[Jacob-list] question on horns

[Neal and Louise Grose]

It is impossible for a sheep to be genetically different on one part of the head from the other. It may be useful to keep in mind that traits that are affected by only one gene are rather rare. For example: the size of an animal is affected by thousands of genes whose effects are additive. This makes it relatively easy to predict the size of an offspring based on the phenotype of the parents. This is a trait with high heritability. Blue eyes vs. brown eyes in humans are also easy to predict because the trait is influenced by one gene (you hazel eyed people don't exist, go away). 

So, horns are influenced by different loci on a variety of chromosomes:
* Horn vs. dominate polled
* Horn vs. recessive polled (I don't know if the dominate and recessive polled are at the same locus)
* Horn vs. scur, which may share a locus with polled
* Sex-linked hornless (Shetlands) which must be on the X or Y chromosomes
* Testosterone production and testosterone receptor genes 
* A couple thousand "size" genes
* Physical blood flow impairment to the lateral horns due to the dominance of the primary horns

Glad I could clear this up for you!

Neal 
  ----- Original Message ----- 
  From: Linda 
  To: Jacobflock at aol.com ; buffgeese at yahoo.com ; Jacob-list at jacobsheep.com 
  Sent: Thursday, May 05, 2005 7:04 PM
  Subject: Re: [Jacob-list] question on horns


  So, is it possible for a sheep to be genetically both horned and scurred? Since they are on different chromosomes?   What could you expect as a phenotype?  I'm confused about just what is behind a four horned ewe with lateral scurs.  Is this an expression of carrying both the horned and scurred gene or is it an expression of carrying the hornless gene?  

  If the hornless gene is expressed in the laterals on ewes, is it also expressed in some way on two horned ewes? 

  It's a fascinating topic, but confusing (to me anyway)

  Linda



  On Tue, 3 May 2005 08:57:45 EDT, Jacobflock at aol.com wrote:

  > The gene that controls polled or horned is located on chromosome
  > 10.  The gene that controls multiple horns has not been reported
  > out yet.  The hornless gene which produces scurs and aberrant horns
  > is evidenced in the lateral horns of ewes.  The gene is known to
  > exist but chromosome location is not known.
  >
  > The location of the hornless gene may well be on another chromosome
  > IF the hornless gene (scurs included) in sheep is siimilar to the
  > gene that produces scurs in cattle.  The poll/horn gene in cattle
  > is on ch 1, the scur gene is on ch 17 or 19 .. I forget which.
  >
  > Fred Horak




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