Construction of midget chromosomes in wheat.

To test the usefulness of breakage-fusion-bridge (BFB) cycles in generating new chromosome aberrations in bread wheat (Triticum aestivum L.) and to extend the range of aberrations available, a series of midget chromosomes was produced from the long arm of chromosome 1B. Using a reverse tandem duplication initiated chromatid type BFB cycle, the 1BL arm was broken and fused with centromeres of either chromosome 5BL or 1RS to form dicentric chromosomes. The 1R and 5B centromeres were broken by centric misdivision. Among the progenies of plants with dicentric chromosomes, two classes of monocentric chromosomes were selected: deficient chromosomes 1B and chromosomes that had 1RS or 5BL for one arm and various fragments of 1BL for the other arm. Following centric misdivision of these monocentrics, midget chromosomes 1BL were isolated: deficient and deletion telocentrics and telocentrics derived from interstitial regions of 1BL. By chance, one deficient chromosome 1BS and one deletion chromosome 1BS were identified in unrelated lines of the same wheat. Following centric misdivision of these chromosomes, two midget chromosomes covering the whole of 1BS were added to the set.     

Chromosomal rearrangements in rock wallabies, Petrogale (Marsupialia: Macropodidae). VII. G-banding analysis of Petrogale brachyotis and P. concinna: species with dramatically altered karyotypes.

G-banded metaphase preparations of cultured fibroblasts were used to construct the karyotypes of Petrogale brachyotis (2n = 18) and P. concinna (2n = 16). The two karyotypes differ significantly from the plesiomorphic karyotype of the genus and from those of all other Petrogale species examined. Petrogale brachyotis and P. concinna are characterised by three synapomorphies: a 1-10 centric fusion, a 3a-6 centric fusion, and a submetacentric chromosome 2 (2s). Both species also possess autapomorphies. Petrogale brachyotis is characterised by submetacentric chromosomes 5 (5s) and 4 (4sm), whereas P. concinna is characterised by a 5-9 centric fusion and a submetacentric chromosome 8 (8m). The 2s, 5s, 4sm, and 8m chromosomes all appear to be derived from their plesiomorphic homologs by centromeric transpositions. Although the rate of chromosome evolution varies considerably in Petrogale, the genus clearly exhibits karyotypic orthoselection, with all the autosomal rearrangements identified being either centric fusions or centromeric transpositions. This study also illustrates the potential for convergent evolution in chromosomally diverse groups and demonstrates the importance of G-banding studies for accurate identification of chromosome rearrangements.     

Centric fusion differences among Oryx dammah, O. gazella, and O. leucoryx (Artiodactyla, Bovidae)

G- and C-banded karyotypes of the genus Oryx were compared using the standard karyotype of Bos taurus. Chromosomal complements were 2n = 56 in O. gazella gazella, 2n = 58 in O. g. beisa and O. g. callotis, 2n = 56-58 in O. dammah, and 2n = 57-58 in O. leucoryx. The number of autosomal arms in all karyotypes was 58. Nearly all variation in diploid number was the result of three independent centric fusions, but one 2n = 57 specimen of O. g. gazella deviated from the normal complement of 2n = 56 due to XXY aneuploidy. A 2;17 centric fusion was fixed in O. g. gazella, whereas O. g. beisa and O. g. callotis lacked this fusion and had indistinguishable karyotypes. Oryx dammah was polymorphic for a 2;15 centric fusion, and O. leucoryx was polymorphic for an 18;19 centric fusion. The five Oryx taxa shared a fixed 1;25 centric fusion; the small acrocentric element involved in the 1;25 fusion was identified by fluorescence in situ hybridization using a cosmid specific to Bos chromosome 25. The X and Y chromosomes were also conserved among the five taxa. Oryx g. gazella differed from the other Oryx species because of the fixed 2;17 centric fusion. This difference reflects an apparently longer period of geographic isolation between O. g. gazella and other populations of Oryx, and it is consistent with the classification of O. gazella and O. beisa as distinct species (see Kingdon, 1997). The lack of monobrachial relationships among the Oryx taxa indicates that sterility barriers between species have not developed. Viability of hybrid offspring constitutes a threat to captive breeding programs designed for endangered species conservation; in the case of Oryx, the 2;15, 2;17, and 18;19 metacentrics could serve as marker chromosomes for assessing hybridization between certain Oryx taxa.     

Reconstruction in wheat of complete chromosomes 1B and 1R from the 1RS.1BL translocation of 'Kavkaz' origin.

Translocation 1RS.1BL originally from the 'Aurora' and 'Kavkaz' wheats has spread to bread wheats all over the world. It offers several resistance genes and appears to significantly increase yields. For future study of the arm location of the yield-increasing factors, complete chromosomes 1B and 1R were reconstructed from the 1RS.1BL translocation. This was accomplished by centric misdivision and fusion in double monosomies 20 II + 1RS.1BL I + 1BS.1RL I. The frequency of misdivision and misdivision-fusion of the two unpaired chromosomes was 23.1%, which was much higher than expected but comparable with that observed in other stocks grown under similar conditions. Transmission of the reconstructed chromosomes to progeny was normal. In addition to all possible misdivision and misdivision-fusion products, two chromosomes of ambiguous origin were recovered: chromosome 1B with a proximal insert of about 40% of 1RS and chromosome 1R with a proximal insert of about 30% of 1BS. The study demonstrates that centric translocations can misdivide and fuse again to produce stable chromosomes with new arm combinations.     

Comparing the somal size and nuclear positions of the monkey stellate and coeliac ganglion cells

The stellate and coeliac ganglia of 2 Macaque monkeys were cut serially at 1 micron thickness and analysed. Results from the analysis of 82 stellate and 60 coeliac ganglion cells in 1 monkey show that in cross-sections, the neuronal nuclei may be eccentric, centric or nearly centric and remain so throughout the longitudinal extent of the neuron. In both ganglia, the majority of neurons possess eccentric nuclei, but in the coeliac ganglion, the percentage of neurons with centric and/or nearly centric nuclei is higher (41.7%) than that in the stellate ganglion (26.3%). While 5% of neurons in the coeliac ganglion are binucleated, no binucleated neurons were found in the stellate ganglion. The somal size ranges of the stellate (10-39 microns) and the coeliac (14.5-45 microns) ganglion neurons as obtained from both monkeys are quite close. The percentage frequency distribution of the stellate ganglion neurons in monkey 1 was also quite similar to that of the coeliac ganglion neurons. It is concluded that different neuronal size is not likely to be associated with different target organs.     

Theoretical bases for karyotype evolution. II. The fusion burst in man and mouse

As a theoretical standard for evaluating the high incidence of centric fusion in man and mouse, the relative probabilities of occurrence of reciprocal translocation (Tr), inversion (In) and centric fusion (Fu) were estimated based on the random-contact-and-exchange model. It was shown by this model that centric fusion was extremely rare (Fu = 0.0002, In = 0.0521 and Tr = 0.9477 for a human haploid karyotype). On the other hand, the occurrence rate of centric fusion in human newborn babies and European feral mice was about 500-1,000 times higher than the theoretically expected values, which is termed here the "fusion burst". We suggest that the fusion burst may be induced by the physical proximity of telomeres on the nuclear membrane, and the exchange of DNA strands by errors of telomere replication mechanisms. The cytogenetical significance of the fusion burst is discussed with regard to the minimum interaction hypothesis proposed by Imai et al. (1986). We suggest two closely linked possibilities that (1) the fusion burst in man and mouse can theoretically be placed in karyotype evolution as a transitional phase in the main stream of the fission-inversion cycle, and (2) it may be accelerated by some unknown (mutagenic) factors other than ionizing radiation.     

The ratio of dicentrics to centric rings produced in human lymphocytes by acute low-LET radiation.

Chromosome aberrations produced by ionizing radiation are assumed to develop from DNA double-strand breaks (DSBs) which interact pairwise, in an exchange event. Dicentrics and centric rings are aberrations that exemplify inter- and intrachromosomal exchanges, respectively. We show from a survey of published data that for acute low-LET irradiation of resting human lymphocytes the observed ratio of dicentrics to centric rings is approximately five times smaller than predicted by a pairwise interaction model which assumes complete randomness. Such a low ratio can be interpreted as evidence for a proximity effect, favoring exchanges of an intrachromosomal type. That is, since DSBs induced close together have an above-average chance of pairwise interaction, the observed excess of centric rings indicates that at the time of irradiation there is some degree of spatial confinement for the two arms of a single chromosome. Assuming the excess of centric rings is indeed due to proximity effects, the data are used to estimate that the volume of a domain, within which any one lymphocyte chromosome is localized at one instant during the G0/G1 phase, is at most approximately 20% of the nuclear volume.     

Unstable inheritance of maize B-type chromosomes that lack centric heterochromatin.

The B chromosome of maize undergoes frequent non-disjunction at the second pollen mitosis. In B-A translocations, the B-A chromosome retains the capacity for non-disjunction. We have collected deletion-derivative TB-9Sb stocks. One derivative, the "type 1 telocentric", has a B-9 chromosome that lacks centric heterochromatin. It produces few recessive (non-disjunctional) phenotypes in pollen parent testcrosses of the translocation heterozygote, 9 9-B telo B-9. The finding helped demonstrate the role of centric heterochromatin in non-disjunction. An isochromo some derivative of the type 1 telocentric was also recovered. It was tested in the 9-B 9-B iso B-9 constitution. This is equivalent to 9 9-B telo B-9 in terms of chromosome 9 dosage. Surprisingly, crosses with the isochromosome gave significant levels of recessive phenotypes. In addition, high levels of variegated phenotypes were found. Recently, a circumstance was found that makes inheritance of the type 1 telocentric chromosome somewhat similar to that of the isochromosome. Crosses with hypoploid 9-B 9-B telo B-9 plants showed significant levels of recessive and variegated phenotypes. These crosses were investigated to help explain the source(s) of the phenotypes. Cytological and genetic studies were performed. Centric misdivision was found to account for the variegated phenotypes. A mixture of conventional B non-disjunction and centric misdivision produced the recessive phenotypes. The significance of conventional non-disjunction in the absence of centric heterochromatin is discussed.     

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.     

Aneuploidy in metaphases II of spermatocytes of wild house mice from a hybrid zone between a Robertsonian population (CD: 2n = 22) and a population with the standard karyotype (2n = 40)

Meiotic metaphases II from archival slides were studied of male house mice caught in a hybrid zone between a population monomorphic for nine centric fusions (2n = 22) and a population with the standard karyotype (2n = 40), near Rome. The frequency of aneuploidy increases, up to 50%, with increasing number of heterozygous centric fusions (1–4). This revised version was published online in July 2006 with corrections to the Cover Date.     

A NEW FRESHWATER CENTRIC DIATOM MICROSIPHONA POTAMOS GEN. ET SP. NOV.1

A new centric diatom, Microsiphona potamos gen. et sp. nov. (family Coscinodiscaceae), is described from the Little Miami River, Cincinnati, Ohio, where it occurred at cell densities ranging from 29 to 20,140/ml in surface grab samples during the period May 18–December 14, 1966, contributing an average of 11% and a maximum of 35% of the centric diatoms. This species has been observed in grab samples from rivers throughout the United States. The cells are 3–4 μ in diameter, 4–8 μ long, and contain 2 to several plate-like chromatophores. They occur singly, or arc held together in short chains by the old girdle bands and by numerous apiculi that connect the opposing valves of adjacent daughter cells.     

Robertsonian translocations introduced into an island population of house mice

In April 1982, 77 house mice from the Orkney Island of Eday were released by R. J. Berry and his associates on the Isle of May, Firth of Forth. The Isle of May had a standard house mouse karyotype (2n = 40), while those from Eday are homozygous for three centric fusions (2n = 34). Within 18 months of introduction (September 1983), each centric fusion had increased in frequency from an estimated starting value of 8% to a value close to 50%, and they were segregating in accordance with Hardy–Weinberg expectations. In essence, the transformed population was behaving as a panmictic unit. The frequencies of introduced chromosomes had apparently stabilized by September 1986 with values around 65% for all three fusions. The cytogenetic data obtained in the Isle of May introduction experiment accord well with data for single gene loci (represented by allozyme data) and morphometric data. Male Eday–May F1 hybrids were found to have a low frequency of non-disjunction (13%). This study is unusual because the successful introduction of mice into an established population, and the introgression and stabilization of three centric fusions, could not have been predicted from previous studies on the mouse.     

Molecular distinction between true centric fission and pericentric duplication-fission

Centromere (centric) fission, also known as transverse or lateral centric misdivision, has been defined as the splitting of one functional centromere of a metacentric or submetacentric chromosome to produce two derivative centric chromosomes. It has been observed in a range of organisms and has been ascribed an important role in karyotype evolution; however, the underlying mechanisms remain unknown. We have investigated four cases of apparent centric fission in humans. Two cases show a missing chromosome 22 or 18 that is replaced by two centric ring products, a third case shows two chromosome-10-derived telocentric chromosomes, whereas a fourth case involves the formation of two chromosome-18-derived isochromosomes. In all four cases, results of gross cytogenetic and fluorescence in situ hybridisation analyses were consistent with a simple centric fission event. However, detailed molecular analyses provided evidence in support of centromere duplication as a predisposing mechanism for the observed chromosomal breakage in two of the cases. Results for the third case are consistent with direct centric fission not involving centromere pre-duplication as the likely mechanism. Insufficient material has precluded the further study of the fourth case. The data provide the first molecular evidence for centromere pre-duplication as a possible mechanism to explain the classically assumed simple centric fission events in clinical cytogenetics, karyotype evolution and speciation.     

Supramolecular organization of fucoxanthin–chlorophyll proteins in centric and pennate diatoms

Fucoxanthin–chlorophyll proteins (FCP) are the major light-harvesting proteins of diatom algae, a major contributor to marine carbon fixation. FCP complexes from representatives of centric (Cyclotella meneghiniana) and pennate (Phaeodactylum tricornutum) diatoms were prepared by sucrose gradient centrifugation and studied by means of electron microscopy followed by single particle analysis. The oligomeric FCP from a centric diatom were observed to take the form of unusual chain-like or circular shapes, a very unique supramolecular assembly for such antennas. The existence of the often disputed oligomeric form of FCP in pennate diatoms has been confirmed. Contrary to the centric diatom FCP, pennate diatom FCP oligomers are very similar to oligomeric antennas from related heterokont (Stramenopila) algae. Evolutionary aspects of the presence of novel light-harvesting protein arrangement in centric diatoms are discussed.     

紫红链霉菌对钉螺酶组织化学的影响

为研究紫红链霉菌灭螺作用的机理,将钉螺分别浸泡于紫红链霉菌培养液(含菌4×106/ml)及去氯水、培养基中36h后,用酶组织化学方法显示各组钉螺肝脏、中枢神经节、头足部及鳃的Mg2 激活的三磷酸腺苷酶(Mg2 ATPase)、胆碱脂酶(ChE)、一氧化氮合酶(NOS)、乳酸脱氢酶(LDH)、琥珀酸脱氢酶(SDH)并观察其变化。结果显示:菌液浸泡组钉螺的Mg2 ATPase活性在肝脏、中枢神经节、头足部及鳃部均明显减弱或完全失活,LDH在中枢神经节、头足部也有一定程度减弱,ChE、NOS、SDH在肝脏、中枢神经节、头足部及鳃部与去氯水组无明显差异;培养基组与去氯水组钉螺相应部位的Mg2 ATPase、ChE、NOS、LDH、SDH活性一致。结果提示:紫红链霉菌的灭螺作用机理主要在于破坏钉螺体内Mg2 ATPase和LDH活性,使ATP生成和利用障碍,最终因能量缺乏而丧失生命功能直至死亡     

OBSERVATIONS ON THE ULTRASTRUCTURE OF THE MALI GAMETES OF BIDDULPHIA LEVIS EHR.1

The marine centric diatom Biddulphia levis produced uniflagellate fusiform male gametes completely within the parent cell frustule. These gametes lacked both a central pair of microtubules in the flagellar axoneme and chloroplasts but did contain a cone of microtubules which passed posteriorly from the base of the kinetosome along the nuclear envelope. The gametes were released through a specialized pore in the girdle band leaving behind a cytoplasmic mass which contained chloroplasts and other cytoplasmic components. Tubules which resembled the flimmer hairs on the gamete flagellum occurred in cisternae of the cytoplasmic reticulum in the residual cytoplasm and in the nuclear envelope of the gametes. Gametogenesis in B. levis is compared with similar processes in other centric diatoms.     

The centromere structure in Robertsonian wheat-rye translocation chromosomes indicates that centric breakage-fusion can occur at different positions within the primary constriction

Univalent chromosomes at meiotic metaphase I have a tendency to misdivide at the centromeres. Fusion of the misdivision products may produce Robertsonian translocations. The fine structure of the centromeres in Robertsonian wheat-rye translocation chromosomes was analyzed by fluorescence in situ hybridization (FISH) using two centromere-specific DNA clones: pRCS1, derived from rice, and pAWRC1, derived from rye. Clone pRCS1 hybridizes to the centromeres of all grasses including wheat and rye, whereas clone pAWRC1 is rye specific and hybridizes only to the centromeres of rye. Four of the six wheat-rye translocations derived from a single centric misdivision event (1st generation translocations) had hybrid centromeres, with approximately half of the centromere derived from rye and half from wheat. In the two other 1st generation translocations, the entire centromere was derived from rye. Among eight reconstructed wheat and rye chromosomes that originated from two consecutive centric misdivision-fusion events (2nd generation translocations), T1BS.1BL (derived from T1BS.1RL and T1RS.1BL) and one of three T2BS.2BL (derived from T2RS.2BL and T2BS.2RL) had hybrid centromeres. T1RS.1RL (derived from T1BS.1RL and T1RS.1BL), two of three T2BS.2BL, and all three T2RS.2RL (derived from T2RS.2BL and T2BS.2RL) had rye centromeres. All three 3rd generation translocations had hybrid centromeres with approximately half of the centromere derived from rye. There were no indications that the composite structure of the centromere in these chromosomes affected their behavior in mitosis or meiosis. These observations support the notion of a compound structure of the centromere in higher organisms, and indicate that during the centric breakage-fusion event, centromere breakage may occur in different positions along the segment of the chromosome that interacts with the spindle fibers. Normal behavior of the 1st, 2nd, and 3rd generation centric translocations in mitosis and meiosis indicates that, at least in wheat and rye, centromeres are not chromosome specific.     

A robertsonian translocation in the fresh-water triclad Dugesia lugubris: karyometric analysis and evolutionary inferences

Biotype E of Dugesia lugubris has a haploid complement of 4, comprising 3 acrocentrics of different length and a short chromosome; biotype F has a haploid complement of 3, with a long metacentric, an acrocentric and a short chromosome. A karyometrical analysis has shown that the metacentric chromosome of biotype F derived from a centric fusion between the acrocentrics 1 and 3 of biotype E. — The evolutionary meaning of this centric fusion is discussed.     

A new case of rob(14;17) in cattle

Robertsonian translocations, also called centric fusions, represent the most frequent chromosome anomalies in cattle, and rob(1;29) is the most widespread. However, centric fusions involving other chromosomes have been discovered in different cattle breeds. Here we report the appearance of a new case of rob(14;17) in an Italian cattle breed more than ten years after the first and only case had been observed, and we demonstrate the independent origin of this anomaly from the previous case.     

中国云南果蝇属暗果蝇种组的核型分化

观察了新近发现于我国云南的果蝇属暗果蝇种组(Drosophila obscura species group)种类D．luguensis、D．dianensis和D．limingi的有丝分裂中期核型,并将3个种的核型与各自的近缘种类进行了比较。D．luguensis具2n=12条染色体,包括3对中央着丝粒(V形)染色体、2对近端着丝粒(棒状)染色体以及1对微小(点状)染色体。其中X和Y染色体均为中央着丝粒染色体。D．dianensis和D．limingi具2n=10条染色体,包括1对大的V形常染色体,1对小的V形常染色体,2对J形(亚中着丝粒型)常染色体和1对点状染色体。其中X染色体为J形,Y染色体为短棒状。基于核型比较的结果以及D．sinobscura亚组地理分布的资料,结合种间系统发育关系研究结果,认为D．luguensis可能保留了该亚组祖先种类的核型。D．sinobscum的核型(2n=12：2V,1J,2R,1D)可能由一个pre-“sinobscura-hubeiensis”谱系的一个分支通过臂间倒位演化而来,而D．hubeiensis的核型(2n=10：4V,1D)可能由该谱系的另一分支通过着丝粒融合(2对近端着丝粒常染色体的融合)而形成。推测在D．dianensis和近缘欧洲种D．subsilvestris(2n=12：3V,2R,1D)间、D．limingi和东亚近缘种D．tsukubaensis(2n=12：3V,2R,1D)间的物种分化过程中,可能有相似的染色体变异类型发生。