|
Dexter
Dun – Brown Mutation Discovery
by John Potter
August 10, 2003 |
|
When I began raising Dexters in 1992, I assumed that dun Dexters were
the result of a brown mutation similar to that which exists in other
species of mammals. Until the summer of 2001 all of the cattle
geneticists and literature that I consulted assured me that no brown
mutation had been discovered in cattle. When Carol Davidson
conducted her color studies in the late 1990s, she confirmed the genetic
basis of our red Dexters and suggested the possibility that our Dexters
are relatively unique from the standpoint that E+/E+ Dexters are red-
for example, the renowned bull Cornahir Outlaw. This is the same E
locus genotype that most Jerseys and Brown Swiss have, and those breeds
certainly aren't red in appearance. Since that time I have found
that E+/E+ animals in a number of other breeds, including Tarentaise,
Red Polls, and Maine-Anjou, are phenotypically red. In Carol's
research, dun Dexters turned up as black animals at the red locus.
Carol then assumed that dun Dexters are the result of a dilution
mutation similar to the ones that exist in other breeds of cattle such
as Simmentals, Highlands, and Galloways. In July 2001 I succeeded
in convincing Dr. Sheila M. Schmutz, a prominent geneticist at the
University of Saskatchewan, that Dexter dun may be unique and would be
worth investigating. I am very pleased that our resulting research
project, begun in October 2001, culminated in the discovery of the first
brown mutation ever confirmed in cattle. As of the date of the
conclusion of the research project, the brown mutation had been found
only in the Dexter breed. We tested 121 cattle from 19 other
breeds, and none of them contained this mutation. The 19 breeds
included Angus, Belgian Blue, Blonde d’Aquitane, Braunvieh, Brown Swiss,
Canadienne, Charolais, Flamande, Galloway, Gelbvieh, Guernsey, Hereford,
Highland, Holstein, Jersey, Limousin, Shorthorn, Simmental, and
Tarentaise. One notable observation that was first made in the
research project and confirmed by subsequent testing is the fact that
red is epistatic to Dexter dun. Animals that are homozygous for
both red and dun (E+/E+ b/b, E+/e b/b, e/e b/b) are phenotypically red.
The Dexter dun study concluded with the publication in 2003 of “TYRP1 is
associated with dun coat color in Dexter cattle or how now brown cow?”
by the International Society for Animal Genetics in their journal,
Animal Genetics, 34, 169-175. |
|
