Transcription factors control comb development in chickens.
There are three comb types in chickens that are each inherited independently as single gene traits: Rose, Pea and Duplex comb. Here the Duplex V-Shaped phenotype is shown to be caused by ectopic expression of the transcription factor Eomesodermin (EOMES). Previous reports have shown Rose and Pea comb to be caused by ectopic expression of transcription factors MNR2 and SOX5, respectively. Remarkably, the causal mutations for all three comb types represent structural genomic variants (duplications and inversions) that disrupt normal expression of these transcription factors and result in vastly different developmental outcomes for the comb. See Dorshorst et al.
Image Credit: Ben Dorshorst and colleagues