Showing papers on "Heterochromatin published in 1977"

The diminution of Heterochromatic chromosomal segments in Cyclops (Crustacea, Copepoda).

Abstract: The chromosomes of Cyclops divulsus, C. furcifer, and C. strenuus, like those of several other Copepods, undergo a striking diminution of chromatin early in embryogenesis. The process is restricted to the presumptive soma cells and occurs at the 5th cleavage in C. divulsus, at the 6th and 7th in C. furcifer, and at the 4th in C. strenus. The eliminated chromatin derives from the excision of heterochromatic chromosome segments (H-segments). Their chromosomal location is different in the three investigated species: Whereas in C. divulsus and C. furcifer the H-segments form large blocks-exclusively terminal in the former and terminal as well as kinetochoric in the latter-the germ line heterochromatin in C. strenuus is scattered all along the chromosomes. Extensive polymorphism exists with respect to the length of the terminal H-segments in C. furcifer, and with respect to the overall content of heterochromatin in the chromosomes of C. strenuus. In a local race of C. strenuus an extreme form of dimorphism has been found which is sex limited: females as a fule are heterozygous for an entire set of large (heterochromatin-rich), and a second set of small chromosomes in their germ line. Males are homozygous for the large set. In the first three cleavage divisions the H-polymorphism is solely expressed through differences of chromosome length. Following diminution the differences between homologous have disappeared. Feulgen cytophotometry demonstrates that in the three species the 1C DNA value for the germ line, as measured in sperm, is about twice that measured in somatic mitoses (germ line/soma C-values in picograms of DNA: C. strenuus 2.2/0.9, C. furcifer 2.9/1.44, C. divulsus 3.1/1.8). - The data imply that chromatin diminution is based on a mechanism which allows specific DNA segments, regardless of their location and size, to be cut out from the chromosomes without affecting the structural continuity of the remaining DNA. The mechanism may be analogous to that of prokaryotic DNA excision.

Variation in nuclear DNA in the genus Secale

Abstract: Estimates of the 4C DNA amount per nucleus in 16 taxa of the genus Secale made by Feulgen microdensitometry ranged from 28.85 picograms (pg) in S. silvestre PBI R52 to 34.58 pg in S. vavilovii UM 2D49, compared with 33.14 pg in S. cereale cv. “Petkus Spring” which was used as a standard. Giemsa C-banding patterns showed considerable interspecific and intraspecific variation and several instances of polymorphism for large telomeric C-bands. The proportion of telomeric heterochromatin in the genome ranged from about 6% in S. silvestre and S. africanum to about 12% in cultivated rye. A detailed comparison of nine taxa showed no overall relationship between 4C DNA amount and the proportion of telomeric heterochromatin in the genome. However, evidence is presented which strongly supports the notion that the major evolutionary change in chromosome structure in Secale has involved the addition of heterochromatin at, or close to, the telomeres. It is suggested that saltatory amplification events at telomeres were initially responsible for each large increase in DNA amount. Subsequently unequal crossing over between homologues may have played an important secondary role by extending the range of variation in the amount of heterochromatin at a given telomere, while crossing over between non-homologues may have provided a useful mechanism allowing an increase in the DNA amount at one telomere to be distributed between chromosomes.

Chromosomes 1 in 14 ovarian cancers. Heterochromatin variants and structural changes.

Abstract: Structurally rearranged chromosomes 1 were found in 9 out of 14 ovarian carcinomas and may also have been present in three others. In the remaining two, pericentric inversions involving the heterochromatic regions of chromosomes 1 were seen, and were also identified in one of the chromosomes 1 in the patient's normal cells (lymphocytes). Altogether, heterochromatin variants (variation in size and/or the presence of a pericentric inversion) were seen in the tumour cells of eight cases, and one or both types of variation were identified in the normal cells of six of these. The possibility of an association between the presence of chromosome 1 heterochromatin variants as a constitutional anomaly, a liability to ovarian (and perhaps other forms of) cancer and structural changes involving the chromosomes 1 in the tumour cells is considered.

Heterochromatin, aberrant endosperm nuclei and grain shrivelling in wheat-rye genotypes

Abstract: Evidence is presented leading to the conclusion that there is, in wheat-rye genotypes, a causal link first, between the presence of late replicating segments of heterochromatin on rye chromosomes and the occurrence of chromosome bridges at anaphase and of other aberrant nuclei in coenocytic endosperm, and second, between the frequency of occurrence of aberrant nuclei in young endosperms and the degree of grain shrivelling at maturity Bridges in coenocytic endosperm of wheat-rye genotypes are caused at anaphase by the failure of rye chromosomes to separate at the telomeres where late replicating DNA is known to be located The frequency of occurrence of aberrant nuclei in endosperms of the seven disomic chromosome addition lines of King II rye to Holdfast wheat fixed at the end of the coenocytic stage is significantly lower in three addition lines lacking a large telomeric block of terminal heterochromatin on one arm (due to its deletion) than in the remaining four addition lines without deletions of terminal heterochromatin Evidence is presented showing a significant positive correlation between the proportion of aberrant nuclei in endosperms of six hexaploid triticales during the first 4 days after pollination, and the degree of grain shrivelling scored at maturity It is concluded that the reduction or elimination of segments of late replicating DNA from rye chromosomes should be a major object in the breeding of economically useful triticales, and the means of achieving this goal are discussed

Why plant chromosomes do not show G-bands.

Abstract: Giemsa techniques have refused to reveal G-banding patterns in plant chromosomes. Whatever has been differentially stained so far in plant chromosomes by various techniques represents constitutive heterochromatin (redefined in this paper). Patterns of this type must not be confused with the G-banding patterns of higher vertebrates which reveal an additional chromosome segmentation beyond that due to constitutive heterochromatin. The absence of G-bands in plants is explained as follows: 1) Plant chromosomes in metaphase contain much more DNA than G-banding vertebrate chromosomes of comparable length. At such a high degree of contraction vertebrate chromosomes too would not show G-bands, simply for optical reasons. 2) The striking correspondence of pachytene chromomeres and mitotic G-bands in higher vertebrates suggests that pachytene chromomeres are G-band equivalents, and that this may also be the case in plants. G-banded vertebrate chromosomes are on the average only 2.3 times shorter in mitosis than in pachytene; the chromomeric pattern therefore still can be shown. In contrast, plant chromosomes are approximately 10 times shorter at mitotic metaphase; their pachytene-like arrangement of chromomeres is therefore no longer demonstrable.

Heterochromatin variation in Cryptobothrus chrysophorus: II. Patterns of C-banding

Abstract: Northern and southern “races” of the Australian grasshopper Cryptobothrus chrysophorus share the same diploid chromosome number (2n=23♂, 24♀). The northern “race” is differentiated from the southern by fixed extra blocks of heterochromatin located distally on five of the six medium pairs of autosomes (M4, 5, 6, 8 and 9). The megameric M7 pair, which is completely heterochromatic in both races, is also frequently larger in the northern “race”. Additionally, while there is considerable polymorphism for the presence of supernumerary heterochromatic segments on the two smallest autosome pairs (S10, 11) in both “races”, the precise character of this polymorphism is strikingly different between them. That found in the north is both more extensive and more variable. An analysis of the patterns of C-banding obtained in neuroblast c-mitoses indicates even more variation within and between “races” than was anticipated from the patterns of heteropycnosis seen at first prophase of male meiosis. Thus, while the distal blocks on the M4, 6, 8 and 9 elements in the northern “race” invariably C-band those of the M5 never do. On the other hand polymorphisms for C-bands on the M5, 6, 8 and 9 are seen in some populations of the southern “race” but in regions which are not visibly heteropycnotic at meiosis. Polymorphisms for the pattern of C-banding also occur in the northern “race” populations in the M4, 6, 8 and 9 elements and some of these are associated with clear length differences in the chromosomes concerned. Others involve differences in the expression of the distal C-bands in M8 and 9 which vary from dark to intermediate. The supernumerary segments on the S10 and 11 pairs are especially variable in respect of their C-banding properties. Some are entirely C-banded, some show no C-banding whatsoever and some are composed of both banded and unhanded regions. Banding is again most pronounced, however, in the northern “race”. Finally the character of the megameric M7 is strikingly different in the two “races” not only in respect of its size, which is sometimes larger than that of the south, but also in respect of the extent of C-banding which is always more complex in the northern form irrespective of its size.

Evidence for a set of closely linked autosomal genes that interact with sex-chromosome heterochromatin in Drosophila melanogaster.

Abstract: It is proposed that there exists a special region in the euchromatin of the left arm of chromosome 2 (contained within sections 31-32 of the standard salivary gland chromosome map) that is defined by a set of genes, each one of which interacts with a specific sex-chromosome heterochromatic segment. The evidence for the existence of this region is, first, the exhibition, mapping, and analysis of five different maternal-effect, embryonic semi-lethals located in region 31-32. Secondly, in each case the consequence of the maternal effect is markedly influenced by the amount of X - or Y -chromosome heterochromatin carried by the progeny of mutant mothers. The nature of this interaction and possible reasons for the existence of the cluster of autosomal genes are discussed

The premeiotic DNA replication of euchromatin and heterochromatin in Lilium longiflorum (Thunb.)

Abstract: The presynaptic stages of Lilium longiflorum have been analyzed in the light microscope. Seven substages can be defined on the basis of changes in morphology of the heterochromatin and the nucleoli. The duration of the presynaptic interval and the substages has been calculated from bud length measurements and cell stage gradients in the anthers. The premeiotic and somatic DNA replication has been investigated using3H-thymidine autoradiography. The premeiotic S phase lasts 50 hours whereas the somatic S phase in root tip nuclei is six times shorter. Moreover, premeiotic S phase nuclei house 2–3 times more heterochromatin than somatic nuclei. The premeiotic DNA replication can be divided into three periods: In early S phase the DNA of euchromatin is replicated; in mid S phase synthesis is arrested for a minimum of 9 hours; and in late S phase the DNA of heterochromatin is replicated. DNA synthesis in heterochromatin is correlated with a dispersal of these chromatin regions. Determinations of volume and staining characteristics of heterochromatin after the application of C and Q banding procedures indicate that the premeiotic heterochromatin comprises C bands, Q bands and interbands. The premeiotic DNA replication is discussed in relation to the observed chromatin dynamics, and a proposal is made for the significance of the replication sequence to the formation of the leptotene chromosome and the control of crossing-over.

Chromosomal polymorphisms of constitutive heterochromatin and inversions in Drosophila.

Abstract: A simple technique for preparing mitotic metaphases from a larval ganglion of Drosophila is described. Parallel examination of polytene and metaphase chromosome groups shows that inversion polymorphism in chromosome 3 of D. recticilia from East Maui (Hawaii) manifests a one-to-one correlation with a metaphase karyotype polymorphism due to the presence of an extra heterochromatic portion. These observations are consistent with the previous findings on other species of Hawaiian Drosophila. They strongly support the hypothesis that when one breakpoint of a long inverted segment of a chromosome element occurs in the vicinity of the constitutive heterochromatin, it may exert an effect in eliciting the production of heterochromatic material in the same chromosome.

Abnormal chromosomes and number 1 heterochromatin variants revealed in C-banded preparations from 13 bladder carcinomas.

Abstract: The chromosomes of 13 carcinomas of the bladder were studied in C- and G-banded preparations. Heteromorphism for the amount of centromeric heteromorphism on the no. 1 chromosomes was apparent in eight tumours, and in three of these the heteromorphism was also found in the patient's normal cells. In four tumours, there were pericentric inversions of the heterochromatic regions of one or more no. 1 chromosomes. Major structural changes involving no. 1 chromosomes appeared to have occurred in at least seven of the tumours. In addition to the high incidence of heterochromatin variants (known or presumed to be constitutional phenomena), and major structural changes involving the no. 1 chromosomes, a further feature, common to four tumours, was the presence of a heterochromatic minute.

The effect of telomeric heterochromatin on chromosome pairing of hexaploid triticale

Abstract: Plants carrying (++) or lacking (−−) most of the telomeric heterochromatic band on the short arm of chromosome 6R(6RS) were isolated from a single plant progeny of Rosner triticale (× Triticosecale Wittmack) heterozygous for this band. Chromosome pairing at first meiotic metaphase was significantly higher in −− than in ++ or +− plants. The changes in chromosome pairing were likely due to the 6RS telomeric heterochromatin which affected the pairing not only of the arm carrying it but of other chromosomes as well.

Genetic dissection of heterochromatin in Drosophila: The role of basal X heterochromatin in meiotic sex chromosome behaviour

Abstract: We have examined the female meiotic behaviour of three X chromosomes which have large deletions of the basal heterochromatin in Drosophila melanogaster. We find that most of this heterochromatin can be removed without substantially altering pairing and segregation of the two Xs. To compare the role of heterochromatin in male meiosis we have constructed individuals which carry two extra identical heterochromatic mini X chromosomes. These minis behave as univalents even though their heterochromatin is known to contain satellite DNA. We conclude therefore that this satellite DNA is not sufficient to allow effectively normal meiotic behaviour. In all other respects our results in the male extend and confirm Cooper's postulate that there exist specific pairing sites in the X heterochromatin. Thus we find no support in either female or male meiosis for the concept that satellite DNA is involved in meiotic chromosome pairing of either a chiasmate or an achiasmate kind.

Distribution of constitutive heterochromatin in carnivores

Abstract: The distribution of constitutive heterochromatin (C-banding) in the genomes of nine species of Felidae, one species of Mustelidae, two species of Procyonidae, one species of Viverridae, one species of Canidae, and one species of Ursidae has been studied. In the chromosomes of several felid species the C-band is apparently absent. A few chromosomes show only telomeric staining in one arm or sometimes in both arms. Centromeric and interstitial distribution of heterochromatin has also been demonstrated in other species of Carnivors, but, in general, the C-banded material in felids is comparatively less in amount, and more weakly staining, than in other mammals. Induction of C-banding patterns in certain carnivore species is rather difficult, probably because of the minimal amount of heterochromatin present.

Isolation of Eukaryotic DNA Fragments Containing Structural Genes and the Adjacent Sequences

Abstract: In Drosophila melanogaster structural genes are located close to moderately reiterated sequences. One of the clones obtained contains the DNA related to intercalary heterochromatin of D. melanogaster. These are individual differences in the distribution of genetic material in polytenic chromosomes of different stocks of D. melanogaster. The techniques that allow isolation of DNA fragments containing structural genes at the beginning, in the middle, or the end of the coding strand have been elaborated.

in the Pocket Mouse, Perognathus baileyi: Meiosis and C-Band Studies

Abstract: The heterochromatin characteristics and meiotic behavior of the B-chromosome system of the pocket mouse, Perognathus baileyi, are de- scribed. B-chromosomes are associated both with a meiotic accumulation mechanism and with an increase in average chiasma frequency in the A-chro- mosome set in males. Three morphological classes of B-chromosomes are recognizable, and the mechanisms of origin of each are discussed.

Extra DNA synthesis in embryo suspensor cells ofPhaseolus coccineus

Abstract: DNA synthesis in the embryo suspensor cells ofPhaseolus coccineus has been studied by autoradiography after 30 minutes and 12 hours feedings with3H-thymidine (3H-TdR). It has been observed that two different DNA syntheses occur in cell nuclei of the suspensor, one concerned with the process of chromosome endoreduplication, the other with the process of extra DNA synthesis in several heterochromatic regions of the genome. Characteristics of the extra DNA synthesis in our material are: i) a greater3H-TdR uptake occurs during extra DNA synthesis than during DNA synthesis involved in chromosome endoreduplication; ii) extra DNA synthesis is not concomitant with the process of chromosome endoreduplication; iii) only some of the DNA strands in one and the same polytene chromosome region seem to be involved in the phenomenon of extra DNA synthesis; iv) extra DNA synthesis occurs in both chromosome regions known to carry ribosomal cistrons and in other regions of the genome.

The distribution of mitomycin C-induced sister chromatid exchanges in the euchromatin and heterochromatin of the Indian muntjac.

Abstract: The frequency of sister chromatid exchanges (SCEs) induced by mitomycin C (MMC) in Indian Muntjac chromosomes was determined by the fluorescence plus Giemsa (FPG) technique. Using scanning cytophotometry the relative DNA content of each chromosome was measured with and without acid or alkali pretreatments for C-banding. During acid and alkali treatments, euchromatin lost 20 to 30% of its DNA, while heterochromatin lost less than 5%; an intermediate DNA loss was observed for the short arm of the X chromosome. After growth of cells in the presence of MMC during the first cycle and in the presence of bromodeoxyuridine (BrdU) during the first and second cycles of DNA replication, SCEs in the euchromatin were proportional to DNA content. SCEs at the junctions between the neck of the X chromosome and the long and short arms occurred more frequently than expected. A threshold effect for the induction of SCEs was observed in regions resistant to DNA extraction by acid and alkali treatments (i.e., the neck and short arm of the X chromosome). At high concentrations of MMC, the frequency of SCE at each junction appears to plateau at 0.5.

Nuclear DNA and heterochromatin contents in theScilla hohenackeri group,S. persica, andPuschkinia scilloides (Liliaceae)

Abstract: DNA contents (presented as 1C-values) have been determined cytophotometrically in 7 species of theScilla hohenackeri group (10.18 to 22.71 pg), and in the systematically more isolated taxaS. persica (21.02 pg) andPuschkinia scilloides (6.80 pg). The heterochromatin amount is not correlated with the nuclear DNA content. Euchromatin, therefore, is not a particularly “conservative” part of the genome. However, high C-values and large but few terminal heterochromatin bands, and lower C-values and numerous but smaller heterochromatin bands are found to be linked in theS. hohenackeri group. Obviously, numerous chromosomal changes have accompanied speciation in this group. DNA contents, and C-banded karyotypes are consistent with systematic affinities based on morphological similarities.

Localization of ribosomal DNA within the proximal X heterochromatin of Sciara coprophila (Diptera, Sciaridae).

Abstract: By means of several reciprocal translocations in Sciara coprophila, each having a break-point in the proximal X heterochromatin, it has been possible in the salivary gland nucleus to bring about separation of specific regions of this heterochromatin and then, by means of in situ hybridization, to determine the relative number of ribosomal RNA cistrons in each. The three blocks of heterochromatin delineated by the translocation break-points have been designated H1, H2, and H3; H1 is the most proximal, lying immediately to the right of the X centromere, and H3 is the most distal, constituting the very end (right) of the chromosome. The distribution of ribosomal RNA cistrons is as follows: 10% are located in H1; 50% in H2; and 40% in H3. For the first time it has been possible to confirm by grain count our previous biochemical estimate of a 60% deletion of rRNA cistrons in the proximal heterochromatin of the X′ W homologue. The grain count data also support the conclusion of our previously published cytological analysis, that the exchange points in the X heterochromatin are identical in translocations T29 and T32 (between H1 and H2), also in translocations T23 and T70 (between H2 and H3). The coincidence of break-points in the X heterochromatin is considered in relation to the chromomere make-up of the region. Also, the occurrence of ribosomal RNA cistrons in all three heterochromomeres is discussed in relation to the functional significance of chromomeres.

X heterochromatin subdivision and cytogenetic analysis in Sciara coprophila (Diptera, Sciaridae): I. Centromere localization

Abstract: Five new translocations recovered from irradiated sperm, each having a break-point in the proximal X heterochromatin, have been designated T23, T29, T32, T40, and T70. These translocations, together with Oak Ridge T1, make possible the precise localization of several genetic components including the X centromere, the controlling element, and the ribosomal cistrons. Only the data pertaining to centromere location are presented here. The ribosomal cistrons and controlling element will be dealt with separately. Full cytological details are given for each of the five translocations. The break-points on the X define three blocks of heterochromatin designated H1, H2, and H3. Together they comprise the right arm of the X. H3 is the smallest and forms the very end of the chromosome. H1 lies immediately to the right of the centromere. In T23 and T70 the breakpoints are located between H2 and H3; in T29 and T32 between H2 and H1. In Oak Ridge T1 the break-point lies between H1 and the centromere and in T40 between the centromere and the whole left arm of the chromosome. For the first time it has been possible to determine the exact breakpoints of the long paracentric inversion that is found on the X′ homologue.

Chromosomes of antelope squirrels (genus Ammospermophilus ): A systematic banding analysis of four species with unusual constitutive heterochromatin

Abstract: The G- and C-banding patterns of mitotic chromosomes from four species of antelope squirrels (Ammospermophilus harrisi, interpres, leucurus and nelsoni) are discussed with special attention payed to the unusual quantities and position of constitutive heterochromatin. Heterochromatin appears to be responsible for the observation that cells from antelope squirrels contain over 70% more DNA than cells from another ground squirrel. A substantial fraction of this excess DNA consists of sequences that band as satellites in neutral CsCl or Cs2SO4-Ag+ density gradients. Interspecies similarities in the distribution of heterochromatin suggest that it has a function of some importance to these species and has therefore been conserved.

Length of human constitutive heterochromatin in relation to chromosomal contraction.

Abstract: Linear measurement of blocks of constitutive heterochromatin and the euchromatin portion 1q-h in three members of a family was used to study the dependence of the size of C blocks on the degree of chromosomal contraction. The results demonstrate that the size of heterochromatin portions decrease regularly with an increases of the degree of euchromatin contraction. The dependence was found to be linear, except for mitoses with an extremely high or low degree of contraction. The finding was used for the development of a new method of evaluation of constitutive heterochromatin.

Heterochromatin as a cyto-taxonomic character in liverworts: Pellia, Riccardia and Cryptothallus

Abstract: Application of a Giemsa C-banding technique to the three British species of Pellia indicates that the original description of heterochromatin was largely if not entirely based on constitutive rather than facultative heterochromatin. The technique is shown to have considerable potential in defining liverwort karyotypes more precisely than has hitherto been· possible and to assist in the cytological comparison of species. In this respect, the similarity between specimens of P. epiphylla and P. neesiana appears to be greater than the resemblance of either of these species to P. endiviifolia. Chromosome inversion is reported for the first time in bryophytes, in P. neesiana, but there is strong evidence to suggest that structural rearrangement, though not necessarily inversion, has also occurred elsewhere in--this genus.Unequal, almost totally euchromatic sex-specific chromosomes are described for a specimen of British Riccardia pinguis. Similarities between the Giemsa C-band patterns of this species ...

Cytologische Lokalisation von 5S und 18/25S RNA Genorten in Mitose-Chromosomen von Vicia faba

Abstract: Homologous in situ hybridization with tritiated 4S, 5S and 18/25S RNA from root tip meristems of Vicia faba has been used to study the pattern of distribution of DNA sequences coding for these RNAs in the diploid nuclei. 5S RNA hybridizes to two regions of the satellites of the pair of satellited chromosomes. The sites differ in the level of in situ hybridization implicating different degrees of redundancy. 18/25S RNA hybridization is concentrated to the secondary constriction of these satellite chromosomes. Both, 5S and 18/25S ribosomal RNA gene sites are located on the same pair of chromosomes, but obviously the sequences are not contiguous. An association of 5S RNA cistrons with heterochromatin is assumed. Additional RNA gene sites as well as 4S RNA gene sites are not detectable.

Gene inactivation as a mechanism for the generation of variability in somatic cells cultivated in vitro

Abstract: It is proposed that a substantial proportion of cell culture variants result from repression or derepression of genetic information which specifies the synthesis of enzymes. The mechanism responsible for this process may be similar to the inactivation of euchromatic segments in Drosophila resulting from their transposition next to heterochromatin. This model could explain a number of confusing observations made in somatic cell culture systems. (1) The generally high mutation rate for markers in somatic cells. (2) The instability and high reversion rates of a number of genetic markers. (3) Failure of certain drug resistance markers to show the expected decreases in mutation rate with increase in ploidy levels. (4) Anomalous mutation induction kinetics, and lack of specificity of mutagenic agents. Means by which this model can be experimentally examined are proposed. They include: (a) correlation of late labeling patterns and transposition of genetic material with phenotypic changes suspected of having their basis in chromosomal inactivation. (b) Mutagenesis studies using markers which would be expected to show phenotypic variation due to chromosomal inactivation. (c) Studies of gene expression in somatic cell hybrids. (d) Examination of gene products from resistant cell lines suspected of arising from chromosomal inactivation.

Genome analysis of Peromyscus (Rodentia, Cricetidae) VII. Localization of satellite DNA sequences and cytoplasmic poly(A) RNA sequences of P. eremicus on metaphase chromosomes.

Abstract: A satellite DNA fraction from P. eremicus, having a buoyant density of 1.705g/ml in neutral CsCl density gradients, was isolated. In situ hybridization experiments, using 3H-RNA complementary to this DNA fraction indicated that the short (heterochromatic) arms of most of the autosomes contained this sequence. Conversely, in situ hybridization using 3H-complementary DNA (cDNA) synthesized from the cytoplasmic poly (A) RNA of P. eremicus (comprising a substantial fraction of total messenger RNA) showed that the number of silver grains in the long arms (euchromatin) was significantly higher than that in the short arms. The X chromosomes showed a distinct localization pattern of both sequences.

N-banding in polytene chromosomes of Chironomus and Drosophila

Abstract: The N-banding patterns of the polytene chromosomes of Drosophila melanogaster, Chironomus melanotus, Ch. th. thummi and Ch. th. thummi x Ch. th. piger were studied. In Chironomus the polytene N-banding patterns correspond to the polytene puffing patterns. This is revealed by comparison of the puffing and N-banding patterns of identical chromosomes. Size and staining intensity of the N-bands reflect the size of the puffs as shown by puff induction. There is no evidence that the N-bands are also located in Chironomus heterochromatin or are restricted to the nucleolar organizer regions. In Drosophila the α-heterochromatin is strongly N-positive, whereas the β-heterochromatin, as well as the Chironomus heterochromatin is not N-banded. Contrary to Chironomus, the puffs in Drosophila polytene chromosomes do not give rise selectively to well stained N-bands. — The N-banding method is interpreted to stain specifically non-histone protein which is (1) accumulated in genetically active chromosome regions and (2) present in a specific type of heterochromatin (α-heterochromatin of Drosophila).

Somatic stability of variant C-band heterochromatin.

Abstract: Prominent C-band markers were found to be unchanged between different tissues of 9 individuals and during long term culture of 8 skin fibroblast and amniotic fluid cell strains.