着丝粒横裂和着丝粒并合及其在高等植物染色体进化中的意义

本文讨论了着丝粒横裂和并合及其在高等植物染色体进化中的意义。着丝粒横裂和着丝粒并合是两个矛盾又辩证统一的过程,是染色体的基本变异形式之一,它们同时影响着植物类群的染色体基数、核型对称性、连锁关系、交叉频率和位点等细胞遗传学的重要方面.从而在高等植物染色体进化中起着重要作用,着丝粒和端粒的复制模型为着丝粒的横裂与并合提供了可能的机理,但尚待直接的生物化学证据的证实,原始基数的确定是判别着丝粒横裂与并合的关键。     

Alteration by centric fission of the diploid chromosome number in Vicia faba L.

An individual with a diploid chromosome complement of 2n=14 instead of 2n=12 is deseribed for the broad bean Vicia faba L. This karyotypic deviation resulted from centromere splitting of the wildtype metacentric satellite chromosome pair as demonstrated by Giemsa banding pattern. It is the first case of centric fission observed in this species. Our data support the hypothetic mechanism of Robertsonian rearrangements suggested by Holmquist and Dancis (Genetica 52–53: 151–163, 1980).     

Dicentric chromosomes and the inactivation of the centromere

Summary The origin and behavior of human dicentric chromosomes are reviewed. Most dicentrics between two non-homologous or two homologous chromosomes (isodicentrics), which are permanent members of a chromosome complement, probably originate from segregation of an adjacent quadriradial; such configurations are the result of a chromatid translocation between two nonhomologous chromosomes, or they represent an adjacent counterpart of a mitotic chiasma. The segregation of such a quadriradial may also give rise to a cell line monosomic for the chromosome concerned (e.g., a 45,X line). Contrary to the generally held opinion, isodicentrics rarely result from an isolocal break in two chromatids followed by rejoining of sister chromatids. In this case the daughter centromeres go to opposite poles in the next anaphase, and the resulting bridge breaks at a random point. This mechanism, therefore, leads to the formation of an isodicentric chromosome only if the two centromeres are close together, or if one centromere is immediately inactivated. Observations on the origin of dicentrics in Bloom syndrome support these conclusions. One centromere is permanently inactivated in most dicentric chromosomes, and even when the dicentric breaks into two chromosomes, the centromere is not reactivated. The appearance and behavior of the acentric X chromosomes show that their centromeres are similarly inactivated and not prematurely divided. Two Bloom syndrome lymphocytes, one with an extra chromosome 2 and the other with an extra chromosome 7, each having an inactivated centromere, show that this can also happen in monocentric autosomes.     

Trisomy 8p: unusual origin detected by fluorescence in situ hybridization

Summary Chromosomal analysis of a neonate with brain and heart abnormalities revealed trisomy for 8p. The mother's karyotype showed 47 chromosomes with one chromosome 8 being represented as two separate chromosomes, an acrocentric 8p and a telocentric 8q. Gbanding and silver staining revealed a satellite and nucleolus organizing region (NOR) on the 8p. Centromericspecific probes to the centromeres of chromosomes 8, 15, 13/21, 22 and the acrocentric chromosomes revealed that only the 8q centromere was of chromosome-8 origin, while the 8p centromere was of chromosome-14 origin.     

Stable telocentric chromosomes produced following centric misdivision in Myrmeleotettix maculatus (Thunb.)

The standard complement of Myrmeleotettix maculatus includes a pair of L ₃ metacentric chromosomes but throughout the germ line of a structurally mutant male individual one of these had been replaced by two telocentrics. These chromosomes divided normally at mitosis and at meiosis paired completely with the arms of the remaining L ₃. There was no tendency for the two terminal centromeres to fuse. At first anaphase the two rods usually segregated from the metacentric which resulted in the formation of a high percentage of balanced gametes. On the basis of this evidence and the morphological appearance of the centric region it has been concluded that the derived telocentrics evolved following misdivision through the inner zone of the metacentric centromere. In view of their apparent stability it has been proposed that, contrary to certain beliefs, centric fission may have played an important role during karyotype evolution in the Acrididae.     

Mapping of five human chromosome 19 DNA markers to owl monkey chromosomes.

Hybridization of DNA from three panels of karyotypically distinct owl monkey x rodent somatic cell hybrids with human DNA probes resulted in the syntenic assignments of INSR-LDLR-TGFB1-APOE-D19S8 to owl monkey chromosome 25 of karyotype VI (2n = 49/50), INSR-LDLR-TGFB1-D19S8 to chromosome 2 of karyotype II (2n = 54), and INSR-APOE to chromosome 2 of karyotype V (2n = 46). The APOE and D19S8 loci are on adjacent regions proximal to the centromere of chromosomes 25q (K-VI) and 2p (K-II), as determined by in situ chromosomal hybridization analysis. These findings support our previous proposals on (1) the homology of these chromosomes of three owl monkey karyotypes, (2) the evolutionary derivation of chromosome 2 of karyotypes II and V as the result of two separate centric fusion events, and (3) the likelihood that owl monkey chromosome 25 (K-VI) (and its homologs) is a conserved genetic homoeolog of human chromosome 19.     

Maize centromere mapping: a comparison of physical and genetic strategies

Centromere positions on 7 maize chromosomes were compared on the basis of data from 4 to 6 mapping techniques per chromosome. Centromere positions were first located relative to molecular markers by means of radiation hybrid lines and centric fission lines recovered from oat-maize chromosome addition lines. These centromere positions were then compared with new data from centric fission lines recovered from maize plants, half-tetrad mapping, and fluorescence in situ hybridizations and to data from earlier studies. Surprisingly, the choice of mapping technique was not the critical determining factor. Instead, on 4 chromosomes, results from all techniques were consistent with a single centromere position. On chromosomes 1, 3, and 6, centromere positions were not consistent even in studies using the same technique. The conflicting centromere map positions on chromosomes 1, 3, and 6 could be explained by pericentric inversions or alternative centromere positions on these chromosomes.     

基于比较核型分析方法追溯百合族 (百合科) 二型性核型的起源

百合族具有非常一致的二型性核型,由4条长染色体以及20条短染色体组成。目前有两个假说解释其二型性核型的来源,着丝粒横裂和多倍化。但是,具体是哪一种机制起主要作用仍然不清楚。根据文献以及自己的实验结果,我们整理并重新分析了百合亚科和美德兰亚科所有属的核型资料。比较核型分析结果表明,来自单条染色体的特征、染色体臂数、核型不对称性以及染色体的相对长度诸方面的证据都支持着丝粒横列是百合族核型进化的主要机制,但不能排除其它的机制也在起着作用,如臂间倒位和易位。臂间倒位和易位可能在郁金香族的核型进化中起着主要的作用。另外,本研究还报道了三个种的核型,粗茎贝母 (Fritillaria crassicaulis)、准格尔郁金香 (Tulipa suaveolens) 和尖果洼瓣花 (Gagea oxycarpa)。     

Dual-color FISH karyotype analyses using rDNAs in three Cucurbitaceae species

Dual-color fluorescence in situ hybridization (FISH) analysis of three Cucurbitaceae species from different genera was conducted using 5S and 45S rDNA probes. In Benincasa hispida (Thunb.) Cogn. (2n=24), the 45S rDNA probe hybridized on two chromosomes, one in the short arm of a medium-sized metacentric chromosome and another at the satellite of a chromosome. The 5S rDNA hybridized at a site proximal to the centromere of the same short arm of the 45S rRNA gene locus that occupied almost the entire short arm. For Citrullus lanatus (Thunb.) Matsum & Nakai (2n=22), the 45S rDNA probe hybridized at sites in the short arms of two chromosomes and the 5S rDNA probe was co-localized with the 45S rRNA locus at the region proximal to the centromere in one chromosome. The 45S rRNA loci occupied almost all of the short arms in both chromosomes. In Cucurbita moschata Duch. (2n=40), the 45S rDNA probe hybridized in five chromosomes in which the 45S rRNA genes occupied almost two-thirds of the chromosomes in two large chromosomes and the entire short arm of a medium-sized chromosome. Two other loci were present in two medium-sized chromosomes, one in the proximal region in the short arm of a chromosome and another at the tip of the long arm of a chromosome. Chromosomes of B. hispida were relatively larger than those of the other two species. The karyotype of B. hispida is composed of two metacentrics and 10 submetacentrics, while that of C. lanatus is composed of seven metacentrics and four submetacentrics and that of C. moschata is composed of 18 metacentrics and two submetacentrics. Comparative chromosome evolution among the three Cucurbitaceae species was attempted using the karyotypes and the chromosomal distribution patterns of the 5S and 45S rDNAs. The results presented herein will be useful in elucidating the phylogenetic relationships among Cucurbitaceae species, and will provide basic data for their breeding programs.     

Karyotype study of 5 species of Costa Rican snakes of the colubrid family

The karyotypes of five species of colubrid snakes from Costa Rica are as follows: Imantodes cenchoa and Drymobius margaritiferus have a diploid number of 36, with 16 macro- and 20 microchromosomes. The fourth pair is heteromorphic in females of I. cenchoa, with a metacentric Z and a submetacentric W chromosomes. Karyotypes of Erythrolampius bizonus and Leimadophis epinephalus have 28 chromosomes, without a clearcut separation between macro- and microchromosomes. In the case of E. bizomus, the fourth pair contains the sex chromosomes Z and W, both are submetacentric, but the W is smaller. Xenedon rabdocephalus has a diploid number of 34 chromosomes (22 macro- and 12 microchromosomes); pair 3 is heteromorphic in females, with a submetacentric Z and a smaller metacentric W. The karyotype of X. rabdocephalus may be derived from a primitive karyotype by means of reduction in the number of microchromosomes and centric fissions of two pairs of metacentric autosomes.     

A comparative chromosome study of twenty killifish species of the genus Fundulus (Teleostei: Cyprinodontidae)

Female karyotypes from ovarian cell cultures of 20 species of killifish (Fundulus) ranged in diploid number from 32 to 48, but in arm number (NF) from 48 to 52. The small F chromosomes, which constituted the fundamental elements in the karyotype, were evenly graded in length. The large biarmed chromosomes (L), which were about twice the length of the average Fs, characterized only those species with 2N less than 48 chromosomes. And among these species, an increase in complement by a pair of L's was always accompanied by a decrease of two pairs of A's, indicating Robertsonian changes by the centric fusion of two A's to form one L chromosome. Other diagnostic chromosome characters included: the number and structure of biarmed and satellited F chromosomes and the percentage of F's with relatively short short-arms (SSA). Besides centric fusion, mechanisms of chromosomal evolution in Fundulus probably included pericentric inversion, producing biarmed F chromosomes from acrocentric F's and partial loss of a chromosome segment producing smaller biarmed F chromosomes from larger ones. The percentage of SSA chromosomes generally decreases from relatively primitive to specialized species. The presumably most primitive species have only SSA type acrocentric F chromosomes. The 20 Fundulus species were classified into 2 major groups according to the percentage of SSA chromosomes: the SSA group, including 3 subgroups, had more than 50% SSA's; the LSA group, including 2 subgroups, had fewer than 50% SSA's. This classification based only on karyotypic characters generally agreed with others based on gross morphological characters. A possible evolutionary scheme is proposed to account for the derived killifish karyotypes.     

夏蜡梅核型的研究

本文首次报道我国特有重点保护植物夏蜡梅的核型为K(2n)=2x=22=18m+2m(SAT)+2sm,属Stebbins的“1A”类型,在演化上处于相当原始的地位。它的核型似比北美的光叶红对称和原始,因此至少夏蜡梅属可能起源于中国。     

Computerized analysis of chromosomal parameters in karyotype studies

Summary A study is presented of the possibilities and limitations of semi-automated karyotype analysis on the basis of chromosome length and centromere index. A number of computer programs have been developed for 1) quick and precise measurements of chromosome arm length with the help of a graphics tablet, 2) computing (relative) length and centromere index and statistical analyses of the data, and 3) representation of these chromosomal parameters in two-dimensional scattergrams. An ellipse representing 95% of the probability mass is drawn around the bivariate mean of each chromosome. The size and orientation of the axes are calculated from repeated measurements of the chromosomes of one metaphase plate. If there is a correlation between length and centromere index, which is often the case, the axes of the ellipse are tilted. Incorporation of such a covariance analysis proved to be of great importance for an accurate karyotype analysis. The Computer Aided Karyotyping package does not contain routines for an automated classification of the chromosomes. The main reason is that the variation in length and centromere index of a given chromosome in different cells is often much larger than the variation between nonhomologous chromosomes. In addition, it was our aim to develop universal karyotyping aids which can be used regardless of the species studied.     

On the continuity of chromosomal subunits: an analysis of induced ring chromosomes in Vicia faba

The proposition that subunits of a chromatid are continuous in a directional sense has been tested by observing the behaviour of induced ring chromosomes in Vicia faba. On the simplest hypothesis, that the subunits are the uninterrupted complementary strands of the DNA molecule, the polarity of rejoining should result in free separation of rings following replication in successive cell cycles. Centric and acentric ring chromosomes were separately assessed in both diploid and colchicine-accumulated tetraploid metaphase cells of primary root tips. Contrary to expectation large numbers of single and interlocked rings were observed in both cell cycles. Spontaneous sister chromatid exchanges and other breakage-reunion events can produce the configurations seen; with the postulated level of sister chromatid exchange equating that determined autoradiographically in rod chromosomes of V. faba. Unless the replication of ring chromosomes produces conditions unusual in rod chromosome replication, spontaneous breakage is probably common in replicating or post replication Vicia chromosomes. — A fundamental difference exists between the behaviour of centric and acentric ring chromosomes. Acentric ring chromosomes behave as if the chromatid arm were one DNA molecule, or a number of DNA molecules with identical directional sense. However, centric ring chromosomes behave as if there were a difference at the centromere in at least one (probably the metacentric) chromosome of the Vicia complement. That is, the two duplication-segregation subunits which extend the length of the chromosome, may contain a change in polarity at the centromere.     

Duplication deficiency as the result of meiotic segregation of a maternal InV (10)

Summary In a family a large pericentric inversion involving nearly 70% of the chromosome 10 has been segregating during three generations, giving several carriers and an affected male with the karyotype 46,XY,der(10)(10pter10q25::10p12 10pter) mat. The patient is trisomic for 10p except for a small segment near the centromere, and monosomic for the distal 10q26. A simple diagrammatic representation explains the behavior of the inv(10) in meiosis. The study of meiotic segregation in the present case, and the reviews of previously reported duplication-deficiencies, agree with established postulates and add some principles to the understanding of duplication deficiencies resulting from the meiotic behavior of inverted chromosomes.     

Molecular Characterization of a Maize B Chromosome Centric Sequence

Supernumerary chromosomes are widespread in the plant kingdom but little is known of their molecular nature or mechanism of origin. We report here the initial cloning of sequences from the maize B chromosome. Our analysis suggests that many sequences are highly repetitive and shared with the normal A chromosomes. However, all clones selected for B-specificity contain at least one copy of a particular repeat. Cytological mapping using B chromosome derivatives and in situ hybridization show that the B specific repeats are derived from the centric region of the chromosome. Sequence analysis of this repeat shows homology to motifs mapped to various plant and animal centromeres and to the maize neocentromere. A precise localization of these sequences among breakpoints within the B centromere and an homology to a facultative centromere, suggest a role for this sequence in centromere function.     

Fusion of two apparently intact human X chromosomes

Summary Cytological studies have been presented from a 15-year-old girl with short stature and failure of puberty. Buccal mucosa preparations revealed X-chromatin mass approximately double in size of that of a normal female. Leukocyte metaphases suggested a two cell line composition of the patient. One population of cells conformed with 45,X chromosome distribution. The chromosome complement of her other cell line had a modal number of 46. In this cell line a C chromosome was replaced by an exceptionally large submetacentric chromosome. This abnormal element exhibited late DNA replicating pattern. G-banding study revealed that the abnormal chromosome was produced as a result of fusion involving telomeric ends of long arms of 2 intact X chromosomes. This translocation X was bearing 2 C-banded areas; one around the centromere and the other at the distal end of the long arm. The distal C-band area did not show any evidence for centromeric function. It appears that a centromere becomes latent in the presence of another centromere in a translocation bearing 2 total chromosomes. Such a change of state in the additional centromere is vital for the stability of the translocation chromosome.     

The pattern of phylogenomic evolution of the Canidae

Canidae species fall into two categories with respect to their chromosome composition: those with high numbered largely acrocentric karyotypes and others with a low numbered principally metacentric karyotype. Those species with low numbered metacentric karyotypes are derived from multiple independent fusions of chromosome segments found as acrocentric chromosomes in the high numbered species. Extensive chromosome homology is apparent among acrocentric chromosome arms within Canidae species; however, little chromosome arm homology exists between Canidae species and those from other Carnivore families. Here we use Zoo-FISH (fluorescent in situ hybridization, also called chromosomal painting) probes from flow-sorted chromosomes of the Japanese raccoon dog (Nyctereutes procyonoides) to examine two phylogenetically divergent canids, the arctic fox (Alopex lagopus) and the crab-eating fox (Cerdocyon thous). The results affirm intra-canid chromosome homologies, also implicated by G-banding. In addition, painting probes from domestic cat (Felis catus), representative of the ancestral carnivore karyotype (ACK), and giant panda (Ailuropoda melanoleuca) were used to define primitive homologous segments apparent between canids and other carnivore families. Canid chromosomes seem unique among carnivores in that many canid chromosome arms are mosaics of two to four homology segments of the ACK chromosome arms. The mosaic pattern apparently preceded the divergence of modern canid species since conserved homology segments among different canid species are common, even though those segments are rearranged relative to the ancestral carnivore genome arrangement. The results indicate an ancestral episode of extensive centric fission leading to an ancestral canid genome organization that was subsequently reorganized by multiple chromosome fusion events in some but not all Canidae lineages.