Identification of the Yellow Skin Gene Reveals a Hybrid Origin of the Domestic Chicken

Jonas Eriksson,Greger Larson,Bertrand Bed'Hom,Michele Tixier-Boichard,Annemieke Jungerius,Ulrika Gunnarsson,Lina Strömstedt,Per Jensen,Leif Andersson,Ettore Randi,Dominic Wright,Addie Vereijken

doi:10.1371/journal.pgen.1000010

Abstract

Yellow skin is an abundant phenotype among domestic chickens and is caused by a recessive allele (W*Y) that allows deposition of yellow carotenoids in the skin. Here we show that yellow skin is caused by one or more cis-acting and tissue-specific regulatory mutation(s) that inhibit expression of BCDO2 (beta-carotene dioxygenase 2) in skin. Our data imply that carotenoids are taken up from the circulation in both genotypes but are degraded by BCDO2 in skin from animals carrying the white skin allele (W*W). Surprisingly, our results demonstrate that yellow skin does not originate from the red junglefowl (Gallus gallus), the presumed sole wild ancestor of the domestic chicken, but most likely from the closely related grey junglefowl (Gallus sonneratii). This is the first conclusive evidence for a hybrid origin of the domestic chicken, and it has important implications for our views of the domestication process.

Highlights

The origin of the domestic chicken has been under debate for centuries [1]
On the basis of observed character differences and cross-breeding experiments, Darwin concluded that domestic chickens were derived solely from the red junglefowl [4], though this was later challenged by Hutt [1], who stated that as many as four different species of junglefowls may have contributed to chicken domestication
In this study we demonstrate that yellow skin is caused by regulatory mutation(s) that inhibit expression of the beta-carotene dioxygenase 2 (BCDO2) enzyme in skin, but not in other tissues

Summary

Introduction

The origin of the domestic chicken has been under debate for centuries [1]. Has the geographical center of the first (and possible additional) domestication event remained contentious [1,2,3], but because several closely related species of junglefowls exist in South Asia (Figure 1), the possibility that chickens originate from multiple wild ancestors has yet to be eliminated. A study that analyzed both repeat nuclear elements and mitochondrial sequences found evidence that grey and Ceylon junglefowls may hybridize with domestic chickens, but did not provide evidence that these two species have contributed to chicken domestication [7]. No studies have compared gene sequences associated with a specific phenotype found in domestic chickens across numerous wild junglefowls and domestic breeds

Methods

Results

Discussion

Conclusion