Estimation of the position and effect of a lethal factor locus on a molecular marker linkage map

In the mapping of DNA markers the distortion of segregation of marker genotypes is often observed, which may be caused by a lethal factor acting in filial generations derived from distant crosses. A method is presented for estimating the recombination values between a lethal factor locus and neighboring molecular markers, and the relative viability or fertilization ability of gametes or zygotes affected by the lethal factor in an F₂ population using the maximum likelihood method and the expectation conditional maximization (ECM) algorithm. Three selection models of gamete or zygote were considered, and the most likely one was determined by goodness of fit of the observed frequency of the phenotypes to the expected ones under the models. The method was applied to segregation data of molecular markers of an F₂ population consisting of 144 individuals derived from a cross between an Indica and a Japonica rice variety. The presence of a lethal factor locus (L) located on chromosome III that caused partial gametic selection in both the male and female sides was suggested. The locus L was tightly linked to RFLP marker number 23 of the RFLP linkage map of Saito et al. (1991a), and the fertilization chance of a male or female gamete possessing the lethal factor was, on average, 41.5% of that of the normal gamete.     

Unilateral incompatibility as a major cause of skewed segregation in the cross between Lycopersicon esculentum and L. pennellii

Skewed segregations are frequent events in segregating populations derived from different interspecific crosses in tomato. To determine a basis for skewed segregations in the progeny of the cross between Lycopersicon esculentum and L. pennellii, monogenic segregations of 16 isozyme loci were analyzed in an F₂ and two backcross populations of this cross. In the F₂, 9 loci mapping to chromosomes 1, 2, 4, 9, 10 and 12 exhibited skewed segregations and in all cases there was an excess of L. pennellii homozygotes. The genotypic frequencies at all but one locus were at Hardy-Weinberg equilibria. In the backcross populations, all except two loci exhibited normal Mendelian segregations. No post-zygotic selection model could statistically or biologically explain the observed segregation patterns in the F₂ and backcross populations. A pre-zygotic selection model, assuming selective elimination of the male gametophytes during pollen function (i.e., from pollination to karyogamy), could adequately explain the observed segregations in all three populations. The direction of the skewed segregations in the F₂ population was consistent with that expected based on the effects of unilateral incompatibility reactions between the two species. In addition, the chromosomal locations of 5 of the 9 markers that exhibited skewed segregations coincided with the locations of several known compatibility-related genes in tomato. Multigenic unilateral incompatibility reactions between L. esculentum pollen and the stigma or style of L. pennellii (or its hybrid derivatives) are suggested to be the major cause of the skewed segregations in the F₂ progeny of this cross.     

A molecular marker-based linkage map of diploid bananas (Musa acuminata)

A partial molecular linkage map of the Musa acuminata diploid genome is presented. This map is based on 58 RFLP, four isozyme and 28 RAPD markers segregating in an F₂ population of 92 individuals. A total of 90 loci was detected, 77 of which were placed on 15 linkage groups while 13 segregated independently. Segregation distortions were shown by 36% of all loci, mostly favoring the male parent. Chromosome structural rearrangements were believed to be one of the main causes of these distortions. The use of genetic linkage data to further the genetic and evolutionary knowledge of the genus Musa, as well as to help improve the design of breeding strategies, is discussed.     

Effects of dynamic impacts on human bones

Flat bones of human skeleton were subjected to dynamic indentation with ball indenters. The impacted surface was studied under high magnification and also by using the technique of multiple beam interferometry. The impulse caused the pile up of material at a little distance from the edge of the indent. The diameter of indent is found to increase as fourth root of the energy of impact. Bone structure also has the tendency to minimize the damage caused by external forces. There was about 90% recovery in deformation in the depth of indents due to internal stresses created inside the bone by the impact.     

兰属(Cymbidium)5种植物叶结构特征

采用光学显微镜和体视镜,对兰属5种植物（春兰、蕙兰、建兰、寒兰、墨兰）的叶结构特征（叶脉结构、叶表皮结构、解剖结构）进行了观察和测量。结果显示,兰属5种植物的叶脉结构相似,叶表皮结构和解剖结构存在较大差异,其中最主要的差异是皮下纤维束的多少和边缘角质层锯齿形态。依据叶结构特征聚类分析结果,5种兰可分为春兰组、建兰组和墨兰组3组。本研究表明叶结构特征对兰属5种植物的分类具有重要意义。     

Destruction and reconstitution of the dictyosome in the chrysophycean flagellate,Poterioochromonas malhamensis,after heat-shock,and other heat-shock effects

Summary The viability of the chrysophycean flagellate,Poterioochromonas malhamensis, was examined after treatment of the cells with high temperatures. The fine structure of the cells was studied after heat-shock (42 °C, 16 minutes). Heat injury effects are visible at the nucleus, the chloroplast (distortion of the thylakoids), the mitochondria (increased occurrence of matrical crystalline inclusions) and, especially, at the dictyosome which is completely destroyed into some single vesicles and remnants of cisternae. Most damages are repaired within one hour; the reconstitution of the dictyosome takes 3–6 hours. It is inhibited severely by actinomycin D.The effect on the dictyosome reflects its labile position in the endomembrane system. The dependence of its reconstitution on protein synthesis indicates that membrane components are destroyed by the heat-shock.     

A quantitative structure-activity relationship study for structurally diverse HIV-1 protease inhibitors: contribution of conformational flexibility to inhibitory activity

In this study, we investigated by linear regression model the SAR data of the 15 HIV-1 protease inhibitors possessing structurally diverse scaffolds. First, a regression model was developed only using the enzyme-inhibitor interaction energy as a term of the model, but did not provide a good correlation with the inhibitory activity (R² = 0.580 and Q² = 0.500). Then, we focused on the conformational flexibility of the inhibitors which may represent the diversity of the inhibitors, and added two conformational parameters into the model, respectively: the number of rotatable bonds of ligands (ΔSrot) and the distortion energy of ligands (ΔElig). The regression model by adding ΔElig successfully improved the quality of the model (R² = 0.771 and Q² = 0.713) while the model with ΔSrot was unsuccessful. The prediction for a training inhibitor by the ΔElig model also showed good agreement with experimental activity. These results suggest that the conformational flexibility of HIV-1 protease inhibitors directly contributes to the enzyme inhibition.     

Double the Capacity of Manganese Spinel for Lithium‐Ion Storage by Suppression of Cooperative Jahn–Teller Distortion

The relatively low capacity and capacity fade of spinel LiMn₂O₄ (LMO) limit its application as a cathode material for lithium‐ion batteries. Extending the potential window of LMO below 3 V to access double capacity would be fantastic but hard to be realized, as it will lead to fast capacity loss due to the serious Jahn–Teller distortion. Here using experiments combined with extensive ab initio calculations, it is proved that there is a cooperative effect among individual Jahn–Teller distortions of Mn³⁺O₆ octahedrons in LMO, named as cooperative Jahn–Teller distortion (CJTD) in the text, which is the difficulty to access the capacity beyond one lithium intercalation. It is further proposed that the cationic disordering (excess Li at Mn sites and Li/Mn exchange) can intrinsically suppress the CJTD of Mn³⁺O₆ octahedrons. The cationic disordering can break the symmetry of Mn³⁺ arrangements to disrupt the correlation of distortions arising from individual JT centers and prevent the Mn³⁺? O bonds distorting along one direction. Interestingly, with the suppressed CJTD, the original octahedral vacancies in spinel LMO are activated and can serve as extra Li‐ion storage sites to access the double capacity with good reversible cycling stability in microsized LMO.     

Pseudo-natural products and natural product-inspired methods in chemical biology and drug discovery

Through evolution, nature has provided natural products (NPs) as a rich source of diverse bioactive material. Many drug discovery programs have used nature as an inspiration for the design of NP-like compound classes. These concepts are guided by the prevalidated biological relevance of NPs while going beyond the limitations of nature to produce chemical matter that could have unexpected or novel bioactivities. Herein, we discuss, compare, and highlight recent examples of NP-inspired methods with a focus on the pseudo-NP concept.