共查询到20条相似文献，搜索用时 31 毫秒
1.
ABSTRACT A total of 360 Xylella fastidiosa strains were isolated from sweet orange (Citrus sinensis) cv. Pera plants growing in five geographic regions in the Brazilian state of S?o Paulo. The genetic variation of these strains was determined by 15 variable number tandem repeat (VNTR) and 58 random amplified polymorphic DNA (RAPD) markers. The mean values of genetic diversity (H) of X. fastidiosa strains within each geographic region determined by RAPD (H(RAPD)) were substantially lower than H(VNTR) values. H(RAPD) values ranged from 0.00 to 0.095, whereas the H(VNTR) values ranged from 0.024 to 0.285. A highly significant value of Nei's coefficient of gene differentiation (G(ST) = 0.355; P = 0.000) was detected among all five populations. Analysis of the molecular variance (AMOVA) also revealed significant genetic differentiation among regions or populations ( phi(STAT) = 0.810; P< 0.001). In addition, genetic differentiation among subpopulations (plants) within the regions (phi(STAT) = 0.699; P < 0.001) and within each plant (phi(STAT) = 368; P < 0.001) were statistically significant. These high values of genetic differentiation among X. fastidiosa strains from different regions suggest a genetic structure according to region of host origin. However, no apparent correlation between genetic distance and region of origin of populations were supported statistically by Mantel analysis (r = 0.27; P = 0.22). 相似文献
2.
Barrier to Gene Flow Between Eastern and Western Populations of Cronartium ribicola in North America
ABSTRACT The population structure of Cronartium ribicola from eastern and western North America was studied to test the null hypothesis that populations are panmictic across the continent. Random amplified polymorphic DNA markers previously characterized in eastern populations were mostly fixed in western populations, yielding high levels of genetic differentiation between eastern and western populations (phi(st) = 0.55; theta = 0.36; P < 0.001). An unweighted pair-group method, arithmetic mean dendro-gram based on genetic distances separated the four eastern and four western populations into two distinct clusters along geographic lines. Similarly, a principal component analysis using marker frequency yielded one cluster of eastern populations and a second cluster of western populations. The population from New Mexico was clearly within the western cluster in both analyses, confirming the western origin of this recent introduction. This population was completely fixed (H(j) = 0.000; n = 45) at all loci suggesting a severe recent population bottleneck. Genetic distances were low among populations of western North America (0.00 to 0.02) and among eastern populations (0.00 to 0.02), indicating a very similar genetic composition. In contrast, genetic distances between eastern and western populations were large, and all were significantly different from 0 (0.07 to 0.19; P < 0.001). Indirect estimates of migration were high among western populations, including the number of migrants among pairs of populations (Nm > 1) between New Mexico and British Columbia populations, but were smaller than one migrant per generation between eastern and western populations. These results suggest the presence of a barrier to gene flow between C. ribicola populations from eastern and western North America. 相似文献
3.
Ling Yin Yali Zhang Yan Hao Jiang Lu 《European journal of plant pathology / European Foundation for Plant Pathology》2014,140(2):365-376
Grape downy mildew is a destructive oomycete disease worldwide for viticulture. A total of 440 infected leaf lesions were collected from nineteen vineyards distributing in the major viticulture regions in China. Six specific SSR markers were used to genetically characterize the Plasmopara viticola populations. A total of 60 alleles were generated and 324 distinct genotypes were identified based on these multi-locus markers. Most populations had high levels of genetic and genotypic diversity. AMOVA analysis showed that majority of the total genetic diversity was distributed within the vineyards while moderate to high genetic differentiation was also observed among some P. viticola populations. Three populations (BJ, GX, and GS2) were clearly separated from the rest of the populations by using PCA and Nei’s genetic distance analysis. Mantel test showed no significant correlation between unbiased Nei’s genetic distance and geographical distance. 相似文献
4.
ABSTRACT The population genetic structure of the fungal pathogen Leptosphaeria maculans was determined in Australia using six microsatellite and two minisatellite markers. Ascospores were sampled from Brassica napus stubble in disease nurseries and commercial fields in different sites over 2 years. The 13 subpopulations of L. maculans exhibited high gene (H = 0.393 to 0.563) and genotypic diversity, with 357 haplotypes identified among 513 isolates. Although the majority of genetic variation was distributed within subpopulations (85%), 10% occurred between the regions of eastern and Western Australia, and 5% within regions. F(ST) analysis of subpopulation pairs also showed the east-west genetic differentiation, whereas factorial correspondence analysis separated Western Australian subpopulations from eastern ones. Bayesian model-based population structure analyses of multilocus haplotypes inferred three distinct populations, one in Western Australia and an admixture of two in eastern Australia. These two regions are separated by 1,200 km of arid desert that may act as a natural barrier to gene flow, resulting in differentiation by random genetic drift. The genetic differentiation of L. maculans isolates between eastern and Western Australia means that these regions can be treated as different management units, and reinforces the need for widespread disease nurseries in each region to screen breeding lines against a range of genetic and pathogenic populations of L. maculans. 相似文献
5.
ABSTRACT Genetic variability and population structure of Cercospora sorghi from wild and cultivated sorghum were investigated to gain insight into their potential impact on epidemics of gray leaf spot of sorghum in Africa. Population structure was examined using data derived from amplified fragment length polymorphism (AFLP) of C. sorghi by Nei's test for population differentiation, G(ST), and analysis of molecular variation (AMOVA). Two ecological populations of C. sorghi in Uganda were devoid of population structure (G(ST) = 0.03, small ef, CyrillicF(ST) = 0.01, P = 0.291). AMOVA revealed that genetic variability was due mainly to variations within (99%) rather than between (0.35%) populations, and Nei's genetic distance between the two populations was 0.014. Phenetic analysis based on AFLP data and polymerase chain reaction-restriction fragment length polymorphism analyses of the internal transcribed spacer regions of rDNA and mitochondrial small subunit rDNA separated Cercospora cereal pathogens from dicot pathogens but did not differentiate among C. sorghi isolates from wild and cultivated sorghum. Our results indicate that Ugandan populations of C. sorghi compose one epidemiological unit and suggest that wild sorghum, while not affecting genetic variability of the pathogen population, provides an alternative host for generating additional inoculum. 相似文献
6.
不同干扰生境中荒漠小灌木红砂种群遗传多样性研究 总被引：2，自引：0，他引：2
应用RAPD标记技术对荒漠小灌木红砂(Reaumuria soongorica)种群在不同扰动下的遗传多样性进行了分析。18条随机引物对红砂6个种群的120个个体进行扩增,共检测102个位点,其中多态位点99个。研究结果表明:红砂种群的多态位点比率(P)为96.86%,显示了不同生境中红砂种群内存在较高的遗传多样性。Shannon多样性指数(0.5007)、Nei基因多样性指数(0.3307)和基因分化系数(Gst=0.1952)揭示了红砂种群遗传变异多存在于种群内,种群间的遗传分化则较小。聚类分析表明:红砂种群遗传距离与地理距离之间存在一定相关性;遗传多样性水平与物种特性和不同干扰生境有关,与生态因子无相关性。 相似文献
7.
引起油茶炭疽病胶孢炭疽菌种群遗传结构研究 总被引：2，自引：0，他引：2
胶孢炭疽菌是引起油茶炭疽病的主要病原之一。目前对于该病原菌种群的遗传结构尚未见报道。研究病菌种群的遗传结构对制定科学的防治方法具有重要意义。本研究比较中国6个省12个不同地区的126个胶孢炭疽菌的ITS序列的差异,以期研究各不同群体的单倍体型多样性,不同地区群体之间的遗传关系,以及遗传距离与地理距离的线性关系。遗传分析发现,得到的126个胶孢炭疽菌样品ITS序列可定义为27种单倍体型。27种单倍体型中,一个主要的单倍体型(Haplotype12)含有78个样品,且基本上每个样品采集地都有分布。遗传分化指数(Fst)表明病菌不同地理种群间的遗传分化较大。AMOVA分析显示,种群间的遗传变异占总变异的6%,种群内部变异占总变异的94%。Mantel测试显示地理距离与遗传距离没有显著的线性关系。对所有地理种群病原菌ITS序列的核苷酸不配对进行分析,发现油茶炭疽病菌未经历过大规模的种群扩张过程。系统发育分析表明,来自不同地区的油茶炭疽病菌散乱的分布在系统树中。研究结果表明油茶炭疽病菌种群具有丰富的遗传多样性。 相似文献
8.
为明确长岭发垫刃线虫(Trichotylenchus changlingensis)的分布,2018年对黑龙江、吉林、辽宁、河北、内蒙古、甘肃6省(自治区)118个地块的玉米根际土壤中长岭发垫刃线虫进行分离及鉴定,结果表明:在6个省(自治区)20个地块的土样中分离到该线虫,分离比例为17.0%。同时采用ISSR分子标记技术对分离到的20个种群进行遗传多样性分析。结果共筛选出16条引物,扩增出93条多态性条带,多态性比率为93.55%。基因分化系数(Gst)为0.4771,遗传变异的47.71%存在于种群间,52.29%存在于种群内。基因流(Nm)值为0.5479,说明所调查地区种群间存在基因流,基因流动较小,但种群间已发生一定程度的遗传分化。UPGMA 聚类分析结果表明,这20个种群具有丰富的遗传多样性,但群体间的遗传关系远近与地理距离无显著相关性。 相似文献
9.
ABSTRACT The genetic structure of Septoria passerinii from nine field populations was examined at several scales (within lesions, among lesions in a leaf, among leaves in a field, and among fields in North Dakota and western Minnesota) by using amplified fragment length polymorphism (AFLP) markers. A total of 390 isolates were sampled from seven barley fields located in North Dakota and two barley fields located nearby in western Minnesota in 2003 and 2004. Based on 57 polymorphic AFLP markers, AFLP DNA fingerprints identified 176 different genotypes among 390 (non-clone-corrected) isolates in nine different fields. In two intensively sampled sites, ND16 (Williston, ND) and ND17 (Langdon, ND), only one to four different genotypes were found within a lesion. A higher level of genetic and genotypic diversity was found within a leaf in which six to nine different genotypes were found from lesions on a leaf. The genetic diversity within a leaf was similar to the genetic diversity within a field. The average genetic diversity (H) within a field across all AFLP loci was approximately 0.3, except at site ND12 (Carrington, ND) where it was 0.16. Genotypic diversity was high in all populations, and with the exception of ND15 (Rothsay, MN), very low multilocus linkage disequilibrium values ( r(d)) were found in all populations. The population differentiation, G(ST), was relatively high (G(ST) = 0.238) among the nine populations due to the high G(ST) in ND12, ND14 (Twin Valley, MN), and ND15. Population differentiation without those three populations was 0.09. A lack of correlation between geographical distance and genetic distance was found, suggesting the potential for a high level of gene flow between different geographical regions. The population genetic structure described in this study for S. passerinii in North Dakota and western Minnesota is consistent with that of a sexually reproducing fungus. 相似文献
10.
The genetic structure of wild populations of Colletotrichum lindemuthianum was evaluated for virulence and molecular markers. Forty-five isolates were collected from five wild common bean populations located in their South-Andean centre of origin. The five pathogen populations were monomorphic in their ITS regions, but 45 polymorphic markers were identified using RAPDs. Polymorphism for virulence was also observed; 15 pathotypes were characterized on an international set of 12 differentials. A molecular variance analysis ( AMOVA ) showed that a very large part of the total genetic variation was within populations. Statistical analysis showed that there was a weak though significant differentiation among the five populations for the RAPD and virulence markers. A positive and significant correlation was found between geographic distance and the distances from RAPD and virulence data, suggesting migration between adjacent populations along the Argentinian transect. Our results suggest that the Andean wild isolates of C. lindemuthianum do not reflect all the putative diversity found in the isolates from cultivated common bean. 相似文献
11.
ABSTRACT Genetic diversity was studied in seven Canadian populations of Ophiostoma piceae, the most prevalent sapstain fungus in Canadian softwoods. A total of 239 single-spore isolates were recovered following a systematic survey of sapstain fungi in logs and lumber at seven selected sawmills in six Canadian provinces (British Columbia, Alberta, Saskatchewan, Ontario, Québec, and New Brunswick). Sampling was carried out on five commercially important softwood species: balsam fir (Abies balsamea), white spruce (Picea glauca), black spruce (Picea mariana), jack pine (Pinus banksiana), and lodgepole pine (Pinus con-torta var. latifolia). The A and B mating types occurred at equal frequency (MAT A/ MAT B = 1.00:1.13) over all populations. Pseudo-allelic frequencies were estimated at each of 24 putative genetic loci by scoring for presence or absence of random amplified polymorphic DNA fragments generated by five primers. A total of 237 haplotypes were found among the 239 isolates, revealing a high level of genotypic diversity among isolates. Total gene diversity (H(T) = 0.414) was mostly attributable to diversity within populations (H(S) = 0.369). Thus, only 11.2% of the total variability was attributable to frequency differences among populations. An analysis of molecular variance revealed that most genetic variability occurred within subpopulations within mills (84.3%; P < 0.001), whereas low but statistically significant levels of genetic differentiation were also observed among subpopulations within populations (5.4%; P < 0.001) and among populations (10.3%; P < 0.001). Estimates of Nei' genetic distances were not correlated with geographic distances among sampling locations (r = -0.092; P = 0.310), although principal component analysis indicated that subpopulations located east of Saskatchewan were grouped on the same side of the second principal component axis. Overall, results suggest moderate genetic differentiation of O. piceae in Canada, which is consistent with the observation that sexual reproduction is frequently observed in this fungus. 相似文献
12.
ABSTRACT Isolates of Tilletia controversa and T. bromi were sampled from wheat and two Bromus species hosts, respectively, in the Pacific Northwest, and genetic variation within and among populations was determined. Fifty-one random amplified polymorphic DNA markers from eleven primers were treated as phenotypic 1 and 0 character state data to estimate similarities and analyze molecular variance (AMOVA) among populations and as putative genetic loci to carry out analyses of gene diversity. Phenotypic analysis of T. controversa and T. bromi isolates revealed two distinct clusters that were 37% similar. The T. bromi cluster was subdivided further into two groups, corresponding to host, with 40% similarity. Cluster analysis based on allele frequencies produced similar results and also supported two T. bromi groups based on host. No evidence of natural hybridization and introgression was detected between the T. controversa and T. bromi populations. Both AMOVA and gene diversity analyses detected moderate levels of differentiation among T. controversa populations, whereas T. bromi populations were highly differentiated. The level of genetic differentiation observed between the T. bromi populations on different Bromus species hosts supports the hypothesis that a high degree of host specificity exists in the wild grass-infecting smuts. We speculate that the higher level of genetic differentiation among the T. bromi populations compared with the T. controversa populations on wheat may be due to selection by a more genetically diverse host population. 相似文献
13.
为了明确我国落选短体线虫群体的遗传多样性,利用mtCOI基因标记对落选短体线虫9个地理群体的遗传结构及遗传分化进行分析。结果显示,9个地理群体中共得到101条mtCOI序列,发现28个碱基变异位点,形成14个单倍型。其中,H1单倍型最常见,为7个地理群体的59个个体共有,推测其可能为祖先单倍型。全部地理群体在物种水平呈现中等遗传多样性(HT = 0.706±0.131),聚类分析显示其可分为类群Ⅰ与类群Ⅱ两个类群,AMOVA分析揭示落选短体线虫整体水平的遗传分化主要来源于种群间。Mantel检验表明落选短体线虫群体的遗传距离与地理距离存在正相关性,但是不同种群之间的遗传分化程度与地理距离没有显著关系。中性检验和错配分布检验均揭示落选短体线虫在整体水平和两个类群上的群体历史动态都处于相对稳定的状态。 相似文献
14.
Richardson BA Klopfenstein NB Zambino PJ McDonald GI Geils BW Carris LM 《Phytopathology》2008,98(4):413-420
Cronartium ribicola, the causal agent of white pine blister rust, has been devastating to five-needled white pines in North America since its introduction nearly a century ago. However, dynamic and complex interactions occur among C. ribicola, five-needled white pines, and the environment. To examine potential evolutionary influences on genetic structure and diversity of C. ribicola in western United States, population genetic analyses of C. ribicola were conducted using amplified fragment length polymorphism (AFLP) molecular markers. The fungus was sampled at six sites. Collections for two of the six sites were from separate plantings of resistant-selected western white pine and sugar pine. Heterozygosity based on polymorphic loci among populations ranged from 0.28 to 0.40, with resistant-selected plantations at the extremes. Genetic differentiation was also highest between these two populations. Principal coordinates analysis and Bayesian assignment placed most isolates that are putative carriers of virulence to major-gene resistance into a discernable cluster, while other isolates showed no clustering by site or host species. These results indicate that C. ribicola in western North America is not genetically uniform, despite its presumed single site of introduction and relatively brief residence. Moreover, major-gene resistance appears to have imposed strong selection on the rust, resulting in reduced genetic diversity. In contrast, no evidence of selection was observed in C. ribicola from hosts that exhibit only multigenic resistance. 相似文献
15.
ABSTRACT Phaeosphaeria nodorum was sampled from nine wheat fields across a 30-km transect representing three geographical regions in Switzerland to determine the scale of genetic differentiation among subpopulations. Three different wheat cultivars were sampled three times to determine whether differences in host genotype correlated with differences among corresponding pathogen populations. Seven restriction fragment length polymorphism (RFLP) loci and one DNA fingerprint were assayed for each of the 432 isolates in the collection. DNA fingerprints differentiated 426 unique genotypes. Though absolute differences were small, five RFLP loci exhibited significant differences in allele frequencies across the nine sub-populations. Gene diversity within all subpopulations was high (H(T) = 0.51), but only 3% of the total genetic variation was distributed among the nine subpopulations. When subpopulations were grouped according to geographical region or host cultivar, less than 1% of the genetic variation was distributed among groups, suggesting widespread gene flow and the absence of pathogen adaptation to specific wheat cultivars. Tests for gametic equilibrium within subpopulations and across the entire Swiss population supported the hypothesis of random mating. 相似文献
16.
不同生境臭柏种群的遗传多样性分析及其与环境因子的相关性 总被引：4，自引：0，他引：4
毛乌素沙地臭柏群体是一个生态过渡带。为了进一步阐明分子变异和基因流与生境或生态过渡带的联系,应用RAPD标记开展了臭柏群体的分子生态学研究。采用随机扩增多态性DNA(RAPD)方法对臭柏(Sabina vulgaris.)的3个种群进行了研究.用11个随机引物扩增出129条清晰谱带,其中117条为多态性谱带。利用POPGENE3.2软件对数据进行处理,结果如下:(1)臭柏有着较丰富的遗传多态性,多态位点百分率达90.70%,各种群多态位点百分比在69.77%~72.87%之间.(2)臭柏的种群间分化较小Gst=0.1872,81.38%的遗传变异存在于种群内,各种群的遗传一致度都在86.22%.(3)聚类分析显示,生境相近的种群被聚到了一起,反映了臭柏种群的遗传分化和生境有着一定的相关性.又利用Nei,s指数统计了RAPD数据,也证实了大部分的遗传变异存在于群体之内。臭柏群体内的遗传多样性与土壤总钾呈显著的负相关。 相似文献
17.
内蒙古地区天然臭柏种群遗传多样性的RAPD分析 总被引：7，自引：0，他引：7
应用随机扩增多态性DNA(RAPD)标记法研究了内蒙古地区臭柏种群的遗传分化,所用的18条引物对4个臭柏种群的55个样本扩增出124个位点,其中多态位点100个,多态率达80.7%。种内的平均Nei's多样性指数和Shannon's多样性指数分别为0.286和0.428,种群内分别为0.232和0.347,基因多样性变化趋势为毛乌素沙地(0.258,0.386)>阴山山脉西部(0.258,0.376)>浑善达克沙地(0.231,0.345)>内蒙古贺兰山(0.184,0.281)。臭柏种群总的基因多样性(Ht=0.288),大于种群间的基因多样性(Hs=0.233)。种群间的遗传分化系数(Gst)为0.183,种群内的遗传变异占总遗传变异的81.7%。臭柏种群间的平均遗传距离为0.086,平均相似性系数为0.918,4个种群之间有比较相似的遗传多样性,由于地理隔离,种群间也存在分化。 相似文献
18.
由丁香假单胞菌猕猴桃致病变种Pseudomonas syringae pv. actinidiae (Psa)侵染引起的猕猴桃细菌性溃疡病(kiwifruit bacterial canker)是全球猕猴桃生产上最具毁灭性的细菌病害。为探明福建、安徽、四川和陕西4省Psa菌株的生物型和遗传多样性,用5对PCR特异性引物PsaJ-F/-R、PsaK-F/-R、Tac-F/-R、Con002-F/-R和avrRps4-F1/-R2检测Psa菌株的生物型;用4对PCR引物27F/1492R、PsaF1/PsaR2、gapA-Fps/Rps和rpoD+364s/-1222ps分别扩增16S rRNA、ITS、gapA和rpoD基因,进行多基因联合分析Psa菌株的遗传多样性。结果表明,特异性引物Tac-F/-R从47株Psa菌株中均能扩增出一条545 bp的特异条带,其他4对引物未扩增出任何条带,说明供试Psa菌株的生物型均为biovar 3。多基因联合分析表明,4省Psa存在丰富的遗传多样性,4个群体共检测出27个单倍型,单倍型多样性为0.955。安徽、福建、四川和陕西群体的单倍型数差异较大,分别为1、8、12个和12个。4个群体的多态性位点数、核苷酸多样性和平均核苷酸差异数差异极显著(P<0.01),其中福建群体的多态性最丰富,而安徽群体的多态性最低。AMOVA分析表明,3.6%的遗传变异来源于种群间,而96.4%的遗传变异来源于种群内,说明种群内变异是遗传变异的主要来源。遗传分化分析表明,安徽省Psa群体与其他3个群体间的遗传分化极高(Fst>0.175),福建、四川和陕西群体间的遗传分化水平较低(Fst<0.017)。研究结果有利于了解福建省Psa的来源,为阻断Psa的传播和猕猴桃细菌性溃疡病的长期可持续控制提供了理论参考。 相似文献
19.
Vishnu Sukumari Nath Muthukrishnan Senthil Vinayaka Mahabaleswar Hegde Muthulekshmi Lajapathy Jeeva Raj Shekhar Misra Syamala Swayamvaran Veena Mithun Raj 《European journal of plant pathology / European Foundation for Plant Pathology》2013,136(3):483-494
The oomycete Phytophthora colocasiae that causes taro leaf blight is the most devastating disease of taro and is widely distributed worldwide. Molecular and phenotypic techniques were employed for assessing and exploiting the genetic variability among four populations of P. colocasiae obtained from a fine spatial scale (multiple leaf blight lesions on single taro leaf). Phenotypic characters such as virulence, morphology and mating type showed no variation. ITS characterization revealed detectable polymorphism among isolates of P. colocasiae. The mean number of haplotypes (H), haplotype diversity (HD), nucleotide diversity (π), and nucleotide substitution rate (θ) among analyzed sequences were 6.75, 1.00, 0.069, and 0.088 respectively. High levels of inter and intra specific variation were detected by random amplified polymorphic DNA (RAPD) assays. Moderate genetic diversity (H?=?0.2651) was observed among populations of P. colocasiae. Analysis of molecular variance (AMOVA) confirmed that most of the genetic variability was confined to within a population (63.54 %). The coefficient of genetic differentiation among populations (G ST ) was 0.2007 and estimates of gene flow (Nm) among populations was 1.991 migrants per generation. Cluster analysis using UPGMA revealed that individuals from the same population failed to cluster in one distinct group. The results of the study reveal considerable genetic diversity among and within populations of P. colocasiae obtained from fine spatial scale. The possible mechanisms and implications of this genetic variation are discussed. 相似文献
20.
山东省小麦禾谷孢囊线虫rDNA-ITS序列特征和基于ISSR的遗传多样性分析 总被引：1，自引：1，他引：0
小麦孢囊线虫病(CCN,Heterodera avenae)已成为山东省小麦生产上的一种重要病害,研究CCN群体间和群体内的遗传多样性可以为其综合防治提供理论依据。本实验研究了山东省17地市34个群体的r DNA-ITS区,并采用ISSR分子标记技术对其中10个地市的27个种群做了遗传多样性分析。结果表明,在r DNA-ITS系统发育树中,山东省34个小麦孢囊线虫群体与H.pratensis、H.australis及中国H.avenae群体亲缘关系较近。3个ISSR引物共扩增出31条条带,多态性条带百分率(PPB)为100%。菏泽、潍坊、烟台群体遗传多样性较高,枣庄、威海、淄博、滨州群体遗传多样性相对较低。M antel检测和聚类结果表明,群体间的遗传分化与地理距离并无显著的相关性,AM OVA分析结果显示,在总的遗传变异中17.7%的变异发生在群体间,82.3%的变异发生在群体内。研究结果显示山东省H.avenae具有较高的遗传多样性,且群体间已发生了一定程度的遗传分化。 相似文献