[Jacob-list] DEF:Freckling, Ticking, Mottling

[Kelly Foster]

Fred,
I have some sheep that have freckles with dark wool coming from that spot and also some that just have dark pigmented spots(white wool covering those). I assumed all were considered freckles and have culled because of it . Am I correct in my thinking?
Thanks, 
Kelly Foster
MapleLane Homestead   
  From: Jacobflock at aol.com 
  To: jacob-list at jacobsheep.com 
  Sent: Sunday, April 07, 2002 3:36 PM
  Subject: [Jacob-list] DEF:Freckling, Ticking, Mottling


  There is confusion among these terms and by using the terms adopted by color geneticists I guess I added to the confusion, i.e., ticking and freckling  

  In 1988 (?), the Committee for Genentic Nomenclature for Sheep and Goats agreed on a set of terms, loci and alleles and expressions for sheep and these were adopted to reduce confusion and provide a common reference for loci, alleles and their effects.

  The COGNOSAG terms related to the Spotting locus and freckling and ticking:
  Freckles describe small melanocytes with pigmented fiber present at birth, not to be confused with the larger Jacob piebald pattern.  Some "freckles" may appear through excitement of the melanocyte by the sun.  Hence, freckles on the back (along the spine) by be induced by ultra violet rays and therefore, might be differentiated from "freckles" on the side ... for pigmented skin with non-pigmented fiber see skin mottling further on.  

  Ticking looks like  an onslaught of freckles but is the appearance, over time, of melanocytes that were not present in the birth coat.  The ticking shows about the size of a dull pencil point, may spread to a density such that it presents, at the extreme, the appearance of a completely pigmented fleece but is actually hundreds of "ticks".    This is most often observed in successive shearings and the fleece may look like a black and gray mix.  It is widely known that the melanin must come from melanocytes near the papilla and the melanin must get moved to the fiber itself.  How the melanocyctes grow in a fashion that does not seem to be in a contiguous area is a question.  Ticking, until 1990(?), was called pigmented multiple spotting (PIMS). Since the Jacob is a full (dark) color ED, dominant black  BB and recessive piebald ss, the piebald activity must in some fashion be compromised such that the piebald allele allows ticking.  Think of Ticking as a "time bomb".

  Skin mottling, (also a function of the Spotting locus) is the presence of melanin in the epidermal layer, but since there are no papilla melanocyte structures in the sub dermal area, migration of the melanin to the fiber can't, by definition, occur.  Hence, you see darker skin and white fiber.  In the Jacob, skin mottling may be the expression of piebald action that subdues the sub dermal melanocyte (expresses white fleece) but not the epidermis (the darker skin color).   Skin mottling (presence of melanin) can also be excited by the sun since "black/eumelanin" is a protective color .. look for this along the back/spine as well.

  What does dominant mean when referring to freckles and ticking?  You see dominant expressions.  When dominant traits are observed ... it is not a matter of degree (the more you see the more dominant, or, its only a little, therefore not dominant).   A dominant gene, paired with its allele, simply covers up the phenotypic expression of that gene (whether homozygous or heterozygous).   If traits seem to be sex linked or sex related (freckles in maternal lines) a body of evidence can be built but would have to be done by all progeny perhaps outside the registration process (which seems to be 'selective').

  It is my OPINION, absent evidence to the contrary and further understanding of the Spotting locus and epistasis, that indiscriminate breeding of freckled, ticked and early grayers (noted by COGNOSAG) will change the basic genetic soup of the Jacob from ED/ED B/B ss and White (Alderson, 1979), to something like Freckle or Gray or  Ticked  ...  and the clear black and white may be gone.  The problem and questions also exist in the JSS in England.

  There is a considerable body of evidence related to the Jacob and other piebald sheep during the period, say 1925 to 1990 but most work has been related to other species since 1990.  Hence my excitement over Gary Anderson's attempts with identical twin Jacobs this past Fall which could lead to avenues to understand color/piebald, breed specific markings/random markings, and the 2 and multiple Horn locus.  (About a year ago, UC Davis made an interesting finding regarding the piebald locus in the Border Collie (?)  ... the piebald mechanism doesn't fit either of the two mechanisms that are generally accepted.)   

  Fred Horak




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