Replication pattern of the X and Y chromosomes in partially synchronized human lymphocyte cultures

The replication pattern of the X and Y chromosomes at the beginning of the synthetic phase was studied in human lymphocyte cultures partially synchronized by the addition of 5-fluoro-2-deoxyuridine (FUdR). The data were evaluated statistically by an analysis of the distribution of silver grain counts over the X and Y chromosomes. —In cells from normal females, one of the X chromosomes began replication later than any other chromosomes of the complement. The short arm of the late replicating X chromosome started replication earlier than the long arm. The telomeric region of the short arm was a preferential site of DNA synthesis at the beginning of replication. —In partially synchronized lymphocyte cultures from a patient with the XXY syndrome, the Y chromosome started replication together with the late replicating X chromosome. The Y chromosome most frequently replicated synchronously with the short arm of the X. The centromeric region of the Y chromosome initiated synthesis before the telomeric region and appeared to replicate synchronously with the telomeric region of the short arm of the X. These findings are discussed with reference to the pairing of the X and Y chromosomes at meiosis.Supported in part by the National Institute of Health Research Grant HD-01979 and National Foundation Birth Defects Research Grant CRCS-40. Dr. Knight was a predoctoral fellow under National Institute of Health Training Program HD-00049-09.     

Karyotypes of three somaclonal variants and wild plants ofAllium tuberosum by bicolor FISH

Using the fluorescence in situ hybridization (FISH) technique, we conducted karyotype analyses to identify the lost chromosomes in three somaclonal variants obtained from tissue culture of wildAllium tuberosum (2n = 4X = 32). The three lost chromosomes of the At29 variant (2n = 29) were all chromosome 2, the two for At30 (2n = 30) were chromosomes 7 and 8, and At31 was missing chromosome 2. Chromosome compositions of these variants were confirmed as being fixed lines during two years of greenhouse cultivation. The bicolor FISH technique, involving both 5S and 18S–5.8S–26S ribosomal RNA genes as probes, was used to assign chromosomal locations and to confirm whether the lost chromosomes contained any rRNA markers. The 5S rRNA gene signals in all variants as well as the wild type were detected as two sets, one on the intercalary region of the short arm of chromosome 3, the other on the intercalary region of the long arm of chromosome 6. One 18S–5.8S–26S rRNA gene site on the secondary constriction included a flanking satellite and terminal region on the short arm of chromosome 8. Signals of the 18S–5.8S–26S rRNA gene in At30 showpd in only three chromosomes, indicating that one of the lost chromosomes was chromosome 8. Overall, three marker chromosomes were established by FISH, using rRNA multigene families.     

Location of the genes for 5S ribosomal RNA in Xenopus laevis

In situ hybridization of 5S RNA and cRNA transcribed in vitro from Xenopus laevis 5S DNA shows that 5S DNA is localized at or near the telomere region of the long arm of many, if not all, of the X. laevis chromosomes. No 5S DNA is detected near the nucleolus organizer in the normal X. laevis chromosome complement, but in a X. laevis kidney cell line, 5S DNA is found at the distal end of the secondary constriction. The arrangement of 5S DNA in several types of interphase nuclei is described. — During the pairing stages of meiosis the telomeres of most or perhaps all of the chromosomes become closely associated so that the regions containing 5S DNA form a single cluster. This close association might be either a cause or a result of the presence of the similar sequences of 5S DNA on many telomeres. It suggests that the uniformity of 5S sequences on non-homologous chromosomes might be maintained by crossing-over between the chromosomes.     

Chromosome analysis and DNA homology in threePicea species,P. mariana,P. rubens,andP. glauca (Pinaceae)

A detailed karyotype analysis was made on the somatic complement ofPicea rubens andP. glauca. B-chromosomes were observed in someP. glauca populations. The karyotypes are generally asymmetrical with most of the chromosomes having median to median-submedian centromeres.Picea glauca chromosomes 2, 3, 7, and 8 have secondary constriction on their short arm and chromosome 10 has a secondary constriction on the long arm. Chromosome 3 was the most easily identifiable, as it has two secondary constrictions located on the short arm. InP. rubens, all the chromosomes but chromosomes 8 and 9 have one to four distinctive secondary constrictions. In general, the diagrammatic comparisons show a high degree of similarity amongP. mariana, P. rubens, andP. glauca. GenomicP. mariana probe strongly hybridized to dots of genomic DNA fromP. rubens andP. glauca indicating that there is a high sequence homology among these three species. The synchronizing agent, hydroxyurea was used at different concentrations to enhance the mitotic index of cell suspensions derived from embryogenic cultures. Hydroxyurea at 1.25 mM increased significantly the mitotic index. An increase of hydroxyurea from 1.25 mM to 5 mM and 10 mM resulted in a steady decrease of mitotic index.     

石貂的染色体研究

本文对分布在我国的石貂北方亚种染色体进行了较详细的研究。结果表明２ｎ＝３８,核型为１４（Ｍ）＋４（ＳＭ）＋１８（ＳＴ）,ＸＹ（Ｍ,Ａ）。Ｃ－带显示该亚种的一些染色体着丝粒区域结构异染色质弱化或消失。Ｎｏ,９染色体的短臂完全异染色质化;Ｘ染色体长臂丰出现插入杂色质带;Ｙ为完全结构异染色质组成。     

Spontaneous chromosomal rearrangements in cultivated and wild barleys

Summary Four of 1,240 cultivated barley lines collected from different regions of the world and 3 of 120 lines of wild barley, Hordeum spontaneum C. Koch, carry spontaneous reciprocal translocations. Break-point positions and rearrangements in the interchanged chromosomes have been examined by both test crosses and Giemsa banding techniques. The four translocation lines in cultivated barley were all of Ethiopian origin and have the same translocation involving chromosomes 2 and 4. The breakpoints are at the centromeres of both chromosomes, resulting in interchanged chromosomes 2S+4S and 2L+4L (S=short arm, L=long arm). A wild barley line, Spont.II, also has translocated chromosomes 2 and 4 which are broken at the centromeres. The resultant chromosomes are, however, 2S+4L and 2L+4S. Another wild barley line, Spont.S-4, has interchanged chromosomes with breakpoints in the short arm of chromosome 3 and the long arm of chromosome 7. In addition, this line has a paracentric inversion in the short arm of chromosome 7 that includes a part of nucleolar constriction, resulting in two tandemly arranged nucleolar constrictions. The third wild barley line, Spont.S-7, has interchanged chromosomes with breakpoints in the long arms of both chromosomes 3 and 6. The translocated chromosome 3 is metacentric and the translocated chromosome 6 has a long arm similar in length to the long arm of chromosome 7.     

MAMMALIAN CHROMOSOMES IN VITRO : XVIII. DNA Replication Sequence in the Chinese Hamster

The complete DNA replication sequence of the entire complement of chromosomes in the Chinese hamster may be studied by using the method of continuous H³-thymidine labeling and the method of 5-fluorodeoxyuridine block with H³-thymidine pulse labeling as relief. Many chromosomes start DNA synthesis simultaneously at multiple sites, but the sex chromosomes (the Y and the long arm of the X) begin DNA replication approximately 4.5 hours later and are the last members of the complement to finish replication. Generally, chromosomes or segments of chromosomes that begin replication early complete it early, and those which begin late, complete it late. Many chromosomes bear characteristically late replicating regions. During the last hour of the S phase, the entire Y, the long arm of the X, and chromosomes 10 and 11 are heavily labeled. The short arm of chromosome 1, long arm of chromosome 2, distal portion of chromosome 6, and short arms of chromosomes 7, 8, and 9 are moderately labeled. The long arm of chromosome 1 and the short arm of chromosome 2 also have late replicating zones or bands. The centromeres of chromosomes 4 and 5, and occasionally a band on the short arm of the X are lightly labeled.     

Nondisjunction of the X chromosomes in females ofDrosophila hydei

An investigation of nondisjunction inDrosophila hydei has disclosed that spontaneous primary nondisjunction of the X chromosomes occurs with a frequency of 1/13000, and secondary nondisjunction with a frequency of 1/3500. These rates are much lower than the ones previously reported forDrosophila melanogaster which are about 1/1000 for primary nondisjunction and 1/50 for secondary nondisjunction.The low rate of secondary nondisjunction inhydei is attributed to the much greater genetic length of the X chromosome and the corresponding reduction in noncrossover X's available for distributive pairing with the Y chromosome.The low rate of primary nondisjunction is attributed to both a reduction in noncrossover X chromosomes, and to the large heterochromatic arm of the X chromosome which, it is suggested, makes the X centromere a strong centromere. Thus, it is further suggested, the reduction in noncrossover chromosomes reduces the opportunity for nonhomologous distributive pairing and nondisjunction of the type involving noncrossover chromosomes. Nondisjunction of the type involving crossover chromosomes then is prevented by the success of the strong centromeres in overcoming entanglements that would lead to nondisjunction in the case of ordinary or weak centromeres.This investigation was supported in part by U.S. Public Health research grant GM 12093 and in part by a National Science Foundation research grant 14200.     

Patterns of replication in the neo-sex chromosomes ofDrosophila nasuta albomicans

Drosophila nasuta albomicans (with 2n = 6), contains a pair of metacentric neo-sex chromosomes. Phylogenetically these are products of centric fusion between ancestral sex (X, Y) chromosomes and an autosome (chromosome 3). The polytene chromosome complement of males with a neo-X- and neo-Y-chromosomes has revealed asynchrony in replication between the two arms of the neo-sex chromosomes. The arm which represents the ancestral X-chromosome is faster replicating than the arm which represents ancestral autosome. The latter arm of the neo-sex chromosome is synchronous with other autosomes of the complement. We conclude that one arm of the neo-X/Y is still mimicking the features of an autosome while the other arm has the features of a classical X/Y-chromosome. This X-autosome translocation differs from the other evolutionary X-autosome translocations known in certain species ofDrosophila.     

Ultrastructure and behavior of the achiasmatic,telosynaptic XY pair of the sand rat (Psammomys obesus)

The behavior of the X and Y chromosomes in somatic and testicular cells of the sand rat (P. obesus) has been investigated with light and electron-microscope procedures. The Y chromosome has been identified as the fourth longest of the complement, both by C-banding and by its meiotic behavior. The X chromosome is the longest of the complement and carries two major C-heterochromatic blocks, one in the distal part of the long arm and the other forming most of the short arm. During presynaptic stages in spermatocytes, separate C-heterochromatic blocks, representing the sex chromosomes, are observed in the nuclei. An XY body is regularly formed at pachytene. During first meiotic metaphase the X and Y chromosomes show variable associations, none of them chiasmatic. Second meiotic metaphases contain, as in other mammals, a single sex chromosome, suggesting normal segregation between the X and the Y. — Electron microscopic observations of the autosomal synaptonemal complexes (SCs) and the single axes of the X and Y chromosomes during pachytene permit accurate, statistically significant identification of each of the largest chromosomes of the complement and determination of the mean arm ratios of the X and Y axes. The X and Y axes always lie close to each other but do not form a SC. The ends of the X and Y axes are attached to the nuclear envelope and associate with each other in variable ways, both autologously (X with X or Y with Y) and heterologously (X with Y), with a tendency to form a maximum number (four) of associated ends. Analysis of 36 XY pairs showed no significant preference for any single specific attachment between arm ends. The eighth longest autosomal bivalent is frequently partially asynaptic during early pachytene, and only at that time is often near or touching one end of the X axis. — It is concluded that while axis formation and migration of the axes along the plane of the nuclear envelope proceed normally in the X and Y chromosomes, true synapsis (with SC formation) does not occur because the pairing region of the X chromosome has probably been relocated far from the chromosome termini by the insertion of distal C-heterochromatic blocks.     

宽耳犬吻蝠(TADARIDA TENIOTIS INSIGNIS)和普氏蹄蝠(HIPPOSIDEROS PRATTI)染色体组型分析

本文分析了宽耳犬吻蝠(Tadarida teniotis insignis Blyth)和普氏蹄蝠(Hipposideros pratti Thomas)的常规核型,现报道如下。     

水貂的染色体研究

采用复制带、C带和硝酸银染色等分带技术研究了水貂的核型和带型。结果表明,2n=30,枝型为10（M）＋16（SM）＋2（A）,XX（M）。C-带显示该水貂的一些染色体的结构异染色质比较丰富,从着丝粒区域延伸到两臂上,No.5染色体着丝粒结构异染色质有些弱化;X染色体的结构异染色质较常染色体的丰富。Ag-NORs有3个,分布在No.8染色体的次缢痕区域和一条No.2染色体长臂接近着丝粒的区域。     

Karyotypes and C-banding patterns in species of Cyphomandra Mart, ex Sendtner (Solanaceae)

The orcein and C-banded karyotypes of 11 species of Cyphomandra (Solanaceae) were described. All species were diploid with 2n = 2x = 24. The chromosomes were large, ranging from 4 to 10 u.m iⁿ length, and in each complement were largely metacentric or submetacentric with few subtelocentrics. There was a significant negative correlation between chromosome length and arm ratio within a complement as well as between taxa. In general, chromosomes of the larger complements were more symmetrical in terms of both relative chromosome length and arm ratio, implying that similar amounts of DNA had been added to or taken away from every chromosome are of each complement during evolutionary divergence. Two pairs of non-homologous chromosomes were seen to contain subterminal secondary constrictions in most species. The two Brazilian species studied differed from those of Andean origin in the location of one of these secondary constrictions, suggesting a major evolutionary divergence between these two groups of specieS. Non-homologous chromosomes were difficult to distinguish from one another without the aid of C-banding, due to a continuum in the distribution of chromosome lengths and arm ratios. Telomeric and interstitial bands were shown in all species but not all chromosomes in each complement were banded. There were no centromeric bandS. Nuclear DNA amount and the length, but not proportional length, of C-bands were correlated in each specieS. One species ( C. Luteoalba (Pers.) Child, section Cyphomandropsis ) was unique in its banding pattern, providing further evidence for the delimitatation of this species and perhaps section from other Cyphomandra taxa.     

白颊长臂猿染色体的研究

本文对我国云南南部的白须长臂猿（Ｈ．ｌｅｕｃｏｇｅｎｙｓ）染色体的Ｇ带、Ｃ带、晚复制带及Ａｇ－ＮＯＲｓ进行了较为详细的研究。它的２ｎ＝５２,核型公式为４４（Ｍ或ＳＭ）＋６（Ａ）,ＸＹ（Ｍ,Ａ）。Ｃ带表明一些染色体着丝点Ｃ带弱化;有的染色体出现插入的和端位的Ｃ带;Ｘ染色体两臂有端位Ｃ带,Ｙ染色体是Ｃ带阳性和晚复制的。Ａｇ－ＮＯＲｓ的数目,雌体有４个,雄体有５个,Ｙ染色体上具ＮＯＲ。本文对白颊长臂猿与其它长臂猿间的亲缘关系、核型进化的可能途径进行了讨论。     

Studies on metatherian sex chromosomes. IX. Sex chromosomes of the greater glider (Marsupialia: Petauridae)

The greater glider, currently but incorrectly known as Schoinobates volans, is widely distributed in forested regions in eastern Australia. All animals studied from six different localities had 20 autosomes but there were four chromosomally distinct populations. At Royal National Park, N.S.W., all female greater gliders studied had 22 chromosomes including two large submetacentric X chromosomes with subterminal secondary constrictions in their longer arms. This form of X chromosome occurred also at Bondo State Forest, Myall Lakes and Coff's Harbour, N.S.W., and at Eidsvold, Qld. At Coomooboolaroo, Qld, the X chromosome was also a large submetacentric but a secondary constriction occurred in the shorter arm. Two chromosomally distinct types apparently occur in Royal National Park, one with XY males as in all other populations, and one with XY1Y2 males. Y or Y1, but not Y2, chromosomes were eliminated from the bone marrow in all populations but were present in spermatogonia, primary spermatocytes and cultured fibroblasts. Animals from Bondo State Forest had three or more acrocentric or metacentric supernumerary chromosomes.     

The behavior and morphology of the X and Y chromosomes during prophase I in the Sitka deer mouse (Peromyscus sitkensis)

Surface-spread, silver-stained primary spermatocytes from individuals of the Sitka deer mouse (Peromyscus sitkensis) were analyzed by electron microscopy. Pairing of the X and Y chromosomes is initiated at early pachynema and is complete by mid pachynema. The pattern of sex chromosome pairing is unique in that it is initiated at an interstitial position, with subsequent synapsis proceeding in a unidirectional fashion towards the telomeres of the homologous segments. One-third the length of the X and two-thirds the length of the Y are involved in the synaptonemal complex of the sex bivalent. Various morphological complexities develop in the heteropycnotic (unpaired) segments as pachynema progresses, but desynapsis is not initiated until diplonema. Analysis of C-banded diakinetic nuclei indicated that sex chromosome pairing involves the heterochromatic short arm of the X and the long arm of the heterochromatic Y. An interstitial chiasma between the X and Y was observed in the majority of the diakinetic nuclei. The observation of a substantial pairing region and chiasma formation between the sex chromosomes of these deer mice is interpreted as indicating homology between the short arm of the X and the long arm of the Y.     

Somatic chromosomes of higher diptera

Summary The chromosome complements of eighty brain cells ofHylemya antiqua have been studied. The eighty cells were found in thirty-three larvae. Total complement length (TCL) is not randomly distributed among the larvae. Because there is an inverse correlation between chromosome length and width, it appears that in the cells studied the different chromosome lengths are partly expressions of different stages of metaphase contraction. It is suggested that synchronous division of cells still occurs in late larvae.The length of each chromosome arm is highly correlated with that of every other arm. It is possible that the correlations are complete but that inadequate technique causes the departures from completeness which are observed. The chromosome lengths are corrected slightly for distortions, but the corrections make very little difference in the correlation coefficients. There is a high value for the correlation between the correlation of two arm lengths and the sum of the two arm lengths. This is to be expected if the perfect correlation between all arm lengths is being obscured by errors of drawing and measurement.The autosomal arms have very similar coefficients of variation. The arm ratios (length of long arm divided by short arm) are not correlated with TCL or with each other, and arm ratio is randomly distributed among the larvae. The sex chromosomes have a smaller coefficient of variation than the autosomes, so that they are relatively large in small cells and relatively small in large cells.Twenty-two cells inHylemya fugax were measured. The autosomes also showed a high correlation between arm lengths. An entirely heterochromatic autosomal arm showed the same phenomenon of a low coefficient of variation which was shown by the heteropycnotic sex chromosomes inH. antiqua. The low variability of heterochromatic regions accompanied by an apparently non-random distribution of the TCL may produce an erroneous picture of the species complement when dealing with small numbers.It is suggested that for simplicity in using cytological observations of this sort for taxonomic purposes, the technique of measuring the percent TCL of a chromosome plus its arm ratio be replaced by the percent TCL of each arm plus the average length difference between the arms of each chromosome pair in units of percent TCL.     

A cytogenetic analysis of X- ray induced male steriles on the Y chromosome of Drosophila melanogaster

A total of 1020 B ^s Yy ⁺chromosomes was screened for the induction of male sterile mutations by X irradiation. The 29 recovered mutations were analyzed by genetic complementation and the metaphase chromosomes stained with Hoechst 33258 and observed with fluorescence microscopy. The cytological and genetic maps derived from this analysis were compared to similar maps of the Y chromosome mutations isolated in an earlier study (Brosseau, 1960). Unlike the previous work we have identified only 6 male fertility loci (2 on the short arm, 4 on the long arm) on the Y chromosome. These loci are distributed along the length of the long arm and are likely to reside at two separate sites on the short arm. There is no apparent clustering of these fertility factors in this heterochromatic chromosome. The deletions obtained in this study were observed to be unstable and the nature of this instability was investigated. The original Y chromosome was marked at both telomeres with normally X-linked genes. The loss of one or the other of these markers was accompanied in many cases by the concomitant loss of large segments of Y chromosome material. The possible mechanism of this loss is discussed.Author to whom correspondence should be sent     

Simple GA C T A repeats characterize the X chromosomal heterochromatin of Microtus agrestis,European field vole (Rodentia,Cricetidae)

The sex chromosomes of Microtus agrestis are extremely large due to the accumulation of constitutive heterochromatin. We have identified two prominent satellite bands of 2.0 and 2.8 kb in length after HaeIII and HinfI restriction enzyme digestion of genomic DNA, respectively. These satellites are located on the heterochromatic long arm of the X chromosome as shown using Microtus x mouse somatic cell hybrids. By in-gel hybridization with oligonucleotide probes, the organization of the two satellites was studied: among the many copies of the simple tandem tetranucleotide repeat GATA are interspersed rare single GACA tetramers. One of the satellites also harbours related GGAT simple tandem repeats. In situ hybridizations with plasmid-carried or oligonucleotide GA _C ^T A probes show clustered silver grains on the long and short arm of the X chromosome. Interspersion of differently organized (GATA)_n elements is also demonstrable in the autosomal complement and on the Y chromosome. These results are discussed in the context of the evolution of vertebrate sex chromosomes in relation to heterochromatin and simple repetitive DNA sequences.     

Die intraspezifische Variabilität des heterochromatischen Armes eines Chromosoms bei der GattungCarabus L. (Coleoptera)

The chromosome complement ofC. auronitens Fabr. is 2n _♂=26+XY. One autosomal pair—called A-chromosomes—is relatively long.A-chromosomes consist of a euchromatic and a heterochromatic arm. Labelling of mitotic chromosomes with³H-thymidine shows that replication of the heterochromatic arm continues when it has ended in the euchromatic arm. In males and females the length of the heterochromatic arm varies intraindividually. In 47 of 99 males the heterochromatic arms were heteromorphic. Calculations of the quotient length of the euchromatic/length of the heterochromatic arm have shown that at least 6 different types of the A-chromosome exist. These types differ from each other in the number of heterochromatic sections separated by constrictions. The longest heterochromatic arm observed consisted of 8 such sections. The genetic significance of the heterochromatin in the genus ofCarabus is at present unknown (Zusammenfassung see p.305).