Summary of Article About Dexters

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"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

This Paper was published in the journal, Animal Genetics, Volume 34, Issue 3,

June 2003, pages 169-175.

The lead researcher for this project was Sheila Schmutz, a member of the Department of Animal and Poultry Science at the University of Saskatchewan, Saskatoon, Canada. T.G. Berryere and R.J. Schimpf were members of the same Department. C.M. Cowan worked for Genetic Visions Inc., Middleton, Wisconsin, USA and John Potter is a Dexter breeder, Spruce Grove Farm, Galien, Michigan, USA.

This is an important article as it is the scientific report on a project which discovered that the dun gene in Dexters is unique, not to be found in other main cattle breeds with dun or brown coat colour that were examined in the project. The implication is that the dun gene was not introduced into the Dexter breed as a result of cross-breeding during the last century. The article concludes that it most likely arose as a mutation within the Dexter breed.

This article is available on the Internet from an academic publisher's website, Blackwell Synergy -  www.blackwell-synergy.com/toc/AGE/34/3 takes you to the relevant issue. Some educational institutions have subscriptions which allow free access to teachers and students. If you don't have a subscription, it will cost you US$26 to obtain a copy of the article.

As this is a scientific article in a specialist genetics journal, it contains many technical terms and assumes a high level of understanding of modern genetics. I have not studied genetics so I am unable to clarify a number of technical sections in the article. I have done my best to provide explanations of some technical ideas and issues - some of these are in the Glossary at the end of the Summary, others are placed in the Summary in square brackets [ ] to show that they are my comments. An excellent resource on cattle genetics has been produced by Sheila Schmutz, "Genes for Cowboys", see http://skyway.usask.ca/~schmutz/Cowboys.html. The Abstract (or summary) of the article below is the actual word-for-word version from the article and it reflects the technical level of the article. 

~~ Abstract of Article ~~

Tyrosinase related protein 1 (TYRP1), which is involved in the coat colour pathway, was mapped to BTA8 between microsatellites BL1080 and BM4006, using a microsatellite in intron 5 of TYRP1. The complete coding sequence of bovine TYRP1 was determined from cDNA derived from skin biopsies of cattle with various colours. Sequence data from exons 2-8 from cattle with diluted phenotypes was compared with that from non-diluted phenotypes. In addition, full-sib families of beef cattle generated by embryo transfer and half-sib families from traditional matings in which coat colour was segregating were used to correlate TYRP1 sequence variants with dilute coat colours. Two non-conservative amino acid changes were detected in Simmental, Charolais and Galloway cattle but these polymorphisms were not associated with diluted shades of black or red, nor with the dun coat colour of Galloway cattle or the taupe brown colour of Braunvieh and Brown Swiss cattle. However, in Dexter cattle all 25 cattle with a dun brown coat colour were homozygous for a H424Y change. One Dexter that was also homozygous Y434 was red because of an "E⁺/E⁺" genotype at MC1R which leads to the production of only phaeomelanin. None of the 70 remaining black or red Dexter cattle were homozygous for Y434. This tyrosine mutation was not found in any of the 121 cattle of other breeds that were examined.

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