两种小车蝗染色体C带核型研究(蝗总科:斑翅蝗科)

采用秋水仙素体内注射法取昆虫精巢,低渗处理,空气干燥制片法制作染色体标本,吉姆萨染色.首次对分布在广西的小车蝗属Oedaleus两个种隆义小车蝗Oedaleus abruptus(Thunberg)和红胫小车蝗Oedaleus manjius Chang染色体核型和C带带型进行了分析研究.结果表明:两种小车蝗的染色体摹数、性别决定机制、染色体组式、染色体着丝粒类型和着丝粒C带等方面有着相同的特征,结构异染色质在染色体组中的总含量也比较接近;染色体是端部着丝粒和染色体都含有着丝粒C带带纹上具有一致性.但在个体大小、相对长度值、性染色体、除着丝粒C带以外的其它C带分布类型方面都有明显差异.所得结果符合传统的形态学分类.研究结果为直翅目的物种亲缘关系、遗传多样性分析提供有价值的生化遗传指标.     

豪猪（Hystris hodgsoni）染色体的研究

豪猪(Hystris hodgsoni)染色体的数目为2n=66,染色体的臂数NF=124。常染色体由8对中着丝粒染色体、16对亚中着丝粒染色体、6对亚末端着丝粒染色体及2对近端着丝粒染色体组成。X和Y性染色体是一对长度大小有明显差异的中着丝粒染色体。对染色体作了G、C、Ag显带处理。C带结果可以看出有些染色体上存在着整个的异染色质短臂。Ag-NORs的数目为3—5个。     

东北梅花鹿染色体限制性内切酶显带

采用限制性内切酶Hae Ⅲ、Hind Ⅲ分别处理梅花鹿中期染色体标本,发现HaeⅢ处理标本21h左右,显出类似G带、C带带型,第1、4、11、18、27、28、31对染色体的结构异染色质区对HaeⅢ敏感而浅染,而HindⅢ处理标本18h左右能诱导梅花鹿中期染色体显出类似G带、C带,第2、6、15、18、29、32对染色体的结构异染色质区对HindⅢ较敏感而浅染,性染色体Y对HaeⅢ敏感呈浅染,性染色体X对HindⅢ敏感呈浅染。表明东北梅花鹿12对常染色体和两条性染色体结构异染色质在这两种酶处理时表现出异质性。     

中国五种高山锄足蟾的核型、Ag-NORs和C-带的研究

作者用核型、Ag-NORs和C-带,对分布于川、滇两省的二属(齿突蟾、齿蟾)五种(胸腺齿突蟾、圆疣齿突蟾、凉北齿蟾、秉志齿蟾、疣刺齿蟾)锄足蟾作了属间和种间关系的比较分析,并讨论了它们的核型演化机制。结果表明:(1)齿突蟾和齿蟾两属间在核型和带型上都有明显的差异,演化途径主要的可能是含有重复DNA染色体片段的相互易位或臂间倒位;(2)属内不同种之间带型无显著差异,但某些对应染色体对间,其相对长度和臂比值差异明显,十分可能是常染色质片段的易位和臂间倒位所致;(3)凉北齿蟾有染色体数目变异多态现象;(4)五种锄足蟾均未发现异形性染色体。     

两种华癫蝗的染色体C一带核型

本文采用染色体C一带技术对癫蝗科Pamphagidae华癫蝗属Sinotrnethis B. Bienko 2个种（友育 华癫蝗S. amicus B. Bienk。和短翅华癫煌S. brachypterus Zheng et Xi）的次级精母细胞减数分裂中 期（中期11)染色体进行了C一带核型比较研究,绘制了C一带核型示意图。结果表明,结构异染色质在 2种华癫蝗的染色体组中有着相似的分布,这反映了同一属内2个物种在系统进化中的亲缘关系。另 外,两者在结构异染色质上的差别主要反映在第6染色体上有无端部C一带发生以及结构异染色质总 的百分含量多少。     

十一种无尾两栖类分带核型的比较研究

本文比较研究11种无尾两栖类的c带型和人Ag-NORs,并报道三种核型（淡肩角蟾,秦岭雨蛙和湖北金线蛙）,结果：（1） 弹琴蛙仅大型染色体着丝点区C带正染,其余10个物种的所有染色体均有明显的着丝点C带,并分别具有数目不等的端部C带或插入型C带。其中天台蛙的C带尤为发达。（2） 中华大蟾蛛有3对Ag-NORs,大树蛙两对,其余9个种均显示1对。（3）新报三种核型中,淡肩角蟾租湖北金线蛙2n=26,N．F=52。淡肩角蟾由6对大型的和7对小型的染色休组成,湖北金线蛙大小型染色体分别为5对和8对。秦岭雨蛙2n=24,含大小型染色休各6对,其N．F=48。三个物种均未见有异型性染色体。     

云南省两栖动物新纪录--棕点湍蛙

20 0 2年 8月 ,笔者在云南省昭通市巧家县东坪乡威宁村进行两栖爬行动物调查时 ,采集到 6号蛙类标本 ,经鉴定为蛙科湍蛙属棕点湍蛙 (Amolopsloloen sis) ,是云南省两栖动物新纪录 ,标本现保存于云南大学生命科学学院生物学系脊椎动物标本室。采集地巧家县东坪乡威宁村地理位置为 1 0 3°0 5′1 0″E ,2 7°1 8′45″N ,海拔 2 2 0 0m左右。生活于灌丛茂密、山溪湍流地带。成蛙白昼多隐蔽在溪流边石下或洞内 ;黄昏时多蹲在水中或岸边石上 ,受惊扰后立即跃入溪水中。省外目前仅分布于四川的部分县市。表 1　棕点湍蛙的量度　　　　　　 (单…     

黑线姬鼠华北亚种染色体研究

本文采用骨髓染色体制片法,对分布于山东的黑线姬鼠华北亚种的染色体组型,C-带、G-带和银染核型进行了分析研究。其核型为2n=48=38 T+8 M+XY。X为较小的端着丝粒染色体,Y为组型中最大的染色体。几乎每个常染色体的着丝粒区都具异染色质。性染色体的异染色质丰富。No.10和No.18染色体具NOR(?)。每条染色体都显示出较清晰的G-带。同时对黑线姬鼠精母细胞的减数分裂进行了观察,并将山东标本与欧洲标本的核型进行了比较,其性染色体有显著差异。     

基于12S和16S rRNA序列的湍蛙属部分物种的系统发育关系

测定了湍蛙属 6个种共 10个种群 ,以及 4个外群种的线粒体 12S和 16SrRNA基因片段 ,比对后有94 0bp序列 ,发现 35 2个变异位点、 186个简约性位点。运用NJ法、MP法、ML法构建了系统关系树 ,各系统树一致表明内群为一单系群 ,分为两组 :第一组中 ,四川湍蛙两种群先聚合 ,再和棕点湍蛙聚为一支 ;第二组中 ,香港湍蛙和戴云湍蛙聚为一支 ,而香港大屿山离岛湍蛙种群首先与华南湍蛙相聚 ,再与武夷湍蛙构成姐妹支。研究结果表明 :香港地区增加 1种湍蛙分布 ;戴云湍蛙是一有效种 ;四川湍蛙的石棉和洪雅种群间遗传差异达到或超过其他种间的分歧水平。     

异爪蝗属及雏蝗属部分种类染色体核型及C带带型分析研究(直翅目,蝗总科)

分析研究异爪蝗属Euchorthippus Tarb.2种和雏蝗属Chorthippus Fieb.5种的染色体核型及C带带型.结果表明,2个属在染色体数目、染色体组式、异染色质含量等方面都有明显的差异.属下种间在染色体数目、染色体组式、性别决定机制、着丝粒C带等方面有相同的特征,在染色体相对长度、异染色质含量等方面有差异.     

Heterogeneous Histories of Recombination Suppression on Stickleback Sex Chromosomes

How consistent are the evolutionary trajectories of sex chromosomes shortly after they form? Insights into the evolution of recombination, differentiation, and degeneration can be provided by comparing closely related species with homologous sex chromosomes. The sex chromosomes of the threespine stickleback (Gasterosteus aculeatus) and its sister species, the Japan Sea stickleback (G. nipponicus), have been well characterized. Little is known, however, about the sex chromosomes of their congener, the blackspotted stickleback (G. wheatlandi). We used pedigrees to obtain experimentally phased whole genome sequences from blackspotted stickleback X and Y chromosomes. Using multispecies gene trees and analysis of shared duplications, we demonstrate that Chromosome 19 is the ancestral sex chromosome and that its oldest stratum evolved in the common ancestor of the genus. After the blackspotted lineage diverged, its sex chromosomes experienced independent and more extensive recombination suppression, greater X–Y differentiation, and a much higher rate of Y degeneration than the other two species. These patterns may result from a smaller effective population size in the blackspotted stickleback. A recent fusion between the ancestral blackspotted stickleback Y chromosome and Chromosome 12, which produced a neo-X and neo-Y, may have been favored by the very small size of the recombining region on the ancestral sex chromosome. We identify six strata on the ancestral and neo-sex chromosomes where recombination between the X and Y ceased at different times. These results confirm that sex chromosomes can evolve large differences within and between species over short evolutionary timescales.     

Sex chromosomal dimorphisms narrated by X-chromosome translocation in a spiny frog (<Emphasis Type="Italic">Quasipaa boulengeri</Emphasis>)

Background

In the general model of sex chromosome evolution for diploid dioecious organisms, the Y (or W) chromosome is derived, while the homogametic sex presumably represents the ancestral condition. However, in the frog species Quasipaa boulengeri, heteromorphisms caused by a translocation between chromosomes 1 and 6 are not related to sex, because the same heteromorphic chromosomes are found both in males and females at the cytological level. To confirm whether those heteromorphisms are unrelated to sex, a sex-linked locus was mapped at the chromosomal level and sequenced to identify any haplotype difference between sexes.

Results

Chromosome 1 was assigned to the sex chromosome pair by mapping the sex-linked locus. X-chromosome translocation was demonstrated and confirmed by the karyotypes of the progeny. Translocation heteromorphisms were involved in normal and translocated X chromosomes in the rearranged populations. Based on phylogenetic inference using both male and female sex-linked haplotypes, recombination was suppressed not only between the Y and normal X chromosomes, respectively the Y and translocated X chromosomes, but also between the normal and translocated X chromosomes. Both males and females shared not only the same translocation heteromorphisms but also the X chromosomal dimorphisms in this frog.

Conclusions

The reverse of the typical situation, in which the X is derived and the Y has remained unchanged, is known to be very rare. In the present study, X-chromosome translocation has been known to cause sex chromosomal dimorphisms. The X chromosome has gone processes of genetic differentiation and/or structural changes by chance, which may facilitate sex chromosome differentiation. These sex chromosomal dimorphisms presenting in both sexes may represent the early stages of sex chromosome differentiation and aid in understanding sex chromosome evolution.

     

Polymorphism and differentiation of rainbow trout Y chromosomes.

Most fish species show little morphological differentiation in the sex chromosomes. We have coupled molecular and cytogenetic analyses to characterize the male-determining region of the rainbow trout (Oncorhynchus mykiss) Y chromosome. Four genetically diverse male clonal lines of this species were used for genetic and physical mapping of regions in the vicinity of the sex locus. Five markers were genetically mapped to the Y chromosome in these male lines, indicating that the sex locus was located on the same linkage group in each of the lines. We also confirmed the presence of a Y chromosome morphological polymorphism among these lines, with the Y chromosomes from two of the lines having the more common heteromorphic Y chromosome and two of the lines having Y chromosomes morphologically similar to the X chromosome. The fluorescence in situ hybridization (FISH) pattern of two probes linked to sex suggested that the sex locus is physically located on the long arm of the Y chromosome. Fishes appear to be an excellent group of organisms for studying sex chromosome evolution and differentiation in vertebrates because they show considerable variability in the mechanisms and (or) patterns involved in sex determination.     

A reciprocal translocation radically reshapes sex‐linked inheritance in the common frog

X and Y chromosomes can diverge when rearrangements block recombination between them. Here we present the first genomic view of a reciprocal translocation that causes two physically unconnected pairs of chromosomes to be coinherited as sex chromosomes. In a population of the common frog (Rana temporaria), both pairs of X and Y chromosomes show extensive sequence differentiation, but not degeneration of the Y chromosomes. A new method based on gene trees shows both chromosomes are sex‐linked. Furthermore, the gene trees from the two Y chromosomes have identical topologies, showing they have been coinherited since the reciprocal translocation occurred. Reciprocal translocations can thus reshape sex linkage on a much greater scale compared with inversions, the type of rearrangement that is much better known in sex chromosome evolution, and they can greatly amplify the power of sexually antagonistic selection to drive genomic rearrangement. Two more populations show evidence of other rearrangements, suggesting that this species has unprecedented structural polymorphism in its sex chromosomes.     

New Y chromosomes and early stages of sex chromosome differentiation: sex determination in <Emphasis Type="Italic">Megaselia</Emphasis>

The phorid fly Megaselia scalaris is a laboratory model for the turnover and early differentiation of sex chromosomes. Isolates from the field have an XY sex-determining mechanism with chromosome pair 2 acting as X and Y chromosomes. The sex chromosomes are homomorphic but display early signs of sex chromosome differentiation: a low level of molecular differences between X and Y. The male-determining function (M), maps to the distal part of the Y chromosome’s short arm. In laboratory cultures, new Y chromosomes with no signs of a molecular differentiation arise at a low rate, probably by transposition of M to these chromosomes. Downstream of the primary signal, the homologue of the Drosophila doublesex (dsx) is part of the sex-determining pathway while Sex-lethal (Sxl), though structurally conserved, is not.     

Sex Determination in the Fly Megaselia Scalaris, a Model System for Primary Steps of Sex Chromosome Evolution

The fly Megaselia scalaris Loew possesses three homomorphic chromosome pairs; 2 is the sex chromosome pair in two wild-type laboratory stocks of different geographic origin (designated ``original' sex chromosome pair in this paper). The primary male-determining function moves at a very low rate to other chromosomes, thereby creating new Y chromosomes. Random amplified polymorphic DNA markers obtained by polymerase chain reaction with single decamer primers and a few available phenotypic markers were used in testcrosses to localize the sex-determining loci and to define the new sex chromosomes. Four cases are presented in which the primary male-determining function had been transferred from the original Y chromosome to a new locus either on one of the autosomes or on the original X chromosome, presumably by transposition. In these cases, the sex-determining function had moved to a different locus without an obvious cotransfer of other Y chromosome markers. Thus, with Megaselia we are afforded an experimental system to study the otherwise hypothetical primary stages of sex chromosome evolution. An initial molecular differentiation is apparent even in the new sex chromosomes. Molecular differences between the original X and Y chromosomes illustrate a slightly more advanced stage of sex chromosome evolution.     

Analysis of repetitive DNA sequences in the sex chromosomes of Oreochromis niloticus

In the Nile tilapia, Oreochromis niloticus, sex determination is primarily genetic, with XX females and XY males. While the X and Y chromosomes (the largest pair) cannot be distinguished in mitotic chromosome spreads, analysis of comparative hybridization of X and Y chromosome derived probes (produced, by microdissection and DOP-PCR, from XX and YY genotypes, respectively) to different genotypes (XX, XY and YY) has demonstrated that sequence differences exist between the sex chromosomes. Here we report the characterization of these probes, showing that a significant proportion of the amplified sequences represent various transposable elements. We further demonstrate that concentrations of a number of these individual elements are found on the sex chromosomes and that the distribution of two such elements differs between the X and Y chromosomes. These findings are discussed in relation to sex chromosome differentiation in O. niloticus and to the changes expected during the early stages of sex chromosome evolution.     

The Staurotypus Turtles and Aves Share the Same Origin of Sex Chromosomes but Evolved Different Types of Heterogametic Sex Determination

Reptiles have a wide diversity of sex-determining mechanisms and types of sex chromosomes. Turtles exhibit temperature-dependent sex determination and genotypic sex determination, with male heterogametic (XX/XY) and female heterogametic (ZZ/ZW) sex chromosomes. Identification of sex chromosomes in many turtle species and their comparative genomic analysis are of great significance to understand the evolutionary processes of sex determination and sex chromosome differentiation in Testudines. The Mexican giant musk turtle (Staurotypus triporcatus, Kinosternidae, Testudines) and the giant musk turtle (Staurotypus salvinii) have heteromorphic XY sex chromosomes with a low degree of morphological differentiation; however, their origin and linkage group are still unknown. Cross-species chromosome painting with chromosome-specific DNA from Chinese soft-shelled turtle (Pelodiscus sinensis) revealed that the X and Y chromosomes of S. triporcatus have homology with P. sinensis chromosome 6, which corresponds to the chicken Z chromosome. We cloned cDNA fragments of S. triporcatus homologs of 16 chicken Z-linked genes and mapped them to S. triporcatus and S. salvinii chromosomes using fluorescence in situ hybridization. Sixteen genes were localized to the X and Y long arms in the same order in both species. The orders were also almost the same as those of the ostrich (Struthio camelus) Z chromosome, which retains the primitive state of the avian ancestral Z chromosome. These results strongly suggest that the X and Y chromosomes of Staurotypus turtles are at a very early stage of sex chromosome differentiation, and that these chromosomes and the avian ZW chromosomes share the same origin. Nonetheless, the turtles and birds acquired different systems of heterogametic sex determination during their evolution.     

No evidence that Y‐chromosome differentiation affects male fitness in a Swiss population of common frogs

The canonical model of sex‐chromosome evolution assigns a key role to sexually antagonistic (SA) genes on the arrest of recombination and ensuing degeneration of Y chromosomes. This assumption cannot be tested in organisms with highly differentiated sex chromosomes, such as mammals or birds, owing to the lack of polymorphism. Fixation of SA alleles, furthermore, might be the consequence rather than the cause of recombination arrest. Here we focus on a population of common frogs (Rana temporaria) where XY males with genetically differentiated Y chromosomes (nonrecombinant Y haplotypes) coexist with both XY° males with proto‐Y chromosomes (only differentiated from X chromosomes in the immediate vicinity of the candidate sex‐determining locus Dmrt1) and XX males with undifferentiated sex chromosomes (genetically identical to XX females). Our study finds no effect of sex‐chromosome differentiation on male phenotype, mating success or fathering success. Our conclusions rejoin genomic studies that found no differences in gene expression between XY, XY° and XX males. Sexual dimorphism in common frogs might result more from the differential expression of autosomal genes than from sex‐linked SA genes. Among‐male variance in sex‐chromosome differentiation seems better explained by a polymorphism in the penetrance of alleles at the sex locus, resulting in variable levels of sex reversal (and thus of X‐Y recombination in XY females), independent of sex‐linked SA genes.     

Semi-automatic laser beam microdissection of the Y chromosome and analysis of Y chromosome DNA in a dioecious plant, Silene latifolia

Silene latifolia has heteromorphic sex chromosomes, the X and Y chromosomes. The Y chromosome, which is thought to carry the male determining gene, was isolated by UV laser microdissection and amplified by degenerate oligonucleotide-primed PCR. In situ chromosome suppression of the amplified Y chromosome DNA in the presence of female genomic DNA as a competitor showed that the microdissected Y chromosome DNA did not specifically hybridize to the Y chromosome, but hybridized to all chromosomes. This result suggests that the Y chromosome does not contain Y chromosome-enriched repetitive sequences. A repetitive sequence in the microdissected Y chromosome, RMY1, was isolated while screening repetitive sequences in the amplified Y chromosome. Part of the nucleotide sequence shared a similarity to that of X-43.1, which was isolated from microdissected X chromosomes. Since fluorescence in situ hybridization analysis with RMY1 demonstrated that RMY1 was localized at the ends of the chromosome, RMY1 may be a subtelomeric repetitive sequence. Regarding the sex chromosomes, RMY1 was detected at both ends of the X chromosome and at one end near the pseudoautosomal region of the Y chromosome. The different localization of RMY1 on the sex chromosomes provides a clue to the problem of how the sex chromosomes arose from autosomes.