[Jacob-list] More than four

[Jacobflock at aol.com]

In a message dated 6/8/2004 6:22:30 AM Central Standard Time, 
patchworkfibers at alltel.net writes:

> Is there a difference, genetically, between a four horned sheep and a six
> >horned sheep?  or is the number past two
> >merely the result of random splitting? Is the propensity for more than four
> >horns heritable?
> 

The literature cites the following types: Polled (P), Hornless (Hohl) a sex 
linked gene which produces scurs and aberrant horns, Horns (presence of two 
true horns), Multiple horns greater than two (HMN).  I have not found anything in 
the literature other than these four types. 

There is also a "rule of thumb" that goes something like "Major genes have 
major effects".  The question is whether the number of horns in excess of four 
is the effect of a major gene or a mutation of the true HMN gene.  One must 
also be cognizant of the nature of the "fifth" and "sixth" horns and determine 
they are true horns.  In one case of trying by positive associative breeding to 
produce horn number in excess of four, a six horn ram covered a five horn ewe 
and produced a four horn ewe. This breeding will be repeated to try to produce 
some meaningful results.  One key to understanding the phenomena is to 
examine the pedigrees and keep track of all progeny from HMN breedings.  I think 
Edie and Wayne VanValkenberg have had rather extensive experience in multiple 
horn breeding.    

I am not sure that I generally accept that "Jacobs carry a horn splitting 
gene" or a "gene that randomly splits horns".  My sense is the H gene on Chr 10 
and HMN are controlled by something like a hox gene and HMN in excess of four 
true horns (opposed to a scur/aberrant horn) is a mutation.

Fred Horak




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