[Jacob-list] gray spotted sheep

[Neal and Louise Grose]

I am going to go out on a limb here and say that not everything is genetic-- as in: passed on through the gametes from one generation to next. These spots do not look like lilac or graying. Spotting pops up rather late in embryonic development. There are not enough genes to determine which of the millions of skin cells exhibit which color. Much of it is random but based on a few over-all pattern markers. 

Mutations can occur between initiation of differentiation of the embryo and the time the spots are actually fixed on the surface of the skin. There is a long chain of events that result in something that looks like black: precursor > precursor > ... > precursor > eumelanin . Each of these requires a gene to pass the process along. If you knock out any of these steps, you get weird stuff. 

I think that this is what has happened in these cases. I have seen this as either grey or reddish spots on Holstein cows. This is seldom passed to the next generation because the mutation did not occur in the gametes that produce sperm or egg cells.

Neal
  ----- Original Message ----- 
  From: Brenalan Farm 
  To: Jacob List 
  Sent: Friday, April 10, 2009 9:27 PM
  Subject: [Jacob-list] gray spotted sheep


  I wrote to Karen off-list, but had some ideas for everyone to kick around. First off- I called Shannon in a panic last year because one of my lambs had a gray spot! The dam has a circle around her eye but doesn't appear to be a lilac. Curiously, the ram was from Bideawee, not a lilac, and he didn't throw any lilac lambs in 2 years here. Then I got a ewe over the summer from different lines that had a gray spot on her hind end. Both these sheep retain their gray spots after shearing and have black spots exposed to the same sunshine (or lack of it here in the northWET.) Anyway, it just seems to me that this has to be something related to the "blue" colors in dogs and cats. And that seems to be a "dilution" gene. What I read is that the gene affects dispersal of pigment in the fiber, and the clear areas are more reflective and create the blue/ lilac (in cats), and "gray". This is differentiated from "salt and pepper" gray that is actually black and white fibers intermixed. I plan to grab a sample from the spots over the wknd and see if my ancient microscope can see that sort of pattern. Anyway, this link explains that there are different genes for eumelanin (black, brown), a dilution gene, and a dilution modifier gene. If the sheep work like cats, and the genes work like this site suggests, the sheep with gray spots would have to have double recessives in both dilution and dilution modifier genes. If this is a new trend popping up (is it?), how do we all feel about it? Just in terms of color and landscaping, I think it is nice... but is it a sign that selective breeding is eliciting new traits?
  http://www.messybeast.com/gene-symbols.htm   Scroll down to near the bottom... 

  Brenda 


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