These English trumpeter pigeons - blue-black on the left and red on the right - display some of the great diversity of colors among some 350 breeds of rock pigeons. (Photo courtesy of Sydney Stringham from University of Utah)

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Scientists have identified a set of three genes that impart feather color in domestic rock pigeons (known scientifically as Columba livia), according to a new study published in Current Biology.

The three genes are Tyrp1, Sox10 and Slc45a2. The Tyrp1 gene leads to either the grayish color of common city pigeons (which is actually a blue-black), red, or brown. Mutations of Sox10 imparts a red color to pigeons irrespective of the activities of the first gene. The third gene Slc45a2, has different forms that may give pigeons either an intense or washed out colors.

In humans, these three genes in control skin pigmentation. In fact, the mutations in these genes can cause skin conditions including albinism and melanoma. "In humans, mutations of these genes often are considered 'bad' because they can cause albinism or make cells more susceptible to UV (ultraviolet sunlight) damage and melanoma because the protective pigment is absent or low," said biology postdoctoral fellow and first author of the study Eric Domyan in a press release. However, the mutations are not actually bad for pigeons — all they do is create different feather colors in them.

From left to right: The first feather is blue-black because all three genes are normal. The second feather is dilute blue because the Tyrp1 and Sox10 genes are normal but the Slc45a2 gene is mutant, which dilutes the intensity of any color. The third feather from the left is ash-red because of a mutant Tyrp1 gene and normal Sox10 and Slc45a2. But if Slc45a2 also is mutant, the feather color is diluted to ash-yellow (fourth from left). The fifth feather from the left is red because the Sox10 gene is mutant, which overrides whatever color Tyrp1 normally would dictate. In the sixth feather, Slc45a2 also is mutant, making the feather yellow, which is the diluted form of red. (Eric Domyan from University of Utah)

Different versions of these three genes impact the distribution of different forms of melanin pigments in feathers including eumelanin that provides black and brown pigmentation and pheomelanin that provides red and yellow pigmentation. Diverse coloration of pigeons is a result of complex interplay among these three genes.

"Mutations in one gene determine whether mutations in a second gene have an effect on an organism," Domyan said. The pigeon color is therefore, determined by mutations in different genes, one of which can mask the effects of another.

There are about 350 different pigeon breeds in the world. The variation between breeds is based on differences in their feather ornaments on their beaks, feet and head, plumage color, and their beak shape. For breeders, color is among the most important traits of pigeons, and they have tinkered with it for centuries, creating specimens in huge color diversity for scientists to study pigmentation genetics.

Top row, first three images from left to right, show ash-red color from a mutant form of the Tyrp1 gene, blue-black from a normal Tyrp1 gene, and brown from another Tyrp1 mutant. The fourth photo, upper right, shows a pigeon that is red due to a mutant Sox10 gene. The pigeons in the bottom four images have the same form of the Tyrp1 or Sox10 genes as the corresponding birds in the top row, but their colors are diluted or watered-down because they also have mutant gene named Slc45a2. (Eric Domyan from University of Utah)

This study has shown the specific mutations responsible for color in rock pigeons, for the first time. A large number of combinations of the three genes and their different versions determine feather colors in 82 breeds of pigeons that scientists studied.

"Our work provides new insights about how mutations in these genes affect their functions and how the genes work together," said Michael Shapiro, associate professor of biology and senior author of the study. There are possibly multiple genes at work to control all sorts of traits in animals, from the superficial (like feather color) to the very serious (such as susceptibility to diseases such as cancer).

If we want to understand how genes work to produce a given trait in humans, it may mean studying animals, according to Shapiro. Interactions among genes in human beings may be difficult to study. For instance, understanding of Tyrp1 and Sox10 in pegioens can help us target these genes for treatment of melanoma in humans. In addition, learning about mutations in Slc45a2 leading to changes in skin color including albinism can be successfully targeted with better understanding of this gene.