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Showing papers on "X chromosome published in 1976"



Journal ArticleDOI
TL;DR: Human fibroblasts containing a translocation between the X chromosome and chromosome 15 were fused with the 6-thioguanine-resistant mouse cell line, IR, and hybrids, selected in HAT medium, retained the X/15 chromosome.
Abstract: Human fibroblasts containing a translocation between the X chromosome and chromosome 15 were fused with the 6-thioguanine-resistant mouse cell line, IR. Resulting hybrids, selected in HAT medium, retained the X/15 chromosome. Hybrids which were counterselected in 6-thioguanine lost this chromosome. The X-linked markers glucose-6-phosphate dehydrogenase (G6PD), phosphoglycerate kinase (PGK), and hypoxanthine phosphoribosyl transferase (HPRT), and the non-X-linked markers pyruvate kinase (PKM2) mannose phosphate isomerase (MPI), N-acetyl hexosaminidase A (HEXA) and β2-microglubulin (β2-m) all segregated in concordance with the X/15 translocation chromosome. The latter markers have been assigned to chromosome 15. Selection against the X/15 chromosome was done using antihuman β2-m serum. Electrophoretic and immunochemical analyses of the N-acetyl hexosaminidases A and B in these hybrids were performed.

122 citations


Journal Article
TL;DR: Results obtained from a fluorescence analysis of DNA replication in X chromosomes are consistent with those from previous autoradiographic studies, but reflect additional sensitivity and resolution offered by the BrdU-Hoechst methodology.
Abstract: The genetically inactive, late-replicating human female X chromosome can be effectively distinguished from its more active, earlier-replicating homologue, when cells are grown according to the appropriate BrdU-33258 Hoechst protocol. Results obtained from a fluorescence analysis of DNA replication in X chromosomes are consistent with those from previous autoradiographic studies, but reflect additional sensitivity and resolution offered by the BrdU-Hoechst methodology. Both qualitative and quantitative differences in 33258 Hoechst fluorescence intensity, reflecting alterations in replication kinetics, can be detected between the two X chromosomes in female cells. The pattern of replication in the single X chromosome in male cells is indistinguishable from that of the early female X. Intercellular fluctuations in the distribution of regions replicating early or late in S phase, particularly with reference to the late female X, can be localized to structural bands, suggesting multifocal control of DNA synthesis in X chromosomes.

116 citations


Journal ArticleDOI
12 Aug 1976-Nature
TL;DR: The Lyon hypothesis as discussed by the authors states that the mammalian female is a natural mosaic for clones of cells with either the maternally derived X chromosome (Xm) or the paternally-derived one (Xp) which is randomly inactivated early in development.
Abstract: THE Lyon hypothesis postulates that the mammalian female is a natural mosaic for clones of cells with either the maternally derived X chromosome (Xm) or the paternally derived one (Xp) which is randomly inactivated early in development1,2. We have presented evidence for the dominance of the inactive Xp in extraembryonic regions of 7.5- and 8.5-d mouse embryos heterozygous for Cattanach's translocation3 in which the two X chromosomes could be readily identified4. Though we presumed that this might not be an exceptional phenomenon restricted to mice bearing this X-autosome translocation, this has been difficult to confirm because of the lack of a system suitable for experiments. Here we report further cytological evidence that the inactive X is predominantly paternal in the yolk sac of the laboratory rat.

103 citations


Journal ArticleDOI
TL;DR: Fluorescence analysis permits identification of late replicating X chromosomes in a very high proportion of cells and affords a high resolution method for determining the interchange points of X-X and X-autosome translocations.
Abstract: BrdU-33258 Hoechst techniques have been used to characterize DNA replication patterns in lymphocytes from human females with supernumerary or structurally abnormal X chromosomes. Fluorescence analysis permits identification of late replicating X chromosomes in a very high proportion of cells and affords a high resolution method for determining the interchange points of X-X and X-autosome translocations. Asynchrony among terminal replication patterns of multiple late replicating X chromosomes within an individual cell can occasionally be demonstrated. The arms of isochromosomes usually exhibit symmetrical fluorescence patterns, with replication terminating in bands Xq21 and Xq23 (predominant pattern) or in bands Xq25 and Xq27 (alternative pattern) in both arms. In the vast majority of lymphocytes containing a balanced X-13 or X-19 translocation, the normal X is late replicating. However, DNA synthesis in the translocation products occasionally appears somewhat delayed relative to that expected for an early replicating X, consistent with possible position effects on replication kinetics.

103 citations


Journal ArticleDOI
26 Feb 1976-Nature
TL;DR: The X linkage of loci coding for glucose-6-phosphate de-hydrogenase (G6PD), hypoxanthine-ph phosphoribosyl transferase (HPRT), and phosphoglycerate kinase (PGK) has been determined for the mouse species Mus musculus and M. caroli.
Abstract: THE X linkage of loci coding for glucose-6-phosphate de-hydrogenase (G6PD), hypoxanthine-phosphoribosyl transferase (HPRT), and phosphoglycerate kinase (PGK) has been determined for the mouse species Mus musculus and M. caroli. Evidence was obtained from a somatic cell genetic analysis of cultured embryonic cells of an interspecific hybrid foetus. The X-chromosomal assignment of these loci has been determined already for several other mammalian species. This evidence was obtained from genetic analyses of electrophoretic variants1 and enzyme deficiencies2,3; from the expression of these genes in viable interspecific hybrids4–6; from somatic cell genetic analyses of heterozygotes7–9, and from the expression of these loci in interspecific somatic cell hybrids10.

77 citations


Journal ArticleDOI
16 Dec 1976-Nature
TL;DR: Serologically by typing male and female wood lemmings for expression of H–Y antigen, and it is found that all female woodLemmings are H-Y−, which is critical for differentiation of the male gonad.
Abstract: THE wood lemming, Myopus schisticolor Liljeborg, is distinguished by an aberrant sex ratio, with a considerable excess of females, and by the fact that some females produce only daughters1,2. Fredga and his associates3 have provided a basis for understanding both these characteristics. They observed that 82 out of 181 female wood lemmings studied (45%) had an XY sex chromosome constitution, with chromosomal G-banding and C-banding patterns indistinguishable from those of XY males. On the other hand, the XY females were anatomically normal and indistinguishable from XX females. Furthermore, meiotic studies3 showed that the germ line in the somatically XY females was XX. The second X chromosome in the germ cells must have arisen by non-disjunction from the single X present in the XY cells. Thus all progeny from such females must have received copies of the same X chromosome. How does one reconcile these observations with the apparent function of the Y chromosome in mammalian sex determination4, or with more recent evidence that a particular Y-linked gene which controls presence of H–Y antigen is critical for differentiation of the male gonad? We have approached these questions serologically by typing male and female wood lemmings for expression of H–Y antigen, and we have found that all female wood lemmings are H–Y−.

73 citations


Journal ArticleDOI
15 May 1976-Genetics
TL;DR: A method for selecting unlinked duplications of a part of the X chromosome of C. elegans is described, and these duplications may prove useful as balancers of recessive lethal mutations.
Abstract: A method for selecting unlinked duplications of a part of the X chromosome of C. elegans is described. Five such duplications have been identified. One of them, Dp ( X ; V ) 1 , is translocated to linkage group V , where it suppresses crossing over along the left half of linkage group V. Dp ( X ; V ) 1 homozygotes grow slowly and are sterile. The other four duplications are associated with chromosome fragments, as observed cytologically by fluorescence microscopy, and tend to be lost. Their frequency of loss is higher in strains homozygous for a mutation that promotes nondisjunction of X chromosomes. The recombination frequencies between two of these duplications and the X have been measured: the frequencies are at least 50 times less than for X-X recombination in the same region. The duplications may prove useful as balancers of recessive lethal mutations.

71 citations


Journal ArticleDOI
01 Sep 1976-Genetica
TL;DR: Meiotic drive in Aedes aegypti is shown by a Giemsa C-banding technique to be associated with preferential isochromatid breakage of the X chromosome during male meiosis, and it is argued that these breaks are directly related to the decreased number of spermatozoa found in distorting males.
Abstract: Meiotic drive in Aedes aegypti (L.) is shown by a Giemsa C-banding technique to be associated with preferential isochromatid breakage of the X chromosome during male meiosis. These breaks remain open at least until anaphase-I and, since the range of cells affected is proportional to the sensitivity of the X chromosome to the Distorter gene, it is argued that they are directly related to the decreased number of spermatozoa found in distorting males. This reduction is considered to be attributable to the degeneration of more X- than Y-bearing spermatids but it is probable that some non-functional X-bearing spermatozoa are also produced. Chromosome breakage is almost completely confined to four sites, two adjacent to the centromere, one just proximal to the intercalary band and another about the centre of the unbanded arm. Although the first three of these lie within a region in which crossing-over does not take place, fragmentation occurs more frequently in a chiasmate arm than in one devoid of chromatid exchange.

58 citations



Journal ArticleDOI
01 Dec 1976-Genetica
TL;DR: A taxonomy has been constructed which differs most markedly from the classical taxonomy in two aspects: the blackbuck, Antilope cervicapra, shows a strong karyotypic affinity to gazelles of the subgenus Nanger; Thomson's gazelle, Gazella thomsoni, lacks the numerous Robertsonian fusions and the X-autosome translocation common to other members of Gazella studied to date.
Abstract: The karyology was studied in nine species of Antilopinae and evaluated with regard to cytotaxonomic relations within the subfamily. Karyotypes of three of these species were previously undescribed. Chromosomes were examined by conventional staining methods, G-, C-, and T-banding techniques, and by autoradiography. Evolutionary differentiation of karyotypes in this group is characterized by extensive Robertsonian fusions and a particular translocation between the X chromosome and an autosome. With comparison of Giemsa-banding patterns a taxonomy has been constructed which differs most markedly from the classical taxonomy in two aspects: the blackbuck, Antilope cervicapra, shows a strong karyotypic affinity to gazelles of the subgenus Nanger; Thomson's gazelle, Gazella thomsoni, lacks the numerous Robertsonian fusions and the X-autosome translocation common to other members of Gazella studied to date. Cases of intraspecific polymorphism of chromosome morphology and number are presented.

Journal ArticleDOI
01 Sep 1976-Cell
TL;DR: Evidence is presented which suggests that X chromosome reactivation does not occur during differentiation of the cells in vitro, and that late DNA replication may not be a necessary adjunct of X inactivation.

Journal ArticleDOI
TL;DR: The hypothesis is put forward that the b region on the Xp always remains active and thus, when the rest of the chromosome forms a Barr body, this segment is extended, allowing the two parts of the X chromatin to get farther apart and at the same time increasing the percentage of bipartite bodies.
Abstract: An idic(Xp-) in which the two X chromosomes are attached short arm to short arm, and which thus has two b regions (the Q-dark segment next to the centromere on Xp) between the inactivation centers, assumed to be situated on the Q-dark region next to the centromere on Xq, showed 63.8% bipartite Barr bodies as compared with 22.2% formed by idic(Xq-). In addition, the mean distance of the two parts of the Barr bodies in the fibroblasts of a patient with idic(Xp-) is significantly greater than in the cases with one or no b region. Contrary to the other patients with abnormal X chromosomes, the buccal cells of a woman idic(Xp-) showed a number of bipartite Barr bodies. — To explain these observations we have put forward the hypothesis that the b region on the Xp always remains active and thus, when the rest of the chromosome forms a Barr body, this segment is extended, allowing the two parts of the X chromatin to get farther apart and at the same time increasing the percentage of bipartite bodies.

Journal ArticleDOI
TL;DR: There is certain evidence that an instability of the proposed mechanism for double mitotic nondisjunction of the sex chromosomes in oogonia accounts for the high rate of sex-chromosome aberrations in wood lemmings, at least when the mother is XY.
Abstract: The wood lemming displays certain peculiar features: (1) The sex ratio shows a prevalence of females (FRANK, 1966; KALELA and OKSALA, 1966), and some females produce only female offspring (KALELA and OKSALA, 1966). (2) In a considerable proportion (in the present material, slightly less than half) of the females, an XY chromosome complement is found in the somatic tissues, but the Y is absent in the germ line of those studied (Fredga et al., 1976). Therefore, (3) a mechanism of double nondisjunction in early fetal life of XY females has to be postulated, which replaces the Y in the germ line by duplication of the X. It is assumed (4) that the X of XY females bears a sex-reversal factor that affects the male determining action of the Y (Fredga et al., 1977). There is (5) a strong presumption that in most cases the XY females are those that produce daughters only, but (6) a few exceptions may occur (FRANK, unpublished observations), suggesting that the regulation according to assumption 3 (perhaps also to 4) is incomplete in XY females. In the present report, four females are described with a 31,XO karyotype, two females with 33,XYY or 32,XY/33,XYY, respectively, two males with a 33,XXY, and one male with a 32,XX/33,XXY karyotype, as observed in a consecutive series of 502 wood lemmings. The incidence of sex-chromosome anomalies in liveborn and adult animals was 2.3%; the overall incidence, including embryos, was 1.79%. Neither the somatic XO constitution nor the existence of an extra Y in females precludes fertility. However, the XXY condition in the male results in sterility. There is certain evidence that an instability of the proposed mechanism for double mitotic nondisjunction of the sex chromosomes in oogonia accounts for the high rate of sex-chromosome aberrations in wood lemmings, at least when the mother is XY.

Journal ArticleDOI
11 Mar 1976-Nature
TL;DR: The absence of this control mechanism in female meiosis, where both X chromosomes are active, could explain why only male gametogenesis is impaired in the carriers of some chromosomal aberrations.
Abstract: ACCORDING to Lifschytz and Lindsley1,2, the basic control mechanism of spermatogenesis of all male heterogametic organisms consists of inactivation of the X chromosome during differentiation of germ cells. The absence of this control mechanism in female meiosis, where both X chromosomes are active3,4, could explain why only male gametogenesis is impaired in the carriers of some chromosomal aberrations.

Journal ArticleDOI
TL;DR: Salivary gland chromosome slides of Anopheles albitarsis from Brasil, Colombia and Venezuela indicate that at least three chromosomally differentiated populations of this species exist in this area as mentioned in this paper.
Abstract: Salivary gland chromosome slides of Anopheles albitarsis from Brasil, Colombia and Venezuela indicate that at least three chromosomally differentiated populations of this species exist in this area. The B1 population from Brasil contains one heterozygous inversion in the X and two in the autosomes. Population B2, sympatric with B1 in Brasil, differs from it by two inversions in the X and ten in the autosomes. Population C in Colombia and Venezuela is closer to B1, from which it differs by three inversions in chromosome 2 and three in chromosome 3. Each population, B1, B2 and C may be distinguished with about 98% certainty using the banding patterns of the X chromosomes. Most of the remaining individuals may be identified using a combination of the X and autosomal paracentric inversions. The scarcity of shared inversions argues for little if any natural hybridization among these populations. A standard salivary gland chromosome map, based on the B1 populations, is presented.

Journal ArticleDOI
TL;DR: Measurements carried out on an XX male show that there is a significant difference between the lengths of the short arm of the 2 X chromosomes of this patient and that the short arms of the longer X is also significantly different from that of the X chromosomes derived from normal individuals.
Abstract: Measurements carried out on an XX male show that there is a significant difference between the lengths of the short arm of the 2 X chromosomes of this patient and that the short arm of the longer X is also significantly different from that of the X chromosomes derived from normal individuals. The difference lies specifically in the size of the terminal band of the short arm. These results are consistent with the X-Y interchange hypothesis of Ferguson-Smith.

Journal ArticleDOI
TL;DR: Results indicate that incorporation and expression of HeLa X chromosomes is accomplished in human-Chinese hamster hybrids which lack a human X chromosome.
Abstract: Evidence is presented for the uptake of the human X chromosome by human-Chinese hamster cell hybrids which lack HPRT activity, following incubation with isolated human HeLa S3 chromosomes. Sixteen independent clonal cell lines were isolated in HAT medium, all of which contained a human X chromosome as determined by trypsin-Giemsa staining. The frequency of HAT-resistant clones was 32 × 10−6 when 107 cells were incubated with 108 HeLa chromosomes. Potential reversion of the hybrid cells in HAT medium was less than 5 × 10−7 The 16 isolated cell lines all contained activity of the human X-linked marker enzymes HPRT, PGK, α-Gal A, and G6PD, as determined by electrophoresis. The phenotype of G6PD was G6PD A, corresponding to G6PD A in HeLa cells. The human parental cells used in the fusion to form the hybrids had the G6PD B phenotype. The recipient cells gave no evidence of containing human X chromosomes. These results indicate that incorporation and expression of HeLa X chromosomes is accomplished in human-Chinese hamster hybrids which lack a human X chromosome.

Journal ArticleDOI
TL;DR: A 27-year-old patient of short stature with primary amenorrhea and other slight Turner signs showed a 46,XX,del(X) (qter→p11:) karyotype, identified by a combination of fluorescence and giemsa-banding technique and the deleted X chromosome was shown to be the late replicating one.
Abstract: A 27-year-old patient of short stature with primary amenorrhea and other slight Turner signs showed a 46,XX,del(X) (qter→p11:) karyotype, identified by a combination of fluorescence and giemsa-banding technique. By BUdR incorporation the deleted X chromosome was shown to be the late replicating one.

Journal ArticleDOI
TL;DR: A male infant with a partial trisomy 18 and a 46,XY, --21, t(18;21)(18qter replaced by 18q12::21 p13 replaced by 21 qter) chromosome complement is described.
Abstract: A male infant with a partial trisomy 18 and a 46,XY, --21, t(18;21)(18qter replaced by 18q12::21 p13 replaced by 21 qter) chromosome complement is described. The translocation chromosome is of special interest because it includes the satellites of chromosome 21. This was shown by differential satellite staining with the ammoniacal-silver technique.

Journal ArticleDOI
29 Nov 1976-JAMA
TL;DR: Using a new serological assay, it is demonstrated the presence of Y-chromosomal genes in a 46-year-old man with an XX karyotype, and a minor population of XXY cells as well as cells bearing and abnormal chromosome 17 among the blood leukocytes of this individual.
Abstract: A number of patients with a male phenotype and a female (46XX) karyotype have been described. Although there is little or no evidence for the presence of a Y chromosome in their cells, these individuals resemble patients with Klinefelter syndrome (47XXY). Using a new serological assay for the presence of H-Y antigen, a cell surface component associated with the Y chromosome, we have demonstrated the presence of Y-chromosomal genes in a 46-year-old man with an XX karyotype. In addition, using standard cytological techniques, we have located a minor population of XXY cells as well as cells bearing an abnormal chromosome 17 among the blood leukocytes of this individual. (JAMA236:2505-2508, 1976)

Journal ArticleDOI
Barbara Meer1
TL;DR: Male hybrids of the cross D. azteca x D. athabasca are larger (hybrid giant males) than their parents, whereas hybrid females are of the same size as the parental species, while in females of either species as well as of hybrids X-chromosomes and autosomes are equally labeled.
Abstract: Male hybrids of the cross D. azteca x D. athabasca are larger (hybrid giant males) than their parents, whereas hybrid females are of the same size as the parental species. Microspectrophotometric measurements have shown that the larval polytene salivary gland chromosomes of hybrid giant males undergo one more endoreplication than those of their sisters or parents. Replication patterns of the larval salivary gland chromosomes were compared after pulse labeling with 3H-thymidine and autoradiography. In females of either species as well as of hybrids X-chromosomes and autosomes are equally labeled, i.e. all chromosome arms replicate synchronously. In males, however, often fewer sites are labeled on the X-chromosome than on the autosomes. In addition, in a significant number of nuclei from D. athabasca males and also from hybrid giant males the converse can also be observed: i.e. more sites are labeled on the X-chromosome than on the autosomes. The modified labeling patterns are interpreted as an indication of a time-shift in the replication of hemizygous X-chromosomes in males, in relation to the autosomes.

Journal ArticleDOI
TL;DR: In this article, a I-year-old girl with severe Christmas disease and a factor IX content less than I% of normal was described. Genetic investigation showed an XXp-karyotype with deletion of the short arm of one X-chromosome, a cytogenetic variant of Turner syndrome.
Abstract: A I-year-old girl with severe Christmas disease and a factor IX content less than I% of normal is described. The family history was negative and coagulation studies on her relatives were normal. Genetic investigation showed an XXp-karyotype with deletion of the short arm of one X-chromosome, a cytogenetic variant of Turner syndrome. The transmission pathway of the haemophilia gene is discussed.

Journal ArticleDOI
T Maeda1, M Ohno1, A Ishibashi1, M Samejima1, K Sasaki1 
TL;DR: Chromosome analysis of lymphocytes in a phenotypically normal male with azoospermia showed a mosaicism 45,X/46,X,r(Y), and seven other cases from the literature are discussed.
Abstract: Chromosome analysis of lymphocytes in a phenotypically normal male with azoospermia showed a mosaicism 45,X/46,X,r(Y). Seven other cases from the literature are discussed.

Journal ArticleDOI
TL;DR: Using C-banded preparations of Mus dunni it is possible to study the behavior of constitutive heterochromatin in early stages of meiotic prophase, suggesting probable incomplete synapsis in autosomes.
Abstract: Using C-banded preparations of Mus dunni it is possible to study the behavior of constitutive heterochromatin in early stages of meiotic prophase. The X and the Y chromosomes, both of which contain a large amount of heterochromatin, lie apart in leptotene but move toward each other during zygotene. They then form the sex vesicle at late zygotene. In autosomes zygotene pairing appears to start from the telomeric ends. The centromere of the Y chromosome associates end-to-end with the terminal end of the long arm of the X chromosome. The autosomal heterochromatic short arms show forked morphology in certain bivalents at pachytene, suggesting probable incomplete synapsis.

Journal ArticleDOI
TL;DR: Results suggest that both arms of the X of D. pseudoobscura, are hyperactive and faster replicating in the male, which might arise due to a primary signal coming from autosomally located regulators controlling the super‐operon structure of theX chromosomal genes.
Abstract: SUMMARY The two arms of the X chromosome of Drosophila pseudoobscura have different phylogenetic origin, the XL being homologous to the X and the XR homologous to the 3L of D. melanogaster. The replicative and transcriptive activities of the two arms have been examined in order to understand how such phylogenetically different components of the X contribute toward the chromosomal basis of dosage compensation. The 3H-uridine labelled autoradiograms of the polytene chromosomes of larval salivary glands reveal that the intensity of labelling in the XL and XR of the male is not significantly different from that in the two arms of the female, respectively. The number of grains on the two arms plotted against the grain number on an autosome follows a linear regression, and neither slope in the male is significantly different from its counterpart in the female. The 3H-thymidine autoradiograms show that in all phases of replication, viz. initial, middle and terminal, both arms of the X chromosome in the male are advanced by one step in the cycle. Results, therefore, suggest that both arms of the X of D. pseudoobscura, are hyperactive and faster replicating in the male. Such a situation might arise due to a primary signal coming from autosomally located regulators controlling the super-operon structure of the X chromosomal genes.

Journal ArticleDOI
TL;DR: A second mechanism of marker formation, selective regional elongation, is proposed to account for the larger number of markers with proximal or distal elongations without evidence of translocation and for the observed alterations in length and banding pattern of markers after growth in vitro.
Abstract: Two common chromosome markers in the 2 plasmacytomas previously examined by Giemsa banding were consistently present in the mouse plasmacytoma X-5563, a transplantable hypertetraploid tumor of spontaneous origin in C3H mice. The 2 markers were found in both induced and spontaneous tumors and in either BALB/c or C3H mice. The derived cell line had 17 fewer chromosomes than the X-5563 tumor and was oncogenic, and its modal karyotype was identical to that of the tumor transmitted by the inoculation of the cell line. The homogeneity of a slight karyotypic modification in a second tumor suggested a possible clonal origin of that tumor. The high frequency of centric fusions between homologues and the structure of certain markers suggests that homologue association may precede marker formation. We proposed a second mechanism of marker formation, selective regional elongation, to account for the larger number of markers with proximal or distal elongations without evidence of translocation and for the observed alterations in length and banding pattern of markers after growth in vitro. Comparison of MOPC-21, MOPC-315, and X-5563 tumors showed preferential involvement of certain chromosomes in marker formation, an inferred association of the 2 common markers with an early stage in the origin of the 3 plasmacytomas, and consistent loss of an X chromosome. Loss of oncogenicity in cell lines was associated with a number of karyotypic changes, but did not require the loss of the characteristic markers or additional copies of a specific normal chromosome.

Journal ArticleDOI
15 Jan 1976-Genetics
TL;DR: The number of rRNA cistrons is measured by filter saturation hybridization in different stocks of D. hydei, where the wild-type X chromosome has one nucleolus organizer (NO) and wild- type Y has two separated NO's.
Abstract: The number of rRNA cistrons is measured by filter saturation hybridization in different stocks of D. hydei, where the wild-type X chromosome has one nucleolus organizer (NO) and the wild-type Y has two separated NO's. (see PDF) females having no X chromosomal NO show an rDNA content exceeding that of a Y chromosome. An even greater increase in the rRNA cistron number is measured in two translocation stocks where the (see PDF) is combined with one half of a Y and, therefore, each stock contains only one of the two Y chromosomal NO's. But when the same Y fragments are brought together with a wild-type X chromosome they lose about one-half of their rRNA cistrons within one generation. Males with two complementary Y fragments but having no X chromosomal NO show a considerably higher rDNA content than the (see PDF) females, although both are equal in respect of their NO number. Consideration is given to related phenomena in Drosophila melanogaster.

Journal ArticleDOI
TL;DR: The clinical symptomatology presents the great variability already observed in association with this karyotype, 45,XO/46,Xr(X), as well as the fact that only a short stature was common to the 3 patients.
Abstract: A detailed chromosome analysis was carried out in 3 patients presenting the mosaicism, 45,XO/46,Xr(X). In 2 patients, the r(X) chromosome was found to be latereplicating using R-banding techniques after a BrdU pulse administered 6 h before harvesting the leukocyte culture. The clinical symptomatology presents the great variability already observed in association with this karyotype. Only a short stature was common to the 3 patients. Case 1 is a 6-year-old girl with moderate mental retardation; case 2 is a 16-year-old girl with primary amenorrhea and absence of secondary sexual characteristics; case 3 is a 24-year-old woman whose puberty and normal sexual development occurred at age 17.

Journal ArticleDOI
TL;DR: This paper examines the possibilities for balancing selection in the kangaroo X chromosome system and shows that balanced polymorphisms are unlikely to occur.
Abstract: Female kangaroos and perhaps other female marsupials have a unique form of dosage compensation for X-linked genes in their soma. In these animals the paternal X is inactive. Heterozygote females therefore have the phenotype of one or the other of the homozygotes, with the allele which is expressed coming from their mother. The unexpressed paternally derived allele may, however, be transmitted to the next generation in the usual Mendelian manner and there be expressed. Such a combination of haploid phenotypic expression and diploid genotypic behaviour on the part of X-linked genes in kangaroos makes their population genetics unique. This paper examines the possibilities for balancing selection in the kangaroo X chromosome system and shows that balanced polymorphisms are unlikely to occur. If 1-a, 1, 1 - band' 1 are the selection coefficients of the 1X1 females, 1X2 females, 1X1 males and 1X2 males respectively (where 1X1 is the phenotype when A1 is expressed and 1X2 the phenotype when A2 is expressed), then the equilibrium is reached when the gene frequency of A1 in females = 0·5(a-1+b-1), which takes values between 0 and 1 for only a few of the biologically likely values of a and b.