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"Comments by Carol Davidson on the Dun Gene in Dexter Cattle"

Carol Davidson is a Canadian Dexter breeder with a keen interest in the history of the breed. She presented a paper to the Second World Congress on Dexter Cattle, held in Australia in 2002, on the findings of the research project led by Sheila Schmutz to find the locus of the dun gene in Dexters. Carol contributes to Dexter discussion boards from time to time. The following is taken from one of her posts on the discussion board on the UK "Dexter Cattle For Sale" website on 19 December 2002, www.dextercattleforsale.co.uk/wwwboard/messages/908.html. It is presented here because of its useful account of the genetics of coat colour in Dexters and some comments on its implications. Comments in square brackets [ ] are mine, mainly to clarify links to other writings on Dex-Info about the dun gene.
 

Dexters carry all three coat colours at the base colour locus [at MC1R, a gene on cattle chromosome 18], and a fourth colour found at a different locus [at TYRP1, a gene on cattle chromosome 8]. The three at the base colour locus are Black (dominant), red (recessive) and a wild gene whose colour varies between breeds but is consistent within a breed. In Dexters, wild is red. Black is dominant over both red and wild. We also have another colour mutation found at a different locus which is recessive and produces dun (well, actually it's brown, but I don't think we are going to change it now— especially when there is Brown Swiss, which isn't brown at all).

For those who think Beryl Rutherford did something funny all those years ago, the same dun/brown genetics is found throughout U.S. herds, where there is no upgrading, and animals relate back to original Irish and English imports from La Mancha, Gort, Castlelough, etc. around 1910 and have never seen a Woodmagic animal. Recent genetic research has unearthed the locus for this gene.

The other breeds who appear brown/dun have been checked and none of them carry this mutation. This means Dexter dun is a unique-to-the-breed mutation, and it has been around for a long time (certainly as long as there have been animals identified as 'Dexters').

Andrew Sheppy briefly cast a glance toward a 'brown' gene but discarded it in favour of mis-registered crossing, going on at length with his 'facts' about Channel Islands influence. Hopefully this DNA proof will silence the dun detractors and straighten out the theorists. It's actually quite amusing to think that for all the criticism and misrepresented facts, if one wants a truly rare animal, dun Dexters are at the top of the list.

The base coat colour locus for duns can be black/black or black/red or black/wild. It is predicted that red and wild will dominate the dun gene, if both are present in the homozygous state [that is, if a Dexter is red/red or wild red/wild red at the base coat colour locus, then this overrides the expression of dun/dun at the other locus and the Dexter will be red, not dun] .

It is genetically impossible for two reds to produce a black. More likely, some other bull (uncut calf?) was the real sire, and the breeder just didn't know it, or it could have been dun which has a black gene. I found several cases of this when I was researching the colour issue originally and worked with Wantsley Rob Roy and Barnston Mickey Mouse.
 

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