[Jacob-list] Horn Genetics

[Hobsickle at aol.com]

Ah--the technicalities I spoke of.
 
One widely held hypothesis is that the gene which causes multiple horns  
works by causing certain cell masses in the embryo to separate and then grow  back 
together.  In some cases the cell masses may not separate far enough  and the 
"horn buds" may reunite, resulting in a two horned sheep and hiding the  fact 
that the "polycerate" allele is present.  (Of course there are other  
proposed answers.)
 
It is useful to realize that from a gene's point of view, its job is to  make 
a protein.  That protein directly or indirectly causes the "trait" we  see.  
In other words, multiple horns may not the primary action  of the gene, but 
just an interesting (from our point of view) secondary  result.  (It may be more 
helpful to think of the "polycerate" gene as a  developmental quirk that 
usually, but not always, results in four horns.)
 
If I remember long enough, I'll upload a picture of a "obviously"  two-horned 
ram that on closer inspection is pretty clearly  "polycerate".
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