Vincent Racaniello has written a blog about this paper and I bow to his expertise. http://www.plosgenetics.org/article/info%3Adoi%2F10.1371%2Fjournal.pgen.1003183
An EAV-HP Insertion in 5′ Flanking Region of SLCO1B3 Causes Blue Eggshell in the Chicken
The eggshell color of birds is of wide interest, but the molecular basis remained unknown until our discovery, reported here. The blue eggshell is found not only in wild birds but also in domestic fowls. In this study, we identified that blue eggshell in chickens from different geographical regions is caused by a ~4.2 kb EAV-HP insertion in the 5′ flanking region of SLCO1B3. The EAV-HP insertion in chicken is a derived mutation in domestic chickens. The genetic determination of blue eggshell in other birds requires further investigation. We also found that the EAV-HP insertions in the chickens from China and America were separate integration events, which presents us with a parallel molecular evolution example driven by artificial selection.