A subset of dog hair patterns has been revealed by new research. The results raise new questions about long-held beliefs regarding dog evolution.
Study findings revealed that structural variants control the expression of the agouti-signing protein (or ASIP) gene at two different locations. This allows for five distinct dog color patterns. These different patterns are widespread, occurring in hundreds of dog breeds and hundreds of millions of dogs around the world.
Researchers were surprised by the question of when these changes occurred.
They discovered that the genetic combination for one of the coat patterns—dominant yellow, or DY—is shared with arctic white wolves and, based on phylogenetic analysis, originated from an extinct canid that diverged from gray wolves more than 2 million years ago.
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“While we think about all this variation in coat color among dogs, some of it happened long before ‘dogs’ were dogs,”Danika Bannasch (coauthor), professor and chair of genetics at University of California Davis School of Veterinary Medicine.
“The genetics turn out to be a lot more interesting because they tell us something about canid evolution.”
The researchers hypothesize that lighter coat colors would have been advantageous to an extinct canid ancestor in an arctic environment during glaciation periods 1.5 to 2 million years ago. Natural selection would have enabled that coat pattern in the population that gave rise to dogs or wolves to be maintained.
“We were initially surprised to discover that white wolves and yellow dogs have an almost identical ASIP DNA configuration,”Chris Kaelin, of the HudsonAlpha Institute for Biotechnology Huntsville, Alabama is the co-first author of this work with Bannasch. “But we were even more surprised when it turned out that a specific DNA configuration is more than 2 million years old, prior to the emergence of modern wolves as a species.”
There are two types of pigments that can be produced by dogs and wolves. One is eumelanin which is a dark pigment and the other is pheomelanin which a yellow pigment. These two pigments are precisely controlled to produce different colors of coats. The ASIP gene produces the agouti signaling proteins that control the production of pheomelanin (yellow).
Researchers realized that there was no one genetic mutation responsible for all five major color phenotypes. To have different coat patterns, dogs need to have mutations in at least two parts of the ASIP gene. Bannasch and his colleagues renamed these phenotypes in order to better explain the differences: dominant yellow; shaded yellow; agouti; black saddle and black back. They also found that the haplotype of dominant yellow was significantly older than they expected.
“It didn’t come from modern wolves. It had been around for much longer,” Bannasch says.
The researchers then tested the genetics in ancient wolves to confirm that the dominant yellow haplotype was present for approximately 2 million years. This is well before the domestication and breeding of dogs around 30,000 years ago.
A sample of 9,500 year old dog showed the black back pattern. It also shows that dogs had a rich range in their coat colors in the early days.
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