Mitochondrial DNA T7719G in tRNA-Lys gene affects litter size in Small- tailed Han sheep

Background: In farm animals, mitochondrial DNA (mtDNA) effect on economic performance remains hot-topic for breeding and genetic selection. Here, 53 maternal lineages of Small-tailed Han sheep were used to investigate the association of mitochondrial DNA variations and the lambing litter size. Results: Sequence sweeping of the mitochondrial coding regions discovered 31 non-synonymous mutations, and the association study revealed that T7719G in mtDNA tRNA-Lys gene was associated with litter size (P < 0.05), manifesting 0.29 lambs per litter between the G and T carriers. Furthermore, using the mixed linear model, we assayed the potential association of the ovine litter size and haplogroups and multiple-level mtDNA haplotypes, including general haplotypes, assembled haplotypes of electron transport chain contained sequences (H-ETC), mitochondrial respiratory complex contained sequences (H-MRC) and mitochondrial genes (H-gene, including polypeptide-coding genes, rRNA genes and tRNA genes). The strategy for assembled mitochondrial haplotypes was proposed for the first time in mtDNA association analyses on economic traits, although none of the significant relations could be concluded (P > 0.05). In addition, the nuclear major gene BMPR1B was significantly correlated with litter size in the flock (P < 0.05), however, did not interact with mtDNA T7719G mutation (P > 0.05). Conclusions: Our results highlight mutations of ovine mitochondrial coding genes, suggesting T7719G in tRNA-Lys gene be a potentially useful marker for selection of sheep litter size.