Dog chromosome-specific paints reveal evolutionary inter- and intrachromosomal rearrangements in the American mink and human

Forty chromosome-specific paint probes of the domestic dog (Canis familiaris, 2n = 78) were used to delineate conserved segments on metaphase chromosomes of the American mink (Mustela vison, 2n = 30) by fluorescence in situ hybridisation. Half of the 38 canine autosomal probes each painted one pair of homologous segments in a diploid mink metaphase, whereas the other 19 dog probes each painted from two to five pairs of discrete segments. In total, 38 canine autosomal paints highlighted 71 pairs of conserved segments in the mink. These painting results allow us to establish a complete comparative chromosome map between the American mink and domestic dog. This map demonstrates that extensive chromosome rearrangements differentiate the karyotypes of the dog and American mink. The 38 dog autosomes could be reconstructed from the 14 autosomes of the American mink through at least 47 fissions, 25 chromosome fusions, and six inversions. Furthermore, comparison of the current dog/mink map with the published human/dog map discloses 23 cryptic intrachromosomal rearrangements in 10 regions of conserved synteny in the human and American mink genomes and thus further refined the human/mink comparative genome map. Copyright (C) 2000 S. Karger AG, Basel.

Identification of native American founder mtDNAs through the analysis of complete mtDNA sequences: Some caveats

In this study, a detailed analysis of both previously published and new data was performed to determine whether complete, or almost complete, mtDNA sequences can resolve the long-debated issue of which Asian mtDNAs were founder sequences for the Native American mtDNA pool. Unfortunately, we now know that coding region data and their analysis are not without problems. To obtain and report reasonably correct sequences does not seem to be a trivial task, and to discriminate between Asian-and Native American mtDNA ancestries may be more complex than previously believed. It is essential to take into account the effects of mutational hot spots in both the control and coding regions, so that the number of apparent Native American mtDNA founder sequences is not erroneously inflated. As we report here, a careful analysis of all available data indicates that there is very little evidence that more than five founder mtDNA sequences entered Beringia before the Last Glacial Maximum and left their traces in the current Native American mtDNA pool.

Molecular evidence for diphyly of the Asian catfish family Amblycipitidae (Teleostei: Siluriformes) and exclusion of the South American Aspredinidae from Sisoroidea

Amblycipitidae Day, 1873 is an Asian family of catfishes (Siluriformes) usually considered to contain 28 species placed in three genera: Amblyceps (14 spp.), Liobagrus (12 spp.) and Xiurenbagrus (2 spp.). Morphology-based systematics has supported the monophyly of this family, with some authors placing Amblycipitidae within a larger group including Akysidae, Sisoridae and Aspredinidae, termed the Sisoroidea. Here we investigate the phylogenetic relationships among four species of Amblyceps, six species of Liobagrus and the two species of Xiurenbagrus with respect to other sisoroid taxa as well as other catfish groups using 6100 aligned base pairs of DNA sequence data from the rag1 and rag2 genes of the nuclear genome and from three regions (cyt b, COL ND4 plus tRNA-His and tRNA-Ser) of the mitochondrial genome. Parsimony and Bayesian analyses of the data indicate strong support for a diphyletic Amblycipitidae in which the genus Amblyceps is the sister group to the Sisoridae and a clade formed by genera Liobagrus and Xiurenbagrus is the sister group to Akysidae. These taxa together form a well supported monophyletic group that assembles all Asian sisoroid taxa, but excludes the South American Aspredinidae. Results for aspredinids are consistent with previous molecular studies that indicate these catfishes are not sisoroids, but the sister group to the South American doradoid catfishes (Auchenipteridae + Doradidae). The redefined sisoroid clade plus Bagridae, Horabagridae and (Ailia + Laides) make up a larger monophyletic group informally termed "Big Asia." Likelihood-based SH tests and Bayes Factor comparisons of the rag and the mitochondrial data partitions considered separately and combined reject both the hypothesis of amblycipitid monophyly and the hypothesis of aspredinid inclusion within Sisoroidea. This result for amblycipitids conflicts with a number of well documented morphological synapomorphies that we briefly review. Possible nomenclatural changes for amblycipitid taxa are noted.

Interplay between s-d exchange interaction and Rashba effect: Spin-polarized transport

The authors investigate the spin-polarized transport properties of a two-dimensional electron gas in a n-type diluted magnetic narrow gap semiconductor quantum well subjected to perpendicular magnetic and electric fields. Interesting beating patterns in the magnetoresistance are found which can be tuned significantly by varying the electric field. A resonant enhancement of spin-polarized current is found which is induced by the competition between the s-d exchange interaction and the Rashba effect [Y. A. Bychkov and E. I. Rashba, J. Phys. C 17, 6039 (1984)]. (c) 2006 American Institute of Physics.

两种聚砜预聚物和多嵌段聚合物的合成及形态结构

以双酚A、酚酞和4，4'-二氯二茉砜为单体，合成了双酚A型聚砜和酚酞型聚砜两系列不同分子量的预聚物。将这两系列预聚物作为硬段，以不同分子量的聚氧化丙烯或聚氧化丙烯-聚二甲基硅氧烷作为软段，以二异氰酸酯二苯甲烷作为硬段和软段间的连接桥，合成了硬、软段分子量不同的双酚A型聚砜-聚氧化丙烯多嵌段聚合物、双酚A型聚砜-（聚氧化丙烯-聚二甲基硅氧烷）多嵌段聚合物的酚酞型聚砜-聚氧化丙烯多嵌段聚合物。经红外光谱分析、分子量测定和粘度测定等表征，确认产物与预想结果相符。用示差扫描量热仪、扭辨分析仪和电子显微镜研究了硬段预聚物和多嵌段聚合物的形态结构及性能。硬段预聚物在实验温度范围（-30到250 ℃）内，具有三种转变，分别为局部短程有序（60到70 ℃）的破坏，玻璃化转变，玻璃化温度与分子量的关系如下式所示：双酚A型聚砜 T_g = 462 - 8.07 * 10~4/M-bar 酚酞型聚砜 Tg = 519 - 8.33 * 10~4/M-bar和较大范围的长程有序性的解离。在双酚A型聚砜-聚氧化丙烯多嵌段聚合物体系中，当硬段分子量固定在1500时，多嵌段聚合物的形态结构随软段的分子量降低由两相结构（软段分子量≥1000）变成为单相结构（软段分子量为450）。当软段分子量固定为2000时，多嵌段聚合物的形态结构随硬段的分子量增加由单相结构（硬段分子量为700）变为两相结构（硬段分子量≥1500）。双酚A型聚砜-（聚氧化丙烯-聚二甲基硅氧烷）多嵌段聚合物均显示两相结构（软段分子量2400，硬段分子量≥700）。在硬段分子量增加到3900就发生相倒转，软段变为分散相，硬段成为连续相。酚酞型聚砜-聚氧化丙烯多嵌段聚合物，当固定分子量为2000时，硬段分子量在本工作的变化范围内，850至1900，所得产物均为两相结构。