Sexually antagonistic genetic variation for fitness in red deer

Evolutionary theory predicts the depletion of genetic variation in natural populations as a result of the effects of selection, but genetic variation is nevertheless abundant for many traits that are under directional or stabilizing selection. Evolutionary geneticists commonly try to explain this paradox with mechanisms that lead to a balance between mutation and selection. However, theoretical predictions of equilibrium genetic variance under mutation-selection balance are usually lower than the observed values, and the reason for this is unknown. The potential role of sexually antagonistic selection in maintaining genetic variation has received little attention in this debate, surprisingly given its potential ubiquity in dioecious organisms. At fitness-related loci, a given genotype may be selected in opposite directions in the two sexes. Such sexually antagonistic selection will reduce the otherwise-expected positive genetic correlation between male and female fitness. Both theory and experimental data suggest that males and females of the same species may have divergent genetic optima, but supporting data from wild populations are still scarce. Here we present evidence for sexually antagonistic fitness variation in a natural population, using data from a long-term study of red deer (Cervus elaphus). We show that male red deer with relatively high fitness fathered, on average, daughters with relatively low fitness. This was due to a negative genetic correlation between estimates of fitness in males and females. In particular, we show that selection favours males that carry low breeding values for female fitness. Our results demonstrate that sexually antagonistic selection can lead to a trade-off between the optimal genotypes for males and females; this mechanism will have profound effects on the operation of selection and the maintenance of genetic variation in natural populations.     

Genome-wide detection and characterization of positive selection in human populations

With the advent of dense maps of human genetic variation, it is now possible to detect positive natural selection across the human genome. Here we report an analysis of over 3 million polymorphisms from the International HapMap Project Phase 2 (HapMap2). We used 'long-range haplotype' methods, which were developed to identify alleles segregating in a population that have undergone recent selection, and we also developed new methods that are based on cross-population comparisons to discover alleles that have swept to near-fixation within a population. The analysis reveals more than 300 strong candidate regions. Focusing on the strongest 22 regions, we develop a heuristic for scrutinizing these regions to identify candidate targets of selection. In a complementary analysis, we identify 26 non-synonymous, coding, single nucleotide polymorphisms showing regional evidence of positive selection. Examination of these candidates highlights three cases in which two genes in a common biological process have apparently undergone positive selection in the same population:LARGE and DMD, both related to infection by the Lassa virus, in West Africa;SLC24A5 and SLC45A2, both involved in skin pigmentation, in Europe; and EDAR and EDA2R, both involved in development of hair follicles, in Asia.     

阴阳直径等分圆的和谐美

用阴阳直径等分圆得到的圆形图案,有简单、对称、和谐之美。     

Oxysterols direct immune cell migration via EBI2

Epstein-Barr virus-induced gene 2 (EBI2, also known as GPR183) is a G-protein-coupled receptor that is required for humoral immune responses; polymorphisms in the receptor have been associated with inflammatory autoimmune diseases. The natural ligand for EBI2 has been unknown. Here we describe the identification of 7α,25-dihydroxycholesterol (also called 7α,25-OHC or 5-cholesten-3β,7α,25-triol) as a potent and selective agonist of EBI2. Functional activation of human EBI2 by 7α,25-OHC and closely related oxysterols was verified by monitoring second messenger readouts and saturable, high-affinity radioligand binding. Furthermore, we find that 7α,25-OHC and closely related oxysterols act as chemoattractants for immune cells expressing EBI2 by directing cell migration in vitro and in vivo. A critical enzyme required for the generation of 7α,25-OHC is cholesterol 25-hydroxylase (CH25H). Similar to EBI2 receptor knockout mice, mice deficient in CH25H fail to position activated B cells within the spleen to the outer follicle and mount a reduced plasma cell response after an immune challenge. This demonstrates that CH25H generates EBI2 biological activity in vivo and indicates that the EBI2-oxysterol signalling pathway has an important role in the adaptive immune response.     

高校体育专业篮球课学生运动损伤情况的调查与研究——以漳州师范学院为例

本文主要运用了文献资料法、问卷调查法、访谈法、数理统计法等研究方法,对漳州师院体育系篮球专项学生的运动损伤情况进行调查.通过调查发现：我系篮球专项学生的运动损伤情况较严重,发生损伤的部位多集中在踝部和膝部.发生损伤的原因主要有：旧伤病未痊愈、准备活动不充分等.结合我系篮球专项学生运动损伤的特点,提出相关的预防措施和建议,为减少运动损伤的发生,保证我院篮球运动的正常开展提供科学的依据.