Hmmm...

   So, I'm breeding for the p' gene (gene? allele? I don't know which is correct?). While doing so, I am and have been seeking out animals that I feel are likely p'/p' to use in my breeding program, and also trying to determine if the p' gene produces thicker or wider sweeping horns in rams (as the current rumor postulates).

  While currently, I have no way of knowing what, if any, horn phenotypes are indicative of the presence of p' as opposed to p in rams (I haven't found the research or gathered convincing data from my own flock to prove it), so my searches have been limited to ewes....kind of the opposite situation someone who would be breeding for P would be in (they, being limited to just the rams).

     Underhill Bridget has proven over and over that she is p'/p'. Every single one of her offspring has had at least one p' gene, when bred to non-carrier rams.




    Based off Bridget, my initial thinking at the beginning of this was that "full horns" meant p'/p', no argument, and anything that didn't resemble what I considered "full horns" must be heterozygous of some sort (either p'/p or p'/P).  However, after doing some more pedigree research, asking around, discovering this article (http://www.wavingpinesfarm.com/the-library/horn-inheritance/), and observing sheep in my own flock, it would appear my initial conclusion was incorrect. There are other genes at play besides the base horn genes, and not all heterozygous animals appear like this:






    While width and length of  horns are still good indicators of the presence of the p' gene, ewes like Korsvejgaard Gidget (background, right) are p'/p and still have "full horns", though they are, at this point, not as sizeable as her dam's. This means Sheltering Pines Kristine (foreground, left) may be p'/p as well. It's very possible Kristine is p'/p', as both her parents carried, but I don't have much in regards to her production record to know for sure. In either case, I suppose it's possible to find heterozygous ewes with "full horns" (think aberrant full horns in P-carrier rams) and homozygous ewes with scurs/smaller horns (teacup horns in horned rams).




    Some of these other "modifier" genes, that Waving Pines Farm points out, affect width and length of horns, as well as curvature, rigidness and smoothness, rise, and run. So, while I'm going to continue to seek out and breed for ewes with large horns (ideally, I would only bring in or keep proven p'/p' ewes, but I don't always have the luxury of knowing), I'll probably also (by default) be selecting for the longer, thicker etc, ends of the spectrum for these "modifier" genes.

   This is only "bad" for one reason, I will have no idea whether p' is the cause for wider or thicker horns in rams or if my selecting for the larger/longer horns in ewes correlates to the thicker/wider horns in rams.... :/

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