In other species: Nile tilapia , dog , domestic cat , water buffalo , Japanese quail

Categories: Pigmentation phene

Mendelian trait/disorder: no

Disease-related: no

Key variant known: no

Key variant is published: no

Cross-species summary: Iris colour

Species-specific name: bull, odd eyes

Species-specific description: Three main iris colours in pigeons have been described as orange, pearl (white) and bull (dark brown). In 2021, three independent groups reported a missense mutation in SLC2A11B as likely causal variant for the pearl iris colour (Andrade et al., 2021; Si et al., 2021; Maclary et al., 2021) – see OMIA:002416-8932 : Eye colour, SLC2A11B-related in Columba livia for details. Maclary et al., 2021 also investigated the bull (dark brown) iris colour: “In bull-eyed pigeons, both white and orange pigments are absent from the iris stroma, so the underlying dark melanin pigment of the iris pigment epithelium is not obscured (Bond 1919; Oliphant 1987). … the bull iris color is primarily found in birds with white plumage (Hollander, 1939). Breeders have also reported birds with a phenotype known as “odd eyes” (Levi 1986; Sell 2012), in which one iris is a dark bull color and the other is either orange or pearl, suggesting that bull eye color may have a stochastic component.”

Mapping: Maclary et al., 2021: “To identify the genetic basis of bull eye color, we used QTL mapping in two independent F2 intercrosses. In a cross between orange-eyed Pomeranian Pouter and bull-eyed Scandaroon pigeon breeds, F2 birds had either two bull eyes (n=41), two orange eyes (n=40), or “odd eyes”, where one eye has a pigmented iris stroma and the other eye is bull (n=12) (Fig. 2A). Using a binary model where odd-eyed birds were included in the “bull eye” group, we identified a QTL on linkage group 15 … . [The QTL included] EDNRB2, a gene involved in neural crest migration and pigment development.” The authors concluded that “bull eye is likely controlled by a heterogeneous collection of alleles across pigeon breeds. We also found that the EDNRB2 region is associated with regionalized plumage depigmentation (piebalding).” Maclary et al. (2023) report a likely causal variant for "recessive white and bull eye" as scaffold 507:11167700C>T; p.(E256K) (see OMIA:000375-8932 : Feather colour, white spotting, EDNRB2-related in Columba livia for details.)