| Breed resource is the basis of sustaining development of animal production industry. China is one of the countries in the world which has the richest goat breed resources. But we have little knowledge on the origin, migration, evolution and breeds genetic status of Chinese indigenous goat breeds. Goat, one of the most adaptive livestock species, is distributed widely in the world, goat products such as meat, milk, skin and fiber are the main income for farmers in the developing countries. The origin of goat has long been considered a valuable research field in animal evolution. Some studies reported that wild goats were domesticated mainly in two zones in history, one was in the Fertile Crescent region of the Near East and the other was in Pakistan. Many Chinese researchers have done much work on the origin of goat and suggested the domestic goat progenitors were Capra aegagrus and Capra falconeri.Mitochondrial DNA (mtDNA) is an important genetic marker because of its maternal inheritance without recombination and high mutation rate. Many mtDNA studies based on the D-loop control region analysis addressed questions of phylogeny and evolution. The research of livestock genetic diversity helps the conservation and utilization of animal breed resources. The sequencing of mtDNA is one of the most common and reliable molecular markers in detecting animal molecular evolution and genetic diversity.In this article, HVI of mitochondrial DNA(mtDNA) control region(CR, D-loop) was sequenced in 167 individuals from 11 domestic goat breeds/strains raised in China (Chaidamu, Huanghuai, Jining grey, Liaoning cashmere, Longdong Black, Nanjiang Cashmere, Inner Mongolia Cashmere, Tibetan, Shaannan White, Taihang),downloading sequences from goat breeds from GenBank were carried out. The results will provide scientific basis for resource protection and utilization. The conclusions are as follows in this study.1. The mtDNA D-loop HVI sequences, 480~481 bp in length were determined for 167 individual in 11 Chinese goat breeds, The variation was caused by the gaps of a pairwise in the 239 bp in the mtDNA D-loop HVI sequence . And only 3 samples was 480bp including 2 goats of Inner Mongolia Cashmere and 1 goat of Longdong Black.2. The 167 mtDNA D-loop HVI sequences contained 126 variable sites, among them, singleton variable sites was 27, parsimony informative sites of two variants was 97 and parsimony informative sites of three variants was 2. The results indicate that the pairwise diversity of Chinese goats is very rich.3. The average content of A, C, T and G was 30.86%, 22.13%, 30.89% and 16.14% respe- cttively. The nucleotide content of the experimental goat breeds was varient but was not significant. A+T and G+C of Chinese goat breeds was 61.73% and 38.27% respectively indicating the nucleotide content of Chinese goat was in accordance with the proportion of mammals.4. Chinese goat breeds had 121 haplotypes but no mainstream type. 92 haplotypes was unique haplotypes. 11 haplotypes were shared among breeds and 18 haplotypes were shared within breeds. The distributions and frequencies were unequilibrium either among breeds or within breeds. NJ tree showed four haplotypes (H43, H68, H90 and H107) were the oldest.5. The transition sites of mtDNA D-loop HVI sequences between the goat breeds were 8 and transversion sites were 118, the ratio of transitions to transversions was 15/1, suggesting Chinese goat has the high transition bias. But there were no transition within the goat breed.6. 121 haplotypes with from 167 samples of 11 Chinese goat breeds were determined. The haplotype diversity and nucleotide diversity in 11 Chinese goat breeds were 0.909~1.000 and 0.01 810~0.03 821, respectively. The haplotype and nucleotide diversity of Taihang goat was the highest (1.000, 0.03 821 respectively). The average number of nucleotide differences variation was 9.289~18.563, The Kimura 2-parameter distance between breeds varied from 0.021~0.047. The results indicate that the genetic diversity of Chinese goats is very abundant.7. NJ tree of Chinese goat analysis indicated there were 5 lineages including lineage A, B, C and D found before and a new lineage found in the article. The new lineage was clustered by the sequences of 480 bp. The new lineage was located between the lineage D and B. The result was first reported in Chinese goats. And there was no significant geographical structure in Chinese goat populations. Compared with the goats from the other nations, Chinese goats had a widely gene flow.8. Phylogenetic analysis and a reduced median network analysis revealed two highly divergent goat mtDNA lineages A and B mainly. The frequency of the lineage A and B was 86.78% and 4.96%, respectively. Two additional lineages C and D are present in China at low frequency (3.31%) respectively. And the frequency of the new lineage was 1.65%.9. The curve of nucleotide mismatch distributions in 11 domestic goat populations took on three unimodal. Pairwise differences ranged from 1 to 48. A major peak presented at 10~11 mutational differences, a secondary one at 27~28 differences and a third one at 39~40 differences. Lineage A showed unimodal distribution and undergo expansions. Lineage B showed near bimodal distribution and did not undergo expansion. Tajima's test of selective neutrality of Chinese goats was not significant (P>0.10 or 0.05 |
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