The molecular clock runs more slowly in man than in apes and monkeys

The molecular clock hypothesis postulates that the rate of molecular evolution is approximately constant over time. Although this hypothesis has been highly controversial in the past, it is now widely accepted. The assumption of rate constancy has often been taken as a basis for reconstructing the phylogenetic relationships among organisms or genes and for dating evolutionary events. Further, it has been taken as strong support for the neutral mutation hypothesis, which postulates that the majority of molecular changes in evolution are due to neutral or nearly neutral mutations. For these reasons, the validity of the rate constancy assumption is a vital issue in molecular evolution. Recent studies using DNA sequence data have raised serious doubts about the hypothesis. These studies provided support for the suggestion made from immunological distance and protein sequence data that a rate slowdown has occurred in hominoid evolution, and showed, in agreement with DNA hybridization studies, that rates of nucleotide substitution are significantly higher in rodents than in man. Here, rates of nucleotide substitution in rodents are estimated to be 4-10 times higher than those in higher primates and 2-4 times higher than those in artiodactyls. Further, this study provides strong evidence for the hominoid slowdown hypothesis and suggests a further rate-slowdown in hominoid evolution. Our results suggest that the variation in rate among mammals is primarily due to differences in generation time rather than changes in DNA repair mechanisms. We also propose a method for estimating the divergence times between species when the rate constancy assumption is violated.     

Sperm competition: motility and the midpiece in primates

In animals with multiple-partner mating systems, the gametes of two or more males must compete to fertilize a given set of ova. Here we show that the volume of the midpiece in individual sperm is significantly greater in primate species in which the females mate with multiple partners, and in which males have larger testes in relation to their body weight, than in those species that mate with only one partner and have relatively small testes. Our results indicate that sexual selection by sperm competition has influenced the evolution of a specific component of male-gamete morphology, the volume of the sperm midpiece.     

浙江省第十二届大学生运动会男排攻防技术效果分析——浙江师范大学与其他院校的比较研究

为了充分了解浙江省普通高校非体育专业学生的排球技术水平,通过文献资料法、录像分析法和数理统计法对参加浙江省第十二届大学生运动会男子排球比赛的9支球队在进攻和防守保护2个方面的各项数据进行了统计分析.结果显示:浙江师范大学男排在接发球、二传、防守3项技术上明显优于其他队的平均水平,在发球、扣球和拦网技术上也有优势但是不明显,特别是和传统强队——浙江大学男排相比在进攻技术、战术上还存在一定的差距.     

Thiobase DNA: the chemistry and some applications in cancer studies

This article reviews the chemical methods for preparation of base-modified DNA with a particular focus on thiobases. Thiobases have certain unique properties, such as easy alkylation, ready oxidation and strong absorption in the near UV longer wavelength. These chemical and physical properties are retained in DNA containing thiobase and are useful for chemical manipulation and photo crosslinking of these modified DNA with other biomolecules of interest. The ability to make DNA containing thiobases or their functionalized analogues has added new research tools for DNA repair studies, and it is believed that such modified DNA can be of great use in many biological studies.     

Plasma protease inhibitors in mouse and man: divergence within the reactive centre regions

The plasma protease inhibitors control a wide variety of physiological functions including blood coagulation, complement activation and aspects of the inflammatory response. The inhibitors function by forming a 1:1 complex with a specific protease within the reactive centre region of the inhibitor. Little is known about the evolutionary relationships of these inhibitors. We report here the sequences of cDNAs which represent the C-terminal halves of the two major murine plasma protease inhibitors. One of these, murine alpha 1-antitrypsin, more appropriately called alpha 1-proteinase inhibitor (alpha 1-PI), has diverged from its human counterpart at a vital position in the reactive centre but this has not led to a physiologically significant change in function. Also, we have determined the partial sequence of a recently characterized protein termed contrapsin, which inhibits trypsin-like proteases. We show, surprisingly, that contrapsin is highly homologous to human alpha 1-antichymotrypsin, an inhibitor of chymotrypsin-like proteases. The reactive centre regions of these two inhibitors have diverged considerably, which may account for the differences in specificity. We propose that the genes for contrapsin and human alpha 1-antichymotrypsin are the descendents of a single gene that have evolved since rodent and primate divergence to encode proteins with different functions.