The delightful word 'oocyan' refers to the trait of blue-green eggshell color that occurs in native chickens of Chile (Mapuche fowl) and some of their descendants in North America and Europe, as well as certain Asian chicken breeds (e.g. Dongxiang, Lushi).
Oocyan is an autosomal dominant trait, and recent papers in PLoS Genetics and PLoS ONE have established that it's occurrence in chickens from different geographical regions is due to an endogenous retrovirus (ERV) insertion upstream of the SLCO1B3 gene [1, 2].
Remarkably, the ERV insertions responsible for oocyan appear to represent separate integration events in Chinese versus American/European chicken breeds - thus it appears that the oocyan phenotype has evolved on two separate occasions, via the same ERV-mediated mechanism, in distinct populations of chickens.
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