[Jacob-list] Hebrideans (Fred's comments)

[gordon johnston]

Fred, what you wrote about Jacob genetics was interesting and helpful.  However, I have to pick you up about your comment on Hebrideans :

<<<A history of the breed color sources, I think, is a helpful lead into understanding the genotype.  Now I know you want to look at a sheep and know its genotype but it is difficult to do.  The best example of how the "phentype" can lie about the "genotype" is the Hebridean, a homozygous recessive black.  About 5 years ago, it was discovered that every once in a while a "white" sheep popped out and would be culled ... and so they did a progeny test with 60 sheep and 75% of the "black" registered Hebrideans turned out to be dominant blacks ... and not true Hebrideans.  The progeny test to prove a pure Hebridean involves accounting for all lambs born and producing 14 white progeny from breedings to pure-bred white ewes and 0 black lambs ... which gives a 99% level of "certainty". >>>

The Hebridean breed was developed from black individuals from the old Scottish Dunface, a multicoloured type (from the days before we had 'breeds' in the modern sense.)  Clearly, these individuals were black recessive, in line with other Northern Shorttailed Sheep colour genetics.  However, these animals were then taken into English parklands with other breeds including the Jacob, where it is thought that the black Dominant gene was acquired. So by the time Hebrideans were recognised as a separate and distinct breed, dominant black was already a part of their genetic make-up. The exact proportion of dominant to recessive black is not known, but to say that those animals which are black dominant are not true Hebrideans is innacurate.  What is true is that you cannot tell the Genotype from looking at the Phenotype.

I contacted David Kinsman, whose book 'The Black Sheep of Windermere' has helped many people to understand colour genetics in Northern Shorttailed Sheep, to ask his opinion on your comments. Here is his reply :

To:Juliet -Short Tailed Sheep Group
From: David Kinsman
Subject: Question - Dominant Black in Hebridean Sheep
Juliet,
Your question regarding comments by Fred Horak on the US Jacob list:
1) to the best of our knowledge the northern short tailed sheep are
all homozygous recessive at the Extension (E) locus. The dominant black
allele almost certainly came into Britain in association with improved
long tailed sheep, i.e. the Jacob, in the early 18th century.
2) The occurrence of white lambs to registered black Hebridean
sheep was discussed in some detail in the early 1980s, some 20 years ago
- it is not a phenomenon of the past 5 years.
3) I am guessing that Horak is referring here to the study by
Parfitt & Sheppy (published in 1994 & 1995). The test animals came from
5 flocks and 4 of these flocks were shown to contain sheep carrying the
dominant black gene. From the numbers of sheep used in the experiment,
Parfitt & Sheppy concluded that around 75% of these experimental animals
carried the dominant black gene.
4) In my 2001 book, Black Sheep of Windermere (ISBN 0-9540283-0-9)
I discuss dominant black in Hebridean sheep in some detail and provide
test procedures and their interpretation. I concluded that in the
national Hebridean flock somewhere between 10% and 50% of the animals
carried the dominant black gene.
5) We do not know the actual proportion of Hebridean sheep that
carry the Jacob derived dominant black gene, but I am fairly sure that
the Parfitt & Sheppy estimate does not apply to the breed as a whole,
but just to their group of experimental sheep.
6) An analogue to the Hebridean is the Black Welsh Mountain sheep
which is now in excess of 95% dominant black, almost certainly derived
from crossing in parklands with Jacob sheep (see my book for details).
Whereas it would still be possible to retrieve the Hebridean (as a few
of us are doing) and return it to being a recessive black breed of
sheep, it is probably too late to retrieve the Black Welsh Mountain.
Trust these comments are helpful - David


Juliet
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