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  Summer Wine Dun Dexters –
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The Genetics of Dun

The Genetics of Dun

A Simplified Summary

The very much simplified guidelines that we have followed in establishing and maintaining our dun Dexter herd are as follows:

Dexter cattle each carry two colour genes – one from each parent. These can be either red, or black, or one of each. (Forget dun for a bit – it is not an ordinary colour gene.) Black is always ‘dominant’ over red, which is called ‘recessive’ (which simply means it stays in the background if there’s a dominant black gene around). So – an animal with a black gene and a red gene (one of each) will always exhibit black – as of course will an animal with two black genes. Only when an animal has two red genes will it exhibit red, because there is no black gene to dominate the red. This basic rule never changes.

Now, enter the ‘dun gene’ —

Besides those two colour genes, Dexters have many other genes, which literally control everything about an animal. Several hundred years ago (so the geneticists think) something happened to make one pair of those other genes mutate – which simply means that their original function changed and they got an entirely new one. These genes were recessive, so an animal had to get two of them – one from each parent – before they could have any effect. But the effect when two of them got together was that they acted upon any black colour gene the animal might be carrying – and caused its coat to exhibit a dun colour instead of black. Because of this effect, today we call this mutated gene the ‘dun gene’.

However, these dun genes affect only any black gene(s) an animal might be carrying – they have no effect at all on red genes. So a Dexter carrying two red genes (i.e. no black) will always exhibit red, even though it might have two dun genes as well – the latter will be totally ineffective.

To summarize, a Dexter with two black colour genes, or with one black and a red, will always be black unless it also happens to have two dun genes acting upon the black – in which case it will be dun. A Dexter with two red genes will always be red, regardless of whether it has any dun genes or not, because these have no effect on red.

Two complicating factors are perhaps worthy of mention. In New Zealand a large number of Dexters come from a “grading up” process, starting by the use of Dexter bull over a cow of a different breed. In 2005 the Herdbook of the Dexter Cattle Society of New Zealand contained 4.8% of first-cross females registered as dun. While they may well have been dun in colour, they could not be the true ‘Dexter dun’ as this requires a dun modifier gene from each parent – non-Dexter cows would not be carrying a Dexter dun gene. Any dun coloured progeny from these cows may well get their colour from the non-Dexter source. And there are some purebred bulls registered as dun in the Herdbook that are actually red, presumably due to wrong identification by the breeders (See Dun and Dunnage). Again, these animals may not be carrying dun genes and thus not produce dun offspring.

Dun herd November 2004

Further Reading

“Color Genetics and the Registration of Dexter Cattle” by John Potter. http://www.dextercattle.org/colorgenetics.htm [Viewed 10.5.2005]

“TYRP1 is associated with dun coat colour in Dexter cattle or how now brown cow?” by T. G. Berryere, S. M. Schmutz, R. J. Schimpf, C. M. Cowan and J. Potter. Animal Genetics, Volume 34 Issue 3, pages 169-175, 2003.

“Genetics of Coat Color in Cattle” by Sheila Schmutz. http://skyway.usask.ca/~schmutz/colors.html [Viewed 10.5.2005]

“How Now, Dun Cow” by Carol Davidson. Paper presented at the Second World Dexter Congress, Australia, 2002. Also on Congress CD.

“Dun Colouring in Dexters” by Beryl Rutherford. In My Love Affair with the Dexter, Triple D Books, Australia, 2005, page 92. Previously published in The Dexter Cattle Bulletin, No.157, 2004.

“We’ve been and gone and dun it: the Summer Wine dun Dexter herd” by Beverley McCulloch and Michael Trotter. Dexter Dispatch 48, May 2005, pages 11-12.

“All purebred bulls are equal – but are some more equal than others?” by Beverley McCulloch. Dexter Dispatch 49, August 2005, pages 18-21.

“Grade One – and the Colour Dun” by Beverley McCulloch and Michael Trotter. Dexter Dispatch 49, August 2005, page 27.


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