[Jacob-list] Basic Jacob color genotype

[Jacobflock at aol.com]

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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