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General Information on Rare Colors
Melanocytes are the cells that produce skin and hair color and they are derived from neural crest cells. These cells arise along the back very early in foetal development and then give rise to a number of cell types, including a large proportion of the peripheral nervous system. If there is a decrease in the number of neural crest cells, other cell types are favored, leading to a reduction in melanocyte formation (see below). The melanoblasts (immature color cells) migrate from the dorsal midline over the surface of the body, so the last areas to be reached are the feet, chest and muzzle (ie where you are more likely to see white toes, etc).

Neural crest cells also form part of the nervous system for the inner ear and eye. Animals selected for extreme white spotting (eg. Dalmatians) can have hearing and/or vision problems in other extreme white patterns (merle series).  Dalmatian deafness is thought to be as a result of the absence of melanocytes in the stria vascularis of the inner ear. Melanoctyes produce melanin by the action of alpha MSH. Large amounts of MSH results in Eumelanin (mainly Tyrosine) which produces black or derivatives of black (blue, chocolate, brown, liver).  Restricted amounts of MSH result in Phaeomelanin (contains varying amounts of cystine and tyrosine) which produces reddish brown or yellowish tan. #Control of melanoctye function is intricate and many loci(genes) have mutations which affect components of melanogenic control mechanisms.

Colour Genes
There are about 10 recognised "loci" of different color genes. Each locus can have a variable number of alleles that can influence the color outcome (dilution, pattern, dominant or recessive effects). All dogs carry these genes, many of which are in a fixed (homozygous) form eg. Gordon Setters, Elkhounds etc.  In these breeds virtually all loci are fixed and there is very little color variation across the breed.  In other breeds some loci are fixed, while others have a degree of variation (number of alleles) present at other loci. Not all breeds carry all the possible alleles at each locus.

Current Research
Many of the colour loci are being extensively studied to precisely locate the position of the various genes on the correct chromosome, and further, which alleles actually occur at that site and how they affect the color outcomes available.  From this, DNA markers may be developed, and thus allow DNA color testing in various breeds prior to mating. The DNA research that is being done at this time is going to continue to change our understanding of color genetics- its a fairly dynamic field- it is certainly not fixed in concrete.

Wendy and Sugar Bear
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"Black and Tan"
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