Balancing selection in Polish Arabian horses

Polish Arabian horses are a good example of a small population derived from a finite number of founders. Pedigree analysis showed significant reduction in the genetic diversity of the population. However, taking into account some circumstances suggesting the presence of balancing selection favouring heterozygotes in Polish breeding, it seems that this referred to pedigree uniformity rather than to a real decrease in genetic variability. The aim of the current study was to verify the hypothesis that balancing selection affects the population. The mare selection process was examined in detail regarding the polymorphism of 10 protein markers. The findings confirmed the tendency to favour the more heterozygous mares with regard to average heterozygosity in total and in relation to particular loci, studs, fathers and inbreeding ranges. The results were discussed in consideration of selection criteria, inbreeding level of Polish Arabs and heterozygosity in other populations.     

茄子青枯病抗性基因的遗传分析及其AFLP标记

 以茄子高感青枯病品种‘三月茄’与高抗品种‘S69’的F1、F2为材料, 对青枯病抗性遗传进行了分析, 同时开展了与抗性基因连锁的AFLP标记鉴定。结果表明: ‘S69’对青枯病的抗病性属于不完全隐性遗传, 感病性属于不完全显性; 抗性由1～2对基因控制。对86个F2单株AFLP分析, 鉴定出1个与‘S69’抗性基因连锁的AFLP标记39A980 (该引物组合为E-ACC /M-CTG) , 该标记与抗性基因间的交换值为4.65% , 遗传距离为4.9 cM。     

Estimation of additive and non-additive genetic parameters for reproduction, growth and survival traits in crosses between the Moroccan D'man and Timahdite sheep breeds

Genetic breed differences, heterosis, recombination loss, and heritability for reproduction traits, lamb survival and growth traits to 90 days of age were estimated from crossing D'man and Timahdite Moroccan breeds. The crossbreeding parameters were fitted as covariates in the model of analysis. The REML method was used to estimate (co)variance components using an animal model. The first estimation of crossbreeding effects for Timahdite and D'man breeds shows that breed differences in litter traits are mainly of maternal genetic origin: +1.04 lambs, +1.88 kg, +0.60 lambs, and +2.23 kg in favour of D'man breed for litter size at lambing, litter weight at lambing, litter size at weaning, and litter weight at 90 days, respectively. The breed differences in lamb growth and survival are also of maternal genetic origin for the majority of traits studied, but in favour of the Timahdite breed: +3.48 kg, +45 g day⁻¹ and +0.19 lambs for weight at 90 days, for average daily gain between 30 and 90 days of age, and for lamb survival to 90 days, respectively. The D'man direct genetic effect was low and negative for survival and birth weight of lambs during the first month of life. All traits studied showed positive heterosis effects. Recombination loss effects were not significant. Therefore, crossbreeding of Timahdite with D'man breeds of sheep can result in an improved efficiency of production of saleable lambs. Heritability estimates were medium for litter size but low for the other reproduction traits. Direct heritabilities were low for body weights and lamb survival at 90 days and the corresponding maternal heritabilities showed, however, low to moderate estimates. For litter traits, the estimates of genetic and phenotypic correlations were positive and particularly high for genetic correlations.     

A review of new PCR-based genetic markers and their utility to weed ecology

Several recent molecular developments provide new genetic tools for addressing difficult problems in weed ecology. In this review, we describe some of the techniques and the DNA markers they generate [including amplified fragment length polymorphisms (AFLPs), simple sequence repeats (SSRs) or microsatellites, and intron-polymerase chain reaction (intron-PCR)], contrast their relative advantages and disadvantages, and discuss how they might be used in weed research. As these new markers generally reveal higher levels of variation than other techniques, they promise to improve our understanding of breeding systems, assist in determining the origin(s) of invaders, help to resolve taxonomic boundaries and relationships between closely related taxa and enable the identification of phenotypic linked markers. In addition, compared with other techniques, some of these markers may be more cost-effective, less technically demanding and more reliable. Regardless of the marker adopted, all genetic studies will benefit from careful consideration of experimental design and the formulation of testable hypotheses with practical outcomes.     

小麦光温敏核雄性不育系BS366和BS1086杂种一代结实率研究

为了解小麦光温敏核雄性不育系BS366和BS1086的育性恢复状况,评估恢复系人工定向改良对其恢复能力的效果,在不育生态区对以55份定向改良的恢复系和33份非改良恢复系(常规小麦)为父本配制的杂种一代的结实率进行了分析。结果表明,BS366和BS1086杂种一代结实率变化范围为15.42%～140.34%和20.28%～119.07%(国际法),平均结实率分别为73.02%和72.21%,二者差异不显著,说明2份母本的育性恢复能力差异不显著。BS366和BS1086杂种一代结实率主要分布于40%～110%和60%～100%间,BS1086杂种一代结实率分布更为集中。BS366和BS1086与改良父本的杂种一代平均结实率分别为84.45%和78.97%,与非改良父本的杂种一代平均结实率分别为53.97%和60.95%,改良父本的平均恢复力高于非改良父本,表明定向改良有利于提高恢复系的恢复力。BS366和BS1086与相同父本的杂种一代结实率差异在-41.66%～61.93%之间,表明相同父本对不同母本的育性恢复力存在差异。BS366和BS1086与相同改良父本的杂种一代中有61.82%的...     

稻瘟病抗性基因的分子定位及克隆

简述了稻瘟病抗性的两种类型,着重阐述了稻瘟病主效抗性基因的分子定位和克隆的研究进展,概述了主要分子标记的种类及其特点,分析了图位克隆法在克隆植物抗病基因中的应用,对其存在的技术瓶颈进行了探讨,并指明了克服这些技术难点的途径。     

7个水稻光温敏核不育系品种(系)的RAPD多态性分析

利用RAPD技术，从60个随机引物(10bp)中落选出了31个引物，能在供试的7个水稻光温敏核不育系不同品种(系)间扩增出180条稳定性较好的多态性片段．聚类分析结果显示，7个水稻光温敏核不育系品种(系)明量地聚为三类，其中同属于株1S体细胞诱变来的SV5，SVl0发生了较大的变异，相似系数均小于0．470，而SVl和SVl4变异较小，相似系数均大于0．890．H155与杂交亲本培矮64S的遗传差异较小，与杂交亲本株1S的遗传差异较大．该结果与田间农艺性状相符：另外，从7个水稻光温敏核不育系品种(系)的整体来看，相似系数均较大，说明遗传差异较小，遗传背景单一，从而在很大程度上限制了水稻杂种化势的利用．     

Is neutral genetic diversity related to quantitative variation in semen traits in bulls?

Conservation decisions based on neutral genetic diversity have been observed to promote retention of useful quantitative variation in biological populations. An experiment was undertaken to determine the association between microsatellite marker polymorphisms and phenotypic variation in semen production and cryosurvival traits in bulls. Thirty-five ejaculates were collected from ten bulls of two breeds and evaluated before and after cryopreservation for several semen traits. The bulls were also genotyped using a set of sixteen bovine-specific microsatellite marker loci. Fixation indices (F_ST), heterozygosity and Nei's genetic distance measures were computed from allele frequency data for each of the bulls. Molecular and phenotypic data were used to compute tri-distance matrices for the ten bulls and correlated using Mantel's test in GenAIEx 6.5. The study revealed extensive heterogeneity in semen traits, heterozygosity and F_ST values among the bulls. Large pairwise phenotypic and genetic distances were also observed. Correlation between pairwise genetic distances and phenotypic distances was significant and highly positive for sperm viability (r = .61, p < .001) and moderately positive for sperm motility (r = .40–42, p < .05) variables. For sperm morphology, ejaculate volume and sperm concentration, correlation with genetic distances was positive, low and not significantly different from zero (p > .05). A tendency for a triangular-shaped relationship between genetic and phenotypic distances for post-thaw motility and viability traits was also observed. Accordingly, association with neutral genetic diversity was absent for semen production traits and moderate to highly positive for sperm cryosurvival traits. Given these findings, conservation decisions based on neutral genetic diversity may capture variation in some adaptive traits, but not others.     

AFLP Analysis of the Phenetic Organization and Genetic Diversity in the Sugarcane Complex, Saccharum and Erianthus

Amplified fragment length polymorphism (AFLP) markers were evaluated for determining the phylogenetic relationships, and the diversity in the Saccharum complex using 30 clones belonging to S. officinarum, S. robustum, S. spontaneum, S. barberi, S. sinense and the related genus Erianthus. The phenetic tree of the species clones based on AFLP data was consistent with the known taxonomical relationships. AFLP gave higher resolution of closely related species into discrete groups than that by RAPD and RFLP markers, reported earlier. The levels of diversity within the various Saccharum species were also found to be higher than those obtained previously with the same set of clones using RAPD markers. The intraspecies similarity in S. barberi and S. sinense was much higher than interspecies similarity suggesting a clear separation of the two, which are considered ‘horticultural species’. The genetic similarity matrix derived from a single primer combination highly correlated (r = 0.980) with that obtained from all the 12 primer combination used in the study, thus highlighting the efficiency of a single primer combination in delineating species relationships. All the primer combinations could identify markers that are specific to each of the species and the genus Erianthus. Among the species, specific markers were highest in S. spontaneum followed by S. robustum, S. barberi, S. officinarum and S. sinense. Erianthus had a distinct profile with 30% of the total amplified fragments being specific to it. This offers great scope for identifying intergeneric hybrids, which has been very difficult using morphological traits and RAPD markers. High degree of correspondence between the results from the cluster analysis based on Jaccard's similarity index, Neighbour Joining tree based on Sokal and Michener distance matrix and AFTD (Analyses Factorielle on Table of Distances) analysis clearly demonstrated that AFLP markers would be an appropriate tool in providing better information about the relationships among the species, estimation of diversity, and in revealing species and genus specific markers that could be directly applied in sugarcane breeding programmes.