Researchers at the Texas A&M University College of Veterinary Medicine have found that the distinctive white-tipped feathers of mottled chicken breeds arise from multiple independent genetic mutations. Their study, published in Animal Genetics, challenges the belief that similar feather patterns in chickens are inherited from a common ancestor.
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The team discovered at least three different genetic variants associated with the same pigmentation gene, EDNRB2, that can produce comparable mottled appearances. This finding sheds light on the complexities of poultry genetics and the impact of selective breeding on domestic chickens.
Mottling is characterized by white tips on feathers, resulting when pigment-producing cells fail to reach the feather ends. Traditionally, researchers thought that most mottled chickens shared the same genetic mutation. However, Dr. Leif Andersson, a Texas A&M professor, emphasized that mottling actually results from at least three distinct mutations that have developed in various chicken populations.
The inquiry began with the Mottled Houdan breed, where prior studies linked a specific mutation in the EDNRB2 gene to mottling in several Japanese breeds. When Andersson's team analyzed the Mottled Houdan, they did not find the anticipated mutation. This led them to explore alternative genetic causes and cross-breed Mottled Houdans with Black Langshan chickens to trace the genomic region responsible for the mottled trait.
The research revealed a different mutation in the EDNRB2 gene linked to mottling in the Houdan and other non-Japanese breeds, suggesting multiple genetic explanations across various chicken populations while supporting a phenomenon known as parallel evolution.
EDNRB2 regulates pigmentation in birds, encoding a receptor that influences the development and migration of pigment cells. Disruption in EDNRB2 signaling can prevent pigment cells from reaching specific tissues, resulting in the unpigmented feather tips. Andersson noted that reduced EDNRB2 function leads to decreased pigmentation, highlighting that multiple mutations can create similar feather patterns.
The study underscores human influence on chicken genetics, as breeders historically selected chickens with desirable traits. This selective breeding allowed varying genetic mutations to persist, producing diverse chicken breeds with similar appearances.
Beyond poultry genetics, findings related to EDNRB2 have implications for understanding human genetic disorders, such as Hirschsprung disease, which affects nerve cell development in the gastrointestinal tract. While the study does not propose new treatments for humans, it contributes to the broader understanding of developmental genetics across species.
Veterinary professionals are reminded that visible traits do not always reflect an animal's underlying genetics, and the research demonstrates the value of genomic technologies in identifying genetic variations. The study identifies at least three alleles linked to mottling, though genetic changes associated with the trait in every breed are not yet fully understood.
The Texas A&M researchers plan to continue exploring other pigmentation-related gene variants, adding to the knowledge of how selective breeding and genetics shape chicken diversity.