Genome-wide association scan suggests basis for microtia in Awassi sheep

Abstract

Hereditary underdevelopment of the ear, a condition also known as microtia, has been observed in several sheep breeds as well as in humans and other species. Its genetic basis in sheep is unknown. 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 were collected from sheep in Jordan. Eight affected and 12 normal individuals were genotyped with the Illumina OvineSNP50(®) chip. Multilocus analyses failed to identify any genotypic association. In contrast, a single-locus analysis revealed a statistically significant association (P = 0.012, genome-wide) with a SNP at basepair 34 647 499 on OAR23. This marker is adjacent to the gene encoding transcription factor GATA-6, which has been shown to play a 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 3000 years ago. Many of the earless sheep breeds may thus share the causative mutation, especially within the subgroup of fat-tailed, wool sheep.

Genome‐wide association study reveals the locus responsible for microtia in Valle del Belice sheep breed

“…) and sheep (Jawasreh et al . ). According to Elias & Bennet (), microtia is more common in ovine in comparison with other ruminants.…”

“…In the Valle del Belice breed, the microtia would seem to be not associated with another defect and appears to be simply inherited, as also reported for Awassi sheep (Jawasreh et al . ). Several interviewed breeders believe that sheep with microtia have higher milk production.…”

“…This marker is adjacent to the gene encoding transcription factor GATA‐6 (Jawasreh et al . ). Recently, Gao et al .…”

“…However, very few studies have been performed to identify the related genes and mutations on a genome‐wide scale for ear size in sheep (Jawasreh et al . ; Gao et al . ).…”

“…Moreover, it should be highlighted that the different investigated phenotypes among studies—anotia (Jawasreh et al . ), ears with different sizes (Gao et al . ) and microtia (this study)—could also be responsible for these discrepancies.…”