wHITE sPOTTING
wHAT iS WHITE sPOTTING?
White spotting is a blanket term meaning 'any white pigment'. It can occur anywhere on a canine, can range from a single white hair or cover the whole body, can appear on any colour coat and accompany any and all markings. The 'rules' for white pigment are very lax, and can make for unique and even downright crazy patterns, however, the explanations below ring true more often than they don't.
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White pigment comes in six alleles all of which appear on the S Locus;
'S' - No White
'si' - Irish Spotting
'sp' - Piebald
'sw' - Extreme White
'Ssp' - Pseudo Irish
'KIT' - Panda
All these genes may be combined with one another in order to obtain something genetically unique.
How white spreads
All white colouring follows the same generalised rules in that; it always starts on the far edges of the canine (tail tip, chest, paws and muzzle) and works inwards (undercarriage, face, neck, lower legs, body and more of the tail) with the ears being the very last things to develop white colouring except in the case of Extreme White.
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The 'non-white' pigment can be either black, red or liver (as shown in the examples), come in any of the ranges shown and be in any pattern.
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Pups are typically born with all the white they will ever show throughout their lifetime, i.e they won't suddenly 'gain' or 'lose' it as they grow, but they may eventually develop light grey hairs if the greying gene ('GG') is present.
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Irish Spotting
Irish Spotting covers the legs, tail tip, chest, neck and muzzle though it is not uncommon to also have a full neck ring and white blaze. The gene is also known as 'mantle'.
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Pairing this gene with others such as piebald or solid spotting may increase/decrease the range of white significantly, but the gene always breeds true (i.e Irish x Solid/Irish x Irish/Irish x Piebald will always breed Irish).
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Irish Spotting is denoted in a genotype by 'sisi'.
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Pseudo-Irish
While Pseudo-Irish looks visually similar to Irish Spotting, there are some obvious differences, such as the fact that it can have small coloured spots anywhere on the white not related to ticking, may only show up to 50% of the true range of Irish Spotting, and is prone to 'mis-marks' and asymmetry in the spread of white.
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Pseudo-Irish is represented by 'Ssp' in a genotype.
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PIEBALD
Denoted by 'spsp', this gene is the most random of the S Locus as it produces white patches anywhere on the body and can be as minimal as a simple white spot on the back, chest, foot, tail or head, or fully extend to cover up to 90% of the body.
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Piebald is a recessive gene, and easily masked by others, so there may be no physical indication that it's even there until a piebald pup is produced by two otherwise 'solid' parents.
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Extreme White
Also known as 'High White' or 'White Factor', Extreme White is responsible for a canine being 91-99% white. It may colour, or partly colour the nose and eyes.
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This gene has been known to cause visual and hearing impairment (both partial and total) when too much white is present on the face and/or ears.
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Extreme White is denoted by 'swsw' and may be combined with any of the other S Locus genes.
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Panda
Panda is a dominant gene which is lethal to embryos is 2 copies of the gene exist, (i.e a canine can never be KITKIT). The gene is known to cause 'Split Face' markings in canines that otherwise would be solid coloured.
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Residual White
Small amounts of white on the chest, toes or tail that otherwise should not be possible on the canine.
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It's thought that this occurrence is down to a fault or illness with the developing embryo or stress put onto the dam whilst pregnant.
fLASHY iRISH
By combining 'si' with 'sp' (making 'sisp'), we can get what is called 'Flashy Irish', which basically extends the range of the Irish pattern all the way up to the knees and underbelly.