中国红原鸡和泰国红原鸡遗传多样性分析

利用29个微卫星DNA标记对来自中国的红原鸡Gallus gallus spadiceus亚种和来自泰国的红原鸡Gallus gallus gallus亚种进行遗传多样性分析, 评估亚种内的遗传变异和亚种间的遗传分化, 结果表明: 共检测到168个等位基因, 每个位点的等位基因数从2到13不等, 所有位点平均的期望杂合度和PIC值分别为0.5780和0.53。中国和泰国红原鸡29个微卫星位点平均有效等位基因数分别为3.79和4.79, 平均基因杂合度为0.5379和0.6385, 两个红原鸡亚种均表现出较高的群体杂合度和丰富的遗传多样性。群体分化系数为19.4%(P<0.01), 两个红原鸡亚种间的Reynolds’遗传距离和Nm值分别为0.157和1.040。由此可见, Gallus gallus spadiceus亚种和Gallus gallus gallus亚种群体具有不同的群体遗传结构, 群体之间存在明显的遗传分化, 并不能将其认定为是同一亚种, 这也为中国家鸡具有独立的起源提供了一定的佐证。     

Genetic structure in Red Junglefowl (Gallus gallus) populations: Strong spatial patterns in the wild ancestors of domestic chickens in a core distribution range

Red Junglefowl (Gallus gallus) are among the few remaining ancestors of an extant domesticated livestock species, the domestic chicken, that still occur in the wild. Little is known about genetic diversity, population structure, and demography of wild Red Junglefowl in their natural habitats. Extinction threats from habitat loss or genetic alteration from domestic introgression exacerbate further the conservation status of this progenitor species. In a previous study, we reported extraordinary adaptive genetic variation in the MHC B‐locus in wild Red Junglefowl and no evidence of allelic introgression between wild and domestic chickens was observed. In this study, we characterized spatial genetic variation and population structure in naturally occurring populations of Red Junglefowl in their core distribution range in South Central Vietnam. A sample of 212 Red Junglefowl was obtained from geographically and ecologically diverse habitats across an area of 250 × 350 km. We used amplified fragment‐length polymorphism markers obtained from 431 loci to determine whether genetic diversity and population structure varies. We found that Red Junglefowl are widely distributed but form small and isolated populations. Strong spatial genetic patterns occur at both local and regional scales. At local scale, population stratification can be identified to approximately 5 km. At regional scale, we identified distinct populations of Red Junglefowl in the southern lowlands, northern highlands, and eastern coastal portions of the study area. Both local and long‐distance genetic patterns observed in wild Red Junglefowl may reflect the species’ ground‐dwelling and territorial characteristics, including dispersal barriers imposed by the Annamite Mountain Range. Spatially explicit analyses with neutral genetic markers can be highly informative and here elevates the conservation profile of the wild ancestors of domesticated chickens.     

Mitochondrial DNA-based analysis of genetic variation and relatedness among Sri Lankan indigenous chickens and the Ceylon junglefowl (Gallus lafayetti)

Indigenous chickens (IC) in developing countries provide a useful resource to detect novel genes in mitochondrial and nuclear genomes. Here, we investigated the level of genetic diversity in IC from five distinct regions of Sri Lanka using a PCR-based resequencing method. In addition, we investigated the relatedness of IC to different species of junglefowls including Ceylon (CJF; Gallus lafayetti ), a subspecies that is endemic to Sri Lanka, green ( Gallus varius ), grey ( Gallus sonneratii ) and red ( Gallus gallus ) junglefowls. A total of 140 birds including eight CJF were used to screen the control region of the mitochondrial DNA sequence for single nucleotide polymorphisms (SNPs) and other variants. We detected and validated 44 SNPs, which formed 42 haplotypes and six haplogroups in IC. The SNPs observed in the CJF were distinct and the D-loop appeared to be missing a 62-bp segment found in IC and the red junglefowl. Among the six haplogroups of IC, only one was region-specific. Estimates of haplotype and nucleotide diversities ranged from 0.901 to 0.965 and from 0.011 to 0.013 respectively, and genetic divergence was generally low. Further, variation among individuals within regions accounted for 92% of the total molecular variation among birds. The Sri Lankan IC were more closely related to red and grey junglefowls than to CJF, indicating multiple origins. The molecular information on genetic diversity revealed in our study may be useful in developing genetic improvement and conservation strategies to better utilize indigenous Sri Lankan chicken resources.     

Genetic characterization of Red Junglefowl (Gallus gallus), Thai indigenous chicken (Gallus domesticus), and two commercial lines using selective functional genes compared to microsatellite markers

Genetic characterization among Red Junglefowl (GS, Gallus gallus spadiceus), Thai indigenous chicken (TIC, Gallus domesticus) and commercial lines has been widely used for studies of genealogical origin, genetic diversity, and effects of selection. We compared the efficiency of genetic characterization of chicken populations that had been under different intensities of selection using selective functional gene versus microsatellite marker analyses. We genotyped 151 chickens from five populations: Red Junglefowl, TIC and commercial lines (BR, broiler and WL, White Leghorn). Genetic structure analyses using six loci of five functional genes - corresponding to heat tolerance (heat shock protein 70, HSP70/C, HSP70/M), broodiness (vasoactive intestinal peptide receptor-1, VIPR-1), egg production-[24-bp indel (insertion or deletion) prolactin, 24bpPRL], ovulation rate (growth hormone receptor, GHR), and growth (insulin-like growth factor-1, IGF-1) - were compared with 18 microsatellite markers. PCR-RFLP and allele specific PCR were used for functional gene typing. A neighbor-joining tree from Nei's genetic distance was constructed to show genetic relationships. A similar pattern was found with both functional genes and microsatellites. Three groups consisting of BR, WL and TIC-GS-GG were formed. A principal component plot based on individual similarity using Dice's coefficient was also constructed to confirm the relationship. Different patterns were found when using functional genes versus microsatellites. A principal component plot with functional genes also gave three clusters consisting of BR, WL and TIC-GS-GG. A principal component plot using microsatellites gave four clusters, consisting of WL, GG, TIC, and BR-GS. Characterization of BR and GS differs from previous studies. We concluded that genetic characterization with appropriate functional genes is more accurate when differences in genetic make-up among populations are known. Genetic characterization using functional gene data was consistent in neighbor joining and principal component plot analyses, while genetic characterization using microsatellite data gave varied results depending on the analysis methodology.     

Playing chicken with red junglefowl: identifying phenotypic markers of genetic purity in Gallus gallus

We report the results of a novel experiment, in which genetically pure male red junglefowl Gallus gallus (Richardson strain) were deliberately crossed with domestic female chickens to create contaminated lines of known purity, reaching as high as 93.75%. Phenotypic characters generally used as indicators of purity (reduced or absent female comb, male eclipse plumage, etc.) all appeared to at least some extent in domestically contaminated progeny and moreso in successively more pure generations of the experiment, suggesting that such phenotypic characters may have little, if any, utility in characterizing red junglefowl stocks as to their genetic purity.     

Genetic structure of a wide-spectrum chicken gene pool

The genetic structure of 65 chicken populations was studied using 29 simple sequence repeat loci. Six main clusters which corresponded to geographical origins and histories were identified: Brown Egg Layers; predominantly Broilers; native Chinese breeds or breeds with recent Asian origin; predominantly breeds of European derivation; a small cluster containing populations with no common history and populations that had breeding history with White Leghorn. Another group of populations that shared their genome with several clusters was defined as 'Multi-clusters'. Gallus gallus gallus (Multi-clusters), one of the subspecies of the Red Jungle Fowl, which was previously suggested to be one of the ancestors of the domesticated chicken, has almost no shared loci with European and White Egg layer populations. In a further sub-clustering of the populations, discrimination between all the 65 populations was possible, and relationships between each were suggested. The genetic variation between populations was found to account for about 34% of the total genetic variation, 11% of the variation being between clusters and 23% being between populations within clusters. The suggested clusters may assist in future studies of genetic aspects of the chicken gene pool.     

Genetic diversity of Guangxi chicken breeds assessed with microsatellites and the mitochondrial DNA D-loop region

The domestic chicken (Gallus gallus domesticus) is an excellent model for genetic studies of phenotypic diversity. The Guangxi Region of China possesses several native chicken breeds displaying a broad range of phenotypes well adapted to the extreme hot-and-wet environments in the region. We thus evaluated the genetic diversity and relationships among six native chicken populations of the Guangxi region and also evaluated two commercial breeds (Arbor Acres and Roman chickens). We analyzed the sequences of the D-loop region of the mitochondrial DNA (mtDNA) and 18 microsatellite loci of 280 blood samples from six Guangxi native chicken breeds and from Arbor Acres and Roman chickens, and used the neighbor-joining method to construct the phylogenetic tree of these eight breeds. Our results showed that the genetic diversity of Guangxi native breeds was relatively rich. The phylogenetic tree using the unweighed pair-group method with arithmetic means (UPGAM) on microsatellite marks revealed two main clusters. Arbor Acres chicken and Roman chicken were in one cluster, while the Guangxi breeds were in the other cluster. Moreover, the UPGAM tree of Guangxi native breeds based on microsatellite loci was more consistent with the genesis, breeding history, differentiation and location than the mtDNA D-loop region. STRUCTURE analysis further confirmed the genetic structure of Guangxi native breeds in the Neighbor-Net dendrogram. The nomenclature of mtDNA sequence polymorphisms suggests that the Guangxi native chickens are distributed across four clades, but most of them are clustered in two main clades (B and E), with the other haplotypes within the clades A and C. The Guangxi native breeds revealed abundant genetic diversity not only on microsatellite loci but also on mtDNA D-loop region, and contained multiple maternal lineages, including one from China and another from Europe or the Middle East.     

Evaluation of genetic diversity in Chinese indigenous chicken breeds using microsatellite markers

China is regarded as one of the domestication cen-ters for chickens and archaeological studies provided evidence of chicken domestication in northern Chinaas early as 6000 BC[1]. At present, China has the larg-est chicken population in the world, represen…     

Evaluation of genetic diversity in Chinese indigenous chicken breeds using microsatellite markers

China is rich in chicken genetic resources, and many indigenous breeds can be found throughout the country. Due to poor productive ability, some of them are threatened by the commercial varieties from domestic and foreign breeding companies. In a large-scale investigation into the current status of Chinese poultry genetic resources, 78 indigenous chicken breeds were surveyed and their blood samples collected. The genomes of these chickens were screened using microsatellite analysis. A total of 2740 individuals were genotyped for 27 microsatellite markers on 13 chromosomes. The number of alleles of the 27 markers ranged from 6 to 51 per locus with a mean of 18.74. Heterozygosity (H) values of the 78 chicken breeds were all more than 0.5. The average H value (0.622) and polymorphism information content (PIC, 0.573) of these breeds suggested that the Chinese indigenous chickens possessed more genetic diversity than that reported in many other countries. The fixation coefficients of subpopulations within the total population (F _ST) for the 27 loci varied from 0.065 (LEI0166) to 0.209 (MCW0078), with a mean of 0.106. For all detected microsatellite loci, only one (LEI0194) deviated from Hardy-Weinberg equilibrium (HWE) across all the populations. As genetic drift or non-random mating can occur in small populations, breeds kept on conservation farms such as Langshan chicken generally had lower H values, while those kept on large populations within conservation regions possessed higher polymorphisms. The high genetic diversity in Chinese indigenous breeds is in agreement with great phenotypic variation of these breeds. Using Nei’s genetic distance and the Neighbor-Joining method, the indigenous Chinese chickens were classified into six categories that were generally consistent with their geographic distributions. The molecular information of genetic diversity will play an important role in conservation, supervision, and utilization of the chicken resources.     

Ten polymorphic microsatellite loci in Tibetan chicken, <Emphasis Type="Italic">Gallus gallus domesticus</Emphasis>

Through an improved enrichment protocol, a genomic library for (AC)₁₂ repeats was constructed and 34 microsatellite loci were isolated and characterized in an endangered animal, Tibetan chicken, Gallus gallus domesticus. In the 34 loci, ten loci showed a distinct allelic variation ranging from 4 to 14 alleles in 54 individuals tested. Polymorphism information content (PIC) ranged from 0.590 to 0.869 with an average of 0.713. Average observed and expected heterozygosities were 0.7988 (ranged from 0.310 to 1.000) and 0.7495 (ranged from 0.609 to 0.897), respectively. These ten microsatellites loci would be the valuable genetic markers for further investigation of Tibetan chicken.     

Genetic Diversity and Population Structure Analysis Between Indian Red Jungle Fowl and Domestic Chicken Using Microsatellite Markers

The present study was conducted to assess the genetic diversity, population structure, and relatedness in Indian red jungle fowl (RJF, Gallus gallus murgi) from northern India and three domestic chicken populations (gallus gallus domesticus), maintained at the institute farms, namely White Leghorn (WL), Aseel (AS) and Red Cornish (RC) using 25 microsatellite markers. All the markers were polymorphic, the number of alleles at each locus ranged from five (MCW0111) to forty-three (LEI0212) with an average number of 19 alleles per locus. Across all loci, the mean expected heterozygosity and polymorphic information content were 0.883 and 0.872, respectively. Population-specific alleles were found in each population. A UPGMA dendrogram based on shared allele distances clearly revealed two major clusters among the four populations; cluster I had genotypes from RJF and WL whereas cluster II had AS and RC genotypes. Furthermore, the estimation of population structure was performed to understand how genetic variation is partitioned within and among populations. The maximum ?K value was observed for K = 4 with four identified clusters. Furthermore, factorial analysis clearly showed four clustering; each cluster represented the four types of population used in the study. These results clearly, demonstrate the potential of microsatellite markers in elucidating the genetic diversity, relationships, and population structure analysis in RJF and domestic chicken populations.     

Analysis of genetic diversity and phylogenetic relationships among red jungle fowls and Chinese domestic fowls

Genetic diversity and phylogenetic relationships among 568 individuals of two red jungle fowl subspe- cies (Gallus gallus spadiceus in China and Gallus gallus gallus in Thailand) and 14 Chinese domestic chicken breeds were evaluated with 29 microstaellite loci, the genetic variability within population and genetic differentiation among population were estimated, and then genetic diversity and phylogenetic relationships were analyzed among red jungle fowls and Chinese domestic fowls. A total of 286 alleles were detected in 16 population with 29 microsatellite markers and the average number of the alleles observed in 29 microsatellite loci was 9.86±6.36. The overall expected heterozygosity of all population was 0.6708±0.0251, and the number of population deviated from Hardy-Weinberg equilibrium per locus ranged from 0 to 7. In the whole population, the average of genetic differentiation among population, measured as FST value, was 16.7% (P<0.001), and all loci contributed significantly (P<0.001) to this differentiation. It can also be seen that the deficit of heterozygotes was very high (0.015) (P<0.01). Reynolds' distance values varied between 0.036 (Xiaoshan chicken-Luyuan chicken pair) and 0.330 (G. gallus gallus-Gushi chicken pair). The Nm value ranged from 0.533 (between G. gallus gallus and Gushi chicken) to 5.833 (between Xiaoshan chicken and Luyuan chicken). An unrooted consensus tree was constructed using the neighbour-joining method and the Reynolds' genetic distance. The heavy-body sized chicken breeds, Luyuan chicken, Xiaoshan chicken, Beijing Fatty chicken, Henan Game chicken, Huainan Partridge and Langshan chicken formed one branch, and it had a close genetic relationship between Xiaoshan chicken-Luyuan chicken pair and Chahua chicken-Tibetan chicken pair. Chahua chicken and Tibetan chicken had closer genetic relationship with these two subspecies of red jungle fowl than other domestic chicken breeds. G. gallus spadiceus showed closer phylogenetic relationship with Chinese domestic chicken breeds than G. gallus gallus. All 29 microstaellite loci in this study showed high levels of polymorphism and significant genetic differentiation was observed among two subspecies of red jungle fowl and 14 Chinese domestic chicken breeds. The evolutional dendrogram is as follows: evolutional breeds→primitive breeds (Chahua chicken and Tibetan)→red jungle fowl in China (G. gallus spadiceus)→red jungle fowl in Thailand (G. gallus gallus). The results supported the theory that the domestic fowls might originate from different subspecies of red jungle fowl and Chinese domestic fowls had independent origin.     

红原鸡与家鸡的亲缘关系研究

对中国红原鸡滇地亚种和海南亚种与我国茶花鸡,泰和鸡和寿光鸡等地方鸡种以及芦花鸡,洛岛红等外国鸡种进行了血型（３个位点,１３个等位基因）,蛋白质（酶）多态（５个位点,１１个等位基因）和ＤＮＡ指纹分析,结果表明,红原鸡与茶花鸡（原始型品种）的亲缘关系较近;与泰和鸡,寿光鸡,芦花鸡,洛岛红（进化型品种）的亲缘关系较远,呈红原鸡－茶花鸡－泰和鸡,寿光鸡或芦花鸡,洛岛红这样一个进化阶梯,以上结果与国外资料（     

Biodiversity of 52 chicken populations assessed by microsatellite typing of DNA pools

In a project on the biodiversity of chickens funded by the European Commission (EC), eight laboratories collaborated to assess the genetic variation within and between 52 populations from a wide range of chicken types. Twenty-two di-nucleotide microsatellite markers were used to genotype DNA pools of 50 birds from each population. The polymorphism measures for the average, the least polymorphic population (inbred C line) and the most polymorphic population (Gallus gallus spadiceus) were, respectively, as follows: number of alleles per locus, per population: 3.5, 1.3 and 5.2; average gene diversity across markers: 0.47, 0.05 and 0.64; and proportion of polymorphic markers: 0.91, 0.25 and 1.0. These were in good agreement with the breeding history of the populations. For instance, unselected populations were found to be more polymorphic than selected breeds such as layers. Thus DNA pools are effective in the preliminary assessment of genetic variation of populations and markers. Mean genetic distance indicates the extent to which a given population shares its genetic diversity with that of the whole tested gene pool and is a useful criterion for conservation of diversity. The distribution of population-specific (private) alleles and the amount of genetic variation shared among populations supports the hypothesis that the red jungle fowl is the main progenitor of the domesticated chicken.     

Crossing over in chicken (Gallus gallus domesticus) oogenesis: Periodic arrangement of chiasmata over chromosomes

The periodic occurrence of chiasmata was studied in lampbrush chromosomes of the chicken (Gallus gallus domesticus). It was shown that the most probable interference distance in chicken macrobivalents 1–3 corresponded to 24.48 Mb. The distance at which absolute interference is observed in chicken macrochromosomes varies from 5.75 to 9.02 Mb.     

Genetic diversity within chicken populations from different continents and management histories

Intra-population variation was assessed in 1970 chickens from 64 populations using 29 autosomal microsatellites. On average, 95% of the loci were polymorphic across populations. In 1456 ( c. 83%) of the 1763 combinations of populations and polymorphic loci, no departure from Hardy–Weinberg equilibrium was observed. On average, there were 11.4 alleles per locus and 3.6 alleles per population across loci. Within populations, the average observed heterozygote frequency was 0.46, with a range between 0.20 and 0.64. Dagu, a Chinese population, and the Red Jungle Fowl ( Gallus gallus gallus ) had the highest average heterozygote frequencies at 0.64 and 0.63 respectively. An inbred line used as a reference population for comparison showed the lowest average of observed heterozygote frequency (0.05), followed by the European population Hamburger Lackhuhn, whose average observed heterozygote frequency was 0.20. A total of 32 private alleles (alleles detected in only one population) for 20 loci were found in 18 populations. H'mong chickens, a Vietnamese population, carried the largest number of private alleles at five, followed by the Red Jungle Fowl with four private alleles. Genetic diversity within populations was low in the NW European fancy breeds and high in the non-commercial Asian populations, in agreement with population management history.     

The origin and genetic diversity of Chinese native chicken breeds

The first 539 bases of mitochondrial DNA D-loop region of six Chinese native chicken breeds (Gallus gallus domesticus) were sequenced and compared to those of the red junglefowl (Gallus gallus), the gray junglefowl (Gallus sonneratii), the green junglefowl (Gallus varius) and Lafayette's junglefowl (Gallus lafayettei) reported in GenBank, and the phylogenetic trees for the chickens were constructed based on the D-loop sequences. The results showed that the four species of the genus Gallus had great differences among each other, the G. g. domesticus was closest to the red junglefowl in Thailand and its adjacent regions, suggesting the Chinese domestic fowl probably originated from the red junglefowl in these regions. The two subs pecies of Thailand, G. g. gallus and G. g. spadiceus, should belong to one subspecies because of their resemblance. In the case of native breeds, there existed a great difference between the egg breeds and general purpose breeds, which suggested different maternal origins of the two types.     

Chicken domestication: from archeology to genomics

Current knowledge on chicken domestication is reviewed on the basis of archaeological, historical and molecular data. Several domestication centres have been identified in South and South-East Asia. Gallus?gallus is the major ancestor species, but Gallus?sonneratii has also contributed to the genetic make-up of the domestic chicken. Genetic diversity is now distributed among traditional populations, standardized breeds and highly selected lines. Knowing the genome sequence has accelerated the identification of causal mutations determining major morphological differences between wild Gallus and domestic breeds. Comparative genome resequencing between Gallus and domestic chickens has identified 21 selective sweeps, one involving a non-synonymous mutation in the TSHR gene, which functional consequences remain to be explored. The resequencing approach could also identify candidate genes responsible of quantitative traits loci (QTL) effects in selected lines. Genomics is opening new ways to understand major switches that took place during domestication and subsequent selection.     

Application of functional genomic information to develop efficient EST-SSRs for the chicken (Gallus gallus)

Many years of domestication and breeding have given rise to the wide range of chicken breeds that exist today; however, an increasing number of local chicken breeds are under threat of extinction. A comprehensive characterization of chicken markers (especially type I markers) is needed to monitor and conserve genetic diversity in this species. The explosion of genomics and functional genomics information in recent years has opened new possibilities for the generation of molecular markers. We analyzed a large number of expressed sequence tags (ESTs) to test the possibility of using EST-derived microsatellite markers for investigating the Gallus gallus genome. Chromosomal locations for the majority of these SSRs were predicted. Of the 31,576 unigenes assembled from the 544,150 redundant EST sequences, 1757 SSR markers were discovered on 1544 ESTs, using the SSRLocator software, with an average density of 28.7 kb per SSR. The dimer motifs were the most frequent (46.38%), followed by trimeric (38.58%), tetrameric (10.19%), pentameric (4.5%), and hexameric (<1%) markers. Different from the case for cattle and sheep, AT/TA was the most abundant dimeric repeat, accounting for 41.71% of all dimeric repeats in the chicken ESTs. The EST-SSR distribution was not uniform among the chromosomes; the majority of the EST-SSRs were located on chromosomes GGA2 and GGA10. We found that most of the EST-SSRs are involved in positive regulation of cellular and metabolic processes. This is the first time that EST sequences have been mined to find chicken microsatellites. On average, 3.8% of the G. gallus UniGene sequences could be exploited for development of EST-SSRs, indicating a good source for molecular markers as well as for functional genome analysis.     

Mitochondrial DNA sequence and haplotype variation analysis in the chicken (Gallus gallus)

Although it is known to be useful for certain genotype:phenotype assignments, our knowledge of the nature and extent of variation in the entire chicken (Gallus gallus) mitochondrial genome (mtGenome) is limited. Here, we used experimental and in silico tools to identify nucleotide variants in the mtGenome, including the coding and non-coding (D-loop) regions. The distribution of the experimentally identified mitochondrial DNA variants in meat- (broilers) and egg-type (White Leghorn) chickens was also assessed. A total of 113 single-nucleotide polymorphisms (SNPs) were identified. The in silico analysis revealed a total of 91 SNPs, with 70 in the coding region and 21 in the non-coding region. Of the 41 experimentally identified SNPs, 27 were in the D-loop. Together, the experimentally identified SNPs in the non-coding region formed 11 haplotypes, whereas the 14 SNPs in the coding region formed 6. Though, 9 of the D-loop region haplotypes were observed only in broilers, 3 of the 6 haplotypes from the coding region occurred at a significantly higher frequency in broilers. To our knowledge, this investigation represents the first whole-mtGenome scan for variation and an evaluation, though limited in sample size, of the haplotype distribution in meat- and egg-type populations, using the SNPs and haplotypes identified.