locus

Well polygenetic inheritiance are traits that is controlled by multiple genes, so for one trait you may have more than two gene controlling it, human eye is an example. For polygenetic inheritance you cannot do a pedigree and calculated the percentage. For mendelian inheritance it all about two alleles for one trait where one is definetly more dominant over the other, it is much simpler than the polygenic trait and can be calculated through a pedigree.

The plural form of locus is loci.

The specific term is gene locus. If the exact location is known then there is more specific terminology that refers to the chromosome number whether the locus is on the short (p) or long (q) arm of the chromosome and it's specific location based on band and sub-band location.

Horse coat color is controlled on several different gene loci so the idea of pure white or pure red is erroneous.

Red Color is controlled at the Extension locus and Non-red color is controlled at the

Agouti locus. The genetics of a horse at the Extension locus masks the genetics at the Agouti locus in some instances.

Any horse that is ee at the Extension locus is chestnut or sorrel.

Any horse that is Ee or EE is not chestnut. The main available alleles at this locus are a (black), A (bay) and At (brown/black bay).

Note that there is no allele for White at either the Extension locus or the Agouti locus.

There are two types of white, Dominant White (there is still a debate on the exsistence of this allele and the original school of thought was that only the Ww white foals were viable and a WW white conceptus died during development) and Maximum expressed Sabino which is SbSb at the

sabino site. Both these genes act as modifiers to the base coat colors. So there really is no "pure".