[Jacob-list] horn question

[Jacobflock at aol.com]

I recollect we chewed on this question in 1999 for a while.   Quite frankly, 
there is NO UNEQUIVOCAL EVIDENCE for the genetic mechanisms of multiple 
horns...and this question involves multiple horns AND scurs or aberrant horns 
for which there is SUPPORTIVE EVIDENCE at least in two horns..but no 
conclusive evidence for multiple horns and (what I think you are talking 
about) aberrant horns.  I don't KNOW the genetics but this is what I THINK is 
involved.

The terms that I am using for the trait observed may seem stupid but defining 
what is observed is rather critical. For years horn related traits were 
observed and probable genetic causes offered. But the probable cause must be 
proved by evidence before concluding it is the genetic cause. Agreeing on the 
recorded factual evidence we observe is critical. 

Horn: The big black things on top and on four horns the smaller drop horns. 
What you don't see is critical for a horn: a horn has a densely constructed 
core of bone like material that grows from and is firmly joined to the 
frontal bone, is veinous, carries blood, has a keratinous, fibrous, exterior. 

The PRESENCE of Horns is probably controlled by a single autosomal locus 
called Ho on Ch10.  There are probably three alleles at this locus: 
(1)  Ho+ produces horns in rams and ewes which is the allele in the Jacob.  
(2) Hohl is called the hornless allele which produces sex limited horns 
(usually rams only).  A Hohl/Hohl produces knobs or bumps, or even scurs in 
ewes but has no effect on two horn rams, i.e., rams have horns...I think this 
is the scurred/hornless Jacob ewe arena.  I've never heard a report of a 
hornless or polled "Jacob" ram.
(3) HoP produces polled sheep (polled being a "hairy depression" or "hairy 
bump"). Is what is called a "polled" Jacob ewe really a Hohl hornless ewe?  
I've never seen a polled Jacob.

Sheep scur: What you see is an observable (1) SHORT SCUR: a keritanous bump 
that is most often very smooth, looks waxy and is very short, say 1 inch; (2) 
LONG SCUR: a keratinous stucture, very smooth, appears waxy, has irregular 
growth and is often assymetrical, longer than 1 inch, or  (3) ABERRANT HORNS: 
looks like a horn, clearly fibrous keratin structure (black) but lacks a 
solid core that penetrates the length of the sheath.  Aberrant horns may 
easily break off; the base has little or no structure to support a core; some 
wobbly horns are aberrant horns, some wobbly horns are the result of fights.  
Look for small diameter or "flat" horns.

The PRESENCE OF SCURS including ABERRANT HORNS is apparently controlled by 
the Sc locus which has three alleles (1) Sc+ the short scur; (2) Scls the 
long scur and (3) ScAh the aberrant horn.  The ScAh is dominant to the Scls 
which is dominant to the Sc+.  Thus one might expect to see a problem start 
with aberrant horns, then long scurs then scurs.  Another way to consider it 
is ScAh horns are smaller, lighter, extremely flat, looser than would be from 
a Ho+/Ho+ or a male Hohl/Hohl.  The scur and aberrant horn alleles interact 
with the Ho locus and are sex influenced.  Is the scur allele a "switch" 
(on/off) or a "rheostat" (dimmer switch) for the Ho allele? 

The NUMBER OF HORNS:  It appears the easiest to count, but errors are made 
and this locus has the least evidence of any horn trait.  It is assumed that 
the allele called HN+ for two horn and HNM for multiple horn (anything above 
2) is an incomplete dominant.  (This is where the HMN and SUED defect may be 
linked; the theory of the gene split for the multiple horn bud splits the eye 
orbit and upper eyelid.)

What appears as a Ho+*HNM (4 horn ram) may be a Ho+*HNM*ScAh ram (2 horn with 
2 aberrant horns).  The incomplete dominance of the four horn might explain 
the ScAh (aberrant horn) but why Sc only on the drop horns on rams and both 
horns on ewes?  Do Sc and Hohl relate to each other and how?

STARTER FLOCKS: Mary Ellen Hansson recompiled the AMBC flock book so it is in 
a researchable form.  The AMBC book is a list of Jacobs and sheep people 
believed might be Jacobs. There is no registration as such, inclusive rather 
than exclusive and probably contains observation errors.  There are over 100 
"double-named sheep".  But it is a place to look for leads to genetic 
information.  

Among the 1,168 sheep in  the AMBC book are 57 "hornless" (Are they truly 
hornless, scurred (scur and aberrant horn) or polled ?) ewes listed.  Only 
37/57 have partial or complete information; 25/37 "hornless" ewes are by 
4horn sires over 6 "hornless" ewes;  6-2horn ewes and 5-4horn ewes. there are 
only two "hornless" records for 2horn sire: 1 by a hornless dam the second by 
a three horn dam.  Of the 57 "hornless" ewes, 21 are from two farms (Shady 
Acres and Tribook) the rest are scattered   Shady Acres Big Al covered a lot 
of "grade or crossbred" 0 horn ewes which I think is a clue to the "hornless" 
and others clue one in to the "scurred" state.  

The same rams and dams that produced "hornless" (hornless, scurred aberrant 
or polled?) produced "horned" sheep which later appear in pedigrees.  Several 
of the 57 "hornless" ewe progeny appear as dams for 2 and 4 horned progeny 
sired by horned Jacobs.  The progeny are all ewes except for one ram, Unique 
Enos by Reddy's out of Unique Claudia (0 horn).  The question on the table is 
the accuracy of reporting a 2 and 4 horn sheep, i.e., were any of these 
aberrant horned or scurred sheep?  The AMBC breeders started the search 
(knowing or not); here we are 10 years later.

Reporting/recording/observation errors? I think so.  Look at the AMBC book 
four horn progeny for Ho+*Sc. Some are reported:  Witruck's Pandora had 4 
scurs, Home Wool Maggie had scurs, Yakob-Tson Nell and Vanessa had 2 horns 
and 2 scurs, Puddleduck Maya had scurs.  Are others not reported? recorded? 
not observed?  I'd bet a dollar.   Are the scurs reported long or short? Did 
the parent or others related by descent have aberrant horns, scurs, horns?  
But don't throw out the baby with the bath.

THE QUESTIONS:
The answer to your first question: Is the ram with two top horns and two side 
scurs a two horn or four horn?  I think, genetically speaking, it is neither.

Your second question: Would he more likely produce a four horn than two horn 
offspring?       As likely to produce a four horn offspring as a four horn 
animal?  
I'd guess, based on the little that is known, the two horn/two scur ram 
(assuming mated a Ho+HNM ewe which you have more of) will produce a 4 horn 
ram every time and a scurred or aberant 4horn ewe half the time...if horns 
are sex influence neutral.  You might produce all two horn/two scur or 
aberrant horns if the ewes are Sclh or ScAh.  But is the 4horn subject to sex 
influence? 

SEX INFLUENCE?  Would he more likely produce 4horn offspring than a 2horn 
that never had scurs?  There is no record of a Sc two horn ram in any flock 
book that I could find.  So assume the two horn is a true two horn (no hidden 
seam stuff)... The AMBC progeny record shows a 2horn sire over 4horn dam 
produced 23  2horns and 56 4horns...a 4horn sire over a 2horn dam produced 23 
2horns and 58 4horns...a 4horn sire over a 4horn dam produced 315 4horns and 
81 2horns.  There does appear to be some 4 horn dominance in this group; but 
I excluded incomplete records and 3,5, and 6 horn pairings. 

So that sort of gets one to 1990.  Without getting deeper into hot water, I 
will leave reviewing flock books for the last ten years and observing horns 
closely to you....or collect pocket change, a bunch of sib and variant horned 
Jacobs, collect their DNA, look at Ch10 and other chromosomes for the 
sequences...Ain't easy but don't bonk all the odd balls.  Odd balls tell us 
who's got the right stuff. Sorry about the length of this.  Maybe there's a 
pony somewhere in the closet.  Fred