[Jacob-list] Striped horns and hooves

[Jacobflock at aol.com]

Fred here with some more questions and reference points for the discussion on 
white striped horns and hooves.  

The Jacob is a dominant black and recessive piebald. 

The Dorset Horn is a recessive black and recessive piebald. The Dorset Horn 
breed standard has some interesting points of departure: Pink nose and lining 
of the mouth. A black spot on the nose or mouth or ear is acceptable if not 
larger than a pencil eraser.  Dark pigment around the eyes and small freckles 
in the ear are acceptable. No black spotting on the body, legs or hocks. A 
hoof more than 50% black is not acceptable....white hoof with black stripping 
is acceptable; black hoof with white stripping is not acceptable.  Horns are 
generally white but nothing in the standard says they cannot be striped.

The Jacob is a dominant black.  But what if one had heterozygous black 
"Jacobs" or an incomplete dominance...the dominant black has been 
compromised.  This is the old saw: Breed a self colored sheep to a Jacob and 
every progeny will be BLACK.  If it is not a dominant black, i.e., it is 
white or spotted, the Jacob is not a dominant black and therefore, by 
definition,  not a Jacob...if one agrees a Jacob is a dominant black.  
  
Thom notes the Jacob Research Project and his flock; but what is genetically 
operative?  Does the same range of white stripe expression follow the 
recessive piebald gene activity or the dominant ticking gene? How much 
evidence can be gathered that the weak or relatively inactive ss piebald gene 
shows up as black horns, black hooves, black cheeks and nose, black knee and 
hocks...what if there were dark skin below some of the white wool....and...is 
there an interaction between the overactive piebald gene and the ticking 
gene.  Stripes come from spots and spots come from genes; we're trying to 
guess the inbetweens.

Does the range of horn expression follow from the primitive genotype like 
this?  The Mouflon generally have black, smooth cased horns, with a low angle 
to the forehead.  The Urial side generally has streaked horns and are sort of 
corrugated.  The former would lose the casing and expose the core; the later 
actually losing the horn to the skull.  

Mark asked about purists.  The purist knows whether...or must 
decide...whether one knows or not, what a pure Jacob is.  Is it a dominant 
black or compromised black? Is the horn a mouflon or urial?   Is the piebald 
gene activiity active or inactive, is the genotype more closely aligned with 
the Black Faced Horned or the Dorset Horn or its predecessor the Portland 
Horn...which was a colored/spotted horned sheep.

And there are the "miracle lambs" that are born with white hooves, pink noses 
and a lot of white keratinous horn material...that turns black over time.  
What is the biochemical melanin activity?  Certainly UV exposure plays a role 
but has anyone kept a "pink nose"/"white hoof"/"white horn" in darkness to 
see if it changes on the basis of the melanocyte tyrosinase transport to form 
eumelanin?  White changes to black...but...black doesn't change to white.

It's 1:30; goodnight.  Fred