THE MEASUREMENT OF SELECTION ON QUANTITATIVE TRAITS: BIASES DUE TO ENVIRONMENTAL COVARIANCES BETWEEN TRAITS AND FITNESS

The use of regression techniques for estimating the direction and magnitude of selection from measurements on phenotypes has become widespread in field studies. A potential problem with these techniques is that environmental correlations between fitness and the traits examined may produce biased estimates of selection gradients. This report demonstrates that the phenotypic covariance between fitness and a trait, used as an estimate of the selection differential in estimating selection gradients, has two components: a component induced by selection itself and a component due to the effect of environmental factors on fitness. The second component is shown to be responsible for biases in estimates of selection gradients. The use of regressions involving genotypic and breeding values instead of phenotypic values can yield estimates of selection gradients that are not biased by environmental covariances. Statistical methods for estimating the coefficients of such regressions, and for testing for biases in regressions involving phenotypic values, are described.     

Physiological and Molecular Basis of Susceptibility and Tolerance of Rice Plants to Complete Submergence

Rice plants are much damaged by several days of total submergence.The effect can be a serious problem for rice farmers in therainfed lowlands of Asia, and runs contrary to a widespreadbelief amongst plant biologists that rice is highly tolerantof submergence. This article assesses the characteristics ofthe underwater environment that may damage rice plants, examinesvarious physiological mechanisms of injury, and reviews recentprogress achieved using linkage mapping to locate quantitativetraits loci (QTL) for tolerance inherited from a submergence-tolerantcultivar FR13A. Progress towards identifying the gene(s) involvedthrough physical mapping of a dominant tolerance locus on chromosome9 is also summarized. Available physiological evidence pointsaway from responses to oxygen shortage as being inextricablyinvolved in submergence injury. An imbalance between productionand consumption of assimilates is seen as being especially harmful,and is exacerbated by strongly accelerated leaf extension andleaf senescence that are ethylene-mediated and largely absentfrom FR13A and related cultivars. DNA markers for a major QTLfor tolerance are shown to be potentially useful in breedingprogrammes designed to improve submergence tolerance.     

RT－PCR联合一步法扩增G蛋白α亚基基因的开放阅读框

报道逆转录－多聚酶链式反应（ＲＴ－ＰＣＲ）联合一步程序,扩增大于１ｋｂ的拟南芥菜Ｇ蛋白α亚基基因的开放阅读框,该程序中,当ＲＮＡ模板和引物变性,并在同一管中加入ＰＣＲ缓冲液,４种ｄＮＴＰ底物,逆转录酶和ＴａｑＤＮＡ聚合酶之后,就不需其它手工操作步骤,因而可同时进行大批量样品的操作,实验结果证明ＡＭＶ（鸟类骨髓性白血病病毒）逆转录酶对ＴａｑＤＮＡ聚合酶的活性没有抑制作用,这种ＲＴ－ＰＣＲ联合一步法可     

MUSCARINIC ACETYLCHOLINE RECEPTOR SUBTYPE mRNAs IN THE HUMAN AND RAT VESTIBULAR PERIPHERY

The expression of the five muscarinic acetylcholine receptor (mAChR) subtypes (m1–m5) in the vestibular end-organs and in the primary afferent vestibular ganglia of the human and rat was studied using RT-PCR from the two tissue populations from both species. In the human, although all five mAChR subtypes were expressed in brain, only the m1, m2, and m5 mAChR subtypes were amplified from both the vestibular ganglia and the vestibular end-organs, while in the rat, all five mAChR subtypes were expressed. These data suggest that the efferent cholinergic axo-dendritic and axo-somatic synapses have a muscarinic component and that there are pharmacologic implications for patients with vestibular dysfunction.     

LDL受体基因cDNA的RT－PCR分离、克隆及其在RFLP中的应用

利用ＲＴ－ＰＣＲ技术分离低密度脂蛋白受体基因ｃＤＮＡ,将长为２６０５ｂｐ的ｃＤＮＡ插入质粒ｐＪＮ６,并经全序列测定证实,该序列与已报道序列相比,存在两个变异碱基,即第７５４位Ｃ→Ｔ,和１６５４位的Ｇ→Ａ,这两个变异碱基并不改变编码的氨基酸,利用ＬＤＬ受体基因ｃＤＮＡ中的ＣｌａⅠ片段作为探针,检测到ＬＤＬ受体基因上外显子８的ＳｔｕⅠ位点是个限制性片段长度多态性位点。所克隆的ｃＤＮＡ含有可译框架的全部密码,因此可作为基因表达材料。     

Causes of covariation of phenotypic traits among populations

Morphological and life-history traits often vary among populations of a species. Traits generally do not vary independently, but show patterns of covariation that can arise from genetic and environmental influences on phenotype. Covariance of traits may arise at an among-population level when genetically influenced traits diverge among populations in a correlated manner. Genetic correlations caused by pleiotropy and/or gene linkage can cause traits to evolve together, but among-population covariance can also arise among traits that are not genetically correlated. For example, “selective covariance” can arise when natural selection directly causes correlated change in a suite of traits. Similarly, mutation, migration, and drift may also sometimes cause correlated genetic changes among populations. Because covariation of traits among populations can arise by several different processes, the evolution of suites of traits must be interpreted with great caution. We discuss the sources of among-population covariance and illustrate one approach to identifying the sources' using data on floral traits of Dalechampia scandens (Euphorbiaceae).     

OPTIMIZATION OF AN IMMUNOFLUORESCENT ASSAY OF THE INTERNAL ENZYME RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE (RUBISCO) IN SINGLE PHYTOPLANKTON CELLS1

Immunochemical probes are widely used to identih different species and to quantify and understand the role that different antigens play within cells. We optimized a single-cell immunofluorescent assay for the carbon fixation enzyme ribulose-1,5-bisphosphate carboxylase (Rubisco) in order to quantify the enzyme by flow cytometry in phytoplankton cells. The criteria for optimization of the immunofluorescent assay for Rubisco in single cells included maximization of Rubisco immunogenicity, minimization of Rubisco diffusion out of the cells, minimization of cell breakage, and maximization of the cell labeling. Several fixatives (cross-linkers and denaturing) and permeabilizing agents were tested on 26 species of phytoplankton. The only fixative / permeabilizing agent that fulfilled the criteria established for the assay was 96% ethanol. Phytoplankton cells collected from the field needed further treatment with a strong oxidant to permeabilize ethanolfixed cells and thus allow the antibody probe to access the Rubisco antigen. This study should have a general applicability to the study of other soluble photosynthetic antigens in single phytoplankton cells.     

Repair mechanisms of UV-induced DNA damage in soybean chloroplasts

In order to better understand the biochemical mechanisms of DNA metabolism in chloroplasts, repair of UV induced plastome damage in vivo was determined by exposure of soybean suspension cells to UV light and subsequent quantitation of the damage remaining in nuclear and chloroplast encoded genes with time by quantitative polymerase chain reaction (QPCR). The kinetics of damage rapir in the nuclear rbcS gene suggest that photoreactivation and dark mechanisms are active, while for the plastome encoded psbA gene only a light-dependent repair process was detected which is considerably slower than would be expected for photolyase-mediated photoreactivation.