Two decades of suspect evidence for adaptive molecular evolution—negative selection confounding positive-selection signals

There has been a large literature in the last two decades affirming adaptive DNA sequence evolution between species. The main lines of evidence are from (i) the McDonald-Kreitman (MK) test, which compares divergence and polymorphism data, and (ii) the phylogenetic analysis by maximum likelihood (PAML) test, which analyzes multispecies divergence data. Here, we apply these two tests concurrently to genomic data of Drosophila and Arabidopsis. To our surprise, the >100 genes identified by the two tests do not overlap beyond random expectation. Because the non-concordance could be due to low powers leading to high false negatives, we merge every 20–30 genes into a ‘supergene’. At the supergene level, the power of detection is large but the calls still do not overlap. We rule out methodological reasons for the non-concordance. In particular, extensive simulations fail to find scenarios whereby positive selection can only be detected by either MK or PAML, but not both. Since molecular evolution is governed by positive and negative selection concurrently, a fundamental assumption for estimating one of these (say, positive selection) is that the other is constant. However, in a broad survey of primates, birds, Drosophila and Arabidopsis, we found that negative selection rarely stays constant for long in evolution. As a consequence, the variation in negative selection is often misconstrued as a signal of positive selection. In conclusion, MK, PAML and any method that examines genomic sequence evolution has to explicitly address the variation in negative selection before estimating positive selection. In a companion study, we propose a possible path forward in two stages—first, by mapping out the changes in negative selection and then using this map to estimate positive selection. For now, the large literature on positive selection between species has to await reassessment.     

信息技术环境下初中化学教学改革研究

随着信息时代的到来,传统的初中化学课堂教学活动发生了很大改变,越来越多的现代化技术被应用到初中化学教学活动中,极大程度地促进了课堂教学效果的提升.对此,在实践中,初中化学教师必须意识到信息技术对于化学教学改革产生的积极影响,并结合实际教学情况,灵活地应用信息技术优化课堂教学活动,以此促进学生的良好发展.     

博古学研究与欧洲近代早期自然史的复兴探析

博古学者对史料的搜集和整理,为后世史学家的深入研究提供材料,并使古希腊、古罗马时期探究事物的根本方法,即自然史在近代欧洲再次盛行。随着自然史的复兴,历史研究开始对知识本身有更深刻的诉求。博古学者借用自然史的方法,质疑古代作品的真实性,将实物史料中蕴含的经验知识纳入历史研究的范畴。学者们提高了对事实的敏感度,想象和虚构也变得不再容易,开始与古典史学那种修辞、演讲的功用有了明显的区分。     

论综合实践活动课程开发的自然维度

综合实践活动课程是基于现实世界视野对生活的探究与体验,自然世界本身成为课程.超越对自然的役用与膜拜,走向对自然的理解、欣赏与看护,是综合实践活动自然维度开发的基本原则."在自然中"的自然探究、"关于自然"的自然探究和"为了自然"的自然探究是综合实践活动自然维度开发的基本内容.此外,在开发的过程中尚须注意季节的变化、在自然探究中渗透人文精神并引导学生慎重对待探究结论.     

关于思维导图在初中化学实验复习中的应用研究

在初中化学复习课教学的过程中,为了加深学生对化学知识的理解,教师要合理运用思维导图的教学模式,将琐碎的知识点以图文的形式展现在学生面前,方便学生记忆的同时还能标注出知识的重点与难点,促使学生能高效解答实验习题.基于此,本文主要围绕初中化学复习课应用思维导图开展分析,并阐述了应用对策,仅供参考.     

Natural selection contributes to the myopia epidemic

The prevalence of myopia, or nearsightedness, has skyrocketed in the past few decades, creating a public health crisis that is commonly attributed to lifestyle changes. Here we report an overall increase in the frequencies of myopia-associated mutant alleles over 25 years among participants of the UK Biobank. Although myopia itself appears to be selected against, many of the mutant alleles are associated with reproductive benefits, suggesting that reproduction-related selection inadvertently contributes to the myopia epidemic. We estimate that, in the UK alone, natural selection adds more than 100 000 myopia cases per generation, and argue that antagonistic pleiotropy be broadly considered in explaining the spreads of apparently disadvantageous phenotypes in humans and beyond.     

“一题十想”实现习题效能最大化

针对学生做了大量习题但收效却不大这种教学中常见的现象，分析了原因，并指出教师要通过引导学生“一题十想”，明晰解题思路，总结解题规律，实现习题效能的最大化。     

农科院校无机及分析化学课程分层教学方法的应用

针对扩招后学生水平差异的显著,根据最近发展区理论,在我校《无机及分析化学》基础课教学中进行分层教学法的实践,按能力对学生进行分组,同时设计多层次的教学目标,有针对有区别地设计教学内容,控制教学进度,促进每个学生在最适合自己的目标层次中求得最佳发展,从而改进传统的大班"一刀切"的授课方式,强化学生的主体地位,有效地提高《无机及分析化学》大班教学的质量,更好地实现扩招后"大众化""多元化"的教育目标。     

The cumulative and residual fatigue response associated with soccer-specific activity performed on different playing surfaces

ABSTRACT

This study aimed to assess the effect of playing surface (Natural [NT] and Artificial [AT] Turf) on the fatigue response to a soccer-specific exercise protocol (SSEP). Eighteen male soccer players completed the SSEP on NT and AT with pre-, post-, and 48 h post-assessments of eccentric knee flexor (eccKF) and concentric knee extensor peak torque (PT), peak countermovement (CMJ) and squat jump (SJ) height, and Nordic hamstring break angle. No significant main effects for surface or any surface and time interactions were observed for any of the outcome measures, except for eccKF PT recorded at 3.14 rad·s^-1, which was significantly lower 48 h post-trial in the AT condition (AT = 146.3 ± 20.4 Nm; NT = 158.8 ± 24.7 Nm). Main effects for time were observed between pre- and post-trial measures for eccKF PT at all angular velocities, Nordic break angle, CMJ and SJ height. Nordic break angle, and both CMJ and SJ height were significantly impaired 48 h post-trial when compared to pre-trial. The findings of the current study suggest surface dependent changes in eccKF PT which may have implications for recovery and subsequent performance after competition on AT.     

工程化素质培养:应用化学专业实践教学改革

工程化素质是本科生进入社会进行科研、工程设计、工程施工等工作必须具备的素质。文章结合许昌学院应用化学专业的办学实际,从实验课程、实习实训和毕业论文(设计)三个实践教学环节论述了工程化素质培养的创新做法及其实践效果,并提出了改进措施。