[Jacob-list] fading

[Jacobflock at aol.com]

Fred Horak here.

The fading (black fading to dark brown or brown) of the Jacob black was 
described in 1926 by Dr. Fraser Roberts but its cause was not entirely 
understood.  The fading of black to dark brown or brown) is probably a 
complex issue for biochemistry: the amount of eumelanin (a tyrosine polymer 
that makes black) in the fiber, ultra violet sun damage, diet and the amount 
of copper (a metal that builds eumelanin), dust in the fiber scales.  

If the fading is to grey (not to be confused with lilac), there is another 
issue to address; a graying gene which promotes "premature" gray and seems to 
be dominant.  Lambs are born black/white but by age two or three are greyed 
(fleece is grey and the root black has significantly diminished in intensity. 
 By way of "simple" explanantion (nothing is really simple), it seems as if 
the follicle from which the fiber grows (melanocyte) has stopped producing 
eumelanin.  Under the microscope, the gray fiber does not seem to have as 
compact and dense chains of black: black fiber looks like this ooooooo; grey 
fiber looks like this o o o o o o (fill in the o's with a black pencil for 
Jacobs, use a red pencil for barbados).

Complex problem but a good observation on fading.  We see a lot of fading 
here in TX.   Fred Horak.