利用SSR标记分析海南普通野生稻的遗传多样性

选用平均分布于水稻基因组的28对SSR引物,对海南不同纬度5个普通野生稻居群的163份材料进行遗传多样性和遗传结构研究。结果表明:(1)海南普通野生稻具有较高的遗传多样性,28个位点共检测到227个等位变异,平均等位变异数A=8.1071,有效等位变异数Ae=4.4190,平均期望杂合度He=0.4004,实际观察杂合度Ho=0.7062,香农指数I=1.6048;(2)居群的遗传分化系数较大,总的遗传变异中有46.40%存在于居群间(Fst=0.4640);(3)居群内杂合体较高(F is=-0.7069),根据固定指数(F=0.0588)计算出的异交率t=0.8889,说明海南普通野生稻的繁育系统属于一种较高的异交混合交配类型。     

花蔺和黄花蔺居群遗传结构比较研究

采用垂直板型聚丙烯酰胺凝胶电泳技术,分别通过１９和２１个等位酶位点测定了花蔺３个居群和黄花蔺４个居群的遗传结构与基因流。两类群都维持较高水平的遗传多样性。花蔺居群期望杂合度、固定指数、异交率和遗传分化分别为０．１４４、０．１７４、９４．０％和０．２００,显示出异交繁育系统类型。黄花蔺居群期望杂合度、固定指数、异交率和遗传分化分别为０．０７６、０．４１５、５８．５％和０．３９１。表明其异交＋自交的敏     

桂东南地区普通野生稻遗传多样性研究

利用25个微卫星位点对广西壮族自治区贺州、崇左、防城港3市8个居群301份普通野生稻材料的遗传多样性和遗传结构进行研究,结果表明桂东南地区普通野生稻遗传多样性丰富,平均等位基因数A=10.2400,有效等位基因数Ae=5.0221,平均期望杂合度He=0.7641,实际观察杂合度Ho=0.4840.根据固定指数(F=0.5653)计算出的异交率(t=0.2777)表明,普通野生稻的繁育系统是典型的混合繁育系统.对其遗传结构分析表明,总的遗传变异中有34.59%存在于居群间(Fst=0.3459).进一步研究发现大多数居群偏离了Hardy-Weinberg平衡且杂合体不足(Fis=0.2680,Fit=0.4817).最后根据各居群的遗传变异特点和遗传多样性比较,建议居群QT、YJ和TJ需要优先保护.     

大别山山核桃天然群体遗传结构的初步分析

利用RAPD分子标记技术检测了大别山山核桃3个天然居群的遗传多样性和遗传结构。20条10 bp随机引物共检测到238个扩增位点,其中多态性位点162个,多态位点百分率(PPB)为68.1%。居群水平Shannon’s多态性信息指数(I)介于0.2651~0.2801之间;居群水平Ne i’s基因多样性指数(H)介于0.1789~0.1890之间。遗传变异计算显示大别山山核桃居群间基因分化系数(Gst)为0.4063,分子方差分析(AMOVA)表明居群间基因分化水平为0.4177,居群间基因流(Nm)为0.7306,说明大别山山核桃大部分变异存在于居群内,居群间基因交流相对较少。这一结果符合大别山山核桃风媒、异交的繁育系统特点,但其居群间基因分化程度明显高于异交植物的平均水平(Gst=0.1930)。地理隔离、居群内近交及居群间基因流受阻可能是形成目前大别山山核桃天然群体遗传结构的主要因素。     

荷叶铁线蕨自然居群的遗传多样性研究

荷叶铁线蕨(Adiantumreniformevar. sinense)为我国特有植物,具有重要的经济价值,目前仅分布于重庆的少数地区。近几十年来,由于过度开发,该种的分布范围日益缩小,已处于灭绝的边缘。本研究利用等位酶标记检测了荷叶铁线蕨 6个自然居群共 136个个体的遗传多样性,共检测到了 5个酶系统的 14个位点,获得了 7个多态位点。结果表明:与其他蕨类植物相比,荷叶铁线蕨居群内的遗传多样性水平比较低。平均每位点的有效等位基因数(Ae)为 1. 778,多态位点百分率(P)为 0. 441,期望杂合度(He)为 0. 199,观察杂合度 (Ho)为 0. 235。其居群间的遗传分化也很低,居群间的遗传变异仅占总变异的 1. 49%,而 98. 51%的变异存在于居群内部。采用Hardy Wein berg平衡和固定指数F对荷叶铁线蕨的居群遗传结构进行了分析,结果表明其种群可能是以配子体间异交为主的混合交配体系。导致荷叶铁线蕨濒危的主要原因是生境的破坏以及过度开采所导致的生境片断化使其居群变小、近交率加大、遗传变异趋低,降低了其生存以及进化的潜力。     

极濒危植物中华水韭休宁居群的遗传结构

采用超薄平板微型聚丙烯酰胺等电聚焦电泳方法对极濒危蕨类植物中华水韭(Isoetes sinensis)现存于安徽休宁的5个亚居群的等位酶多样性和遗传结构进行了研究。结果表明：中华水韭居群每位点平均等位基因数A=1．7,平均多态位点比率P=55．56％,平均预期杂合度He=0．201。居群中半数的多念位点表现为等位基因的“固定杂合”,5个亚居群的遗传多样性无显著差异,但都表现出严重偏离Hardy—Weinberg平衡的杂合子过昔;其遗传变异主要发生于亚居群内(94．27％),亚居群之间的遗传分化较小(Gsl=0．0573),亚居群间遗传一致度较高(I=0．960—0．999)。我们推断这可能是由于居群构建之初的奠基者效应或者原种群曾经历了较为严重的遗传瓶颈所导致;此外亚居群间便利的基因交流也可能起到了很大作用(Nm=4．5062)。取自休宁居群的75株样品由13个专一多位点基因型(18个位点等位酶基因型)组成,亚居群及个体间高度遗传均质。本文还就中华水韭休宁野生居群濒危的遗传因素进行了探讨,并提出了相应的保育策略。     

用遗传标记监测不同环境和经营措施下的加勒比松森林群体遗传动态

对古巴加勒比松的6个群体（包括天然林、采伐林、母树林和种子园）进行了同功酶分析,根据5个酶系统8个位点的同功酶数据,对各群 交配系统以及群体遗传变异和结构进行了分析,天然林、种子园和母树林的多位点异交率和绝大多数单位点异交率都和完全异交无显著差异,过渡采伐的松树岛群体多位点异交率显著小于完全异交,而只有一半单位点异交率显著小于完全异交,而且该群体单位点平均异交率和多位点异交率均低于其它3个群体的估计值。采伐群体中同功酶变异和基因多样性与天然林群体JAG的相似,但低于其它群体,其近交系数较大,但小于天然林MAN和中国栽培群体的近交系数。中国引种栽培群体无论是同功酶变异还是基因多样性都显著高于古巴群体,与所有古巴群体的遗传距离都显著大于古巴群体之间的遗传距离。结果表明过度采伐导致群体自交程度增加,营建种子园可有效减少近交。自然分布区以外的引种栽培群体遗传变化量大,无论遗传变异和基因多样性都比参试其它群体大。     

黄花杓兰云南中甸居群遗传结构及克隆多样性的分析

采用AFLP分子标记方法对云南中甸的6个黄花杓兰( Cypripedium flavum )居群进行了遗传多样性水平、遗传结构及克隆多样性研究,其中两个居群用样方取样法分析其克隆空间结构.POPGENE软件分析结果表明:两组引物共产生104个位点,其中86个为多态位点,多态位点百分率为82.69%.黄花杓兰具有丰富的遗传变异(物种水平上, He=0.2884, Ho=0.4312;居群水平上,P=64.59%, He=0.2449, Ho=0.3606),黄花杓兰居群的遗传分化不大( Gst=0.154),居群间基因交流较为频繁( Nm=2.7460).居群的克隆多样性水平高( D=0.9638-0.9960,G/N=0.83-0.96),同一克隆的分株相邻,克隆生长延伸范围狭窄.黄花杓兰居群之所以保持较高水平的遗传多样性,可能与其既能通过实生幼苗增加基因的杂合度,又能通过无性分株把杂合体固定下来有关.     

泡沙参复合体(桔梗科)的物种生物学研究 Ⅳ. 等位酶水平的变异和分化

利用聚丙烯酰胺凝胶电泳技术,对采自泡沙参复合体整个分布区的15个天然居群进行了等位酶 分析。7种酶系统共10个等位酶基因位点的检测表明,本复合体植物具有高水平的遗传变异性,居群 水平上的遗传多样性指标分别为:多态位点百分率P=0.40～0.70,等位基因平均数A=1.5～2.5,平 均期望杂合度He=0.102～0.291。3个类群在居群水平上的平均多样性水平由高至低依次为;A． wawreana(A=2.10,P=0.63, He=0.237),A．lobophylla(A=1.85,P=0.60,He=0.204)和A． potaninii(A=1.83,P=O.60,He=0.188)。居群遗传结构和交配系统的分析表明,本复合体植物的大 部分遗传变异存在于居群之内,Fst=0.176(A．wawreana)和0.115(A．potaninii),并以异交为主,异 交率估计值分别为t=0.86(A．wawreana),0.74(A．potaninii)和0.63(A．lobophylla),这是本复合 体植物具有丰富遗传变异的主要原因之一。根据15个居群的遗传一致度(I)值进行聚类分析发现, 15 个居群可分为明显的2支,由A．lobophylla 2个居群构成的一支与由A. wawreana 和A．potaninii 13 个居群构成的一支在遗传上的分化十分明显,而6个A．wawreana 居群和7个A．potaninii 居群间的 遗传差异不明显,是两个分化不充分的类群。因此,本文的等位酶证据说明,A．lobophylla是遗传上独立的好种,同时不支持将A．wawreana 和A. potaninii 分别作为独立种的处理。     

重金属污染芒萁居群遗传分化的RAPD分析

利用随机扩增多态DNA标记技术(random amplified polymorphic DNA,RAPD)对自然生长的芒萁洁净居群和铅锌矿尾矿居群的遗传多样性和遗传分化进行分析。结果表明在170个检测位点中发现有102个位点呈多态性,在尾矿居群中有2个RAPD标记位点发生了丢失,推测可能为重金属的敏感基因片段;尾矿居群的多态位点百分率(52.94%)、Shannon信息指数(0.3059)和Nei基因多样性(0.2084)均略低于洁净居群(分别为53.53%、0.3196和0.2198),总的遗传多样性水平较高(分别为70.59%、0.3723和0.2472)。尾矿居群与洁净居群之间发生了一定的遗传分化(Φst=0.1900,Gst=0.1339),但居群间的变异程度远远小于居群内的变异程度,居群间的基因流较大。重金属胁迫对芒萁居群的遗传分化有较大程度的影响,可能是导致芒萁适应重金属污染的分化和微进化的一个重要驱动力。     

The mating system and genetic significance of polycarpy in the neem tree (Azadirachta indica)

The objectives of this study were to estimate the outcrossing rate and to explain genetic consequences of the development of seed in the endocarp in a natural population of neem in Bangladesh. Cotyledons of germinated open-pollinated seeds of individual trees were analyzed by starch-gel electrophoresis to examine allozymes. Three loci with clear Mendelian segregation were used to estimate outcrossing rate. A multilocus mixed mating model was used to evaluate the mating system. The population exhibited high outcrossing rates both for multilocus (t_m=0.90±0.024) and mean single-locus (t_s=0.92±0.020) estimates. The difference between these two parameters (t_m–t_s=0±SE 0.038) was insignificant, indicating that there was no ’biparental inbreeding’ in the population. The degree of variance of the estimates of multilocus outcrossing rates decreased when two or more loci were included. In order to elucidate the significance of polycarpy a total of 471 seeds were counted out of 440 endocarps. This mechanism appears to be a possible way of avoiding inbreeding. The results indicated that the studied neem population was predominantly allogamous. Received: 10 January 1999 / Accepted: 10 April 1999     

Mating system analysis in a natural population of Acacia nilotica subspecies leiocarpa

The mating-system was investigated in a natural population of the tetraploid taxon Acacia nilotica ssp. leiocarpa using open-pollinated seeds from 15 families. Six-day-old germinated seeds were used for starch-gel electrophoresis. Three enzyme systems (ADH, EST-1, and 6PGD) were scored. Isozyme banding patterns and segregation of isozyme variants within families suggest that the species is an autotetraploid displaying tetrasomic inheritance. Estimates of single-locus (t_s=0.358) and multilocus (t_m=0.384) population outcrossing rates were homogeneous, and indicate substantial selfing in the population. Heterogeneity of outcrossing estimates among loci and families were marked, suggesting departure from the assumptions of the mixed-mating model. Implications of the result for the utilization of germplasm in tree-improvement programmes are noted.     

Mating system of wild Phaseolus lunatus L. and its relationship to population size

Using isozyme variation in a naturally pollinated seed family for 10 wild Phaseolus lunatus L. (Lima bean) populations, ranging in sizes from 10 to 60 reproductive individuals, we estimated levels of outcrossing (t) and parental inbreeding coefficient (F). We also examined the relationship between outcrossing rate and population size. Average estimates of the single-locus outcrossing rate (ts) ranged from 0.024 to 0.246 (mean=0.091+/-0.065). Estimates of the multilocus outcrossing rate (tm) ranged from 0.027 to 0.268, and averaged 0.096+/-0.071. Inbreeding coefficients based on genotypic frequencies of maternal plants were positive and significantly greater than zero (F=0.504), suggesting an excess of homozygotes in all the populations studied. There was indirect evidence of nonrandom mating for outcrosses and this was mainly attributed to self-fertilisation since the averaged difference between tm and ts, which provides a measure of biparental inbreeding, represents only 1% of the autogamy rate. No significant correlation was observed between outcrossing rate and population size. Estimates of t showed significant heterogeneity among populations and factors explaining this tendency are suggested.     

Genetic conservation of small populations of the endemic tree <Emphasis Type="Italic">Swartzia glazioviana</Emphasis> (Taub.) Glaz. (Leguminosae) in the Atlantic Forest

Swartzia glazioviana is a threatened legume tree species from the Brazilian Atlantic Forest characterized by aggregations of individuals and endemism to an area with extensive human occupation. It is critical to conduct studies on the species to conserve the remaining populations. Using ten nuclear microsatellite loci, we examined the genotypic and genetic diversity and structure, inbreeding, stand-level spatial genetic structure (SGS), effective population size, mating system, and pollen flow in three isolated remnant populations, aiming to inform conservation strategies. All adult individuals found in the populations were mapped and sampled and open-pollinated seeds were collected from two populations. The genotypic diversity (>0.85) indicates that sexual reproduction is predominant and the short distance between ramets indicates that asexual reproduction occurs by root development. In general, populations present SGS which is explained, in part, by root development. The genetic differentiation among populations was greater between more distant populations, suggesting a gene dispersal pattern of isolation by distance. Pollen flow (>27%) indicates that populations are not reproductively isolated, but fertilization followed an isolation by distance pattern. The outcrossing rate was high (\({t_m}\)?>?0.8), but some mating occurred among related individuals (\({t_m}\; - \;{t_s}\)?>?0.1) and were correlated (\({r_p}\)?>?0.15), indicating inbreeding and varying levels of relatedness within families. Inbreeding was higher in seed cohorts than adults, suggesting selection against inbred individuals between seed and adult stages. The results are discussed considering in situ conservation and strategies for seed collection for environmental reforestation.     

Estimation of outcrossing rate in a breeding population of Eucalyptus urophylla with dominant RAPD and AFLP markers

 Eucalyptus breeding is typically conducted by selection in open-pollinated progenies. As mating is controlled only on the female side of the cross, knowledge of outcrossing versus selfing rates is essential for maintaining adequate levels of genetic variability for continuous gains. Outcrossing rate in an open-pollinated breeding population of Eucalyptus urophylla was estimated by two PCR-based dominant marker technologies, RAPD and AFLP, using 11 open-pollinated progeny arrays of 24 individuals. Estimated outcrossing rates indicate predominant outcrossing and suggest maintenance of adequate genetic variability within families. The multilcous outcrossing rate (t_m) estimated from RAPD markers (0.93±0.027), although in the same range, was higher (α>0.01) than the estimate based on AFLP (0.89±0.033). Both estimates were of similar magnitude to those estimated for natural populations using isozymes. The estimated Wright’s fixation index was lower than expected based on t_m possibly resulting from selection against selfed seedlings when sampling plants for the study. An empirical analysis suggests that 18 is the minimum number of dominant marker loci necessary to achieve robust estimates of t_m. This study demonstrates the usefulness of dominant markers, both RAPD and AFLP, for estimating the outcrossing rate in breeding and natural populations of forest trees. We anticipate an increasing use of such PCR-based technologies in mating-system studies, in view of their high throughput and universality of the reagents, particularly for species where isozyme systems have not yet been optimized. Received: 25 March 1997 / Accepted: 13 May 1997     

Estimation of outcrossing rates in Duglas-fir using isozyme markers

Summary Seeds produced under open-pollination were collected from eight natural stands and a plus-tree seed orchard of Douglas-fir. These seeds were germinated and both diploid embryos and haploid gametophytes were analyzed by starch-gel electrophoresis. Eleven variable loci were resolved for both kinds of tissue and used as genetic markers for estimating outcrossing rates. Estimates made with single-locus and multilocus methods both indicated that the proportion of viable embryos resulting from outcrossing is about 0.90 for the natural stands, and for the seed orchard. Comparison of single-locus and multilocus estimates of outcrossing rates indicated that little or no inbreeding other than selfing occurred. Estimated outcrossing rates were higher for seeds from the upper portion of the crown than for seeds from the lower crown. It was also found that some trees selfed at a much higher rate than other trees.     

Mating system and multilocus associations in a natural population of Pseudotsuga menziesii (Mirb.) Franco

Summary Arrays of open-pollinated seeds were assayed for allozyme polymorphisms at ten loci (Aat2, Est1, G6pd, Idh, Mdh2, Mdh3, Pgm, Sod, 6Pgd1, 6Pgd2) to obtain estimates of the outcrossing rate and assess multilocus association in a natural population of coastal Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco. The allele frequencies in the samples of adult trees and pollen-gamete pool were similar. Maximum-likelihood estimators of the outcrossing rate for individual loci and two multilocus models were derived using counting methods. The single-locus maximum likelihood estimates (MLEs) of the outcrossing rate were significantly heterogeneous; they varied over a more than two-fold range from 0.404 to 0.935, with an average MLE of 0.741. Both multilocus MLEs of the outcrossing rate were 0.887. The sample of trees was in random mating equilibrium when assessed on a pairwise-locus basis using Burrows' composite measure of gametic disequilibrium, with one exception (Mdh2 Sod) that was attributable to a rare gametic class. In the sample of pollen gametes, 5 of the 45 pairwise-locus associations were nominally significant at the 0.05 level: Idh Est1, Mdh2 Sod, Aat2 Est1, Aat2 Mdh3, and Est1 Mdh3. These apparent associations were attributable in most cases to the relative excess of uncommon or rare paternal gametes of discernibly outcrossed embryos. An additional two-locus association was identified for Mdh2 Pgm which was marginally significant for the major partition of the contingency table that excluded paternal gametes with the rare allele Mdh2 ² .     

Evolution of Multilocus Genetic Structure in an Experimental Barley Population

Data from 311 selfed families isolated from four generations (F8, F13, F23, F45) of an experimental barley population were analyzed to determine patterns of change in character expression for seven quantitative traits, and in single-locus allelic frequencies, and multilocus genetic structure, for 16 Mendelian loci that code for discretely recognizable variants. The analyses showed that large changes in single-locus allelic frequencies and major reorganizations in multilocus genetic structure occurred in each of the generation-to-generation transitions examined. Although associations among a few traits persisted over generations, dynamic dissociations and reassociations occurred among several traits in each generation-transition period. Overall, the restructuring that occurred was characterized by gradual decreases in the number of clusters of associated traits and increases in the number of traits within each cluster. The observed changes in single-locus frequencies and in multilocus genetic structure were attributed to interplay among various evolutionary factors among which natural selection acting in a temporally heterogeneous environment was the guiding force.     

Fine-scale genetic structure enhances biparental inbreeding by promoting mating events between more related individuals in wild soybean (Glycine soja; Fabaceae) populations

Outcrossing between genetically distant individuals in a plant population enhances allelic heterozygosity-an important source for genetic diversity and adaptive evolution. Fine-scale spatial genetic structure (FSGS) can interfere with outcrossing by promoting mating between more related individuals. To test the influence of FSGS on outcrossing, FSGS and outcrossing rates were analyzed with four wild soybean (Glycine soja) populations from different habitats, using simple sequence repeat (SSR) fingerprints. Spatial autocorrelation analysis indicated variable FSGS (15.44-25.87 m) in all four populations. Multilocus mixed-mating analysis of 1605 progeny indicated substantial variation in single-locus outcrossing (T(s) = 6.3-12.6%) although the total outcrossing rates as estimated by multilocus outcrossing (T(m) = 12.8-17%) did not vary significantly among populations. The comparison between FSGS and outcrossing rates demonstrated that strong FSGS with large genetic patch size can enhance biparental inbreeding by promoting mating between more related individuals in a population. The results suggest that patch size management can aid in situ conservation by avoiding formation of strong FSGS and encouraging true outcrossing among individuals.     

Mating system of Carapa procera (Meliaceae) in the french guiana tropical forest

The mating system of the tropical rainforest tree Carapa procera was studied for a population located within a sylvicultural trial in French Guiana. We used the mixed-mating model with the genotypes of 47 open-pollinated progenies at ten polymorphic loci, obtained through isozyme analysis. Seeds were collected on both logged and unlogged (control) plots, which were interspersed. A high multilocus outcrossing rate (0.78) was found for the global population. and there was indirect evidence for nonrandom mating for outcrosses. It is argued that this may be due to some kind of positive assortative mating, probably biparental inbreeding. Correlation of selfing between sibs was not significantly different from zero. and the proportion of full-sibs among outcrossed sib-pairs was significant but low (0.16). We found significant differences between outcrossing rates when computing separate estimates for the 14 trees located on logged plots (tm = 0.63) and the 33 trees located on undisturbed plots (tm = 0.85). It is argued that the decrease in density is probably not the only cause of the decrease in outcrossing rate on logged plots. Lastly, several points concerning the reliability of the estimation are outlined. In particular. the downward bias due to ignoring null alleles during genetic interpretations of zymograms is quantified in a few cases by simulating artificial populations.