Tiger-eye iris pigmentation in Puerto Rican Paso Fino horses
Tiger-eye is an eye colour unique to Puerto Rican Paso Fino (PRPF) horses and is characterised by a bright yellow, amber or orange iris. Earlier pedigree analysis has shown that tiger-eye pigmentation is inherited by simple autosomal recessive inheritance.
In humans studies have shown that several genes are associated with brown/ blue iris colour variation. In horses, some knowledge on iris colour variation comes from studying coat colour variation. Several white coat pattern mutations and a cream dilution allele have been implicated in blue iris pigmentation. While horses with a champagne dilution allele have amber eyes. Beyond the coat-colour specific iris variants, no studies have investigated the genetics of iris pigmentation in horses. In this study the genetics behind the tiger-eye pigmentation in horses are unravelled.
Photographs of eyes were collected from 216 PRPF horses. Additional information collected was: pedigree information, coat colour, date of birth and sex. The observers determined if the horses had tiger-eyes, when confirmed they were included in the study. The final sample set included 32 horses with tiger-eye pigmentation and 122 wild type horses. From these horses hair samples were collected and sequenced.
The results identified a locus on ECA1, which harbours the candidate gene, SLC24A5, with known roles in pigmentation in humans, mice and zebrafish. Two mutations in SLC24A5 are assumed to affect iris pigmentation in tiger-eye PRPF horses.
Expert opinion by Anouk van Breukelen
This study is a foundation for further unravelling the genetics involved in iris pigmentation in horses.
> From: Mack , G3: Genes, Genomics, Genetics 7 (2017) 2799-2806. All rights reserved to Creative Commons . Click here for the online summary.