Matrilineal genetic inter-introgression of Bos taurus and Bos indicus in China

Abstract

The genetic resources of cattle breeds in China are very abundant, with the existence of 28 indigenous and other cattle breeds. To further understand the population structure of these indigenous breeds from different geographical locations, we carried out a phylogenetic analysis in maternal lineages by employing mtDNA polymorphisms. The entire mtDNA D-loop sequences of 73 individuals from 14 representative native cattle breeds were determined and analyzed in conjunction with the published 144 D-loop sequences for 19 Chinese cattle breeds retrieved from GenBank. These sequences belonged to 100 haplotypes defined by polymorphisms at 122 polymorphic sites. These haplotypes were clustered into two distinct lineages: taurine Bos taurus and zebu Bos indicus. The two main peaks of the poly-peaked mismatch curve revealed the inter-mismatch distribution between the Bos taurus and Bos indicus sequence types within the cattle samples. The zebu mtDNA dominated in the southern breeds (62.5%), while taurine mtDNA dominated in the northern breeds (96.7%). The geographical distribution of these frequencies revealed an inter-introgression pattern of Bos taurus and Bos indicus in maternal lineages in China. The significant genetic divergence between the northern and the southern breeds resulted from the dominant geographical segregation of the Qinling Moutains and temperature weather conditions. The heterogeneous distribution of taurine and zebu types in other regions could be attributed to the historical events and introgression of taurine cattle imported from home and abroad.