应用BrdU-Hoechst33258-Giemsa技术对黑斑蛙性染色体的研究

黑斑蛙染色体数目为2n=26。利用血细胞培养和骨髓制片及BrdU-Hoechst 33258-Giemsa技术研究表明,黑斑蛙的性别决定为XY型。其第9染色体可能是性染色体,该染色体长臂近中部SRR区可能是与性别决定有关的区域。该区域在雌性中是同步复制的;在雄性中是非同步复制的,一个比另一个更晚复制。这一复制异态开始于中S期,终止于晚S期。     

黑斑侧褶蛙的两性异形和雌性繁殖特征

测定了黑斑侧褶蛙成体的体长、体重、头长、头宽、眼径、鼓膜径、前肢长、后肢长等形态指标以及雌体的怀卵数量。黑斑侧褶蛙雌体的体长和体重显著大于雄体。其它局部形态特征指标与体长呈正相关,协方差分析表明,雄体的鼓膜径大于雌体,其余形态指标不存在明显的两性差异。黑斑侧褶蛙雌体怀卵数量与体长和体重皆成正相关关系,表明黑斑侧褶蛙通过增加个体大小增加繁殖输出。     

中国产酸模性染色体的初步观察

中国产的酸模也有明显的性染色体,雌株:2n=12A+XX;雄株:2n=12A+X+Y_1Y_2。雄株的性染色体在减数分裂终变期时,形成 Y_1—X—Y_2的链状三价体,中期Ⅰ时形成“v”字形或环状,偶有形成 XY 二价体和一个 Y 单价体。最后形成6A+X 和6A+Y_1Y_2的小孢子。酸模中可出现雌雄同株而具22条染色体(2n=18A+XX+YY)的三倍体不育株。酸模中还可见到同一株内有不同染色体数目的细胞,这一株至死未见开花。     

广东白腹巨鼠的G带核型和银染色

本文报道了广东白腹巨鼠的核型、G带和银染色。结果表明,二倍体染色体数目为2n=40,常染色体包括4对近端着丝粒染色体,6对末端着丝粒染色体,8对中着丝粒染色体,1对近中着丝粒染色体。性染色体XY为大小不等的末端着丝粒染色体。G分带可鉴别每对染色体的特征,Ag-NORs位于1对近端着丝粒染色体（3号）和2对中等大小的末端着丝粒染色体。     

转座子在植物XY性染色体起源与演化过程中的作用

XY性染色体决定系统是决定植物性别的主要方式,但是对于其起源与演化机制却知之甚少。目前认为,携带控制雌蕊或雄蕊发育基因的一对常染色体由于某种未知原因的突变形成早期的neo-Y或neo-X性染色体,随着演化的进行,早期XY性染色体之间的重组逐渐受到抑制,非重组区域扩展最终形成异型的性染色体。研究发现,重复序列的累积以及DNA甲基化等因素都可能参与了XY性染色体的异染色质化、重组抑制及Y染色体体积增大过程。转座子作为一种基因组中含量最高的重复序列在性染色体演化中扮演了重要的角色,包括性染色体演化的起始激发,以及导致性染色体局部表观遗传修饰使其发生异染色质化扩展和重组抑制。文章综述了转座子在植物性染色体上的累积及其与性染色体异染色质化之间的关系,并简要分析了转座子在性染色体演化过程中的作用。     

中国黑斑蛙种群的线粒体DNA多样性和生物地理演化过程的初探

本文通过对黑斑蛙 8个地方种群 2 5 7个标本的线粒体基因组Cytb基因片段的序列分析 ,探讨了其种群遗传多样性的现代分布格局及其生物地理演化过程。对所检测出的 79个单倍型的分析表明 :黑斑蛙在我国分布区内中部地区的种群遗传多样性高于南北边缘种群。种群间基因流同地理隔离距离呈显著负相关 ,种群遗传分化符合距离隔离或脚踏石模型。线粒体单倍型以广西和四川种群的个体的遗传分化为最深 ,反映出西部山区的屏障隔离效应。单倍型歧点分布分析表明 ,约 10 3- 2 2 6万年前 ,即在末次间冰期 ,黑斑蛙在其分布范围内经历过一次大规模的种群扩张事件。单倍型的分布格局和共享情况显示黑斑蛙种群在冰期后的重新扩张过程主要表现为由南往北的递进式扩散形式。第四纪冰期气候的反复波动导致了黑斑蛙适宜生境在纬度方向上的平移 ,进而导致黑斑蛙种群随生境变化而进行扩张或收缩 ,使黑斑蛙种群的遗传多样性能始终保持在分布区中间高而南北两端低 ,并形成了现代的分布格局     

性别决定与伴性遗传的教学

教学目的1. 以XY型性别决定为例,使学生了解雌雄异体的生物,其性别主要是由性染色体组成的差异决定的。2. 以人的红绿色盲为实例,使学生了解性染色体上基因所控制的性状与性别相关联的特殊遗传现象。3. 通过性别决定及伴性遗传的讲解,对学生进行有关性知识及近亲婚配危害的思想教育。     

PHA活体注射诱发黑斑蛙淋巴细胞转化的观察

本文应用PHA一次性注入黑斑蛙腹腔的方法,系统地研究了不同剂量的PHA对黑斑蛙的细胞遗传学效应。结果表明,PHA剂量为0.3mg/g(体重)时,骨髓和血淋巴细胞转化率分别为77.49％和79.17％;分裂指数为9.40％和10.87％;此外,统计结果说明,PHA处理24小时和处理48、72小时相比,骨髓和血淋巴细胞转化率均有显著性差异(P<0.05)。     

黑斑蛙核型、C-带及Ag-NORs 研究

本文采用外周血淋巴细胞培养法制备染色体标本,观察黑斑蛙的染色体标本,研究黑斑蛙的核型,C-带和Ag-NORs。研究结果表明：（1）黑斑蛙淋巴细胞染色体数目为2n=26,其中有5对大染色体和8对小染色体,核型是二型性核型;（2）分别对雌雄个体的中期分裂相进行观察,在第11号染色体长臂中部有明显的次缢痕,但变异核型次缢痕在第8号染色体长臂的中部;（3）在第5号染色体长臂上有一条明显的近端粒C-带;（4）第11号染色体是一对具有银染核仁形成区的同源染色体,且雌雄个体的银染位置相同。     

蛆症异蚤蝇减数分裂染色体观察

以蛹精巢和卵巢组织为材料,采用空气干燥法制备染色体标本,Giemsa和硝酸银分别染色,对蛆症异蚤蝇Megaselia scalaris减数分裂染色体行为进行研究。结果表明:蛆症异蚤蝇的染色体数目n=3,由2条中着丝粒染色体和1条端着丝粒染色体组成;粗线期,第2条二价体具有较强的嗜银性,可能为性染色体;晚粗线期,第1条二价体的同源染色体之间出现一条细线,类似于联会复合体;终变期,第2条二价体形成环状结构;晚终变期,在3条二价体染色体臂上均产生条带,根据二价体着丝粒处是否成环可以将3条二价体分开。     

Conventional and ultrastructural analyses of the chromosomes of Discocyrtus pectinifemur (Opiliones, Laniatores, Gonyleptidae)

Among the Opiliones, species of the suborders Cyphophthalmi, Eupnoi, Dyspnoi and Laniatores have shown very diverse diploid chromosome numbers. However, only certain Eupnoi species exhibit XY/XX and ZZ/ZW sex chromosome systems. Considering the scarcity of karyotypical information and the absence of structurally identifiable sex chromosomes in the suborder Laniatores, we decided to analyse the chromosomes and bivalents of Discocyrtus pectinifemur (Gonyleptidae) to identify possible sex differences. Testicular cells examined under light microscopy showed a high diploid number, 2 n  = 88, meta/submetacentric chromosome morphology and a nucleolar organizer region on pair 35. Prophase I microspreading observed in transmission electron microscopy exhibited 44 synaptonemal complexes with similar electron density and thickness. The total and regular synapsis between the chromosomes of the bivalents was also noted in pachytene nuclei. Male mitotic and meiotic chromosomes revealed no distinct characteristic that could be related to the occurrence of heteromorphic sex chromosomes. Evolutionary trends of chromosome differentiation in the four suborders of Opiliones are discussed here.     

Meiotic chromosome structure. Kinetochores and chromatid cores in standard and B chromosomes of Arcyptera fusca (Orthoptera) revealed by silver staining.

The behaviour of two chromosome structures in silver-stained chromosomes was analyzed through the first meiotic division in spermatocytes of the acridoid species Arcyptera fusca. Results showed that at diakinesis kinetochores and chromatid cores are individualized while they associate in bivalents of metaphase I; only kinetochores and distal core spots associate in the sex chromosome. Metaphase I is characterized by morphological and localization changes of both kinetochores and cores which define the onset of anaphase I. These changes analyzed in both autosomes and in the sex chromosome allow us to distinguish among three different substages in metaphase I spermatocytes. B chromosomes may be present as univalents, bivalents, or trivalents. Metaphase I B univalents are characterized by separated cores except at their distal ends and individualized and flat sister kinetochores. At anaphase I sister kinetochores of lagging B chromatids remain connected through a silver-stained strand. The behaviour of cores and kinetochores of B bivalents is identical with that found in the autosomal bivalents. The differences in the morphology of kinetochores of every chromosome shown by B trivalents at metaphase I may be related to the balanced forces acting on the multivalent. The results show dramatic changes in chromosome organization of bivalents during metaphase I. These changes suggest that chromatid cores are not involved in the maintenance of bivalents. Moreover, the changes in morphology of kinetochores are independent of the stage of meiosis but correlate with the kind of division (amphitelic-syntelic) that chromosomes undergo.     

Improved resolution of the meiotic chromsomes in both sexes of Euxoa species and their hybrids (Lepidoptera: noctuidae).

An air drying and Giemsa staining technique produces consistently good quality cytological preparations when applied to different species of Euxoa (Lepidoptera: Noctuidae) and, in particular, it allows an imporved resolution of the meiotic chromosomes in both sexes. All species so far investigated have a basic haploid chromosome complement of n (male) = 31(XX): n(female) = (XY). A single chiasma per individual bivalent is clearly visible in the male sex. Some chiasmata are formed in interstitial positions, but, by metaphase I, they have all undergone complete terminalization while the bivalents orient axially on the first division spindle. Direct evidence for lack of chiasma formation in the 31 hormorphic bivalents in the female sex is reported for the first time for species of Noctuidae. Evidence in favor of an XY system in the female sex is discussed. Preliminary studies of the meiotic divisions in hybrid material reveal the presence of cryptic structural differences between certain taxa, and will help to elucidate taxonomic problems within this complex genus.     

Chromosome banding in Amphibia

The mitotic and meiotic chromosomes and interphase nuclei of the South American tree-frog Centrolenella antisthenesi were studied with various banding techniques. The karyotype is distinguished by a new category of heteromorphic XY/XX sex chromosomes in an initial stage of differentiation. In diakinesis of male meiosis the XY chromosomes exhibit the same pairing configuration as the autosomal bivalents. Analysis of the chromosomes with DNA base pair-specific fluorochromes revealed that unusual large amounts of brightly labeled AT-rich constitutive heterochromatin are located in the centromeric and pericentromeric regions of all autosomes and in the X chromosome. In most types of interphase cell nuclei the brightly fluorescent heterochromatic regions fuse to very large chromocenters.     

麦蓝菜的花粉母细胞减数分裂及核型分析

采用压片法,对麦蓝菜的花粉母细胞减数分裂及体细胞核型进行了研究。结果表明,麦蓝菜的绝大多数花粉母细胞减数分裂中染色体的行为正常,在终变期同源染色体配对后可形成15个二价体;在少数花粉母细胞减数分裂中观察到落后染色体、染色体桥等异常行为;其减数分裂为同时型,其花粉粒育性为88.04%。麦蓝菜的染色体数目为2n=2X=30,核型公式为K(2n)=2X=30=22m(2SAT)+8 sm,染色体相对长度组成为2n=16M2+14M1,其核型为"1A"型。     

Change of the heterogametic sex from male to female in the frog

Two different types of sex chromosomes, XX/XY and ZZ/ZW, exist in the Japanese frog Rana rugosa. They are separated in two local forms that share a common origin in hybridization between the other two forms (West Japan and Kanto) with male heterogametic sex determination and homomorphic sex chromosomes. In this study, to find out how the different types of sex chromosomes differentiated, particularly the evolutionary reason for the heterogametic sex change from male to female, we performed artificial crossings between the West Japan and Kanto forms and mitochondrial 12S rRNA gene sequence analysis. The crossing results showed male bias using mother frogs with West Japan cytoplasm and female bias using those with Kanto cytoplasm. The mitochondrial genes of ZZ/ZW and XX/XY forms, respectively, were similar in sequence to those of the West Japan and Kanto forms. These results suggest that in the primary ZZ/ZW form, the West Japan strain was maternal and thus male bias was caused by the introgression of the Kanto strain while in the primary XX/XY form and vice versa. We therefore hypothesize that sex ratio bias according to the maternal origin of the hybrid population was a trigger for the sex chromosome differentiation and the change of heterogametic sex.     

The prototype of sex chromosomes found in Korean populations of Rana rugosa

The seventh largest chromosome in Japanese populations of the frog Rana rugosa morphologically evolved as a sex chromosome. The sex chromosome is XX/XY type in one geographic form and ZZ/ZW type in another. In contrast, the seventh chromosomes are still homomorphic between the sexes in the other two geographic forms: they are more subtelocentric in the Kanto form and subtelocentric in the western Japanese form. To identify a prototype of the sex chromosomes, we extended our investigation in this study to the Korean form, which is supposed to be close to the phylogenetic origin of this species. The karyotype, a sex-linked gene sequence, and mechanisms of sex determination and gonadal differentiation were all examined. In addition, phylogenetic analyses were performed based on mitochondrial gene sequences and the results of crossings between the Korean and Japanese forms. As a consequence, the more subtelocentric seventh chromosome, shared by the Korean and Japanese Kanto forms, was concluded to be the prototype of the sex chromosomes. Starting at the prototype, a whole process of morphological sex chromosome evolution was reconstructed.     

Meiosis and pollen mitosis in diploid and triploid Colocasia antiquorum Schott.

The relationship between diploid and triploid forms of Colocasia antiquorum Schott. was assessed through comparative meiotic and pollen mitotic studies. Owing to poor spreading of the chromosomes of both materials, karyological observations on pachytene nuclei were limited to a few chromosomes. Among the two nucleolar chromosomes and a metacentric, telochromomere-bearing chromosome of the diploid, the latter and one of the nucleolar chromosomes characterized by a heteropycnotic short arm were identified in both bivalent and trivalent associations in the triploid. The homologues in these cases were homomorphic and intimately paired. Two types of heteromorphic bivalents exhibiting partial pairing of homomorphic segments were also recorded in the triploid. Among the 14 bivalents of the diploid at diakinesis, two were nucleolus-associated. In the triploid, chromosomal associations at diakinesis included trivalents (2 to 9), bivalents and univalents, and the chiasma frequency per paired chromosome was lower than in the diploids. In 21.6 percent of the PMCs at this stage intragenomic pairing of one or two chromosomes was observed. Post-diakinesis stages in the diploid were regular while in the triploid they were marked by various irregularities in a majority of the cells. However, fertility (stainability), size and divisional frequency of pollen in both materials were remarkably similar. Chromosome numbers in pollen nuclei in the triploid ranged from 8 to 25. Based on these data an autopolyploid origin for the triploid Colocasia and a lower base number than the gametic chromosome number for this genus are advanced.     

Male meiosis and behaviour of sex chromosomes in different populations of Rumex acetosa L. from the Western Himalayas, India

Detailed meiotic analysis in 28 North West Himalayan populations of dioecious plant Rumex acetosa L. was carried out. The species is generally discussed as an important plant having sex chromosomes. Male meiosis in all the studied populations clearly showed the formation of six bivalents and one trivalent during diakinesis and metaphase-I. The sex chromosomes in male plants exhibit a chain of trivalent (Y₁–X–Y₂). In addition, among the presently investigated populations ring-shaped trivalents were also observed for the first time in the species. Varied frequency of abnormal segregation of sex trivalent was also observed leading to XY:Y segregation instead of normal X:Y₁Y₂ segregation. A majority of the populations exhibit normal meiosis. Plants of six populations show meiotic abnormalities like cytomixis, laggards, bridges, chromatin stickiness, etc., leading to reduced pollen fertility. Translocation between an autosome and sex chromosomes was also observed in some of the populations. 0–1B chromosomes were noticed in one population. This is the first ever meiotic analysis of the species from India.     

The origin and differentiation of the heteromorphic sex chromosomes Z, W, X, and Y in the frog Rana rugosa, inferred from the sequences of a sex-linked gene, ADP/ATP translocase

Sex chromosomes of the Japanese frog Rana rugosa are heteromorphic in the male (XX/XY) or in the female (ZZ/ZW) in two geographic forms, whereas they are still homomorphic in both sexes in two other forms (Hiroshima and Isehara types). To make clear the origin and differentiation mechanisms of the heteromorphic sex chromosomes, we isolated a sex-linked gene, ADP/ATP translocase, and constructed a phylogenetic tree of the genes derived from the sex chromosomes. The tree shows that the Hiroshima gene diverges first, and the rest form two clusters: one includes the Y and Z genes and the other includes the X, W, and Isehara genes. The Hiroshima gene shares more sequence similarity with the Y and Z genes than with the X, W, and Isehara genes. This suggests that the Y and Z sex chromosomes originate from the Hiroshima type, whereas the X and W chromosomes originate from the Isehara-type sex chromosome. Thus, we infer that hybridization between two ancestral forms, with the Hiroshima-type sex chromosome in one and the Isehara-type sex chromosome in the other, was the primary event causing differentiation of the heteromorphic sex chromosomes.