Site-specific recombination between homologous chromosomes in Drosophila

The ability to mark a cell and its descendants genetically so that the resulting cell clone can be distinguished from neighboring cells facilitates studies in animal biology and development. A method of generating clones by inducing homologous mitotic recombination in Drosophila with a site-specific yeast recombinase is described. This method allows for frequent mosaicism after mitotic exchange is induced at predefined sites in the genome.     

Gene encoding the beta subunit of S100 protein is on chromosome 21: implications for Down syndrome

S100 protein is a calcium-binding protein found predominantly in the vertebrate nervous system. Genomic and complementary DNA probes were used in conjunction with a panel of rodent-human somatic cell hybrids to assign the gene for the beta subunit of S100 protein to the distal half of the long arm of human chromosome 21. This gene was identified as a candidate sequence which, when expressed in the trisomic state, may underlie the neurologic disturbances in Down syndrome.     

A chromosome 21 critical region does not cause specific Down syndrome phenotypes

The "Down syndrome critical region" (DSCR) is a chromosome 21 segment purported to contain genes responsible for many features of Down syndrome (DS), including craniofacial dysmorphology. We used chromosome engineering to create mice that were trisomic or monosomic for only the mouse chromosome segment orthologous to the DSCR and assessed dysmorphologies of the craniofacial skeleton that show direct parallels with DS in mice with a larger segmental trisomy. The DSCR genes were not sufficient and were largely not necessary to produce the facial phenotype. These results refute specific predictions of the prevailing hypothesis of gene action in DS.     

An aneuploid mouse strain carrying human chromosome 21 with Down syndrome phenotypes

Aneuploidies are common chromosomal defects that result in growth and developmental deficits and high levels of lethality in humans. To gain insight into the biology of aneuploidies, we manipulated mouse embryonic stem cells and generated a trans-species aneuploid mouse line that stably transmits a freely segregating, almost complete human chromosome 21 (Hsa21). This "transchromosomic" mouse line, Tc1, is a model of trisomy 21, which manifests as Down syndrome (DS) in humans, and has phenotypic alterations in behavior, synaptic plasticity, cerebellar neuronal number, heart development, and mandible size that relate to human DS. Transchromosomic mouse lines such as Tc1 may represent useful genetic tools for dissecting other human aneuploidies.     

21种常用灌木降温能力比较研究

为了对沈阳市绿化树种的合理配置提供科学依据,本文以沈阳典型城市森林类型为试验区,利用LI-6400光合作用测定系统,采用自然条件下离体定位观测和室内分析相结合的方法,在常用灌木树种蒸腾生理特性分析的基础上,首次对沈阳市主要灌木树种的降温生态环境效益进行了系统研究。结果表明,21种常用灌木单位叶面积的降温效应表现为接骨木蔷薇风箱果东北山梅花京山梅花大花水亚木五叶地锦黄刺玫水腊朝鲜黄杨鸡树条荚迷紫叶小檗金银忍冬金钟连翘珍珠绣线菊忍冬榆叶梅紫丁香锦带花红瑞木茶条槭。     

Beta amyloid gene duplication in Alzheimer's disease and karyotypically normal Down syndrome

With the recently cloned complementary DNA probe, lambda Am4 for the chromosome 21 gene encoding brain amyloid polypeptide (beta amyloid protein) of Alzheimer's disease, leukocyte DNA from three patients with sporadic Alzheimer's disease and two patients with karyotypically normal Down syndrome was found to contain three copies of this gene. Because a small region of chromosome 21 containing the ets-2 gene is duplicated in patients with Alzheimer's disease, as well as in karyotypically normal Down syndrome, duplication of a subsection of the critical segment of chromosome 21 that is duplicated in Down syndrome may be the genetic defect in Alzheimer's disease.     

Nonrandomness of translocations in man: preferential entry of chromosomes into 13-15-21 translocations

Lymphocytes from 20 individuals with Down's syndrome due to 13-15/21 centric-fusion translocations were studied by autoradiography after continuous late labeling with tritiated thymidine. In no case was chromosome 13 involved; chromosome 14 was involved in 18 cases, and chromosome 15 in two cases. These results are similar to those from 13 previously studied cases and indicate that the entry of chromosomes 13-15 into translocations is nonrandom. This nonrandomness is not a simple function of chromosome size or shape, since chromosomes 13-15 are acrocentrics of similar size.     

减缓出口龙眼肉果冻褐变的初步研究

龙眼肉果冻褐变是影响出口龙眼肉果冻品质的很重要因素。主要针对影响出口龙眼肉果冻褐变主要因素展开研究,并由此提出减缓出口龙眼肉果冻褐变的最佳生产工艺配方。首先对杀菌温度、乙二胺四乙酸二钠(EDTA)浓度、维生素C(Vc)浓度、胶液的pH值、糖度等进行单因素试验,从而选择较优水平再进行正交试验。最终确定延缓该果冻褐变的最佳生产工艺配方:Vc浓度0.01%,EDTA浓度0.02%,糖度16°Bé,胶液pH值为3.3。     

淮南猪染色体的研究

采用微量外周血淋巴细胞培养以及核仁组成区银染色(Ag—NORs)技术,对淮南猪体细胞核型以及核仁组成区进行了研究,结果表明,淮南猪二倍体细胞染色体组成为38xy(公)或38xx(母),NF=64;细胞分裂中期银染阳性核仁组成区为1、2、3和4的频率分别为0.3659、0.2683、0.1951和0.1707,平均有2.17条染色体的核仁组成区被正染。     

分蘖洋葱组织培养染色体数目变化

采用茎尖分生组织培养技术 ,获得分蘖洋葱无毒试管苗。通过染色体压片 ,对分蘖洋葱组培染色体数目变化进行了研究。结果表明 ,茎尖分生组织培养苗遗传稳定 ,其染色体未发生变异 ,均为 2 n=16 ;愈伤组织及其再生苗遗传稳定性差 ,愈伤组织染色体变异率为 33.85 % ,其中单倍体占 9.2 3% ,四倍体占 15 .39.,非整倍体占 9.2 3% ;愈伤组织分化苗染色体变异率为 2 4 .6 2 % ,其中四倍体占 16 .93% ,非整倍体占 7.6 9%。未发现三倍全的存在。     

农资打假四方说

春耕时节,当农民朋友满心欢喜地选购化肥时,各种假冒伪劣化肥也在一双双“黑手”掩护下,流向广大农村。面对化肥产销通道上为非作歹的行为,我们必须彻底揭开其面目,让其在厂家、经销商、职能部门和农民的注视下无藏身之地。     

Evidence for addiction-like behavior in the rat

Although the voluntary intake of drugs of abuse is a behavior largely preserved throughout phylogeny, it is currently unclear whether pathological drug use ("addiction") can be observed in species other than humans. Here, we report that behaviors that resemble three of the essential diagnostic criteria for addiction appear over time in rats trained to self-administer cocaine. As in humans, this addiction-like behavior is present only in a small proportion of subjects using cocaine and is highly predictive of relapse after withdrawal. These findings provide a new basis for developing a true understanding and treatment of addiction.     

Isotopic evidence for reduced productivity in the glacial southern ocean

Records of carbon and nitrogen isotopes in biogenic silica and carbon isotopes in planktonic foraminifera from deep-sea sediment cores from the Southern Ocean reveal that the primary production during the last glacial maximum was lower than Holocene productivity. These observations conflict with the hypothesis that the low atmospheric carbon dioxide concentrations were introduced by an increase in the efficiency of the high-latitude biological pump. Instead, different oceanic sectors may have had high glacial productivity, or alternative mechanisms that do not involve the biological pump must be considered as the primary cause of the low glacial atmospheric carbon dioxide concentrations.