Showing papers on "X chromosome published in 1970"

Definitive Evidence for the Short Arm of the Y Chromosome associating with the X Chromosome during Meiosis in the Human Male

Abstract: MEIOTIC studies on the human male during the past thirty years, notably those of Koller1 and Ford and Hamerton2, have shown that the X and Y chromosomes associate at meiotic prophase. Whether the chromosomes form a true chiasma or not has never been demonstrated convincingly. Because the position of the centromeres of the chromosomes cannot be identified with certainty in meiotic preparations, there has been much speculation as to whether it is the long or the short arms of the Y chromosome which associate with the X. Thus, Sasaki and Makino3 suggested that the X–Y chromosome association involved the short arms of the Y, and Hulten et al.4 suggested the long arms of the Y. The best cytological evidence has come from McIlree et al.5 on a male with a dicentric Y chromosome involving a presumptive deletion of the short arms. At diakinesis the dicentric Y chromosome did not associate with the X, and Jacobs therefore suggested that in normal circumstances the Y chromosome might have associated with the X by its short arms6. From phenotype–karyotype correlations, Ferguson-Smith7,8 deduced that part of the long arms of the Y chromosome was homologous with part of the short arms of the X, and that this region was involved in the X–Y association. From the appearance of the X–Y association at diakinesis in testicular biopsies from a population of normal males, we have tentatively concluded that the short arms of the Y chromosome are involved in associating with the X chromosome.

X-Autosome Translocations in The Mouse: Total Inactivation Versus Partial Inactivation Of The X Chromosome

Abstract: Publisher Summary This chapter reviews that the use of data from the X-A translocations in the mouse allowed hypothetical answers to be formulated regarding the selection of one active X chromosome, physical linkage of autosomal genes to the active or inactive X chromosomal material regarding inactivation or activation, complete inactivation of an intact X chromosome versus incomplete inactivation of the X portion of an X-A segment, and random versus nonrandom inactivation with respect to primary and secondary causes. The chapter also discusses an interesting model for a gene regulation control system, which is proposed in higher organisms. The inactivation of the X chromosome would indicate that there are hierarchies of gene regulation. The X chromosome would be expected to have all the control systems. This latter system is hypothesized to be the determination mechanism for which X chromosome will be the inactive X chromosome.

Unusual sex chromosome inheritance in mammals.

Abstract: The male has proven to be the heterogametic sex in all mammals studied so far. As is well known, the males usually have the sex chromosomes XY and the females XX. In recent years, however, many exceptions from this general pattern have been discovered. With our present knowledge, the different sex chromosome mechanisms in mammals may be divided into five main groups, and the first of them into subgroups, as follows: (i) Species with XX/XY sex chromosomes: (a) X of original size (see below), Y small; (b) X large, Y small; (c) X large, Y large: (i) end-to-end association of X and Y at male meiosis, (ii) chiasma between X and Y at male meiosis. (ii) Species with XX/XY1Y2 sex chromosomes. (iii) Species with X1X1X2X2/X1X2Y sex chromosomes. (iv) Species with complicated or unknown mechanisms for sex determination. (v) Species with mosaicism of the sex chromosomes, but apparently with an XX/XY mechanism for sex determination. The present contribution will mainly deal with unusual sex chromosome inheritance, that is the groups (ii), (iii) and (iv) above, but the other two groups will also be briefly discussed and examples will be given. Recently Raicu, Kirillova & Hamar (1969) described a new sex chromosome mechanism ( X1X1X2X2/X1X2Y1Y2) in the vole Microtus arvalis , but this observation was not confirmed by Schmid (1969), who found an ordinary XX/XY mechanism with both X and Y readily identifiable and of ‘normal’ size, the X comprising 5.6% of ( n A + X) and Y being the smallest chromosome of the complement. Late DNA replication was demonstrated in the allocyclic X and in the Y. Also Wolf (1969) found normal sex chromosomes in this species with no multivalents at male meiosis.

Fluorescent staining of the Y chromosome in meiotic stages of the human male.

Abstract: It has been previously reported that the distal half of the long arm of the human Y chromosome shows a differential affinity for fluorescent acridine derivatives (Zech, 1969; Pearson, Bobrow & Vosa, 1970). By the use of this staining reaction, the Y chromosome can be detected in interphase nuclei of lymphocytes, cultured skin fibroblasts and buccal mucosal cells. This technique has also been used to demonstrate that the X chromosome pairs with the short

CHROMOSOMAL BASIS OF DOSAGE COMPENSATION IN DROSOPHILA : III. Early Completion of Replication by the Polytene X-Chromosome in Male: Further Evidence and Its Implications

Abstract: Thymidine-3H labeling patterns on the X (section 1 A to 12 E of Bridges' map) and 2 R (section 56 F to 60 F of Bridges' map) segments in the salivary gland chromosomes of Drosophila melanogaster have been analyzed in male and female separately The observed patterns fit, with a few exceptions, in a continuous to discontinuous labeling sequence In nuclei with similar labeling patterns on the 2R segment in both sexes, the number of labeled sites on the X in male is always less than in female X's The labeling frequency of the different sites on the male X is considerably lower than those on the female X's, while the sites on the 2R segment have very similar frequency in the two sexes The rate of thymidine-3H incorporation (as judged by visual grain counting) is relatively higher in male X than in female X's It is concluded that the model sequence of replication in polytene chromosomes follows a continuous to discontinuous labeling sequence, and that the single X in male completes its replication earlier than either the autosomes in male or the X's in female This asynchronous and faster rate of replication by the polytene X-chromosome in male substantiates the hypothesis of hyperactivity of the single X in male as the chromosomal basis of dosage compensation in Drosophila

Chromosome Loss compared with Chromosome Size, Age and Sex of Subjects

Abstract: STUDIES of human chromosomes1–7 have demonstrated that ageing increases hypodiploidy. Sex differences were said to account for different rates of increase in hypodiploidy as well as the preferential loss of an X chromosome in females and a Y chromosome in males2,4–6.

Genetic activity of sex chromosomes in somatic cells of mammals

Abstract: Mammals are thought to have a type of dosage compensation not so far known in any other animal group: however many X chromosomes are present, only one remains genetically active in somatic cells. Considerable evidence for this idea exists, in spite of criticism; the greatest difficulty is presented by the abnormalities in human individuals with X chromosome aberrations. Possible explanations for these abnormalities include: wrong X chromosome dosage in early development before X inactivation, reversal of inactivation, partial inactivation of both X chromosomes, activity of the X while in the condensed inactive state, and the presence of a homologous non-inactivated region of the human X and Y. In female germ cells X inactivation apparently does not occur, but the situation in male germ cells is less clear. The Y chromosome is probably also inactive in somatic cells of adults, but again its function in germ cells is not yet clear. Some species have a presumed doubly inactive X chromosome region, as well as the singly active one. The origins and functions of this region are unknown; it may have a role in female germ cells.

The discriminating fluorescence patterns of the chromosomes of Drosophila melanogaster.

Abstract: Mitotic and salivary gland chromosomes of D. melanogaster show striking fluorescent patterns when stained with Quinacrine. In the salivary gland chromosomes there are up to five strongly fluorescing bands located on the fourth chromosome and at the proximal end of the X chromosome.—In mitotic cells the Y chromosome shows four fluorescent segments and other fluorescent regions are found proximally on the third pair and on the X chromosome. It is, therefore, possible to distinguish male and female interphase cells by their patterns of fluorescence.—A comparison between the position of heterochromatic, late replicating and fluorescing segments in the mitotic chromosomes, shows differences which demonstrate, for the first time, the chemical, morphological and genetical diversity of these three types of segments.

Xg locus: failure to detect inactivation in females with chronic myelocytic leukaemia.

Abstract: THE inactive-X hypothesis states that only one of the two X chromosomes in each somatic cell of adult mammalian females is genetically active. The initial event in early embryogenesis which determines whether the paternal or the maternal X chromosome will remain active in any given cell is presumably random; once made, the choice is fixed for that cell and for all its descendants1–4. Although this type of inactivation has been demonstrated in man for a number of X-linked loci5, it is not known whether the entire X chromosome is inactivated.

Late DNA replication in male mouse meiotic chromosomes.

Abstract: Parts of the male mouse meiotic complement comprising the Y chromosome, the whole X chromosome, and near-centromeric parts of autosomal bivalents are synthesized late, as judged by tritiated thymidine autoradiography. This confirms the occurrence of end-to-end association between X and Y chromosomes and suggests that paired heterochromatic segments in autosomes must synthesize DNA at the same time.

Cytogenetics and sex determination in man and mammals.

Abstract: Sex in man and probably throughout the class mammalia is normally determined by the presence of a Y chromosome (male) or its absence (female). The presence of genetic loci on both the long and the short arm of the X chromosome in double dose appears to be essential for the development of mature functional ovaries in the human female though a single X suffices in the female mouse.The development of masculine genital anatomy and phenotype is a consequence of prior formation of testes. In the absence of gonads of either kind, female internal and external genitalia are formed but secondary sex development fails. In rare human families a mutant gene suppresses the development of male external genitalia in 46, XY embryos but permits the development of testes and male internal genitalia. The external phenotype is normal female (syndrome of testicular feminization). A sex-linked mutant gene in the mouse has a similar effect.The locus or loci directly concerned with male development might lie wholly on the Y chromosome or might be located on another chromosome or chromosomes. In the latter case it (or they) must be repressed in the female and normally activated by a locus or loci on the Y chromosome in the male. Present evidence does not permit the exclusion of either possibility.

An analysis of white-mottled mutants inDrosophila hydei, with observations on X-Y exchanges in the male

Abstract: Chromosomes and phenotypes of four different sex-linkedwhite-mottled mutants of the position-effect variogation type were studied. Three mutants (w m1,w m2,w m3) are X-chromosomal rearrangements which shift the w+ locus into a position close to heterochromatin, but which have different ouchromatic and heterochromatic breaks. The fourth, a spontaneous derivative ofw m1, is an insertional duplication of part of the X chromosome, including thew + andN +loci. The duplicated segment is inserted into the distal part of the long arm of the heterochromatic Y chromosome. It is designated,w m CoY, orXw m Co when transferred to the X chromosome. Three chromosomal types (w m1,w m CoY) and (Xw m Co) having the same cuchromatic break near thew + locus, cause large-spotted eyes whereas two others (w m2,w m3) produce a popper-and-salt type of mottling. From the position of the various eu- and heterochromatic breaks, it appears that the distance of thew + locus to the point of reunion with heterochromatin, rather than the amount or type of adjoining heterochromatin, dietates the phenotypic action of the displacedw + locus, in the sense of a spreading effect on two proposed functional subunits within thew + locus. The pigmentation background against which the mottling effect is produced, i.e., a givenw-allele with its characteristic colour, or other eye colour mutations, does not seem to affect the type of mottling. Drosopterins and ommochromes react in the same way to modifing factors like temperature and supernumerary Y chromosomes. Two mutants (w m2 andw m CoY) while reacting in the same manner to Y chromosomes showed an opposite temperature response. By exchange between the heterochromatin of the Y and X chromosome inw/w m CoY males thew m Co duplication was transferred between the sex chromosomes with a certain regularity. It is not yet known wether the exchanges are mitotic or meiotic in origin but their heterochromatic nature has been demonstrated cytologically.

Replication of the mouse sex chromosomes early in the S period

Abstract: The late-replicating X of the mouse can be clearly identified in a large proportion of metaphase spreads as an unlabelled chromosome when labelling of cells is done early in the S period. The Y chromosome follows this same pattern. Studies on Cattanach’s translocation are also reported, and it has been shown that the Xt can be distinguished from the normal X in early labelled material.

Glucose 6-phosphate dehydrogenase activity in the early rbbit and mouse embryo.

Abstract: Glucose 6-phosphate dehydrogenase (G6PD) activity was measured in individual preimplantation rabbit and mouse embryos. Substrate turnover by the enzyme is at least 30 times greater than glucose oxidation by the pentose shunt in the early rabbit embryo. There was no evidence during the preimplantation period of the embryos in either species of a bimodal distribution of G6PD activities among the embryos. Since cytological studies have not shown that inactivation of the X chromosome occurs during the early cleavage period and G6PD activity is sex-linked and gene-dose dependent in most higher animals, the evidence from the enzyme studies suggests that there is little or no synthesis of G6PD during the early preimplantation period. It is suggested that the enzyme is synthesized during oocyte development and the high levels of the enzyme found during the preimplantation period reflect the requirement of an earlier stage in oocyte development rather than the requirements of cleavage.

Chromosomal basis of dosage compensation in Drosophila. II. The DNA replication patterns of the male X-chromosome in an autosome--X insertion in D. melanogaster.

Abstract: The functional morphology and the replication pattern of the male X -chromosome in an autosome- X insertion stock ( T (1;3) 05) of Drosophila melanogaster have been examined. In larval salivary glands carrying this insertion neither the enlargement and pale staining of the single male X , nor the characteristic early completion of replication cycle, as revealed by 3 H-TdR autoradiography is in any way changed. The normal properties of the inserted autosomal segment are also unaltered. The results appear to support a ‘piecemeal’ type of dosage compensation mechanism in Drosophila operating through the male.

Y Heterochromatin and XX Males

Abstract: IN man the role of the Y chromosome in sex determination is unquestionable1,2. To explain the development of gonadal tissues with normal and abnormal sex-chromosome constitutions, the presence of male and female determining factors in the X and Y chromosomes (with positive and negative effects) has been postulated3. The regulation of sexual differentiation in early embryonic life has been attributed to the interaction between heterochromatins of the heterochromatic X and Y chromosomes4,5, and the masculinizing activity of the Y chromosome has been considered to result from a special heterochromatic effect of this chromosome on gonadal growth6. Evidence has been presented to show that in man the male-determining factors are located in the short arm of the Y chromosome7.

Chromosome Structure and Function in Man, III. Pachytene Analysis and Identification of the Supernumerary Chromosome in a Case of Down's Syndrome (Mongolism)

Abstract: Recently developed pachytene maps of the two small acrocentric autosomes (numbers 21 and 22) of man have been applied to a case of Down's syndrome mosaic for normal and trisomic cells (46,XY/47,XY,21+). Trivalents in trisomic spermatocytes, and thus the supernumerary chromosome, were recognized as compatible in length and chromomere pattern with the shorter of these two chromosomes at the pachytene stage. With the exception of the region of the centromere and the short arm, association among constituents of the trivalent appeared complete.

Is inactivation of the X chromosome in the female mule non-random?

Abstract: HAMERTON et al.1 have presented evidence which they interpret as a demonstration of preferential late replication of the donkey X chromosome (paternal X) in the female mule complement. This is in disagreement with cytological evidence2 for random X-inactivation3 in the female mule complement. This apparent contradiction prompted us to repeat the latter study and we report here our observations.

Ring chromosome D (13).

Abstract: A girl with a ring chromosome of No. 13 (D group) is alive and active at 10 years of age. Patients with partial deletion of a D chromosome,1-22including those with a ring D chromosome,1,2,4-7,10,13-15,17-19,22present a variety of clinical findings; one infant had many anomalies and was stillborn,2others are less affected. Several of these patients, whose deleted chromosome appears to be No. 13,13,14have unusual patterns of inheritance of haptoglobin, suggesting that a haptoglobin locus might be on this chromosome. Since a comparison of our patient with others could lead to more understanding of the functions of the involved chromosome, her story is presented. Report of a Case This white girl, weighed 1,650 gm (3 lb 10 oz) at term following a normal pregnancy. The primigravida mother was 18 years old; the father was 20. Both parents and a paternal half-sister are apparently normal

Genetic and clinical considerations of long-arm deletion of the x chromosome

Abstract: A 13-year-old girl with short stature and obesity was found to have 46, XXq-in 90% of cultured leukocytes and 45, X in 10%. Autoradiographic studies showed the long-arm deleted X to be the late replicating X chromosome. In no cell was the normal X chromosome found to be late replicating. Our findings, combined with others from the literature, imply genetic inactivation of all structurally abnormal X chromosomes. Therefore, a previous hypothesis regarding the location of the Xga gene on the short arm of the X chromosome is not valid. The hypothesis that normal somatic development in females may require the presence of the short arm of both X chromosomes prior to X inactivation remains likely. The XO line found in our patient probably accounts for her short stature.

Incomplete dosage compensation for glucose-6-phosphate dehydrogenase in human embryos and newborns.

Abstract: IN man, dosage compensation is achieved by random genetic inactivation of one X chromosome in each female cell early in embryonic life1; all descendants of this X chromosome then remain genetically inactive. The inactive X chromosome is late replicating and manifests itself as a sex chromatin body in the interphase somatic nuclei of females2,3. Because sex chromatin appears in human embryos approximately 12 days after conception4, it is presumed—although not certain—that X inactivation (Lyonization)5 occurs at this time. All human X-linked loci which have been tested hitherto have shown evidence of dosage compensation1. It is significant, however, that with one exception all these studies have been on older children or adults. A problem with the Lyon hypothesis is the existence of clinical abnormalities, particularly those of a non-sex-related nature, in patients with an abnormal number of X chromosomes. It suggests1,6 either that great damage can be done to human development by an abnormal number of X chromosomes before X-inactivation or that at least some X-linked loci must escape dosage compensation to a significant extent. This study supports the latter concept.

Multiple sex chromosomes and configuration polymorphism in the monochamus scutellatus-oregonensis complex (coleoptera: cerambycidae)

Abstract: Fission-fusion polymorphism of the X chromosome and multiple sex chromosome configurations were observed in the Monochamus scutellatus-oregonensis complex. Segregation of fission X chromosomes oppo...