genotype) and the result set (the phenotype).

In simple breedables (such as horses, chickens, bunnies, turtles, dogs and cats) the mapping from genotype to phenotype is straightforward. First off each Phenotype is determined by exactly one Locus. Each Locus has exactly two Alleles. One Allele determines the Phenotype: this is the Dominant Allele. The other Allele is either the same, or plays no part (the Recessive Allele).

This mapping scheme used by simple breedables is a precise, literal implementation of Mendel's Laws without omission or modification.

One can think of this as a "one-to-one" mapping. The problem is, for those breedables, we use the word "trait" freely to mean both the genotype and the phenotype. This works because of the simple mapping of those breedables. For Meeroos this can lead to all sorts of confusion. When I say "trait" I mean a phenotype, but I'm trying to completely switch over the saying "genotype" or "phenotype" because those terms are more clear.

One consequence of simple mapping, as we see in other breedables, it is only possible to have three results from the four Alleles. Using letters: no matter how we arrange them, no matter which parent has how many of which, given four Alleles (A B C and D) we can't get any more than three results. (Example: Genotypes Ac and Bd can yield Ab Ad (genotypes resulting in Phenotype A) Bc (Phenotype B) or Cd (Phenotype C) and we will never see a Phenotype D result.

A further consequence is that if a different Phenotype appears from a pair with the same Phenotype, we can never see the parent's Phenotype appear from the offspring. By this I mean, no matter what Alleles appear, no matter how we arrange the, it is impossible, for Phenotype A produce a Phenotype B offspring and also have two Phenotype B produce a Phenotype A offspring.

This utter impossibility is important because, with Meeroos, we've seen EXACTLY such a result. The only possible conclusion is that Meeroos do NOT use the simple, direct, unmodified implementation of Mendel's Laws seen in most other breedables.

Now, before you cry foul, I need to point out that every single one of you should be well aware of a Real Life genetic system which, life Meeroos cannot possible rely solely upon Mendel's Laws .. Human Blood Type.

In Human Blood Type we have one locus and three alleles: A B and O; yet we have FOUR Phenotypes: A, B, AB and O. The mapping for this is:

Genotype Aa and Ao produce Phenotype A
Genotype Bb and Bo produce Phenotype B
Genotype AB produces Phenotype AB
Genotype Oo produces Phenotype O

Three of these mappings are exactly what Mendel's Laws would lead us to expect. A is dominant over O, B is dominant over O. O is recessive and can only appear if both alleles are O. BUT .. and this is important .. neither A nor B is dominant over the other. If both appear, a fourth Phenotype (AB). This AB result can NOT be explained by Mendel's Laws alone. It requires additional theories.

Some of those theories are what I'm setting out to describe. I've made references to them before, and provided link to Wikipedia pages for them.

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Imprinting

This is a process which determines the Phenotype mapping based upon WHICH PARENT passed the allele to the offspring.

It has been proven that this is what determines Meeroo Eye Color. Each parent select one of their two Alleles to pass to the offspring, but the Phenotype is determined by the Allele passed from the mother.

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Incomplete Dominance

This is a process where both alleles passed to the offspring contribute to the resulting Phenotype.

It has been proven that this is what determines Meeroo Eye Clarity. If both parents pass the same allele to the offspring, the eye is Clear; otherwise the eye is Dusty.

This form of incomplete dominance is seen in nature. But a more common form is seen in (and often as only a part of) other patterns. For example, in determining pigmentation of hair, eyes or skin, or in determining size or height, the alleles are combined. One parent can pass an allele which causes dark pigmentation, another passes an allele which causes medium, and the result would be, for example, somewhere between medium and dark. There can be many alleles in this case, each subtly different from the other and, when combined with the other at that locus, produces a very wide range of results.

While we can see this in a single locus, it's most often seen when several loci for several different genetic factors combine into a larger Phenotype. This is a poly-genetic phenotype, which I'll speak more on later.

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Epistasis

This is a process where the mapping for one loci depends upon another loci. The result of the first loci can be suppressed (or enabled: same thing) or modified by the other loci.

In nature, peas show this. At one locus is a gene which determines whether the pea has any pigmentation at all. If so, another locus determines the amount of pigmentation. If not, that locus determining the amount of pigmentation has no effect upon the White Pea phenotype.

There can be many epistatic relationships within a group of phenotypes.

In Meeroos, for example (and this is only my theory based upon thinking about the issue and no data) the "coat tiers" could well be the result of epistatis with several factors combined.

Consider this possibility: In the top-most tier there is one locus with several alleles. Several results (or none) may map to a set of Phenotypes. But one or more results may suppress those phenotypes, passing the determination to another locus. This "second tier" locus behaves as the first, possibly producing several phenotypes or, in some cases, passing the job on to yet another locus.

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Co-dominance

This is how Human Blood Type operates. With incomplete dominance, all alleles combined (potentially several loci as well) to produce a phenotype. In co-dominance, some alleles suppress (dominate) others, yet combine with other alleles to create new phenotypes. A and B alleles suppress O, yet combine together to produce AB .. A and B are BOTH dominant, just not to each other, O is recessive.

Human Blood Type is a simple case. There can be many alleles at the locus. For example, we could define a locus where A is dominant of all others, B and C are co-dominant to each other yet dominant over D, E and F; D is dominant over E and F; yet E and F are co-dominant. At this locus we have six (6) alleles determining eight (8) Phenotypes (in order of probability distribution these are: A, B or C, D, BC or EF, and E or F).

One interesting result from co-dominance is the probability distributions in the offspring .. all of the co-dominant pairs (BC and EF in my example) have the same probability; that probability is lower than those for all non- co-dominant phenotypes (A, B, C and D in my example) appearing less often than those and exactly twice as often as the most-recessive (E and F in my example), which appear in only one case each.

Note that, with co-dominance, it is possible to have MORE THAN ONE TRUE RECESSIVE and MORE THAN ONE TRUE DOMINANT for a given locus!

I believe co-dominance is used extensively in Meeroo Species and/or Fur, and possibly other traits such as Ears, Tail, and Mane.

I've seen some discuss their idea that co-dominance exists in Meeroos, and I consider that highly likely to be the case. Unfortunately, the discussions and examples I've seen seem to speak more to the effects of epistatis or poly-genetics than to actual co-dominance.

In Meeroos, the pattern of "up traiting" and "down traiting" are more likely to be the result of co-dominance than the observation that a group of furs at one tier seem about equal to each other and all dominant or recessive to those in another tier.

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Linkage

You're probably all familiar with the double-helix of chromosomes. Chromosomes are a series of loci. An allele appears on one half, or the other, of the chromosome at the gene's location (locus).

In a simple model, as we're usually taught in school, when reproducing, the parent splits the chromosome and passes either one half, or the other, to the offspring. When the other parent does the same, the halves are assembled into a new chromosome determining the genetic traits (phenotypes) of the offspring.

While this is good as a working model for simple study, it's NOT what happens!

Actually, there's a chance, as the chromosome is being zipped apart, that the bits switch sides! Perhaps an example:

Mom's Chromosome"
AAABBBCCC (Blue eyes, blond hair)
aaabbbccc (Brown eyes, black hair)

What she passed:
aaabbbCCC (Blue eyes, black hair)

One would think either AAABBBCCC or aaabbbccc would be passed, as a whole, to the offspring. Well, not always. Sometimes it could be AAAbbbccc or aaaBBBccc or ...

The chromosomes _sometimes_ split and make a new sequence which is different than either half in the parent.

When we're comparing the rates of appearance (probabilities) between genes on different chromosome, it 50/50 just as Mendel describe.

But, it turns out, that the chance of a split appearing is related to the distance between two loci. If they are on different chromosomes, the probability of one trait NOT appearing with the other is exactly 0.5 (50%, 1 in 2). If they are on the same chromosome, that probability is less. How much less? That turns out to be determine simply by distance. A distance of 0.0 would mean there is NO distance between the loci .. they are the same locus. A distance of 0.5 (the maximum) would mean the loci are on different chromosomes. But a distance between 0.0 and 0.5 indicates the distance between them, and the probability of one appearing without the other. So, an allele only 0.1 away from another means the pair is 90% likely to pass together, and 10% likely to pass the allele for one locus from one of the chromosome and the other allele for the other locus from the other half.

This is cool. If it happens, can measure it by observation and analysis; meaning we can actually map out the chromosomes for Meeroos. What fun!

But it's a real pain if you WANT one allele from one half and one allele from the other. You're expecting even 50/50 odds but, due to linkage, you're fighting a system bias .. if the loci are very close to each other it's a STRONG BIAS.

I'm hoping this model from the real world is NOT in Meeroos. But I present it because there is SOME evidence that it's the reason it can be so hard getting some trait combinations (such as "this" ear with "that" tail) when you don't already have parents with that allele combination.

Unfortunately, linkage is so important to real organisms that virtually all rely upon it. So, if Meeroos are an attempt to model real genetics, it's probable we'll have to deal with linkage. Ug.

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Poly-genetics

OK, I don't remember the term precisely .. this is the term I use in my head. It means there are more than one locus contributing to a phenotype.

It's a simple concept. Each locus determines something, but the results of those somethings, taken together, is a phenotype with a wide range of possible values.

Height is a good example. The size of a given element (foot, calf, thigh, hip, each vertebra, head) all add up to "height".

If we consider Species as a separate phenotype with separate loci from fur then Fur is a poly-genetic trait. The exact same encodings in the fur loci give a different phenotype, based upon the encoding for Species.

Is this correct? Do Meeroos actually do this? I don't know .. but it's easy to implement, and it fits what we see.

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That about covers the ideas I think people should consider as far as possibilities for how Meeroo genetics operate. I also think Genetic Drift is important, but it results from genetics, rather than effects them, so I'll leave that for later (if ever).