Independent evolution of bitter-taste sensitivity in humans and chimpanzees

It was reported over 65 years ago that chimpanzees, like humans, vary in taste sensitivity to the bitter compound phenylthiocarbamide (PTC). This was suggested to be the result of a shared balanced polymorphism, defining the first, and now classic, example of the effects of balancing selection in great apes. In humans, variable PTC sensitivity is largely controlled by the segregation of two common alleles at the TAS2R38 locus, which encode receptor variants with different ligand affinities. Here we show that PTC taste sensitivity in chimpanzees is also controlled by two common alleles of TAS2R38; however, neither of these alleles is shared with humans. Instead, a mutation of the initiation codon results in the use of an alternative downstream start codon and production of a truncated receptor variant that fails to respond to PTC in vitro. Association testing of PTC sensitivity in a cohort of captive chimpanzees confirmed that chimpanzee TAS2R38 genotype accurately predicts taster status in vivo. Therefore, although Fisher et al.'s observations were accurate, their explanation was wrong. Humans and chimpanzees share variable taste sensitivity to bitter compounds mediated by PTC receptor variants, but the molecular basis of this variation has arisen twice, independently, in the two species.     

Comparison of amino acid sequence of troponin I from different striated muscles.

The sequence of troponin I from fast and slow skeletal and cardiac muscle shows strong homology in the region which binds to actin and is responsible for inhibition of the actomyosin AT Pase. More differences are found in the N-terminal region which binds to troponin C.     

Independent evolution of structural and coding regions in a Neurospora mitochondrial intron

The discovery of intervening sequences (introns) in eukaryotic genes has raised questions about the origin and evolution of these sequences. Hypotheses concerning these topics usually consider the intron as a unit that could be lost or gained over time, or as a region within which recombination can occur to facilitate the production of new proteins by exon shuffling. Additional complexities are observed in introns of mitochondrial and chloroplast genes which contain secondary structures required for messenger RNA splicing and open-reading frames encoding proteins. Here we describe differences in the organization of protein-coding sequences in the intron of the mitochondrial ND1 gene in two closely related species of Neurospora. These differences show that intron sequences involved in secondary structure formation and in protein coding can evolve as physically distinct elements. Indeed, the secondary structure elements of the ND1 intron can contain two different coding sequences located at two different positions within the intron.     

Independent recruitment of a conserved developmental mechanism during leaf evolution

Vascular plants evolved in the Middle to Late Silurian period, about 420 million years ago. The fossil record indicates that these primitive plants had branched stems with sporangia but no leaves. Leaf-like lateral outgrowths subsequently evolved on at least two independent occasions. In extant plants, these events are represented by microphyllous leaves in lycophytes (clubmosses, spikemosses and quillworts) and megaphyllous leaves in euphyllophytes (ferns, gymnosperms and angiosperms). Our current understanding of how leaves develop is restricted to processes that operate during megaphyll formation. Because microphylls and megaphylls evolved independently, different mechanisms might be required for leaf formation. Here we show that this is not so. Gene expression data from a microphyllous lycophyte, phylogenetic analyses, and a cross-species complementation experiment all show that a common developmental mechanism can underpin both microphyll and megaphyll formation. We propose that this mechanism might have operated originally in the context of primitive plant apices to facilitate bifurcation. Recruitment of this pathway to form leaves occurred independently and in parallel in different plant lineages.     

Comparison of alpha-tropomyosin sequences from smooth and striated muscle

Tropomyosins are a closely related family of proteins with a dimeric alpha-coiled-coil structure. Skeletal isoforms are composed of two types of subunits, alpha and beta which, in turn, are assorted into two main molecular species alpha alpha and alpha beta. Both isoforms are present in different molar ratios in individual skeletal muscle types. In small mammals, however, only alpha-chain is expressed in cardiac muscle. Tropomyosin, in association with the troponin complex (troponin-I, -T and -C) plays a central role in the Ca2+-dependent regulation of vertebrate striated muscle contraction. On the other hand, despite structural similarities with the striated isoforms, the function of this protein in smooth muscle and non-muscle cells remains unknown, because in these cells contraction is thought to be regulated by myosin-linked processes independently of tropomyosin. Here we report the nucleotide sequences of cloned complementary DNAs for rat striated and smooth muscle alpha-tropomyosin. Comparison of the derived amino-acid sequences reveals the existence of tissue-specific peptides that delimit the putative troponin-I and troponin-T binding domains of tropomyosin. S1-nuclease mapping studies reveal the existence of three distinct alpha-tropomyosin messenger RNA isoforms each encoding a different protein; these isoforms are tissue-specific, developmentally regulated and most probably encoded by the same gene.     

独立学院非英语专业学生英语自主学习能力的培养

根据《大学英语课程教学要求》,很多高校都在实施基于计算机和课堂的英语教学模式,将课堂教学与学生的自主学习结合起来。在传统的教学中,学生对于教师的依赖很大。因此学生自主学习能力的培养需要很长一段时间,尤其是在独立学院。自主学习首先要想学,然后才能学习如何来学。因此自主学习能力的培养需要先培养学生自主学习的愿望,然后再培养其自主学习的能力。独立学院侧重于应用型人才的培养,因此在自主学习能力培养的过程中,要因人制宜,结合其专业、未来择业、个人兴趣爱好、学习特点制定不同的计划,进行有侧重的培养,以最大程度的发挥学生的特长,满足未来工作的需要。     

股后肌和小腿三头肌蹬地拉伤的分析

采集了不同运动项目引起的股后肌和小腿三头肌蹬地拉伤的病例92份,结果表明,业余运动员蹬地动作引起股后肌和小腿三头肌的拉伤,其中半腱肌和半膜肌拉伤多于股二头肌,腓肠肌内侧头拉伤多于外侧,腿后屈肌的后内侧部多于后外侧部,疾跑后蹬引起肌肉拉伤的部位多偏向于股后,向上跳起的蹬地动作引起肌肉拉伤的部位似有相对下移小腿的趋势.     

论独立担保中担保人的权利与义务

文章通过分析独立担保中的主体——担保人的权利与义务，试图揭示独立担保中的一些热点问题。     

二分图中相互独立的圈

证明了下面的结论：设k≥1是一个整数，G＝（V1,V2；E）是一个二分图，满足|V1|=|V2|=n≥2k 1。若对G中任意两个不相邻的面点x∈V1，y∈V2，都有d(x) d(y)≥2k 2，并且δ（G）≥2，则G包含k个相互独立的图。     

自主创新与法律风险

自主创新已经成为我国政府和公民的共同追求。然而,自主创新作为一项涉及各方利益主体和多重法律关系的资源运用与价值创造活动,必然与法律风险相伴而生、相携而行。有效的法律风险防范工作,可以起到掌握创新法治动态、激励共同创新、巩固创新成果、促进成果转化等作用,成为促进自主创新的有效保障。