C,Q and H-banding in the analysis of Y chromosome rearrangements in Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae)

In Lucilia cuprina C-banding produces procentric bands on all autosomes and deep staining over most of the X and Y chromosomes which conciderably facilitates the analysis of complex Y chromosome rearrangements. The Y chromosome is generally darkly C-banded throughout while in the X chromosome a pale staining segment is found in the distal portion of the long arm. Modulation of the banding reaction results in grey areas in both X and Y. When C-banding is compared with allocycly it is clear that not all heteropycnotic regions in the sex chromosomes C-band to the same extent. Secondary constrictions in the short arms of both X and Y chromosomes are clearly revealed by C-banding, the X satellite being polymorphic for size.— Q-banding results in a brightly fluorescing band in the short arm of structurally normal Y chromosomes. This band loses its fluorescence in some translocations, probably through a position effect. Hoechst 33258 staining does not produce any brightly fluorescing bands.     

Sex chromosome pairing patterns in male mice of novel Sxr genotypes

The influence of the sex-reversal factor (Sxr) on X and Y chromosome pairing was examined by comparing males with novel and standard Sxr genotypes. The novel Sxr males were exceptional in carrying Sxr on their X rather than their Y chromosome, or homozygously on both their X and Y chromosomes, or on a Y chromosome of different origin to that on which the factor arose. Regardless of its chromosomal location, Sxr was found to elevate the frequency of X-Y separation. Univalent X and Y chromosomes were observed to undergo self-association in a variable proportion of spermatocytes of all Sxr-carrying males. There was a suggestion that chromosomal location of the factor could influence the frequency of univalent self-association. Our observations do not support the published hypothesis of Y self-pairing as the cause of the elevated rate of X-Y separation at pachytene in Sxr-carrying males. Rather, they suggest that heterozygosity due to the presence of Sxr in the XY pairing region may be sufficient to disrupt pairing and cause univalence, or alternatively, that Sxr is an inefficient promoter of X-Y pairing initiation.     

Robertsonian translocation between the chromosome Y and 15

Summary The Robertsonian translocation 45,X,t(Y;15q) was detected in four generations of male progeny. The karyotypes were studied by G-, Q-, and C-banding techniques. The chromosome Y involved in this translocation was of a short, nonfluorescent variant. The normal male phenotypes in all three adult translocation carriers (the great grandfather, the grandfather, and the father) support the hypothesis that the locus for the male determining factor is on the short arm of the chromosome Y.

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Zusammenfassung Eine Robertsonsche Translokation 45,X,t(Y;15q) wurde in vier Generationen der männlichen Linie entdeckt. Die Karyotypen wurden mittels der G-, R- und C-Banding-Techniken untersucht. Das in diese Translokation verwickelte Y-Chromosom gehörte zu der kurzen, nichtfluorescierenden Variante. Alle Translokationsträger aus vier Generationen hatten einen normalen männlichen Phänotyp. Dadurch wird die Hypothese bestätigt, daß der Locus für den die Männlichkeit bestimmenden Faktor auf dem kurzen Arm des Y-Chromosoms gelegen ist.

     

A strongly fluorescing abnormal chromosome in a malformed child

Summary The case of a sexchromatin negative girl with multiple malformations is presented. A small metacentric chromosome was found to replace her second X chromosome, half of which was strongly fluorescing after staining with Quinacrinedihydrochloride, and late replicating after labelling with tritiated thymidine. The chromosome was interpreted as a translocation chromosome between the long arms of a Y and a partially trisomic autosome.     

Is crossover between the X and Y a regular feature of meiosis in mouse and man?

There has long been an assumption that normal disjunction of the sex chromosomes of all mammals is assured by synapsis of a region of homology between the X and Y and that an obligatory crossover with chiasmata formation follows. Evidence is presented here that much (if not all) observed synapsis between the X and Y in mouse and man is nonhomologous and that crossing over most likely does not occur as a normal event in these organisms. The X and Y have desynapsed to a mere terminal association by the time of pachytene DNA synthesis, generally considered to be associated with crossing over. Recombination nodules or bars observed on the X and Y of human spermatocytes are also present at the wrong substage of pachytene and are insufficient in frequency to accounf for an obligatory crossover between the X and Y and thus assure normal disjunction. Instead it is suggested that orientation and disjunction of the sex chromosomes is mediated in these species by an achiasmatic telomeric association.     

C-banding and non-homologous associations

A chromosome complement formed by 16 autosomes and an Xy_p sex chromosome system was found in Epilachna paenulata Germar (Coleoptera: Coccinellidae). All autosomes were metacentric except pair 1 which was submetacentric. The X and the Y chromosomes were also submetacentric but the Y was minute. The whole chromosome set carried large paracentric heterochromatic C-segments representing about 15% of the haploid complement length. Heterochromatic segments associated progressively during early meiotic stages forming a large single chromocenter. After C-banding, chromocenters revealed an inner networklike filamentous structure. Starlike chromosome configurations resulted from the attachment of bivalents to the chromocenters. These associations were followed until early diakinesis. Thin remnant filaments were also observed connecting metaphase I chromosomes. Evidence is presented that, in this species, the Xy_p bivalent resulted from an end-to-end association of the long arms of the sex chromosomes. The parachute Xy_p bivalent appeared to be composed of three distinct segments: two intensely heterochromatic C-banded corpuscles formed the canopy and a V-shaped euchromatic filament connecting them represented the parachutist component. The triple constitution of the sex bivalent was interpreted as follows: each heterochromatic corpuscle corresponded to the paracentric C-segment of the X and Y chromosomes; the euchromatic filament represented mainly the long arm of the X chromosome terminally associated with the long arm of the Y chromosome. The complete sequence of the formation of the Xy_p bivalent starting from nonassociated sex chromosomes in early meiotic stages, and progressing through pairing of heterochromatic segments, coiling of the euchromatic filament, and movement of the heterochromatic corpuscles to opposite poles is described. These findings suggest that in E. paenulata the Xy_p sex bivalent formation is different than in other coleopteran species and that constitutive heterochromatic segments play an important role not only in chromosome associations but also in the Xy_p formation.     

Sex chromosome positions in human interphase nuclei as studied by in situ hybridization with chromosome specific DNA probes

Summary Two cloned repetitive DNA probes, pXBR and CY1, which bind preferentially to specific regions of the human X and Y chromosome, respectively, were used to study the distribution of the sex chromosomes in human lymphocyte nuclei by in situ hybridization experiments. Our data indicate a large variability of the distances between the sex chromosomes in male and female interphase nuclei. However, the mean distance observed between the X and Y chromosome was significantly smaller than the mean distance observed between the two X-chromosomes. The distribution of distances determined experimentally is compared with three model distributions of distances, and the question of a non-random distribution of sex chromosomes is discussed. Mathematical details of these model distributions are provided in an Appendix to this paper. In the case of a human translocation chromosome (XqterXp22.2::Yq11Y qter) contained in the Chinese hamster x human hybrid cell line 445 x 393, the binding sites of pXBR and CY1 were found close to each other in most interphase nuclei. These data demonstrate the potential use of chromosome-specific repetitive DNA probes to study the problem of interphase chromosome topography.     

Cloning of genomic sequences from the human Y chromosome after purification by dual beam flow sorting

Summary Human Y chromosomes were purified by dual beam flow sorting from a human x Chinese hamster cell line retaining the Y as the only free human chromosome. DNA was extracted from the Y fraction and cloned into gtWES.B vector arms. More than 100 recombinant clones carrying human inserts have been characterised by Benton-Davis plaque screening and Southern blotting or in situ hybridisation. Several repetitive sequences were found to be predominantly located on the Y, whereas the majority also cross-hybridised with autosomal DNA. One repetitive clone gave a specific hybridisation signal with the X and the Y chromosome but not with autosomes. Preliminary evidence indicates that many clones contain single copy as well as repetitive sequences. However, no Y-specific single copy sequence has yet been identified.     

A deletion panel of the long arm of the X chromosome: subregional localization of 22 DNA probes

Summary Two males and two females with different but overlapping deletions on the proximal long arm of the X chromosomes have been investigated. Their karyotypes, which have been well characterized by high resolution banding techniques, are 46,Y,del(X)(pterq21.1:: q21.33qter); 46,Y,del(X) (pterq21.2::q21.31qter); 46,X,del(X) (pterq21.31::q24.3qter) and 46,X,del (X)(pterq21.1:). A deletion panel, which makes it possible to subdivide the long arm of the X chromosome into seven subregions, has been established using the genomic DNA from the four families, and applied to the fine subregional localization of the loci for 22 DNA probes. Based on the results obtained, the possible location of the loci in question has been narrowed down considerably, in some cases to an area of only 5% of the previously assigned region; hybridization to Southern blots of a panel with well-characterized chromosome deletions is thus a powerful means of localizing DNA probes, especially with respect to the X probes.Part of the results from this investigation were published at Human Gene Mapping 9 as abstracts     

Cytological dissection of sex chromosome heterochromatin of Drosophila hydei

Prophase chromosomes of Drosophila hydei were stained with 0.5 g/ml Hoechst 33258 and examined under a fluorescence microscope. While autosomal and X chromosome heterochromatin are homogeneously fluorescent, the entirely heterochromatic Y chromosome exhibits an extremely fine longitudinal differentiation, being subdivided into 18 different regions defined by the degree of fluorescence and the presence of constrictions. Thus high resolution Hoechst banding of prophase chromosomes provides a tool comparable to polytene chromosomes for the cytogenetic analysis of the Y chromosome of D. hydei. — D. hydei heterochromatin was further characterized by Hoechst staining of chromosomes exposed to 5-bromodeoxyuridine for one round of DNA replication. After this treatment the pericentromeric autosomal heterochromatin, the X heterochromatin and the Y chromosome exhibit numerous regions of lateral asymmetry. Moreover, while the heterochromatic short arms of the major autosomes show simple lateral asymmetry, the X and the Y heterochromatin exhibit complex patterns of contralateral asymmetry. These observations, coupled with the data on the molecular content of D. hydei heterochromatin, give some insight into the chromosomal organization of highly and moderately repetitive heterochromatic DNA.     

Identification of a 4A/7R and a 7B/4R wheat-rye chromosome translocation

Summary By producing chromosome substitutions with Imperial rye chromosomes 4R (C) and 7R (D) in the wheat cultivar Chinese Spring two spontaneous translocation lines were obtained. One involves segments of wheat chromosome 4A and rye chromosome 7R, the other involves portions of wheat chromosome 7B and rye chromosome 4R     

Sex determination in Sarotherodon (tilapia)

Summary The simplest possible model of the sex determination process adding autosomal influence to a minimal number of sex chromosomes was developed to explain matings of Tilapia (Sarotherodon) species. Eighteen different genotypes, each having two autosomes (AA, Aa, or aa) and two sex chromosomes (WX, WY, WW, XY, XX or YY) involved in sex determination, are predicted by the theory. Their sex (10 males and 8 females) were determined using a series of directed graphs, showing the relative strength of the chromosome pairs, developed on the basis of Chen's sex ratio results (Chen 1969). This theoretical model predicts eight different sex ratios (01, 13, 35, 11, 97, 53, 31, 10 ); three of them are not predicted by the WXYZ theory. The greatest part of these sex ratios have been obtained experimentally in extensive series of crosses between related species of Tilapia and their hybrids, carried out by several authors. The theory succeeds in explaining all of Chen's results, including those ratios 53 and 01 seen in certain crosses but not predicted by the WXYZ theory. The importance of the autosomes is seen in comparisons of the genotype pairs (AaWY, aaWY), (AaXY, aaXY) and (AAWW, AaWW) in which the first genotype in each case is male while the second is female as proven by the sex ratio results. The members of the pair differ only in the substitution of one autosome for the other. To test the theory, experiments consisting of hormonal sex reversion and a series of crosses are proposed. Finally, theoretical and practical implications of the theory are discussed.     

Cytogenetics of the parthenogenetic grasshopper Moraba virgo and its bisexual relatives

An undescribed bisexual grasshopper species closely related to the all-female parthenogenetic Moraba virgo has an X₁X₂Y sex chromosome mechanism which incorporates 7 chromosomes of the ancestral karyotype (the original X and three pairs of autosomes). Apparently three separate chromosomal fusions have occurred, one of these being a tandem fusion followed by a crossover which stabilized it in the sex chromosome system. M. virgo probably arose from an ancestor which had X₁X₂Y males but lacked the tandem fusion present in the new species, the females of virgo having the constitution X₁X₁X₂O.Supported by Public Health Service Grant GM-07212 from the Division of General Medical Sciences, U.S. National Institutes of Health, and by a grant from the Australian Research Grants Committee.     

Characterisation of a human Y chromosome repeated sequence and related sequences in higher primates

The human Y chromosome carries 2000 copies of a tandemly repeated sequence, 2.47 kb long, which constitutes about 20% of the DNA of this chromosome. These sequences are localised on the tip of the long arm of the Y chromosome. Related sequences are present in DNA of females with a related but distinguishable restriction pattern. These autosomal sequences are distributed in tandem arrays on a number of autosomes. Related sequences are also present in gorilla and chimpanzee. In gorilla they resemble the human sequences in their restriction map but are not found on the Y chromosome whereas in chimpanzee the related sequences behave as a dispersed repeat. Changes in the level of methylation of this sequence in different tissues of human males can be detected with the lowest levels found in sperm and placental DNA.     

Variation in preleptotene chromosome contraction among three cultivars of Lilium longiflorum

Preleptotene chromosome contraction was observed in several clones of Lilium longiflorum cultivars Ace, Nellie White and Croft. The degree of chromosome contraction was variable, among microsporocytes of single anthers, buds of individual plants, and clones of single cultivars. It is suggested that one of the sequence of genetically controlled events that determine the orderly development of meiosis provides for the temporary inhibition of mitotic coiling, thus allowing the development of leptotene; and if this gene action is delayed or out of sequence, a period of mitotic-like chromosome contraction precedes leptotene. These cultivars appear to share an inherited predisposition for such an irregularity in sequence of gene action. Differences between clones may be attributed to differences in other genes affecting these earliest stages of meiosis. There is some evidence of external environmental influence upon this genetic predisposition for preleptotene chromosome contraction, that is, there appears to be an inverse correlation between degree of preleptotene contraction and temperature. The degree of chromosome contraction may also be influenced by different metabolic conditions affecting microsporocytes developing sequentially in the anther. Experiments are presently underway to determine whether the degree of preleptotene chromosome contraction is related to chiasma frequency.     

Chromosome banding in Amphibia. XV. Two types of Y chromosomes and heterochromatin hypervariabilty inGastrotheca pseustes (Anura,Hylidae)

The chromosomes of the newly discovered South American marsupial frogGastrotheca pseustes were analyzed by conventional methods and by various banding techniques. This species is characterized by XY/XX sex chromosomes and the existence of two different morphs of Y chromosomes. Whereas in type A males the XY^A chromosomes are still homomorphic, in type B males the Y^B chromosome displays a large heterochromatic region at the long arm telomere which is absent in the X. In male meiosis, the homomorphic XY^A chromosomes exhibit the same pairing configuration as the autosomal bivalents. On the other hand, the heteromorphic XY^B chromosomes form a sex bivalent by pairing their short arm telomeres in a characteristic end-to-end arrangement. Analysis of the karyotypes by C-banding and DNA base pair-specific fluorochromes reveals enormous interindividual size variability of the autosomal heterochromatin.     

Identification of a 1B/1R wheat-rye chromosome translocation

Summary The common wheat selection 79-4045 was identified as a wheat-rye 1B/1R chromosome translocation line, by means of C-banding patterns and test cross with Chinese Spring double-ditelosomic line. The translocation chromosome consisted of the long arm of wheat chromosome 1B, including its centromere, and the short arm of rye chromosome 1R or tis portion.     

Control of lectins in Triticum aestivum and Aegilops umbellulata by homoeologous group 1 chromosomes

Summary Each of the three genomes in hexaploid wheat controls the expression of a specific lectin in the embryo. The chromosomes which control their synthesis were determined using nullisomic-tetrasomic and inter-varietal chromosome substitution lines of Chinese Spring. All three wheat lectins were shown to be controlled by the homoeologous group 1 chromosomes. Using ditelosomic lines of Chinese Spring the lectin genes could be localized on the long arms of chromosomes 1A and 1D. Inter-specific addition and substitution lines of Aegilops umbellulata chromosomes to Chinese Spring indicated that chromosome 1U, which is homoeologous to the group 1 chromosomes of wheat, controls lectin synthesis.     

Autoradiographic studies of the human Y chromosome

An autoradiographic analysis (using continuous labeling with tritiated thymidine) was made on 317 cells from four normal males. The labeling pattern of the Y chromosome was compared to the first and the last chromosomes to complete replication as well as to G21–22. The Y chromosome was never found to be the last chromosome in the cell to complete replication. Instead, it completed DNA synthesis relatively early (usually among the first 10 chromosomes) but had a distinctively heavy label during the earliest stages of late-S. In 51% of those cells with one labeled G+Y chromosome, a G21–22 was labeled and the Y was not.—It was concluded, therefore, that the human Y chromosome is not a late-replicating chromosome but terminates replication earlier than most of the autosomes. In addition, the Y chromosome cannot be distinguished from the G chromosomes on the basis of a consistent and differential labeling pattern.Supported by USPHS Grant GM 15361.     

Two phases of DNA replication in human cells

The course of DNA synthesis in the chromosomes was studied in synchronized human lymphocyte cultures, by means of the BrdU-Hoechst-Giemsa method. In comparing replication patterns and G-banding it was found that with regard to banding the process of DNA replication can be divided into two separate phases, an early replication period which is characterized by DNA synthesis in R bands of the autosomes and active X chromosome, and a late replication period which concerns the G-positive regions of the autosomes and all the bands of the heterochromatic X and Y chromosomes. No overlapping was found between the two phases mentioned. The possible role of regulatory mechanisms was discussed.