4 | DISCUSSION
The mtDNA genome of donkeys is 16 670 bp, of which the D-loop region is
1 207 bp (Xu et al., 1996). As reported in previous genetic studies on
donkeys (Lopez et al., 2005; Ma et al., 2020; Ozkan Unal et al., 2020),
the D-loop region of ancestral mtDNA supplies adequate information to
assess genetic variation, evolutionary relationships, and matrilineal
genetic origins.
We detected a total of 23 nucleotide polymorphic sites in the D-loop
region sequences of HGDs. For the D-loop 418 bp sequence, nucleotide
polymorphic sites account for 9.21%, among which 94.44% are
transformed or transposed, with two insertion sites accounting for
5.56% (Ivankovic et al., 2002). Therefore, the frequency of
transposition was much higher than transversion, which is consistent
with the results of our study.
At present, there is a traditional view on the origin and evolution of
the Chinese donkey, which is that the Chinese donkey originated from the
African wild ass after domestication. Lei et al. (Lei et al., 2007)
found two mitochondrial origins of African wild ass, lineage Somali
(Clade Ⅱ) and lineage Nubian (Clade Ⅰ) in Chinese domestic donkeys and
that Clade Ⅱ was prevalent in Chinese domestic donkey breeds. These
findings are consistent with those of our study.