美丽胡枝子核型分析

采用常规制片法,对青岛崂山地区野生美丽胡枝子的染色体数目、核型、染色体体积等进行了研究.结果表明,美丽胡枝子为二倍体,体细胞染色体数目为2n=22,核型公式为2n=2x=12m+8sm+2st;染色体长度组成为2L+6M2+14M1,染色体总长为20.87 μm,核型不对称系数为65.8%,属于2A型.染色体总体积为11.54 μm3,染色体较小,进化上属于较原始状态.     

Repeated losses of TTAGG telomere repeats in evolution of beetles (Coleoptera)

We studied the occurrence of (TTAGG) _n telomere repeats in 12 species of beetles, representing main lineages of the Coleoptera phylogenetic tree, by Southern hybridization and fluorescence in situ hybridization (FISH). In contrast to other insect orders, beetles were heterogeneous with respect to the occurrence of TTAGG repeats. In addition, the presence or absence of (TTAGG) _n motif was irrespective of phylogenetic relationships. In the suborder Polyphaga, six species displayed positive hybridization signals. These were Silpha obscura, Agrilus viridis, Ampedus sanguineus, Stegobium paniceum, Oryzaephilus surinamensis, and Leptinotarsa decemlineata. Whereas negative signals were obtained in three polyphagan species, Geotrupes stercorarius, Thanasimus formicarius, and Sitophilus granarius. In the suborder Adephaga, the TTAGG sequence was present in one species, Graphoderus cinereus, and absent in two species, Orectochilus villosus and Pterostichus oblongopunctatus. We concluded that the telomerase-dependent (TTAGG) _n motif had been repeatedly lost in different phylogenetic branches of Coleoptera and probably replaced with another mechanism of telomere elongation. This had to happen at least 5–6 times. The results suggest a predisposition or a backup mechanism of telomere maintenance in the genome of beetles that enabled them to make frequent evolutionary changes in the telomere composition.     

Autotetraploids of Vicia cracca show a higher allelic richness in natural populations and a higher seed set after artificial selfing than diploids

Background and Aims

Despite the great importance of autopolyploidy in the evolution of angiosperms, relatively little attention has been devoted to autopolyploids in natural polyploid systems. Several hypotheses have been proposed to explain why autopolyploids are so common and successful, for example increased genetic diversity and heterozygosity and the transition towards selfing. However, case studies on patterns of genetic diversity and on mating systems in autopolyploids are scarce. In this study allozymes were employed to investigate the origin, population genetic diversity and mating system in the contact zone between diploid and assumed autotetraploid cytotypes of Vicia cracca in Central Europe.

Methods

Four enzyme systems resolved in six putative loci were investigated in ten diploid, ten tetraploid and five mixed-ploidy populations. Genetic diversity and heterozygosity, partitioning of genetic diversity among populations and cytotypes, spatial genetic structure and fixed heterozygosity were analysed. These studies were supplemented by a pollination experiment and meiotic chromosome observation.

Key Results and Conclusions

Weak evidence of fixed heterozygosity, a low proportion of unique alleles and genetic variation between cytotypes similar to the variation among populations within cytotypes supported the autopolyploid origin of tetraploids, although no multivalent formation was observed. Tetraploids possessed more alleles than diploids and showed higher observed zygotic heterozygosity than diploids, but the observed gametic heterozygosity was similar to the value observed in diploids and smaller than expected under panmixis. Values of the inbreeding coefficient and differentiation among populations (ρ_ST) suggested that the breeding system in both cytotypes of V. cracca is mixed mating with prevailing outcrossing. The reduction in seed production of tetraploids after selfing was less than that in diploids. An absence of correlation between genetic and geographic distances and high differentiation among neighbouring tetraploid populations supports the secondary contact hypothesis with tetraploids of several independent origins in Central Europe. Nevertheless, the possibility of a recent in situ origin of tetraploids through a triploid bridge in some regions is also discussed.     

Cytogenetic studies on Apareiodon affinis (Pisces, Characiformes) from Paraná river basin: sex chromosomes and polymorphism

Comparative cytogenetic studies were carried out on Apareiodon affinis from an important hydrographic system at South America, the Paraná river basin. Two distant regions were chosen, which were separated by Guaíra Falls (formerly Sete Quedas); the region in the upper part of the hydrographic basin is called Upper Paraná (Brazil), whereas and the other in the lower part is called Lower Paraná (Argentina). Individuals from Upper Paraná have diploid numbers of 2n = 54 (NF = 108) for males and 2n = 55 (NF = 110) for females, showing female heterogamety with a ZZ/ZW₁W₂ multiple sex chromosomes system that is endemic for the region. In different localities at Lower Paraná, the specimens presented diploid number of 2n = 54 for both sexes, without any sex chromosomes heteromorphism. However, they have an accentuated polymorphism characterized by variation in number of acrocentric chromosomes, constituting something new for family Parodontidae. The most likely hypothesis to explain the origin of such polymorphism is based on successive pericentric inversions giving rise to acrocentric chromosomes. Thus, it was possible to detect 10 cytotypes along the Lower Paraná basin. Such chromosomal variations possibly are the consequence of an adaptative process. Our data probably indicate the occurrence of distinct species in each region that share the same denomination. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mitotic evidence for the tetraploid nature of Glycine max provided by high quality karyograms

The high number, very small size and morphological similarity of the chromosomes, and low metaphasic indexes obtained in root meristems have hindered the progress in cytogenetic and evolutionary studies of Glycine max. In order to contribute to the solving of these problems, we have developed a method based on the use of DNA synthesis inhibiting and anti-microtubule solutions and enzymatic maceration and air-drying techniques. Besides, we have employed a digital image analysis system tool. This method provided prometaphasic and metaphasic chromosomes showing well-defined primary and secondary constrictions, which facilitated the pairing of homologues and assembly of the first karyogram for G. max. This species possesses twenty chromosome pairs, being six metacentric and fourteen submetacentric. The karyograms support its tetraploid nature (4x = 40), specifically for the presence of chromosomes with identical morphology, and suggest that chromosome rearrangements may have occurred during the speciation of G. max.     

两步PCR介导的Red重组技术快速敲除鼠疫耶尔森菌sRNA及染色体大片段

【目的】利用Red同源重组系统,通过二步PCR法建立一种适合鼠疫耶尔森菌s RNA和大片段染色体基因敲除的方法。【方法】第一步PCR先扩增出目的基因的上、下游同源臂(600–1000 bp)及卡那抗性盒,再以上、下游同源臂及卡那抗性盒等摩尔混合物为模板,通过融合PCR获得含上下游同源臂及卡那抗性盒的线性突变盒,再将此突变盒的PCR产物电转到含有pKD46质粒的鼠疫201菌株,在阿拉伯糖的诱导下,p KD46质粒表达Red重组酶,促使卡那抗性盒替换目的基因,最后对获得的重组克隆进行PCR鉴定。【结果】本研究通过两步PCR法构建600–1000 bp的同源臂,提高了同源重组效率,并将鼠疫菌sRNA RyhB1(108 bp)和RyhB2(106 bp)和染色体大片段47-2(10.4 kb)、47-3(21.6 kb)、47-3a(9.2 kb)及47-3b(6.1 kb)成功敲除。【结论】基于Red重组系统构建的二步法突变技术,是一种简单、高效的精确修饰鼠疫菌s RNA及大片段染色体的方法,适合于鼠疫菌全基因组的基因敲除,为鼠疫菌基因表达与调控、致病和毒力等研究提供有力的工具。     

Comparison of genetic and physical maps of group 7 chromosomes from Triticum aestivum L.

We present a high density physical map of homoeologous group 7 chromosomes from Triticum aestivum L. using a series of 54 deletion lines, 6 random amplified polymorphic DNA (RAPD) markers and 91 cDNA or genomic DNA clones from wheat, barley and oat. So far, 51 chromosome segments have been distinguished by molecular markers, and 54 homoeoloci have been allocated among chromosomes 7A, 7B and 7D. The linear order of molecular markers along the chromosomes is almost identical in the A- B- and D-genome of wheat. In addition, there is colinearity between the physical and genetic maps of chromosomes 7A, 7B and 7D from T. aestivum, indicating gene synteny among the Triticeae. However, comparison of the physical map of chromosome 7D from T. aestivum with the genetic map from Triticum tauschii some markers have been shown to be physically allocated with distortion in more distal chromosome regions. The integration of genetic and physical maps could assist in estimating the frequency and distribution of recombination in defined regions along the chromosome. Physical distance did not correlate with genetic distance. A dense map facilitates the detection of multiple rearrangements. We present the first evidence for an interstitial inversion either on chromosome arm 7AS or 7DS of Chinese Spring. Molecularly tagged chromosome regions (MTCRs) provide landmarks for long-range mapping of DNA fragments.     

Evolution of the Larval Cuticle Proteins Coded by the Secondary Sex Chromosome Pair: X2 and Neo-Y of Drosophila miranda: II. Comparison at the Amino Acid Sequence Level

The larval cuticle proteins (LCPs) are encoded by a multigene family, Lcp1–4, located at the right arm of the metacentric autosome 2 (2R) in Drosophila melanogaster. Due to a chromosome fusion the Lcp locus of Drosophila miranda is situated on a pair of secondary sex chromosomes, the X2 and neo-Y chromosomes. Comparing the deduced amino acid sequences of the autosomal D. melanogaster loci with the sex-chromosomal loci of D. miranda, we were able to trace the evolution of the Lcp loci with respect to their different chromosomal inheritance. The length of the signal peptide is conserved in all four LCPs, while the size of the mature LCPs varies. Conserved protein motifs became obvious from the alignment, indicating regions of structural and functional importance. Analyzing intra- and interspecific sequence similarities of the Lcp gene families allowed us to reconstruct the phylogeny of the gene cluster. Alignment with cuticle amino acid sequences originating from divergent insect species reveals motifs already present in the primordial insect LCPs. These motifs indicate different levels of constraint acting during the evolution of the LCPs. Received: 27 December 1995 / Accepted: 30 April 1996     

Sex chromosome complement affects nociception in tests of acute and chronic exposure to morphine in mice

We tested the role of sex chromosome complement and gonadal hormones in sex differences in several different paradigms measuring nociception and opioid analgesia using "four core genotypes" C57BL/6J mice. The genotypes include XX and XY gonadal males, and XX and XY gonadal females. Adult mice were gonadectomized and tested 3-4 weeks later, so that differences between sexes (mice with testes vs. ovaries) were attributable mainly to organizational effects of gonadal hormones, whereas differences between XX and XY mice were attributable to their complement of sex chromosomes. In Experiment 1 (hotplate test of acute morphine analgesia), XX mice of both gonadal sexes had significantly shorter hotplate baseline latencies prior to morphine than XY mice. In Experiment 2 (test of development of tolerance to morphine), mice were injected twice daily with 10 mg/kg morphine or saline for 6 days. Saline or the competitive NMDA antagonist CPP (3-(2-carboxypiperazin-4yl) propyl-1-phosphonic acid) (10 mg/kg) was co-injected. On day 7, mice were tested for hotplate latencies before and after administration of a challenge dose of morphine (10 mg/kg). XX mice showed shorter hotplate latencies than XY mice at baseline, and the XX-XY difference was greater following morphine. In Experiment 3, mice were injected with morphine (10 mg/kg) or saline, 15 min before intraplantar injection of formalin (5%/25 microl). XX mice licked their hindpaw more than XY mice within 5 min of formalin injection. The results indicate that X- or Y-linked genes have direct effects, not mediated by gonadal secretions, on sex differences in two different types of acute nociception.     

Reduced Rates of Sequence Evolution of Y-Linked Satellite DNA in Rumex (Polygonaceae)

One characteristic of sex chromosomes is the accumulation of a set of different types of repetitive DNA sequences in the Y chromosomes. However, little is known about how this occurs or about how the absence of recombination affects the subsequent evolutionary fate of the repetitive sequences in the Y chromosome. Here we compare the evolutionary pathways leading to the appearance of three different families of satellite-DNA sequences within the genomes of Rumex acetosa and R. papillaris, two dioecious plant species with a complex XX/XY₁Y₂ sex-chromosome system. We have found that two of these families, one autosomic (the RAE730 family) and one Y-linked (the RAYSI family), arose independently from the ancestral duplication of the same 120-bp repeat unit. Conversely, a comparative analysis of the three satellite-DNA families reveals no evolutionary relationships between these two and the third, RAE180, also located in the Y chromosomes. However, we have demonstrated that, regardless of the mechanisms that gave rise to these families, satellite-DNA sequences have different evolutionary fates according to their location in different types of chromosomes. Specifically, those in the Y chromosomes have evolved at half the rate of those in the autosomes, our results supporting the hypothesis that satellite DNAs in nonrecombining Y chromosomes undergo lower rates of sequence evolution and homogenization than do satellite DNAs in autosomes.[Reviewing Editor: DR. Jerzy Jurka]