关键词: 鸡, 线粒体DNA, D-loop区, 遗传多样性, 遗传起源

Abstract:

【Objective】 The purpose of this study was to investigate the genetic diversity and origin characteristics of the whole sequence of mitochondrial DNA D-loop region in chicken breeds (complete set line) with different growth rates, so as to provide a theoretical basis for breeding and traceability of broiler breeds. 【Method】 15 broiler breeds with different growth rates were used as research materials, including eight yellow-feathered broiler lines (5 medium-fast and 3 slow lines), two local chicken breeds (Gushi chicken and Tibetan chicken), two introduced chicken breeds (Recessive White and Anka), one white-feathered broiler (Ross 308), 817 hybrid broiler and one commercial layer line (Dawu Brown Eggshell Hens). Chicken blood was collected, and DNA was PCR amplified. The full sequences of mtDNA D-loop region of 683 individuals from 15 chicken breeds were sequenced, and the genetic diversity and haplotype characteristics of each chicken breed were analyzed using DnaSP 5.10 software. The genetic distance between breeds was calculated using MEGA 4.0 software, and then a phylogenetic tree was constructed between different haplotypes and the red original chicken. 【Result】The full sequence size of the D-loop region of 15 chicken breeds ranged from 1 231 to 1 232 bp, and individuals with sequence length of 1 231 bp had C-base deletion at 859 bp. 45 variant loci were detected in 683 individuals, which were combined into 53 haplotypes and could be divided into four haplotype groups, including A, B, C and E. Among them, the medium-fast broilers, 817 hybrid broilers and high-yielding laying hens were all haplotype E as the dominant haplotype (≥48.89%); the dominant haplotypes were B haplotypes for Hongguang black chickens, A haplotypes for Jinghai yellow chickens, and four haplotypes were relatively balanced for Xueshan chickens (the proportion of E haplotypes ≤38.46% for three chicken breeds); the haplotypes of local chicken breeds were A and C haplotypes for Gushi chickens and A and B haplotypes for Tibetan chickens. The genetic diversity of the 15 chicken breeds ranged from 0.496 to 0.853 for Hd and from 0.00146 to 0.00673 for Pi. The relatively rich genetic diversity was found in the Xinxing Dwarf Yellow Chicken, Xueshan Chicken, Jinghai Yellow Chicken and Ross 308; the relatively low genetic diversity was found in the Tibetan Chicken, the High Laying Chicken, the Anka Chicken, the Xinxing partridge Chicken No. 4 and the Xugang Yellow Chicken No. 1. The range of Kiumura two-parameter distance of 15 chicken breeds was 0.0016-0.0113, among which the intra-breed genetic distance of Ross 308 was the largest while the intra-breed genetic distance of 817 hybrid broiler and high-yielding chicken was the smallest; the inter-breed genetic distance was the largest between high-yielding chicken and Tibetan chicken, and the smallest between high-yielding chicken and 817 hybrid broiler; the genetic distance between medium-fast broiler was relatively small while the genetic distance between medium-fast broiler, slow-fast and local chicken breeds was relatively large; the genetic distance between Jinghai and local chicken breeds was relatively large. Cluster analysis showed that the haplotypes A, B, and gallus gallus spadiceus were clustered in one group. Haplotype E and gallus gallus murghi were clustered in another group. Haplotype C was clustered with four subspecies of jungle fowl, including gallus gallus murghi, gallus gallus spadiceus, gallus gallus gallus and gallus gallus bankiva. 【Conclusion】The genetic diversity of mitochondrial D-loop region varied among different chicken breeds; E haplotypes were strongly correlated with broiler growth rate, and E haplotypes were the dominant haplotypes in all medium and fast populations, while the proportion of E haplotypes in slow populations was less than 40%; the national chicken population had multiple red proto-chicken maternal origins, indicating that it was domesticated under neutral selection. The results of the study provided a theoretical basis for broiler breed selection and tracing as well as resource exploitation.

Key words: chicken, mitochondrial DNA, D-loop region, genetic diversity, genetic origin