2.2 | Sample collection and DNA isolation
Blood samples were obtained and genomic DNA was isolated using a blood DNA extraction kit (TIANGEN, Beijing, China) and then stored at -20 ℃. DNA integrity was evaluated by 1.5% agarose gel electrophoresis. The most variable region in the mtDNA D-loop was assessed using data for each of the samples. One female HGD was randomly selected to determine the complete mtDNA sequence.