Constitutive heterochromatin polymorphism in Lagothrix lagothricha cana,Cebus apella,and Cebus capucinus

We describe the C-bands in the karyotypes of Lagothrix lagothricha cana, Cebus apella and Cebus capucinus. The C-banding patterns show both a high degree of polymorphism as well as the presence of terminal and interstitial C-bands. Varying amounts of heterochromatin result in dimorphism of some chromosome pairs. The high incidence of chromosome rearrangements found in the Cebidae may be due to the presence of terminal and interstitial C-bands.     

Constitutive heterochromatin distribution in monocentric and polycentric chromosomes

Monocentric chromosomes of Vicia faba (2n=12) and polycentric chromosomes of Luzula purpurea (2n=6) and L. multiflora (2n=36) were studied by the C-banding technique. C-positive regions exhibited a restricted distribution in V. faba nuclei and were located near the centromeres of the chromosomes. Each chromosome had both a characteristic number and distribution of C-positive regions permitting homologue identification. L. purpurea and L. multiflora C-bands were much more numerous than those of V. faba and were widely distributed throughout both nuclei and chromosomes. Three distinct constitutive heterochromatin distribution patterns were present in L. purpurea metaphase chromosomes permitting homologous chromosome identification. One of three C-band distribution patterns was also evident in L. multiflora chromosomes.     

Constitutive heterochromatin and transposable elements in Drosophila melanogaster

Several families of transposable elements (TEs), most of them belonging to the retrotransposon catagory, are particularly enriched in Drosophila melanogaster constitutive heterochromatin. The enrichment of TE-homologous sequences into heterochromatin is not a peculiar feature of the Drosophila genome, but appears to be widespread among higher eukaryotes. The constitutive heterochromatin of D. melanogaster contains several genetically active domains; this raises the possibility that TE-homologous sequences inserted into functional heterochromatin compartments may be expressed. In this review, I present available data on the genetic and molecular organization of D. melanogaster constitutive heterochromatin and its relationship with transposable elements. The implications of these findings on the possible impact of heterochromatic TEs on the function and evolution of the host genome are also discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Intraspecific polymorphism of sex chromosome heterochromatin in two species of the Anopheles gambiae complex

The Hoechst 33258 banding pattern of the mitotic chromosomes of several laboratory and natural populations of the sibling species A. gambiae and A. arabiensis has been analyzed. A clear intraspecific polymorphism of sex chromosome heterochromatin has been observed. Nevertheless in each species heterochromatic variations fall within a characteristic species-specific pattern. Moreover, while laboratory populations tend to be monomorphic for a given heterochromatic variant, natural populations exhibit a high degree of intrapopulation polymorphism. The possible role of sex chromosome heterochromatin in controlling fertility and mating behaviour of Anopheles mosquitoes is discussed.     

Intra-individual polymorphism of human Y chromosome as a result of deletion in the heterochromatin region

Two equal cell populations with Y-heterochromatin of different lengths were found in a sterile male with azoospermia. There was no evidence for translocation of the heterochromatic material to other chromosomes. Both cell lines have the same Q-, C- and Ag-NOR patterns of chromosomal differential staining. The Y-chromosomes of both the father and brother were as long as the longest of the two populations in the proband. This intraindividual heteromorphism of Y-chromosome is, probably, a result of Y-heterochromatin deletion during the first mitotic division of the zygote, with the loss of a fragment as long as the difference between the long and the short Y populations in the proband. Intraindividual chromosomal heteromorphism is a convenient model to study reasons for variability in the heterochromatin regions of chromosomes.     

Constitutive heterochromatin patterns of G-group chromosomes in Down's syndrome

Summary 2 male patients with G-trisomic Down's syndrome, were studied for constitutive heterochromatin pattern by the technique of Arrighi and Hsu (1971). 2 G-chromosomes were found to have heterochromatin distributed around the centromeric areas and the remaining 3 were free of such localized heterochromatin blocks; the extra G-chromosome belonging to the non-localized heterochromatin members.

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Zusammenfassung 2 männliche Patienten mit G-Trisomie (Down-Syndrom) sind im Hinblick auf das konstitutive Heterochromatinmuster mit Hilfe der Technik von Arrighi u. Hsu (1971) untersucht worden. Es fanden sich 2 G-Chromosomen, die eine Heterochromatinverteilung um die Zentromerregion zeigen, während die restlichen 3 frei von derartig lokalisierten Heterochromatinblocks sind; das überzählige G-Chromosom gehört zu den letztgenannten.

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Supported in part by the Robert A. Welch Foundation, The National Foundation —March of Dimes and USPHS Grant No. FR-05425.     

Centromeric heterochromatin polymorphism in the house mouse

Polymorphism of Giemsa-specific centromeric heterochromatin (C.H.) has been described in the laboratory and wild mice. All examined wild mice and inbred mouse strains display some chromosomes with considerably reduced or enlarged C.H. regions. The quantity of C.H. could be an inherent property of a chromosome as inferred from (a) the finding of the identical C.H. pattern within inbred strains, (b) the finding that two genetically related inbred strains, C3H and CBA, separated from each other for more than 150 generations, possess the same two chromosome pairs with tiny C.H. marker regions. These chromosomes were identified as No. 1 (l.g. XIII) and No. 14 (l.g.III) by means of T(14;15)6Ca translocation, and C- and G-band analysis. The neutrality of C.H. polymorphism in murine genome is inferred from the heterozygosity for the C.H. variants found in all studied wild mice. The possible relationship of C.H. polymorphism to the centromere interference phenomenon is hypothesized.     

Structural complexity of Y chromosome heterochromatin

Following a standard C-banding procedure early metaphase chromosomes demonstrate a discontinuous distribution of heterochromatin in the long arm of the human Y chromosome. The discrete blocks of heterochromatin can be shown to be separated into nonrepeating sequences by in situ hybridization using probe pHY 2.1. The number of heterochromatin blocks vary from person to person.     

Constitutive heterochromatin in early embryogenesis of Drosophila melanogaster

Summary The formation of constitutive heterochromatin was studied during the embryonic development of Drosophila melanogaster, using the C-banding technique. During embryonic cleavage, C-banded material is not seen in mitotic chromosomes; the differentiation between euchromatin and heterochromatin only occurs at blastoderm. This event correlates with the establishment of position-effect variegation.     

Constitutive heterochromatin: a surprising variety of expressed sequences

The organization of chromosomes into euchromatin and heterochromatin is amongst the most important and enigmatic aspects of genome evolution. Constitutive heterochromatin is a basic yet still poorly understood component of eukaryotic chromosomes, and its molecular characterization by means of standard genomic approaches is intrinsically difficult. Although recent evidence indicates that the presence of transcribed genes in constitutive heterochromatin is a conserved trait that accompanies the evolution of eukaryotic genomes, the term heterochromatin is still considered by many as synonymous of gene silencing. In this paper, we comprehensively review data that provide a clearer picture of transcribed sequences within constitutive heterochromatin, with a special emphasis on Drosophila and humans.     

Analysis of Y chromosome heterochromatin in Rumex thyrsiflorus

The Y chromosome heterochromatin in Rumex thyrsiflorus has been analyzed. In natural populations the Y chromosome shows a higher morphological variability than the X chromosome. The total duration of replication of Y chromosomes is about 2 hrs longer than that of euchromatin. Autoradiography with tritiated thymidine showed that chromocentres formed by Y chromosomes in interphase nuclei retain their heterochromatic form during DNA replication. — Y chromosome heterochromatin in interphase nuclei is stained pink, while the rest of the nucleus stains green after fast green-eosin staining for histones. — During the premeiotic stage of PMC development Y chromosomes are no longer visible as compact bodies and become more fuzzy in appearance. A diffuse state of Y coincides with intense RNA synthesis. Therefore genetic activity of Y chromosomes or their parts during premeiotic stage of microsporogenesis is postulated.