首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   20篇
  完全免费   3篇
  2018年   1篇
  2014年   1篇
  2013年   2篇
  2010年   1篇
  2009年   2篇
  2007年   1篇
  2006年   1篇
  2005年   4篇
  2004年   2篇
  2002年   1篇
  1998年   1篇
  1997年   1篇
  1996年   1篇
  1990年   1篇
  1989年   1篇
  1988年   1篇
  1986年   1篇
排序方式: 共有23条查询结果,搜索用时 109 毫秒
1.
从中国晚期智人颅牙特征看中国现代人起源   总被引:22,自引:5,他引:17  
吴新智 《人类学学报》1998,17(4):276-282
本文提供或授引了中国晚期智人头骨的额骨鳞部最突出点位置、颊部骨骼下缘的形状、头骨最宽处位置等特征和铲形门齿等特征的出现率等的有关数据,并探讨了这些特征系来源于非洲“夏娃”的后裔,还是中国当地更早的人群。所得结论更倾向于后者而不利于前者。中国旧石器朝代中期和晚期的文化之间缺乏显著的反差,没有中断的迹象,也是不利于中国现代人起源的替代说的有力佐证。  相似文献
2.
Genetic variation was examined in the Japanese apogamous and sexual forms ofAsplenium unilaterale by electrophoretic analysis of eight enzyme systems. The apogamous form consisted of four biotypes (A, B, C, and D) which show different band patterns. Biotypes C and D were distinguished from biotype A by a difference at only one locus each:Mdh-1 andPgi-2, respectively. Biotypes A, C, and D were sufficiently differentiated from the sexual form (Nei's genetic distance (D)=0.50). This suggests that the apogamous form is not directly derived from the sexual form. However, biotype B expressed the combined band pattern of biotype C and the sexual form, leading to the conclusion that biotype B probably originated by hybridization between those two.  相似文献
3.
To investigate the origin of the triploid agamosporous speciesD. yakusilvicola, an electrophoretic analysis was made for five enzymes of theD. sparsa complex.Dryopteris yakusilvicola showed a monomorphic banding pattern for the five enzymes and was heterozygous in all six gene loci coding them. Comparison of enzyme banding patterns suggests that the genome ofD. yakusilvicola was derived through hybridization betweenD. sabaei and either a sexual tetraploid or an agamosporous triploid ofD. sparsa. Cytological evidence (Darnaediet al., 1989) supports the idea that of the two types ofD. sparsa the sexual tetraploid is a parent. The monomorphic pattern implies thatD. yakusilvicola originated from a single hybrid between the parental species, and that it is a neo-endemic of Yakushima Island.  相似文献
4.
Abstract Electrophoretic data were used to assess levels of clonal diversity within and among populations of Taraxacum albidum Dahlst., a pentaploid obligate agamosperm indigenous to Japan. All specimens sampled from the entire distribution range shared the same 19-locus genotypic profile except for one. This single mutant differed in one allele at one locus only. Contrary to this extreme monomorphism, clonally reproducing species usually consist of multiclonal populations. It is hypothesized that T. albidum recently originated through hybridization between a sexual diploid species of the section Mongolica (most likely T. japonicum Koidz.) and an unknown polyploid Mongolica species.  相似文献
5.
Abstract Peroxidase phenotypes of two all-agamospermous "species" of Eupatorium in the southeastern United States were examined. The result supported a hybrid origin ( E. recurvans × E. rotundifolium ) for E. scabidum and an autopolyploid origin from E. recurvans for E. mohrii. Notable variations of E. scabridum in its leaf morphology and peroxidase phenotype were suggestive of occasional sexuality in this agamospermous "species".  相似文献
6.
Natural populations of Trypanosoma cruzi are structured into five genetic lineages, T. cruzi I and T. cruzi II a to e, as the result of clonal evolution with rare genetic recombination events. To explore more in depth these phenomenons, a multigene sequencing approach was used, for the first time in the case of T. cruzi. Three nuclear loci and a maxicircle locus were sequenced on 18 T. cruzi stocks. Sequences were used to build phylogenetic trees from each locus and from concatenated sequences of all loci.The data confirmed the hybrid origin of DTUs IId and IIe, as the result of an ancient genetic recombination between strains pertaining to IIb and IIc. The data confirmed also a hybrid origin of DTUs IIa and IIc. Contrary to previous reports, we failed to detect mosaic genes. The phylogenetic relationship between DTUs and the respective roles of recombination and selection were tested.  相似文献
7.
Hybridization and polyploidization are important evolutionary processes in higher plants and have greatly enriched the diversity of the genus Potamogeton (Potamogetonaceae). To study the phylogenetic relationships and hybrid origin of Potamogeton species, 35 accessions representing 20 species, including diploids, tetraploids and hexaploids, and three hybrids were collected in China and their ribosomal internal transcribed spacers (ITS) were cloned, sequenced and statistically analyzed. The data showed that ITS sequences were informative to analyze the phylogeny of Potamogeton, and the phylogenetic tree revealed that Potamogeton species examined could be mainly divided into two groups (Group I and II), corresponding to subgenus Potamogeton and subgenus Coleogeton, respectively. Then, the evolutionary mechanism on the polyploidy of Potamogeton species was discussed. P. natans probably was an allotetraploid and one of its parent might result from aneuploidy change of species with 2n=28. P. hubeiensis might be derived from the hybridization between P. octandrus and P. cristatus. We suggested that both P. lucens and P. maackianus probably were allotetraploids, and P. obtusifolius might be a diploid hybrid between P. compressus and P. pusillus. Moreover, P. malainoides might have undergone biased concerted evolution toward one of its parent P. wrightii, and P. intortusifolius might be a synonymy of P. × anguillanus.  相似文献
8.
9.
We investigated the anatomical expression of leaf traits in hybrids between evergreen Vaccinium vitis‐idaea and deciduous V. myrtillus. We compared parents from four populations with their respective F1 hybrids and tested whether (i) transgression can be the source of novel anatomical traits in hybrids; (ii) expression of transgressive traits is more probable for traits with similar values in parents and intermediate for more distinct values, as predicted by theory; and (iii) independent origin of hybrids leads to identical trait expression profiles among populations. We found that anatomical leaf traits can be divided into four categories based on their similarity to parents: intermediate, parental‐like, transgressive and non‐significant. Contrary to the common view, parental‐like trait values were equally important in shaping the hybrid profile, as were intermediate traits. Transgression was revealed in 17/144 cases and concerned mainly cell and tissue sizes. As predicted by theory, we observed transgressive segregation more often when there was little phenotypic divergence, but intermediate values when parental traits were differentiated. It is likely that cell and tissue sizes are phylogenetically more conserved due to stabilising selection, whereas traits such as leaf thickness and volume fraction of the intercellular spaces, showing a consistent intermediate pattern across populations, are more susceptible to directional selection. Hybrid populations showed little similarity in expression profile, with only three traits identically expressed across all populations. Thus local adaptation of parental species and specific genetic background may be of importance.  相似文献
10.
脊椎动物行孤雌生殖的物种中,绝大多数都是杂交起源的。本文从孤雌生殖物种的外部形态特点、同工酶分析、核酸分子标记、染色体涂染法等方面,综述了脊椎动物中孤雌生殖杂交起源的研究进展,分析了其核内有丝分裂模式的细胞学机制。  相似文献
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号