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Showing papers on "Heterochromatin published in 1984"



Journal ArticleDOI
TL;DR: Observations suggest that in highly differentiated cells, the nuclear position of centromeres is maintained in evolution despite species differences in centromeric DNA sequence, which may be integral to specific functional capacities.
Abstract: Paraformaldehyde-fixed tissue from mouse cerebellum was hybridized with biotin-labeled satellite DNA for identification of centromeres. By using avidin-peroxidase conjugates, it was possible to define the nuclear position of centromeres at the ultrastructural level. Three-dimensional analysis of well-resolved centromere arrays were aided by computer reconstruction of serial sections. Different cell types displayed distinct, nonrandom centromere locations. In Purkinje neurons, the majority of detected sequences were clustered together around the central nucleolus, whereas in granule neurons, more numerous, dispersed centromere clusters were associated with the nuclear membrane. In Purkinje cells, peroxidase-labeled regions corresponded to dense heterochromatic aggregates were detected in Purkinje cells of several different species. These observations suggest that in these highly differentiated cells, the nuclear position of centromeres is maintained in evolution despite species differences in centromeric DNA sequence. Such defined ordering of centromeres may be integral to specific functional capacities.

205 citations


Journal ArticleDOI
01 Jul 1984-Cell
TL;DR: It is demonstrated that revertants of the variegating mutant, wm4, are reinversions that leave the initial wm 4-heterochromatic junction intact so that some heterochromatin-derived sequences remain joined to white at its new location.

160 citations


Journal ArticleDOI
TL;DR: Results indicate a high degree of chromosome structural change induced by tissue culture may be a useful tool in alien gene introgression and manipulation of heterochromatin in triticale improvement.
Abstract: The spontaneous occurrence of chromosome breaks, deletions, and translocations in plant tissue cultures is well documented. This study investigated the usefulness of tissue culture as a method of introgressing alien genes into wheat. Wheat X rye hybrids were regenerated from embryo scutellar calli maintained in culture for 222 days. The regenerated seedlings then were treated with colchicine to produce amphidiploids (AABBDDRR). The karyotypes of ten amphidiploids were analyzed by C-banding to determine chromosome structural changes that occurred during tissue culture. Three wheat/rye and one wheat/wheat chromosome translocations, seven deletions, and five amplifications of heterochromatin bands of rye chromosomes were identified. One amphidiploid contained a reciprocal translocation between wheat chromosome 4D and rye chromosome 1R. Non-reciprocal translocations between 2B and 3R, and between an unidentified wheat chromosome and 2R, were found independently in two amphidiploids. An additional plant had a translocation between wheat chromosomes 6B and 5A. All deletions involving rye chromosomes were noted in all 10 amphidiploids. Twelve of the 13 breakpoints in chromosomes involved in translocations and deletions occurred in heterochromatin. Amplification of heterochromatin bands on 2RL and 7RL chromosome arms also was observed in five plants. These results indicate a high degree of chromosome structural change induced by tissue culture. Therefore, tissue culture may be a useful tool in alien gene introgression and manipulation of heterochromatin in triticale improvement.

151 citations


Journal ArticleDOI
TL;DR: The reduced level of chromosome pairing that is often observed in intercultivar hybrids of wheat may be due to heterochromatic differentiation, genic and structural heterozygosity, or hybrid dysgenesis.
Abstract: Heterochromatin distribution and structural differentiation of somatic chromosomes of five common wheat cultivars — Chinese Spring, Wichita, Cheyenne, Timstein, and Hope — were studied by an acetocarmine/N-banding technique. Detailed morphological observations on acetocarmine stained somatic chromosomes of Chinese Spring were made on all A genome chromosomes (except 1A), all B genome chromosomes, and chromosomes 1D, 2D, and 7D. N-banding patterns of chromosomes 2A, 3A, 5A, 6A, 1D, 2D, and 7D were described for the first time. Substitution lines of 21 individual chromosomes each of Cheyenne, Timstein, and Hope in Chinese Spring were analyzed by N-banding. A high frequency of N-band polymorphism was observed, especially for most of the B genome chromosomes. Chromosomes 3A, 5A, 2D, and 7D showed a constant banding pattern. Three cases of doubtful substitutions, Hope 2A, 2B, and Timstein 7A, and several cases of incomplete and chromosomally modified substitutions were observed. The reduced level of chromosome pairing that is often observed in intercultivar hybrids of wheat may be due to heterochromatic differentiation, genic and structural heterozygosity, or hybrid dysgenesis.

143 citations


Journal ArticleDOI
TL;DR: The mitotic and meiotic chromosomes of the American cyprinodont fish Poecilia sphenops var.
Abstract: The mitotic and meiotic chromosomes of the American cyprinodont fish Poecilia sphenops var. melanistica were analysed. All 46 chromosomes are telocentric. By specific staining of the constitutive heterochromatin with C-banding and various AT-specific fluorochromes, the homomorphic chromosome pair 1 could be identified as sex chromosomes of the ZW/ZZ type. All female animals exhibit a W chromosome with a large region of telomeric heterochromatin that is not present in the Z chromosome. These sex chromosomes cannot be distinguished by conventional staining; they represent the first demonstration of sex chromosomes in fishes in an early stage of morphological differentiation. The W heterochromatin and the telomeric heterochromatin in the two autosomes 18 show a very bright fluorescence when stained with AT-specific fluorochromes. This allows the direct identification of the chromosomal sex by examining the interphase nuclei: females exhibit three, males only two brightly fluorescent heterochromatic chromocenters in their nuclei. The significance of these ZW/ ZZ sex chromosomes and their specific DNA sequences, the dose compensation of the Z-linked genes, and the experimental possibilities using sex-reversed “ZW males” are discussed.

123 citations


Journal ArticleDOI
TL;DR: In this paper, the major DNA sequence component of knob heterochromatin in maize, teosinte and Tripacum has been characterised in situ hybridization, and it has been shown that this repeating DNA sequence, which is the major component of maize knob heter-chromatin, is also the major components of knobs in teopsinte, zea diploperennis and tripsacum, is not detectable in three species of Coix, an Old World genus of the Maydeae.
Abstract: We have characterised the major DNA sequence component of knob heterochromatin in maize, teosinte andTripsacum. Sequence analysis of this DNA gives strong support to the proposal that maize originated by selection of variants in teosinte. In situ hybridization has confirmed that this repeating DNA sequence, which is the major component of maize knob heterochromatin, is also the major component of knobs in teosinte,Zea diploperennis andTripsacum. In Southern blot hybridizations the repeat has a similar basic organization in all taxa;Tripsacum, however, is differentiated from maize and teosinte by a number of sequence features. Maize and teosinte knob heterochromatin are indistinguishable with regard to the distribution of mutations in the 180-bp repeat and the presence and organization of a 202-bp variant sequence. The knob DNA sequence was not detectable in three species ofCoix, an Old World genus of the Maydeae.

99 citations


Journal ArticleDOI
TL;DR: Repeated base sequences, particularly (CA)n sequences, are believed to be the basis of telomere pairing, and likewise repeated base sequences of heterochromatin may explain the association of 1qh and telomeres.
Abstract: About 20% of leukemic bone marrow cells from each of two patients with B-cell lymphoid leukemias showed apparent translocations which appeared to be the result of telomeric association. In one patient, whole chromosomes were associated telomere to telomere in pairs; in the other patient, telomeres of whole chromosomes were associated with breakpoints located close to the proximal or distal ends of the heterochromatic band 1q12. Repeated base sequences, particularly (CA)n sequences, are believed to be the basis of telomere pairing, and likewise repeated base sequences of heterochromatin may explain the association of 1qh and telomeres. Telomeric association may be considered as a potential origin of new stable cytogenetic combinations that have a role in oncogene transposition and tumor etiology.

99 citations


Journal ArticleDOI
TL;DR: A combined light- and electron-microscopic examination of chromosomes from two angiospermous plants and a mammal was performed, and a difference in the structure of SCs in euchromatin versus heterochromatin was observed that could be associated with the lack of crossing over in heterochromaatin.
Abstract: A combined light- and electron-microscopic examination of chromosomes from two angiospermous plants, Plantago ovata and Lycopersicon esculentum, and a mammal, Mus musculus, was performed. From this investigation three observations have been made that may be relevant to the observed lack of crossing over in heterochromatin. (1) Differential staining indicates that heterochromatin represents a smaller fraction of the length of pachytene chromosomes than it represents in the length of mitotic metaphase chromosomes. Since the synaptonemal complex (SC) runs throughout the length of these pachytene chromosomes, it is under-represented in heterochromatin. Considering the evidence for a rough correlation between the length of SC and the amount of crossing over, this could result in less crossing over in heterochromatin than expected on the basis of its length in mitotic metaphase chromosomes. (2) Electron microscopy indicates that, unlike the SC in euchromatin, the SC in heterochromatin is densely ensheathed in highly compact chromatin. If crossing over occurs in the SC or even in the surrounding chromatin, the compaction of the chromatin may prevent the penetration of enzymes needed in recombination. (3) Finally, a difference in the structure of SCs in euchromatin versus heterochromatin was observed that could be associated with the lack of crossing over in heterochromatin.

98 citations


Journal ArticleDOI
TL;DR: The acetocarmine–Giemsa C-banding technique was used to study heterochromatin distribution in somatic chromosomes of diploid Elymus junceus (= Psathyrostachys juncea).
Abstract: The acetocarmine–Giemsa C-banding technique was used to study heterochromatin distribution in somatic chromosomes of diploid Elymus junceus (= Psathyrostachys juncea) (2n = 14) (genome designation ...

90 citations


Journal ArticleDOI
01 Aug 1984-Heredity
TL;DR: A unique euchromatic supernumerary segment was present in the five populations of Omocestus bolivari analysed, which appears negatively heteropyenotic during the first prophase of meiosis and does not C-band.
Abstract: C-Heterochromatin content of supernumerary chromosome segments of grasshoppers: Detection of an euchromatic extra segment

Journal ArticleDOI
01 Dec 1984-Genetica
TL;DR: C-banding analysis of the mitotic chromosomes revealed constitutive heterochromatin in the centromeric regions of all acrocentrics, however, small metacentrics were C-band negative.
Abstract: Chromosomes of Eigenmannia sp. (7 males and 15 females) collected from the Tiete River in Botucatu (SP, Brazil) were examined from gill, kidney and testicular cells. The diploid chromosome number in males was 2n=31 and in females, 2n=32. In both sexes the number of chromosomal arms was 40. The difference in diploid number was due to the fusion of two acrocentrics. Mitotic and meiotic studies suggested that one of the fused acrocentrics was the Y chromosome. The sex-determining mechanism in Eigenmannia sp. could therefore be XX, AA in the female and X, \-YA A in the males. One of the males presented 2n=30 chromosomes due to the occurrence of another fusion of acrocentrics. C-banding analysis of the mitotic chromosomes revealed constitutive heterochromatin in the centromeric regions of all acrocentrics. However, small metacentrics were C-band negative. The YA chromosome is C-band negative except for a small amount of heterochromatin in the centromeric region. The nucleolar organizer region as identified by Ag-staining is present in the interstitial region of chromosome pair No. 10.

Journal ArticleDOI
01 Jan 1984-Genetics
TL;DR: The results demonstrate that the alteration in the distribution of crossovers caused by inversion heterozygosity results from the response of a normal controlling system to an overall increase in the frequency of crossing over, rather than from a disruption of the system of regional constraints on exchange that is disrupted by meiotic mutations.
Abstract: The frequency of crossing over per unit of physical distance varies systematically along the chromosomes of Drosophila melanogaster . The regional distribution of crossovers in a series of X chromosomes of the same genetic constitution, but having different sequences, was compared in the presence and absence of normal genetically mediated regional constraints on exchange. Recombination was examined in Drosophila melanogaster females homozygous for either normal sequence X chromosomes or any of a series of X chromosome inversions. Autosomally, these females were either (1) wild type, (2) homozygous for one of several recombination-defective meiotic mutations that attenuate the normal regional constraints on exchange or (3) heterozygous for the multiply inverted chromosome TM2. The results show that the centromere, the telomeres, the heterochromatin and the euchromatic-heterochromatic junction do not serve as elements that respond to genic determinants of the regional distribution of exchanges. Instead, the results suggest that there are several elements sparsely distributed in the X chromosome euchromatin. Together with the controlling system affected by recombination-defective meiotic mutations, these elements specify the regional distribution of exchanges. The results also demonstrate that the alteration in the distribution of crossovers caused by inversion heterozygosity (the interchromosomal effect) results from the response of a normal controlling system to an overall increase in the frequency of crossing over, rather than from a disruption of the system of regional constraints on exchange that is disrupted by meiotic mutations. The mechanisms by which regional constraints on exchange might be established are discussed, as is the possible evolutionary significance of this system.

Journal ArticleDOI
TL;DR: In the domestic pig (2n=38), the significance of the chromosome disposition in the pachytene nucleus is discussed with regard to heterochromatin composition and karyotype evolution.
Abstract: In the domestic pig (2n=38) two types of constitutive heterochromatin can be differentiated by fluorescence counterstaining techniques. All 24 biarmed autosomes and the X chromosome have chromomycin A3-positive centromeric C-bands, whereas all 12 acrocentric chromosomes exhibit DA-DAPI-positive centromeric heterochromatin. Fluorescence analysis of male pachytene nuclei revealed that the DA-DAPI-positive C-bands form one or two large chromocentres per cell, while the chromomycin A3-bright C-material is well scattered. Hence, the bivalents formed by the acrocentric chromosome pairs are centromerically associated, whilst the submetacentric bivalents are not. —Counce-Meyer spreading techniques were used to study the structure of synaptonemal complexes (SCs) both by light and electron microscopy. In general, the SCs of the domestic pig resemble those described for other mammals. The SC formed by the X and the Y may include up to 94.5% of the Y chromosome. In silver-stained microspreads each of the bivalents (nos. 8 and 10) bearing the nucleolus-organizer-regions (NORs) is connected to a pair of nucleoli, indicating that all four NORs are active during early meiotic stages. By contrast, in the majority of mitotic metaphases of phytohaemagglutinin-stimulated lymphocytes only one pair (no. 10) exhibited Ag-NOR staining. — The significance of the chromosome disposition in the pachytene nucleus is discussed with regard to heterochromatin composition and karyotype evolution.

Journal ArticleDOI
TL;DR: Three of the seven chromosomes of rye (Secale cereale L.) 2R, 3R, and 6R have been identified individually by their N-banding pattern, which reveals the heterogeneity of rye heterochromatin.
Abstract: Three of the seven chromosomes of rye (Secale cereale L.) 2R, 3R, and 6R have been identified individually by their N-banding pattern. Each of the N-banded chromosomes possesses a single band which...

Journal ArticleDOI
TL;DR: C-banding shows constitutive heterochromatin at the centromeres, associated with the satellites on a small pair of metacentric chromosomes and in the interstitial regions of the long arms of a number of chromosomes.
Abstract: Chromosome preparations from lymphocyte cultures of 30 Atlantic salmon were studied. Robertsonian polymorphisms were observed with different individuals having diploid numbers of 56, 57 and 58 but a constant arm number of 74. C-banding shows constitutive heterochromatin at the centromeres, associated with the satellites on a small pair of metacentric chromosomes and in the interstitial regions of the long arms of a number of chromosomes.

Journal ArticleDOI
01 Jul 1984-Cancer
TL;DR: It is suggested that multisomy of lq gives tumor cells a proliferative advantage and is secondary to the basic neoplastic event.
Abstract: Two patients fulfilled the clinical and hematologic criteria for B-cell acute lymphoblastic leukemia: the malignant cells had L3 morphology, bore B-cell markers, and carried the specific t(8;14) translocation. The leukemic cells of one patient were tetrasomic for 1q, and those of the other patient showed several separate cell lines with complete or partial trisomy of 1q. In the latter patient it appeared that a break close to the heterochromatin of 1q produced an unstable chromosome end which formed associations with the telomeres of at least seven other chromosomes. It is suggested that multisomy of 1q gives tumor cells a proliferative advantage and is secondary to the basic neoplastic event.

Journal ArticleDOI
TL;DR: Frequently occurring sites of mdg-1 hybridization were revealed, most of which coincided with regions of intercalary heterochromatin, especially in chromosome 2.
Abstract: The localization of mobile dispersed genes (mdg-1 and mdg-3) was studied by in situ hybridization with the polytene chromosomes of 20 laboratory stocks of Drosophila melanogaster. The average number of sites was 20 for mdg-1 and 12 for mdg-3, but the actual number varied from stock to stock (14–27 for mdg-1 and 5–18 for mdg-3). A total of 182 possible sites have been detected for mdg-1 and 123 sites for mdg-3. In spite of the individual and interstock variation, the distribution over chromosomes was found to be nonrandom for mdg-3 and especially for mdg-1. Frequently occurring sites of mdg-1 hybridization were revealed, most of which coincided with regions of intercalary heterochromatin, especially in chromosome 2.

Journal ArticleDOI
27 Apr 1984-Science
TL;DR: A cytological analysis by modern banding techniques of gonial metaphases in two Parascaris forms that have been considered varieties but now seem to be two species reveals a different chromosome organization in each.
Abstract: A cytological analysis by modern banding techniques of gonial metaphases in two Parascaris forms that have been considered varieties but now seem to be two species [P. univalens (karyotype 2n = 2) and P. equorum (karyotype 2n = 4)] reveals a different chromosome organization in each. Parascaris univalens chromosomes contain only terminal heterochromatin, while P. equorum chromosomes also contain intercalary heterochromatin. In the somatic cells of both species during early embryogenesis, chromatin diminution occurs in and consists of the elimination of all heterochromatin independent of its localization in the chromosomes.

Journal ArticleDOI
TL;DR: Observations on autoradiographic labelling of partially lysed polytene chromosomes provide evidence for a lack of temporal and spatial agreement in the activation of origin points in homologous regions of the lateralPolytene strands; these observations also suggest local variations in levels of polyteny within a chromosome.
Abstract: It is widely known that the bulk of the pericentromeric heterochromatin (α-heterochromatin) does not replicate during polytenization in Drosophila. However, a recent DNA-Feulgen cytophotometric study (Dennhofer 1982a) has claimed equal polytenization of all heterochromatin regions. To re-examine this issue, the amount of Hoechst 33258-bright heterochromatin in non-polytene and polytene nuclei in salivary glands and Malpighian tubules of late third instar larvae of D. nasuta has been compared by cytofluorometry. Since the amount of Hoechst 33258-bright heterochromatin is similar in non-polytene and polytene nuclei in spite of the latter having an enormously high euchromatin DNA content, it is concluded that the α-heterochromatin does not replicate during polytenization. The present results further indicate that in the polytene nuclei of Malpighian tubules the α-heterochromatin remains at the 2C level whereas in salivary gland polytene nuclei it varies between the 2C and 4C levels.

Journal ArticleDOI
TL;DR: The karyotype of the European wild pig was analysed by means of silver-staining and the chromomycin A3/distamycin A/DAPI fluorescent banding technique to locate active NORs and to differentiate types of C-bands.
Abstract: The karyotype of the European wild pig (Sus scrofa scrofa L.) was analysed by means of silver-staining and the chromomycin A3/distamycin A/DAPI fluorescent banding technique to locate active NORs and to differentiate types of C-bands. The ribosomal RNA genes are localized at the secondary constrictions of chromosomes 8 and 10. All biarmed chromosomes, with the exception of chromosome 15/17 and the Y, had a chromomycin bright centromeric region that was moderately fluorescent with distamycin A/DAPI (DA/DAPI). Conversely, all acrocentric chromosomes and the Robertsonian fusion product (15/17) exhibited DA/DAPI bright centromeric heterochromatin. The results are compared with the chromosomal staining behavior of the domestic pig (Sus scrofa domestica L.) and discussed with respect to presumptive mechanisms of karyotypic evolution.

Journal ArticleDOI
TL;DR: It is observed that the percent m5C (percentage of cytosines which are methylated) varied between the two species, between males and females of the same species, and between lines with and without supernumerary B chromosomes.
Abstract: Purified nuclear DNA from two mealybug species was analyzed for its 5-methylcytosine (m5C) content by reversed-phase high-pressure liquid chromatography. We observed that the percent m5C (percentage of cytosines which are methylated) varied between the two species, between males and females of the same species, and between lines with and without supernumerary B chromosomes. This is the first case of a sex-specific difference in overall DNA methylation level. In contrast to a recent report (Deobagkar et al., J. Biosci. [India] 4:513-526, 1982), we found no other modified bases in the DNA. Overall, the percent m5C in Pseudococcus obscurus was two to three times higher than in Pseudococcus calceolariae. In both species, the percent m5C in males was higher than in females, although only in P. calceolariae was the difference statistically significant (0.68 +/- 0.02 versus 0.44 +/- 0.04). The high m5C content in males was correlated with the presence of a paternally derived, genetically inactive set of chromosomes which is facultatively heterochromatic. The presence of constitutive heterochromatin, however, was associated with a lower m5C content. Thus, for example, the percent m5C in females of a P. obscurus line with heterochromatic B chromosomes (1.09 +/- 0.04) was significantly lower than that of a related line lacking such chromosomes (1.26 +/- 0.06). Our findings are discussed with respect to the possible relationship between DNA methylation and heterochromatization.

Journal ArticleDOI
01 Mar 1984-Genetics
TL;DR: It was found that X heterochromatic deficiencies disrupt recovery not only of the Y chromosome but also of the X and autosomes, that both heterochromeatic and euchromatic regions of chromosomes are affected and that the "sensitivity" of a chromosome to meiotic drive is a function of its length.
Abstract: In Drosophila melanogaster males, deficiency for X heterochromatin causes high X-Y nondisjunction and skewed sex chromosome segregation ratios (meiotic drive). Y and XY classes are recovered poorly because of sperm dysfunction. In this study it was found that X heterochromatic deficiencies disrupt recovery not only of the Y chromosome but also of the X and autosomes, that both heterochromatic and euchromatic regions of chromosomes are affected and that the "sensitivity" of a chromosome to meiotic drive is a function of its length. Two models to explain these results are considered. One is a competitive model that proposes that all chromosomes must compete for a scarce chromosome-binding material in Xh- males. The failure to observe competitive interactions among chromosome recovery probabilities rules out this model. The second is a pairing model which holds that normal spermiogenesis requires X-Y pairing at special heterochromatic pairing sites. Unsaturated pairing sites become gametic lethals. This model fails to account for autosomal sensitivity to meiotic drive. It is also contradicted by evidence that saturation of Y-pairing sites fails to suppress meiotic drive in Xh- males and that extra X-pairing sites in an otherwise normal male do not induce drive. It is argued that meiotic drive results from separation of X euchromatin from X heterochromatin.

Journal ArticleDOI
TL;DR: A recombinant Charon 4 bacteriophage has been isolated on the basis of RNAs which are enriched in the head of the adult Drosophila melanogaster and hence are likely to be of neural origin.
Abstract: A recombinant Charon 4 bacteriophage has been isolated on the basis of RNAs which are enriched in the head of the adult Drosophila melanogaster and hence are likely to be of neural origin. The cloned insert maps to the near vicinity of the uncoordinated locus in polytene chromosome band 19E8. This band is within the transition zone between the euchromatic and heterochromatic regions of the X chromosome, a region which has been well characterized cytogenetically. The insert contains both repetitious and low copy number sequences, some of which vary extensively in both frequency and restriction fragment size between different laboratory strains. One particular family of moderately repeated sequences occurs predominantly in divisions 19 and 20 of the X chromosome and perhaps the distally located X heterochromatin. The molecular landscape surrounding the initial entry point contains many repeated sequences and is thus unlike those observed in most published chromosomal walks. The possible significance of the presence of repeated sequence families in the distinct properties of this region are discussed.

Journal Article
TL;DR: Using a recombinant DNA probe, it is demonstrated the presence of residual 3.4-kilobase (kb) repeat sequences in a family with a Yq- chromosome and data suggest that the breakpoint of the deletion occurs at the heterochromatin region proximal to the euchromatin/heterochromaatin junction.
Abstract: Using a recombinant DNA probe, we have demonstrated the presence of residual 3.4-kilobase (kb) repeat sequences in a family with a Yq- chromosome. The heterochromatin of this Y variant was not readily detectable with conventional chromosome-banding techniques. These data suggest that the breakpoint of the deletion occurs at the heterochromatin region proximal to the euchromatin/heterochromatin junction.

Journal ArticleDOI
01 Nov 1984-Genetics
TL;DR: This report describes cytological, genetic and biochemical studies designed to characterize two gamma-radiation induced, apparent "underproducer" variants of the rosy locus (ry:3-52.0), rYps1149 and ryps11136, associated with rearrangements that place heterochromatin adjacent to the roSy region of chromosome 3 (87D).
Abstract: This report describes cytological, genetic and biochemical studies designed to characterize two gamma-radiation induced, apparent "underproducer" variants of the rosy locus (ry:3-52.0), ryps1149 and ryps11136. The following observations provide a compelling basis for their diagnosis as heterochromatic position effect variants. They are associated with rearrangements that place heterochromatin adjacent to the rosy region of chromosome 3 (87D). The effect of these mutations on rosy locus expression is subject to modification by abnormal Y chromosome content. The rearrangement alters only the expression of the rosy allele on the same chromosome (cis-acting). The Y chromosome modification is only on the position-affected allele's expression. The recessive lethality associated with the rearrangements relate to specific rosy region vital loci, and for ryps11136, the lethality is not Y chromosome modified. The peptide product of the position-affected allele is qualitatively normal by several criteria. Heterozygous deletion of 87E2-F2 is a suppressor of the rosy position effect. The rosy position effect on XDH production may be assayed in whole larvae and larval fat body tissue as well as in adults.

Journal ArticleDOI
TL;DR: The lateral asymmetric appearance of the large heterochromatic segments in Gerbillus is interpreted as reflecting an uneven distribution of adenine and thymidine between the two strands of DNA.
Abstract: A large amount of heterochromatin is observed in two species of the genus Gerbillus, G. nigeriae and G. hesperinus. The C-band material represents about one-half of the total karyotype length in the former species, and about one-third in the latter. Several banding techniques and various 5-bromodeoxyuridine (BrdU) treatments were used to characterise these heterochromatic segments. After applying the R-banding technique, three different staining responses of the heterochromatin can be distinguished. In G. nigeriae, strongly stained segments (R-band positive) appear in most chromosomes and, in particular, constitute the short arms of all the larger chromosomes. Palely staining heterochromatic segments (R-band negative) are less abundant in G. nigeriae but predominate in G. hesperinus. In addition, in both species an intermediate staining of heterochromatin is observed near the centromere or in the heterochromatic short arms of some acrocentric and small submetacentric chromosomes. Very short BrdU treatment during the end of the last cell cycle results in asymmetrical staining of chromatids in heterochromatic segments after applying the acridine orange or FPG (fluorescence plus Giemsa) technique. The alternating location of strongly staining segments in one or the other chromatid simulates sister chromatid exchanges (“pseudo-SCE”). This pattern persists after longer BrdU treatment during different stages of the last cell cycle and is independent of the R-staining properties of the heterochromatin. The lateral asymmetric appearance of the large heterochromatic segments in Gerbillus is interpreted as reflecting an uneven distribution of adenine and thymidine between the two strands of DNA.

Journal ArticleDOI
TL;DR: Mammalian chromosome replication was studied by the aid of premature chromosome condensation (PCC) and “gaps” and condensed particles as observed after PCC induction are obviously homological to chromosome replication units.
Abstract: Mammalian chromosome replication was studied by the aid of premature chromosome condensation (PCC). After induction of PCC the sites of DNA replication appear as "gaps" between condensed chromosomal regions. These condensed particles are unineme before and bineme after DNA replication. The two phases are due mainly to the unineme or bineme nature of the particles. During early S-phase almost all particles are unimene, during late S-phase they are bineme and there is only one transitory stage between these two main stages. Premature chromosome condensation was studied in detail on a specific human chromosome 22 which is marked by its heterochromatin constitution. This led to easy identification of these elements in S-phase PCC (S-PCC) preparations. For each stage of the S-phase there was a reproducible pattern of condensed chromosomal particles making up the whole chromosome. The number of these particles was rather limited and a complementary pattern was found in early versus late S-phase. The pattern of early S-PCC corresponded to the banding pattern of G-banded prometaphase chromosomes; the pattern of late S-PCC, to R-banded prometaphase chromosomes. Thus, "gaps" and condensed particles as observed after PCC induction are obviously homologous to chromosome replication units. Replication of constitutive heterochromatin occurred during the very late S-phase. During this stage PCC induction led to condensation of the heterochromatin into several small, highly fluorescent particles.

Journal ArticleDOI
TL;DR: The optimal culture conditions under which an undercondensation of the Y heterochromatin and an induction of the fragile site in 16q22 can be achieved by in vitro treatment of lymphocytes were determined and permits the use of distamycin A in routine diagnostics of human chromosomes.
Abstract: The effect of the oligopeptide antibiotic distamycin A on human lymphocyte cultures was examined. Distamycin A specifically inhibits the condensation of the Y heterochromatin and induces a fragile site in the chromosome 16 (band q22) in some individuals. The optimal culture conditions under which an undercondensation of the Y heterochromatin and an induction of the fragile site in 16q22 can be achieved by in vitro treatment of lymphocytes were determined. This also permits the use of distamycin A in routine diagnostics of human chromosomes. The use of this technique in the analysis of translocations involving the Y chromosome is presented. The distamycin A-DNA interaction and the different possible explanations for the distamycin A-induced undercondensations of the Y heterochromatin and fragile sites 16q22 are discussed.

Journal ArticleDOI
TL;DR: A female of the endemic New Zealand frog Leiopelma hochstetteri was found to have 3n=33 chromosomes plus 2 supernumerary chromosomes, which may have resulted from the fertilisation of a diploid egg produced when the second meiotic division had been suppressed.
Abstract: Autotriploidy is described in a female of the endemic New Zealand frog Leiopelma hochstetteri. This frog was found to have 3n=33 chromosomes plus 2 supernumerary chromosomes. All the chromosomes in the karyotype of this species contained C-band heterochromatin at the centromeres. A prominent C-band was found to be associated with a secondary constriction on chromosome no. 7. The supernumerary chromosomes in this species appear to be mitotically stable and contain C-band heterochromatin at the centromeres. From the limited data presently available, the triploid individual may have resulted from the fertilisation of a diploid egg produced when the second meiotic division had been suppressed.