Genome-Wide Association Scan Suggests Basis for Microtia in Awassi Sheep
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John Wiley & Sons, Ltd. ;
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Microtia, the underdevelopment of the pinna, the structural part of the outer ear, has been observed in many species,including humans, mice, dogs and various livestock. Microtia is relatively prevalent in sheep, observed in multiple breeds including some entire populations, but its genetic basis has not been described. The Awassi sheep, a breed native to Southwest Asia, carries this phenotype and was targeted for molecular characterization via a genome-wide association study . DNA samples wer e collected from sheep flocks in Jordan, within the native range of the Awassi. Samples from eight affected and twelve normal individuals were genotyped with the Illumina OvineSNP50 ® chip. Haplotype-based analyses failed to identify any major runs of homozygosity associated with the trait. In contrast, a single-locus genome-wide association analysis revealed a solitary statistically significant association (P= 0.012, genome wide) with a single-nucleotide polymorphism at base-pair 34,647,4 99 on OAR23. This marker is adjacent to the gene encoding transcription factor GATA-6, which has been shown to play a critical role in many developmental processes, including chondrogenesis. The lack of extended homozygosity in this region suggests a fairly ancient mutation, and the time of occurrence was estimated to be approximately 860 generations ago. This result suggests that many of the sheep breeds showing this phenotype may share the causative mutation, especially within the sub- group of fat-tailed, wool sheep.