中华蚊母树染色体制片及核型分析

以中华蚊母树根尖为材料,采用常规压片法制片,比较材料的不同采集时间、预处理方法、固定剂、解离方法、解离时间及染色方法对中华蚊母树根尖染色体制片的影响.结果表明最佳的制片技术为:取材时间为上午9:00~11:00或下午13:00~15:00,以饱和对二氯苯预处理3 h,用1 mol?L-1盐酸60℃下解离8 min,卡诺固定剂固定,以改良石碳酸品红染色10 min.以该最佳制片方案对中华蚊母树进行体细胞染色体核型分析,首次揭示了中国特有植物———中华蚊母树体细胞染色体数目为2n=2x=24,染色体基数x=12,染色体核型公式为2n=2x=24=12m(2SAT)+10sm+2st,主要由中部和近中部着丝点染色体组成;染色体相对长度组成为2n=24=2L+8M2+12M1+2S,核型不对称指数为64.29%,属于2A型.结果显示中华蚊母树核型对称程度较高,在进化中属于比较原始的类型.     

两种榕属植物的染色体核型分析

采用根尖压片法对菩提树(Ficus religiosa Linn.)和小叶榕(Ficus microcarpa L.f.)进行染色体核型分析.结果显示两种植物的染色体数目均为2n=30,核型类型均为1B,核型公式分别为菩提树2n=2x=30=24m(2SAT)+6sm,小叶榕2n=2x=30=28m(2SAT)+2sm.比较发现,两种植物的核型相似,亲缘关系相近,二者中小叶榕的不对称系数较小(58.16%),为较原始的类型.两者的核型均为首次报道.     

中国2种短鼻蝗染色体C带核型研究(蝗总科:癞蝗科)

染色体C带核型在物种鉴定、分类阶元间的比较及其系统演化关系的推断中是一个有用的指标,染色体组内C带分布位置、大小、数量及异染色质含量可以反映出属、种及种下阶元的细胞学异同.本研究报道了中国2种短鼻蝗--裴氏短鼻蝗Filchnerella beicki和宽顶短鼻蝗Filchnerella amplivertica的染色体C带核型.结果表明:2种短鼻蝗均为XO(♂)型性别决定机制;染色体组成均为2n ♂=19,染色体为端着丝粒染色体;在各染色体相对长度、C带的大小、位置和着色程度上又存在不同程度的差异,可以作为区分种的依据.     

崇明水仙根尖体细胞染色体的观察和核型分析

以崇明水仙(Narcissus tazetta L.var.chinensis Roem.)根尖体细胞为实验材料,对适宜于崇明水仙细胞学研究的前处理液和前处理时间进行了筛选,在此基础上,应用根尖压片法对重瓣花型和单瓣花型崇明水仙体细胞染色体数、核型及倍性进行了比较分析.结果显示:适宜的前处理液是对二氯苯饱和溶液,适宜的前处理时间为12 h.重瓣花型和单瓣花型崇明水仙的染色体核型差异较小,相同点为:不对称二型核型,染色体基数x=10,三倍体,体细胞染色体数2n=3x=30,第7号染色体的短臂具随体,核型均属于"3B"型,臂比大于2的染色体比率为90%.不同点为:重瓣花型的第7号和第8号染色体分别为sm和st型,单瓣花型的第7号和第8号染色体分别为st和sm型;前者的核型不对称系数(76.48%)略小于后者(76.71%);前者的相对长度系数为12L+6M2+12S,后者的相对长度系数为12L+3M1+3M2+12S;前者的最长染色体与最短染色体长度的比值(3.10)略小于后者(3.19).重瓣花型的核型公式为2n=3x=30=15st+15sm(3SAT),单瓣花型的核型公式为2n=3x=30=15st(3SAT)+15sm,崇明水仙根尖体细胞染色体的平均核型公式为2n=3x=30=15st(3SAT)+15sm.根据研究结果初步推测崇明水仙为节段异源三倍体.     

The karyotype of Adenomera diptyx (Boettger 1885) (Anura, Leptodactylidae) from northeastern Argentina

In this work we analyzed the karyotype of five populations of Adenomera diptyx from Argentina after conventional staining, Ag-NOR and C-banding. All specimens presented 2n = 26 and FN = 34. The karyotype was formed by three submetacentric, one metacentric and nine telocentric pairs. Silver staining revealed that the NOR was located on a secondary constriction in pair 7. C- banding evidenced constitutive heterochromatin at the pericentromeric region of all chromosomes. The karyotype of A. diptyx was similar to that of A. hylaedactyla (2n = 26, FN = 34) and different from that of A. andreae (2n = 26, FN = 40) in the fundamental number and secondary constriction position. It also differed from the karyotypes of A. marmorata (2n = 24, FN = 34 and 36) and of A. aff. bokermanni (2n = 23, FN = 34) in diploid number. Until a comprehensive cytogenetic analysis of all the species of the genus is performed, their chromosome evolution will remain poorly understood.     

Ancestry of American polyploid Hordeum species with the I genome inferred from 5S and 18S-25S rDNA

* BACKGROUND AND AIMS: The genus Hordeum exists at three ploidy levels (2x, 4x and 6x) and presents excellent material for investigating the patterns of polyploid evolution in plants. Here the aim was to clarify the ancestry of American polyploid species with the I genome. * METHODS: Chromosomal locations of 5S and 18S-25S ribosomal RNA genes were determined by fluorescence in situ hybridization (FISH). In both polyploid and diploid species, variation in 18S-25S rDNA repeated sequences was analysed by the RFLP technique. * KEY RESULTS: Six American tetraploid species were divided into two types that differed in the number of rDNA sites and RFLP profiles. Four hexaploid species were similar in number and location of both types of rDNA sites, but the RFLP profiles of 18S-25S rDNA revealed one species, H. arizonicum, with a different ancestry. * CONCLUSIONS: Five American perennial tetraploid species appear to be alloploids having the genomes of an Asian diploid H. roshevitzii and an American diploid species. The North American annual tetraploid H. depressum is probably a segmental alloploid combining the two closely related genomes of American diploid species. A hexaploid species, H. arizonicum, involves a diploid species, H. pusillum, in its ancestry; both species share the annual growth habit and are distributed in North America. Polymorphisms of rDNA sites detected by FISH and RFLP analyses provide useful information to infer the phylogenetic relationships of I-genome Hordeum species because of their highly conserved nature during polyploid evolution.     

Localization of the 5S and 45S rDNA sites and cpDNA sequence analysis in species of the Quadrifaria group of Paspalum (Poaceae, Paniceae)

BACKGROUND AND AIMS: The Quadrifaria group of Paspalum (Poaceae, Paniceae) comprises species native to the subtropical and temperate regions of South America. The purpose of this research was to characterize the I genomes in five species of this group and to establish phylogenetic relationships among them. METHODS: Prometaphase chromatin condensation patterns, the physical location of 5S and 45S rDNA sites by fluorescence in situ hybridization (FISH), and sequences of five chloroplast non-coding regions were analysed. KEY RESULTS: The condensation patterns observed were highly conserved among diploid and tetraploid accessions studied and not influenced by the dyes used or by the FISH procedure, allowing the identification of almost all the chromosome pairs that carried the rDNA signals. The FISH analysis of 5S rDNA sites showed the same localization and a correspondence between the number of sites and ploidy level. In contrast, the distribution of 45S rDNA sites was variable. Two general patterns were observed with respect to the location of the 45S rDNA. The species and cytotypes Paspalum haumanii 2x, P. intermedium 2x, P. quadrifarium 4x and P. exaltatum 4x showed proximal sites on chromosome 8 and two to four distal sites in other chromosomes, while P. quarinii 4x and P. quadrifarium 2x showed only distal sites located on a variable number of small chromosomes and on the long arm of chromosome 1. The single most-parsimonious tree found from the phylogenetic analysis showed the Quadrifaria species partitioned in two clades, one of them includes P. haumanii 2x and P. intermedium 2x together with P. quadrifarium 4x and P. exaltatum 4x, while the other contains P. quadrifarium 2x and P. quarinii 4x. CONCLUSIONS: The subdivision found with FISH is consistent with the clades recovered with cpDNA data and both analyses suggest that the Quadrifaria group, as presently defined, is not monophyletic and its species belong in at least two clades.     

Comparative cytogenetic analysis of eleven species of subfamilies Neoplecostominae and Hypostominae (Siluriformes: Loricariidae)

The family Loricariidae with about 690 species divided into six subfamilies, is one of the world’s largest fish families. Recent studies have shown the existence of several problems in the definition of natural groups in the family, which has made the characterization of the subfamilies and even of some genera quite difficult. With the main objective of contributing for a better understanding of the relationships between loricariids, cytogenetic analysis were conducted with two species of Neoplecostominae and nine species of Hypostominae that, according to morphological and molecular data, may belong to a new monophyletic unit. The results obtained showed a marked chromosomal conservation with the presence of 2n = 54 chromosomes and single interstitial Ag-NORs in all species analyzed. Considering that Neoplecostominae is the primitive sister-group of all other loricariids, with exception of Lithogeneinae, this karyotypic structure may represent the primitive condition for the family Loricariidae. The cytogenetic characteristics partaken by the species of Neoplecostominae and Hypostominae analyzed in the present study reinforce the hypothesis that the species of both these subfamilies might belong to a natural group.     

Genomic heterogeneity and instability in colorectal cancer: spectral karyotyping, glutathione transferase-Ml and ras

Genomic instability in cancer is frequently described as being either chromosomal instability or microsatellite instability, although when events within chromosomes are monitored, extensive intrachromosomal instability is also found. Spectral karyotyping was used to visualize how extensively genomic instability gives rise to intratumor genomic heterogeneity in sporadic colorectal carcinomas. Two factors were then examined which might relate to intrachromosomal instability in colorectal cancers: the presence of the glutathione transferase-Ml gene to detoxify potential carcinogens, and the presence of activated ras which has been associated with chromosomal instability when first expressed. Intrachromosomal genomic instability was previously determined by inter-(simple sequence repeat) PCR (inter-SSR PCR) and by fractional allelic loss rate for 348 markers. GSTM1 status was determined for each of 49 tumors through use of specific PCR, and 28 of the tumors showed the GSTM1 null genotype. A significant association was found between GSTMl-null status and elevated inter-(simple sequence repeat) PCR instability. In contrast, no association was found with fractional allelic loss rate. The first exons of the K-ras and H-ras oncogenes were sequenced in 72 colorectal cancers; 19 of the tumors had a mutation in codon 12 of the K-ras gene (24.5%), but no H-ras mutations were found. A weak correlation (p=0.10) was observed between mutant K-ras and inter-(simple sequence repeat) PCR genomic instability, and no association existed with fractional allelic loss rate.