[Jacob-list] Basic Jacob color genotype

[Dr. David Lincicome]

1625 hrs/Wednesday14 May 2003

Fred,

Elequent my dear Watson, elequent!  I hope you will run this in the 
Journal.  Humor and plain English are good tools to get a point across.

David

Jacobflock at aol.com wrote:

> When I graduated from high school my summer job was tilling Friar 
> Mendel's garden.
> In high school I had to have a science project ... so from the four 
> elements that were then known (air, earth, fire, water) ...  I chose 
> "Why is fire hot?"
>
> Before the discussion of color possibilities rages out of control, I 
> am offering this as a point of reference to put a little color on the 
> discussion.  It is for adult audiences.
>
> When we dumped Dorsets and started with Jacobs, we read all we could 
> about the breed and the Jacob "breed standards" (plural) and history.  
> But among all the standards which describe the phenotype 
> (Phenotype=genotype+environment)) there was one common thread in Great 
> Britain and North America: A dominant black with a recessive piebald, 
> polycerate.  This is the basic THEORETICAL genotype ... THEORY being 
> the best explanation available based on the current science and 
> technology; tested and not found wanting.
>
> In North America there was another phenotype: Jacobs may be lilac.  If 
> all the "Jacobs" in North America came from Great Britain; what is the 
> source of the lilac ... the only "record" of a lilac import I recall 
> finding involved the Scottish four horned at the zoo in Winnepeg.  I 
> know nothing about "lilacs" except that in our breeding, the lilac 
> body (and eye halo) seems to be recessive.  The mode of inheritance is 
> a hypothesis; the genotype has not been hypothesized as yet.
>
> The dominant black, piebald genotype of the Jacob is THEORIZED as:  Ed 
> Ed BB  ss Awh, or, instead of Awh perhaps aa. 
>
> THEORIZED becasue the result is obtained by the "scientific method" 
> ... that's the way science works.  The theory, is proved, retested, 
> and accepted until proven otherwise.  Theory seeks a true cause for an 
> observed effect:  "the sun does not rise" despite the evreyday use by 
> the weatherman.  A hypothesis is a guess waiting to be tested.
>
> The genotype of the Jacob is rather straight forward.  I think of 
> genes, loci and alleles as chemical factories: (I saw a 'new' table of 
> elements including hydrogen and oxygen, and now there are amino acids, 
> hormones, etc.).  These factories are specialized to make sheep into 
> sheep (sheep genes) and Jacobs into Jacobs (yup).
>
> E is called the extension locus and is a chemical factory that is 
> 'programmed' to produce a color (yup, chemicals) all over the sheep.   
> E with a capital D superscript produces a dominant black.  What color? 
> B is black and b is brown.  The recessive brown b would be in 
> Shetlands and Soays ... brown is recessive to black. Where do you 
> identify the color?  Next to the skin.  Fiber can be affected by ultra 
> violet light ... copper/molybdenum imbalance ... etc.  As was noted in 
> another post ... look at the fiber at the skin at shearing time.  The 
> piebald gene s is the recessive form of the dominant S spotting gene.  
> A capital S or dominant S covers the "whole animal", the little s 
> makes little spots called "piebalds".  The s (piebald gene) is a 3M 
> chemical factory (a division of Mother Nature Inc.) that puts duct 
> tape or post it notes over areas where the B gene is supposed to put 
> the "black" melanocytes to put in melanin (another chemical process).  
> Melanin comes in two extreme colors: eumelanin (black) phenomelanin 
> (yellow) but, the genetic chemical factory can change the input 
> chemical (copper - tyrosine - tyrosynase) from extreme colors to a 
> range of colors.  Finally we come to the A chemical factory called 
> agouti.  This factory produces the color (or blanks out color as in 
> the case of the S or s gene) that produces "wild colors".  This locus 
> says .. When I fill in any s spots, what color should I put in?  I am 
> not going to put in any "wild color", I am going to "put in" white ... 
> the wh ... or "nothing is going in there" ... white is the absence of 
> color. 
>
> I've butchered the science but tried to simply explain what has 
> apparently been going on in the Jacob gene machine (chemical 
> conglomerate owned and operated by Mother Nature Inc.) since first 
> observed about a hundered years ago.  But the dominant black with 
> recessive piebald is the "basic Jacob" genotype. 
>
> It happens that North American breed standards include the "lilac" but 
> the nature of its genotype and historic origins (other than Whipsnade 
> zoo) are a continuing mystery.   The "lilac" has yet to be pressed to 
> the scientific method.  What is equally elusive is the "black 
> pattern"/non-piebald area - some are breed specific (nose, eyes) 
> others family/line (knees, hocks) others random on the body  ... etc. 
>
> I am not making any judgement about a breed standard.  It is what it 
> is today.  A breed standard is a statement about the phenotype (what 
> we observe, not judge) and the phenotype is the sum of the genotype 
> (the sum of the genetic machinery) and environment.  What I guess is 
> an answer to the genotype question is not the answer to the question.  
> What will cause the right question to be asked in a scientific process 
> and what will be the effect of the answer if it does not agree with 
> our guess? 
>
> As for an Extension locus recessive e instead of E.  I never should 
> have said that.  A "yellow" sheep would confirm an e but none has ever 
> been documented.  Dogs and cats have recessive e's.  
>
> While I have questions about the "lilac", we have lilacs, it is in the 
> North American Breed Standards. While I continue to have a burning 
> question I will refrain from adding fuel to the fire. 
>
> The Jacob (American) has been an unimproved landrace type breed for 
> the past ten + years under the aegis of breed associations and say 30 
> years before that.  There will be flock, local and regional variation 
> and similarities.   Breeding pure Jacobs is not hard ... breeding pure 
> breeding Jacobs is the challenge. 
>
> Fred Horak
>
>
>
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