Quantitative studies on the arrangement of human metaphase chromosomes

Summary The spatial relationships between the homologous pairs of chromosomes in the normal human colcemid-treated metaphase plate were tested by two different mathematical approaches: (a) determination of the distances between the centromeres of the homologous chromosomes compared to the mean distance of all centromeres of the mitosis in question; (b) measuring the distances of the different chromosomes from the center of the mitosis.The following results were obtained: (1) The arrangement of human metaphase chromosomes does not follow a normal distribution; the distribution is narrower and taller, probably due to an impairment of free chromosome spreading by the cell membrane. We believe that only in membraneless mitotic cells should the chromosome-spread correspond to a normal distribution under the same preparation conditions. (2) There is a positive correlation between decreasing chromosome size and decreasing mean distance between homologous chromosomes. (3) A close positive correlation exists between increasing chromosome size and increasing distance to the barycenter of the mitosis. (4) There is also a close positive correlation between the distance of homologous chromosome pairs and their distance from the center of the mitosis, i.e., with increasing distance from the center of the mitosis, the distance between the homologous partners increases. (5) The following statistically significant deviations from these rules could be established: (a) The large acrocentric chromosomes are closer associated, as one would expect from their size, probably due to their participation in the nucleolus organization; (b) in the female cell one of the two X chromosomes has an extremely peripheral localization; the X chromosomes are furthest apart of all pairs of homologous chromosomes; (c) the chromosome pairs 6 and 8 are relatively close together in spite of their peripheral position, suggesting a truc close association of the homologus partners; (d) the chromosome pair 18 has a more peripheral position than expected, and a relatively large mean distance between the homologous partners; (e) the chromosome pair 1 has a much more central position and a closer association than is expected from its size.     

The volumes and morphology of human chromosomes in mitotic reconstructions

Summary Ten unpretreated normal human male fibroblast cells in mitosis were completely reconstructed from micrographs of between 82 and 119 consecutive serial sections. All 46 chromosomes and their centromeres could be reconstructed in every cell. Measurements of chromosome volumes and centromere indices are presented. The data enabled allocation of all chromosomes to their groups (A to G), and chromosomes 1, 2, 3, 6, 9, 16, 17, 18 and Y were individually identified. Comparisons with published karyotypes showed that volume measurements correlated well with measurements of DNA content and chromosome length. Centromere indices also showed good correlation, but the acrocentric chromosomes were more unequally armed than found by length measurement. Secondary constrictions at the nucleolar organising region were visible on about a third of the acrocentric chromosomes. One chromosome of the C group, number 9, had a diffuse subcentromeric region (DSR) on the long arm, at the position of the constitutive heterochromatin and (in meiotic cells) the paramere.     

Relative position of trypsin banded homologous chromosomes in human (female) metaphase figures.

"Generalized distances" between centromeres were statistically analyzed (chi2 test) on 50 normal female trypsin-banded metaphase figures. This study revealed that the homologous chromosomes of the pairs 13, 17, 14, and 21 lie closer together than would be expected by a reference distribution, and this in a statistically significant way. The same relative position was demonstrated for the chromosome groups 13-14, 13-21, 14-21, 15-22, and 14-22. Evidences were collected that also showed that homologous chromosomes of the pairs 1, 19, and 20 and the chromosome groups 15-21, 13-15, and 18-20 tend to lie closer together. Giving a functional interpretation to the phenomenon of non-random distribution of chromosomes in metaphase figures, it may be suggested that the chromosomes 13, 14, and 21 are involved in the organization of the human nucleolar organizers, more frequently than the other D- and G-group chromosomes.     

Sequential staining for G- and C-banding of chromosomes in the analysis of the morphology of the short arms of human acrocentric chromosomes]

Sequential staining for G- and C-banding of acrocentric chromosomes of 8 persons showed that the large heterochromatin region occurred more frequently in chromosome 15 than in chromosomes 13 and 14, and in chromosome 22 more frequently than in chromosome 21. There proved to be no correlation between the size of the heterochromatic region and the short arm of the acrocentric chromosomes. The frequency of occurrence of the satellites in the 8 persons was approximately the same for all the acricentric pairs. The C-banded satellite region of the homologous chromosomes is often heteromorphic.     

Somatic association of chromosomes in asynaptic genotypes of Avena sativa L.

The distribution of distances between homologous chromosomes in root tip cells of Avena sativa was studied in synaptic and asynaptic genotypes. The distances between homologous chromosomes were smaller than that calculated for two randomly distributed chromosomes, while non-homologous chromosomes did not deviate from the random theoretical distribution. The distances between homologous chromosomes in the asynaptic genotype were significantly greater than in synaptic plants. The loose association of homologous chromosomes in somatic tissue is correlated with the failure of chromosome pairing at meiosis in asynaptic plants.     

Synapsis and chiasma distribution in mice heterozygous for translocations in chromosomes 16 and 17

Electron microscopic analysis of synaptonemal complexes and analysis of chiasmata distribution in male mice heterozygous for Robertsonian translocation T(16; 17)7Bnr - (Rb7), for synaptonemal reciprocal translocation T(16;17)43H - (T43), in double heterozygotes for these translocations and in males with partial trisomy of the proximal region of chromosome 17 was carried out. Synaptic disturbances around the breakpoints of the translocations, such as asynapsis of homologous regions of partners and non-homologous synapsis of centromeric regions of acrocentric chromosomes, were revealed. Synaptic regularity in the proximal part of the chromosome 17 appeared to be affected by no t12 haplotype. Good coincidence between sizes of mitotic chromosomes and corresponding lateral elements of synaptonemal complexes was found for all chromosomes, with the exception of Rb7 in trisomics. In the latter karyotype, the proximal part of chromosome 17 involved in Robertsonian fusion seems to be shortened in the course of zygotene and never synapted with homologous segment of neither the acrocentric chromosome 17 nor large product of reciprocal translocation. Drastic increase in chiasmata frequency in the proximal part of chromosome 17 was revealed in heterozygotes for T43H and in trisomics, as compared with the double heterozygotes Rb7/T43. The latter finding was explained by the existence of two independent pairing segments in the former karyotypes.     

Evidence for a relatively random array of human chromosomes on the mitotic ring

We used fluorescence in situ hybridization (FISH) to study the positions of human chromosomes on the mitotic rings of cultured human lymphocytes, MRC-5 fibroblasts, and CCD-34Lu fibroblasts. The homologous chromosomes of all three cell types had relatively random positions with respect to each other on the mitotic rings of prometaphase rosettes and anaphase cells. Also, the positions of the X and Y chromosomes, colocalized with the somatic homologues in male cells, were highly variable from one mitotic ring to another. Although random chromosomal positions were found in different pairs of CCD-34Lu and MRC-5 late-anaphases, the separations between the same homologous chromosomes in paired late-anaphase and telophase chromosomal masses were highly correlated. Thus, although some loose spatial associations of chromosomes secondary to interphase positioning may exist on the mitotic rings of some cells, a fixed order of human chromosomes and/or a rigorous separation of homologous chromosomes on the mitotic ring are not necessary for normal mitosis. Furthermore, the relative chromosomal positions on each individual metaphase plate are most likely carried through anaphase into telophase.     

An ordered arrangement of chromosomes in the somatic nucleus of common wheat Triticum aestivum L.

Spatial relationships between chromosomes of the same genome, both homologous and non-homologous, were studied in root-tip cells of common wheat, Triticum aestivum (2n = 6x = 42). Mean distance between members of all the 21 homologous pairs (seven in each of the three genomes) and of 45 out of the 63 possible non-homologous combinations of two (21 in each genome) were determined. To minimize disruption of nuclear chromosomal arrangement, the cells were pretreated with cold temperature either in tap water or in a physiological medium (White solution) and distances between cytologically marked chromosomes were measured at metaphase. Comparison of distances for homologues with those for non-homologues indicated clearly that, within each genome, the homologous chromosomes were significantly closer to one another than were the non-homologues. Distances between homologues were similar in all three genomes, as were distances between non-homologues. The data are consistent with the hypothesis that the chromosomes of each genome of common wheat are arranged in the somatic nucleus in a highly specific ordered pattern. In this hypothetical arrangement, homologous chromosomes are closely associated, while the nonhomologues occupy definite positions with respect to one another. The universality of the phenomenon and its cellular mechanism and biological significance are discussed.     

Chromosome distribution in a23 chinese hamster fibroblasts

This study deals with a systematic chromosome position analysis of 116 anti-mitotic and hypotonic treated a₂₃ chinese hamster cells. No chromosome or pair of chromosomes was found to be located nearer the center or the periphery of the metaphase plate than would be expected by the reference distribution. The homologous chromosomes of pair 2 lie nearer to each other but they do not form a specific angle. The same relative position was shown for the chromosome groups 1–2, 1-E1 and 2-E5 (E standing for an extra chromosome). On the other hand the chromosomes of the combinations X-7, X-8, 7–8, 8–11 and X-E2 were lying further from each other, while chromosomes 10-E1 had a greater mean angle. The non random distribution of the chromosomes 1 and 2 may be interpreted as function of their possibly more frequent participation in the organization of nucleoli. — To obtain more information about the influence of preparation techniques on the alteration of the chromosome position in metaphase plates, this study deals with some overall considerations about chromosome position. It is shown that in a₂₃ cells the smaller chromosomes do not tend to lie nearer the metaphase plate center (as it happens in human cells). Also a significant correlation between the chromosome position with respect to the metaphase plate center and the mean interchromosomal distances was not found in this type of cells.     

Co-occurrences of polymorphic heterochromatin regions of chromosomes and effect on reproductive failure

Although the polymorphic heterochromatin regions of chromosomes (heteromorphisms) have been extensively studied for their phenotypic effects on humans, co-occurrences of chromosome 1, 9, 16 and Y heteromorphisms and of acrocentric variants have never been studied on humans with an objective scoring system. Here we compared the frequencies of individual heteromorphisms on a total of 602, 768 and 224 patients with the indications of infertility, recurrent miscarriage and in vitro fertilization (IVF) failure, respectively and on 272 controls. Then we examined whether there were significant co-occurrences between heteromorphisms within and between the groups. There were no statistically significant differences in the frequencies of heteromorphisms between the groups. Both statistically significant and non-significant correlations were observed within the non-acrocentric and certain acrocentric heteromorphisms in each group. When these co-occurrences were examined between the groups, a 2.2 fold increased risk of IVF failure in males in the presence of either chromosome 13 or chromosome 21 variants was observed (95 %CI:1.1–4.2). We conclude that the simultaneous manifestations of heteromorphisms have no effect on reproductive failure. There seems to be a correlation between the non-acrocentric heteromorphisms (1qh+, 9qh+, 16qh + and Yqh+/-), which might be the result of complex interactions of formation of these heterochromatin regions. The correlations observed between certain acrocentric chromosomes might be related to satellite association and nucleolus formation. The increased risk observed in males with IVF failure in the presence of either chromosome 13 or 21 variants should be interpreted cautiously due to the heterogeneity of the group.     

Random arrangement of chromosomes inUvularia (Liliaceae)

Chromosome arrangement in interphase has been inferred from an analysis of the relative positions of the chromosomes and the chromosome arms in untreated haploid pollen grain metaphases ofUvularia grandiflora. The distances between centromeres forming the smallest possible circle were measured in 43 metaphases. The relative positions of the chromosomes did not differ significantly from randomness. Neither did similar-sized chromosome arms show any tendency to be next to each other. The results thus disagree both with the hypothesis ofComings (1968) that each chromosome occupies a definite position in the interphase nucleus and with the claim ofBennett (1982) that similar-sized chromosome arms lie next to each other.     

The absence of the somatic association of centromeres of homologous chromosomes in grass mitotic metaphases

Root-tip metaphases from Hordeum vulgare (19 cells), H. marinum (11 cells), Aegilops umbellulata (10 cells) and Zea mays (10 cells) were completely reconstructed from electron micrographs of serially sectioned nuclei. The identity of each chromosome was found by measuring the volumes of its two arms and the presence or absence of a secondary constriction at the nucleolar organising region. With the position of the centromere in three dimensions, these data were used to analyse the relative positions of homologous and heterologous centromeres. In 31 out of the 50 cells analysed, homologues were on average further apart than heterologues. Except for two nucleolar organising chromosomes, there was no evidence of any tendency for the distances between different homologue types to be differently distributed from distances between heterologues. Average distances between homologues of the single nucleolar organising chromosome (linkage group 6) of Zea (2n = 20) were lower than the average for heterologues and the interhomologue distances were distributed significantly differently from the separation distances of chromosome 6 to other chromosomes. Presumably this association occurred because of nucleolar fusion in the previous interphase. Homologues of one of the two nucleolar organising chromosomes of A. umbellulata were also distributed significantly differently from heterologues, with a tendency for homologues to lie farther apart than the average heterologous pair. These results do not support previous work using squashed and spread metaphase preparations (some including abnormal, marked chromosomes) for these species.     

中国金色果蝇复合种的染色体研究——Ⅱ.中国及日本金色果蝇复合种的体细胞同源染色体联会

对采自北京、上海等7个地区及来自日本的金色果蝇Ⅰ(Drosophila auraria)和金色果蝇Ⅲ(Orosophila triauraria)的三龄幼虫的脑神经节进行核型分析。发现在其有丝分裂的晚前期、中期阶段,4对同源染色体都在进行联会。联会发生的频率约为34％。XY染色体往往无联会的表现。常染色体联会时,各对染色体的常染色质区紧密靠拢,而着丝粒区则彼此稍有分开。 本文并提出了以每对同源染色体着丝粒距离的“R_d”值作为判断同源染色体联会的数量指标,通过随机取得的119个细胞的476个R_d值的分析,发现同源染色体联会频率与在显微镜下所观察的结果相吻合。 体细胞同源染色体联会,在双翅目昆虫的特殊现象和在真核生物及其他高等动、植物中作为一般现象的遗传进化意义,本文亦作了初步探讨。     

Nondisjunction in human sperm: comparison of frequencies in acrocentric chromosomes.

Acrocentric chromosomes may be particularly predisposed to nondisjunction because of the frequency of trisomy for these chromosomes in human spontaneous abortions and liveborns. Studies of aneuploidy in human sperm have provided data on only a few acrocentric chromosomes, with evidence that chromosome 21 has a significantly increased frequency of disomy. To determine whether other acrocentric chromosomes have a higher frequency of nondisjunction or if chromosome 21 is anomalous, disomy frequencies for chromosomes 13 and 22 were studied by fluorescence in situ hybridization (FISH) analysis of 51,043 sperm nuclei from five normal men for whom the frequency of disomy for chromosomes 15 and 21 was known. The mean frequency of disomy for chromosome 13 (0.19%) did not differ significantly from that for other autosomes; however, the frequency of disomy 22 (1.21%) was significantly elevated (P < 0.001, Mantel-Haenszel chi(2) test). The G-group chromosomes (Nos. 21 and 22) also showed a significantly increased frequency of disomy (0. 75%) compared to acrocentric D-group chromosomes (viz., chromosomes 13 and 15; 0.15%) (P < 0.001, Mantel-Haenszel chi(2) test) and other autosomes (chromosomes 1, 2, 4, 9, 12, 13, 15, 16, 18, and 20; 0. 13%) studied in the same men (P < 0.001, Mantel-Haenszel chi(2) test).     

On the position of chromosomes in prepared mitosis figures of human fibroblasts

Summary The square distances of chromosome centromeres to the center of the mitosis plate, after circular transformation, were measured on each 100 mitosis plates of cultured fibroblasts from a man and a woman. It is proved statistically, that the larger chromosomes are located more in the periphery than the smaller chromosomes.

---

Zusammenfassung An je 100 Mitoseplatten einer männlichen und weiblichen Fibroblastenkultur wurden nach zirkulärer Transformation die Abstandquadrate der einzelnen Chromosomenpaare zum Zentrum der Platte gemessen. Es ergibt sich eine signifikante Zuordnung der großen Chromosomen zur Peripherie, der kleinen Chromosomen zur inneren Zone der Mitoseplatte.

---

---

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Attraction between centric heterochromatin of human chromosomes.

An analysis of the pattern of association of acrocentric chromosomes with nonacrocentric chromosomes in human lymphocyte metaphases was performed. This pattern in nonrandom with respect to chromosome length and intrachromosomal distribution. There is a general preference for the centric regions, most pronounced at the proximal segments of the long arms of chromosomes 1, 9, and 16, which is interpreted to reflect heterochromatin attraction during interphase. Comparison of the association patterns of homologous chromosome 1's differing with regard to the size of their heterochromatic regions corroborates this interpretation. The possible significance of heterochromatin attraction for the formation of spontaneous and induced chromosome anomalies is discused.     

RHG-band polymorphism of the short arms of human acrocentric chromosomes and relationship of variants to satellite associations

Summary The extent of RHG-band variation of short arms of human acrocentric chromosomes was investigated in a group of 100 subjects by visually comparing the variants with the size of reference bands 7p22, 21q22 and 11q13. Marked differences were found among the chromosomes in the distribution of variants; the largest mean size of RHG-band was associated with chromosome 21, whereas the variants of chromosome 22 had the smallest band size. The study further showed that the involvement of acrocentric chromosomes in satellite association did not depend upon the size of RHG-band variants.     

Quantitative studies on the arrangment of human metaphase chromosomes

Summary The pattern of association of acrocentric chromosomes was examined in ten and five carriers of a 15/21 and a 13/14 Robertsonian translocation, respectively, and was compared with that of the same numbers of relatives with normal karyotypes. In the carriers of 15/21 translocation, the number of large associations (involving more than two acrocentrics) and the association frequencies for individual acrocentric chromosomes, were significantly higher than in the control group. The mean number of associations of the single homologs of the translocation chromosomes was much higher than that of the other acrocentrics. In the carriers of 13/14 translocations, only the association frequency for chromosome 13 was higher than in the normal relatives. The uninvolved chromosomes homologous to those involved in translocations showed an insignificant increase in associations in comparison with the other acrocentrics. These results suggest that some mechanism within the cells compensates for the effect of missing acrocentrics or of acrocentrics lacking NORs on the number of associations. The possible relations of this phenomenon to the activity of the nucleolus organizing regions are discussed.     

Behavior of dicentric chromosomes in budding yeast

DNA double-strand breaks arise in vivo when a dicentric chromosome (two centromeres on one chromosome) goes through mitosis with the two centromeres attached to opposite spindle pole bodies. Repair of the DSBs generates phenotypic diversity due to the range of monocentric derivative chromosomes that arise. To explore whether DSBs may be differentially repaired as a function of their spatial position in the chromosome, we have examined the structure of monocentric derivative chromosomes from cells containing a suite of dicentric chromosomes in which the distance between the two centromeres ranges from 6.5 kb to 57.7 kb. Two major classes of repair products, homology-based (homologous recombination (HR) and single-strand annealing (SSA)) and end-joining (non-homologous (NHEJ) and micro-homology mediated (MMEJ)) were identified. The distribution of repair products varies as a function of distance between the two centromeres. Genetic dependencies on double strand break repair (Rad52), DNA ligase (Lif1), and S phase checkpoint (Mrc1) are indicative of distinct repair pathway choices for DNA breaks in the pericentromeric chromatin versus the arms.     

Evolution of alpha-satellite DNA on human acrocentric chromosomes

In situ hybridization of five new and one previously described alpha-satellite sequences isolated from chromosome 21 libraries gave the following chromosomal distribution patterns: (a) two sequences (pTRA-1 and -4) hybridizing to chromosomes 13, 14, 15, 21, and 22 (also 19 and 20); (b) one sequence (pTRA-7) hybridizing to chromosome 14; and (c) three sequences (pTRA-2, -11 and -15) hybridizing to chromosomes 13, 14, and 21, with significant but weaker signals on 15 and 22. These results suggested the sharing of alphoid domains between different acrocentric chromosomes and the coexistence of multiple domains on each chromosome. Analysis of somatic cell hybrids carrying a single human acrocentric chromosome using pTRA-2 demonstrated a higher-order repeating structure common to chromosomes 13, 14, and 21, but not to 15 and 22, providing direct evidence for sequence homogenization in this domain among the former three chromosomes. We present a model of evolution and genetic exchange of alpha sequences on the acrocentric chromosomes which can satisfactorily explain these and previous observations of (a) two different alphoid subfamilies, one common to chromosomes 13 and 21 and the other common to chromosomes 14 and 22, (b) a different alphoid subfamily on chromosome 22, and (c) nonrandom participation of chromosomes 13 and 14, and 14 and 21 in Robertsonian translocations.