Characterization and chromosomal distribution of satellite DNA sequences of the water buffalo (Bubalus bubalis).

Satellite DNA sequences were isolated from the water buffalo (Bubalus bubalis) after digestion with two restriction endonucleases, BamHI and StuI. These satellite DNAs of the water buffalo were classified into two types by sequence analysis: one had an approximately 1,400 bp tandem repeat unit with 79% similarity to the bovine satellite I DNA; the other had an approximately 700 bp tandem repeat unit with 81% similarity to the bovine satellite II DNA. The chromosomal distribution of the satellite DNAs were examined in the river-type and the swamp-type buffaloes with direct R-banding fluorescence in situ hybridization. Both the buffalo satellite DNAs were localized to the centromeric regions of all chromosomes in the two types of buffaloes. The hybridization signals with the buffalo satellite I DNA on the acrocentric autosomes and X chromosome were much stronger than that on the biarmed autosomes and Y chromosome, which corresponded to the distribution of C-band-positive centromeric heterochromatin. This centromere-specific satellite DNA also existed in the interstitial region of the long arm of chromosome 1 of the swamp-type buffalo, which was the junction of the telomere-centromere tandem fusion that divided the karyotype in the two types of buffaloes. The intensity of the hybridization signals with buffalo satellite II DNA was almost the same over all the chromosomes, including the Y chromosome, and no additional hybridization signal was found in noncentromeric sites.     

Chromosomal segregational mechanisms in ant-lions (Myrmeleontidae,Neuroptera)

In a single male specimen of Myrmeleon mexicanum Banks the sex chromosomes, normally X and Y, were replaced by what appeared to be X¹X² and Y. These segregated as expected on that interpretation in only half of the spermatocytes — in the other half, one X and the Y segregated from the other X. This atypical segregation is explicable on the assumption that one of the supposed Xs is a supernumerary, not a sex chromosome, and the diploid complement of the male comprises six pairs of autosomes plus a supernumerary and the X and Y sex chromosomes. The orientation of the X chromosomes at first metaphase was variable: kinetochoric activity may be localized midway the length of the chromosome, as in gonial mitosis, or terminally. Comparative study of three congeneric species, seven of Brachynemurus, one of Psammoleon, and one of Vella showed normal segregation in all, and no evidence for secondary kinetochoric activity. In nine of the species studied one pair of autosomes was unconjoined at first metaphase in 0.3%–1.2% of primary spermatocytes. These autosomes segregated precociously with the sex chromosomes in the central unit of the spindle. In one exceptional male of Brachynemurus hubbardi Currie all first meiotic metaphases showed this behavior, and a compound X¹X²/Y¹Y² system was thus simulated. Bivalent formation replaced distance segregation of sex chromosomes in 0.4%–3.2% of the spermatocytes in seven of the thirteen species studied. These sex-bivalents frequently displayed partial or complete failure in congression.     

Satellite DNA in the kangaroo Macropus rufogriseus

Two distinct satellite DNAs, amounting to 25% of the total DNA, were isolated from the nuclei of the red-necked wallaby, Macropus rufogriseus. The physical properties of native, single-stranded and reassociated molecules were studied in buoyant-density gradient centrifugation. The homogeneity of each satellite fraction was examined using melting characteristics of native and reassociated DNA, and renaturation kinetics. These data suggest that sequence heterogeneity exists in both fractions. Each satellite fraction was found by in situ hybridization to be localized in heterochromatin of interphase nuclei and in the centromeric regions of metaphase chromosomes. The chromosomal distributions of the two satellite DNAs differentiate the sex chromosomes, which have sequences of only one satellite, from the autosomes which have sequences of both satellites in the centromeric heterochromatin. Giemsa C-banding techniques also showed a differentiation of the centromeric regions of sex chromosomes from those of the autosomes.     

Reduced Rates of Sequence Evolution of Y-Linked Satellite DNA in Rumex (Polygonaceae)

One characteristic of sex chromosomes is the accumulation of a set of different types of repetitive DNA sequences in the Y chromosomes. However, little is known about how this occurs or about how the absence of recombination affects the subsequent evolutionary fate of the repetitive sequences in the Y chromosome. Here we compare the evolutionary pathways leading to the appearance of three different families of satellite-DNA sequences within the genomes of Rumex acetosa and R. papillaris, two dioecious plant species with a complex XX/XY₁Y₂ sex-chromosome system. We have found that two of these families, one autosomic (the RAE730 family) and one Y-linked (the RAYSI family), arose independently from the ancestral duplication of the same 120-bp repeat unit. Conversely, a comparative analysis of the three satellite-DNA families reveals no evolutionary relationships between these two and the third, RAE180, also located in the Y chromosomes. However, we have demonstrated that, regardless of the mechanisms that gave rise to these families, satellite-DNA sequences have different evolutionary fates according to their location in different types of chromosomes. Specifically, those in the Y chromosomes have evolved at half the rate of those in the autosomes, our results supporting the hypothesis that satellite DNAs in nonrecombining Y chromosomes undergo lower rates of sequence evolution and homogenization than do satellite DNAs in autosomes.[Reviewing Editor: DR. Jerzy Jurka]     

DNA REPLICATION PATTERNS AND CHROMOSOMAL PROTEIN SYNTHESIS IN OPOSSUM LYMPHOCYTES IN VITRO

DNA replication patterns were determined in the autosomes and sex chromosomes of phytohemagglutinin-stimulated lymphocytes from the opossum (Didelphis virginiana) by employing thymidine-³H labeling and high-resolution radioautography. Opossum chromosomes are desirable experimental material due to their large size, low number (2n = 22), and morphologically distinct sex chromosomes. The autosomes in both sexes began DNA synthesis synchronously and terminated replication asynchronously. One female X chromosome synthesized DNA throughout most of the S phase. Its homologue, however, began replication approximately 3.5 hr later. The two X's terminated DNA synthesis synchronously, slightly later than the autosomes. This form of late replication, in which one X chromosome begins DNA synthesis later than its homologue but completes replication at the same time as its homologue, is apparently unique in the opossum. The male X synthesized DNA throughout S while the Y chromosome exhibited late-replicating characteristics. The two sex chromosomes completed synthesis synchronously, slightly later than the autosomes. Grain counts were performed on all chromosomes to analyze trends in labeling intensity at hourly intervals of S. By analyzing the percent of labeled mitotic figures on radioautographs at various intervals after introduction of arginine-³H, chromosomal protein synthesis was found not to be restricted to any portion of interphase but to increase throughout S and into G₂.     

Localization of satellite DNAs in the chromosomes of the guinea pig

The in situ hybridization method has been used to investigate the localization of each of the three satellite DNAs present in the genome of the guinea pig. Purified fractions of the satellite DNAs were utilized as templates for synthesis of ³H-labeled complementary RNA (cRNA) by E. coli RNA polymerase, then each cRNA was hybridized to metaphase spreads of embryonic guinea pig cells. The cRNAs of all three satellite DNAs hybridized predominantly to the centromeric region of the chromosomes. The cRNAs of satellite DNAs II and III hybridized to all chromosomes except the Y chromosome. The cRNA of satellite DNA I did not hybridize to the Y chromosome nor to two pairs of small acrocentric chromosomes. Satellite II cRNA hybridized to the telomeric region of chromosomes 3 and 4.     

Repetitive centromeric satellite RNA is essential for kinetochore formation and cell division

Chromosome segregation requires centromeres on every sister chromatid to correctly form and attach the microtubule spindle during cell division. Even though centromeres are essential for genome stability, the underlying centromeric DNA is highly variable in sequence and evolves quickly. Epigenetic mechanisms are therefore thought to regulate centromeres. Here, we show that the 359-bp repeat satellite III (SAT III), which spans megabases on the X chromosome of Drosophila melanogaster, produces a long noncoding RNA that localizes to centromeric regions of all major chromosomes. Depletion of SAT III RNA causes mitotic defects, not only of the sex chromosome but also in trans of all autosomes. We furthermore find that SAT III RNA binds to the kinetochore component CENP-C, and is required for correct localization of the centromere-defining proteins CENP-A and CENP-C, as well as outer kinetochore proteins. In conclusion, our data reveal that SAT III RNA is an integral part of centromere identity, adding RNA to the complex epigenetic mark at centromeres in flies.     

Meiotic association and segregation of the achiasmatic giant sex chromosomes in the male field vole (Microtus agrestis)

Controversy exists regarding the meiotic behaviour of the giant sex chromosomes during spermatogenesis in the field vole, Microtus agrestis. Both univalents and bivalents have been observed between diakinesis and metaphase I. These differences seem to be dependent on the technique used. The present study employs electron microscopy of serially sectioned testes tubules and light microscopy of microspread preparations to re-examine the behaviour of sex chromosomes during meiosis. In microspreads, about one-third of the early pachytene nuclei examined showed end joining of the X and Y axes. The longitudinal heterogeneity of the chromosomes in the form of axial thickenings allowed the detection of two different end-joining patterns. In the remaining early pachytene cells as well as in all mid to late pachytene cells seen, the X and Y axes had, though near to each other, no contact in the form of a synaptonemal complex. If a synaptonemal complex is a prerequisite for genetic exchange, the sex chromosomes in M. agrestis males must be achiasmatic. The analysis of serial sections through an early pachytene and a late prophase I nucleus with the electron microscope revealed that the sex chromosomes occupied a common area. By metaphase I, the centromeres of the X and Y were oriented towards opposite spindle poles while the chromosomes remained attached to one another by their distal segments at the level of the metaphase I plate. As a consequence of the large size of the sex chromosomes their centromeres lay close to the spindle poles. In anaphase I the sex chromosomes maintained their metaphase position until the autosomes approached the spindle poles. During autosomal migration a medial constriction developed where the sex chromosomes were mutually associated, the X and Y became separated, and joined the autosomes. In metaphase II the chromatids of the sex chromosomes lay side by side and exhibited a delayed separation in the subsequent anaphase. It is suggested that heterochromatin, which represents a major part of both sex chromosomes, plays a role in the association of the two achiasmatic sex chromosomes in metaphase I and in the delayed separation of the chromatids of the sex chromosomes in anaphase II.Dedicated to Prof. C.-G. Arnold (Erlangen) on the occasion of his 60th birthday     

Distribution of gamma satellite DNA on the human X and Y chromosomes suggests that it is not required for mitotic centromere function

The bulk of the DNA found at human centromeres is composed of tandemly arranged repeats, the most abundant of which is alpha satellite. Other human centromeric repetitive families have been identified, one of the more recent being gamma satellite. To date, gamma satellite DNAs have been reported at the centromeres of human chromosomes 8 and X. Here, we show that gamma-X satellite DNA is not interspersed with the major DZX1 alpha-X block, but rather is organised as a single array of approximately 40-50 kb on the short-arm side of the alpha satellite domain. This repeat array is absent on two mitotically stable Xq isochromosomes. Furthermore, a related repeat DNA has been identified on the human Y chromosome. Fluorescence in situ hybridisation has localised this satellite DNA to the long arm side of the major DYZ3 alpha-Y domain, outside the region previously defined as that required for mitotic centromere function. Together, these data suggest that while blocks of highly related gamma satellite DNAs are present in the pericentromeric regions of both human sex chromosomes, this repeated DNA is not required for mitotic centromere function.     

Karyotype and heterochromatin pattern of the field mouse,Apodemus argenteus Temminck

The field mouse,Apodemus argenteus Temminck, has 46 chromosomes. The autosomes comprise 20 pairs of acrocentrics and 2 pairs of metacentrics. The X chromosome is represented by an outstandingly large submetacentric element, while the Y is an acrocentric corresponding in size to the 5th or 6th pair of autosomes. All of the autosomes and gonosomes can be unequivocally identified by their characteristic Q-band or G-band patterns. The constitutive heterochromatin, as revealed by C-banding, is localized at the centromeric regions of all autosomes, the short arm and the proximal 1/3 of the long arm of the X chromosome, and the entire Y chromosome. The C-band-positive segments which constitute 33.5% of the genome exhibit dark fluorescence after Q-banding, late DNA replication, faint or positive staining reaction to G-banding, fast reassociation of DNA revealed by AO staining, and allocyclic behavior of the sex-bivalent in male meiosis. An exception to the above is the distal segment of the Y which is positive to both C- and Q-banding. The giant X chromosome occupies 13.1% of the genome, leaving 5.6% of euchromatic segments, the latter value being equivalent to that of the original type X.     

Chromosomal localization of complex and simple repeated human DNAs

Complex repeating restriction multimers and a simple AT rich satellite isolated with Hoechst 33258 (<= 0.5% of the human genome) were localized by in situ hybridization to human chromosomes. The complex repeats were clustered at the centromeres, consonant with their integration in tandem arrays at these loci; these sequences were very prominent on chromosomes 7, 10 and 19, sites not previously identified with any specific human repeated sequence. The Hoechst simple satellite labelled predominantly the long arms of the Y chromosome. Although this simple satellite and the complex restriction multimers did not hybridize with each other, and did not contain detectable ribosomal sequences, both isolates additionally labelled the nucleolus organizing regions (NORs) of acrocentric chromosomes. —The possible relationship of complex and simple repeated DNAs, and their assignment to specific chromosomal domains, is discussed.     

Sequence of Centromere Separation: Role of Centromeric Heterochromatin

The late metaphase-early anaphase cells from various tissues of male Mus musculus, M. poschiavinus, M. spretus, M. castaneus, female and male Bos taurus (cattle) and female Myopus schisticolor (wood lemming) were analyzed for centromeres that showed separation into two daughter centromeres and those that did not show such separation. In all strains and species of mouse the Y chromosome is the first one to separate, as is the X or Y in the cattle. These sex chromosomes are devoid of constitutive heterochromatin, whereas all autosomes in these species carry detectable quantities. In cattle, the late replicating X chromosome appears to separate later than the active X. In the wood lemming the three pairs of autosomes with the least amount of centromeric constitutive heterochromatin separate first. These are followed by the separation of seven pairs of autosomes carrying medium amounts of constitutive heterochromatin. Five pairs of autosomes with the largest amounts of constitutive heterochromatin are the last in the sequence of separation. The sex chromosomes with medium amounts of constitutive heterochromatin around the centromere, and a very large amount of distal heterochromatin, separate among the very late ones but are not the last. These observations assign a specific role to centromeric constitutive heterochromatin and also indicate that nonproximal heterochromatin does not exert control over the sequence in which the centromeres in the genome separate. It appears that qualitative differences among various types of constitutive heterochromatin are as important as quantitative differences in controlling the separation of centromeres.     

Analysis of transposable elements and organellar DNA in male and female genomes of a species with a huge Y chromosome reveals distinct Y centromeres

Few angiosperms have distinct Y chromosomes. Among those that do are Silene latifolia (Caryophyllaceae), Rumex acetosa (Polygonaceae) and Coccinia grandis (Cucurbitaceae), the latter having a male/female difference of 10% of the total genome (female individuals have a 0.85 pg genome, male individuals 0.94 pg), due to a Y chromosome that arose about 3 million years ago. We compared the sequence composition of male and female C. grandis plants and determined the chromosomal distribution of repetitive and organellar DNA with probes developed from 21 types of repetitive DNA, including 16 mobile elements. The size of the Y chromosome is largely due to the accumulation of certain repeats, such as members of the Ty1/copia and Ty3/gypsy superfamilies, an unclassified element and a satellite, but also plastome‐ and chondriome‐derived sequences. An abundant tandem repeat with a unit size of 144 bp stains the centromeres of the X chromosome and the autosomes, but is absent from the Y centromere. Immunostaining with pericentromere‐specific markers for anti‐histone H3Ser10ph and H2AThr120ph revealed a Y‐specific extension of these histone marks. That the Y centromere has a different make‐up from all the remaining centromeres raises questions about its spindle attachment, and suggests that centromeric or pericentromeric chromatin might be involved in the suppression of recombination.     

C,Q and H-banding in the analysis of Y chromosome rearrangements in Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae)

In Lucilia cuprina C-banding produces procentric bands on all autosomes and deep staining over most of the X and Y chromosomes which conciderably facilitates the analysis of complex Y chromosome rearrangements. The Y chromosome is generally darkly C-banded throughout while in the X chromosome a pale staining segment is found in the distal portion of the long arm. Modulation of the banding reaction results in grey areas in both X and Y. When C-banding is compared with allocycly it is clear that not all heteropycnotic regions in the sex chromosomes C-band to the same extent. Secondary constrictions in the short arms of both X and Y chromosomes are clearly revealed by C-banding, the X satellite being polymorphic for size.— Q-banding results in a brightly fluorescing band in the short arm of structurally normal Y chromosomes. This band loses its fluorescence in some translocations, probably through a position effect. Hoechst 33258 staining does not produce any brightly fluorescing bands.     

The characteristics of karyotype and telomeric satellite DNA sequences in the cricket, Gryllus bimaculatus (Orthoptera, Gryllidae)

The chromosomes derived from the Japanese population of Gryllus bimaculatus were characterized by C-banding and Ag-NOR staining. The chromosome number, 2n = 28 + XX (female)/XO (male), corresponded with that of other populations of G. bimaculatus, but the chromosome configuration in idiograms varied between the populations. NORs were carried on one pair of autosomes and appeared polymorphous. The positive C-bands located at the centromere of all chromosomes and the distal regions of many chromosome pairs, and the size and the distribution pattern of the distal C-heterochromatin showed differences among the chromosomes. In addition, this paper reports on the characteristics of HindIII satellite DNA isolated from the genome of G. bimaculatus. The HindIII repetitive fragments were about 0.54 kb long, and localized at the distal C-bands of the autosomes and the interstitial C-bands of the X chromosome. Molecular analysis showed two distinct satellite DNA sequences, named the GBH535 and GBH542 families, with high AT contents of about 67 and 66%, respectively. The two repetitive families seem to be derived from a common ancestral sequence, and both families possessed the same 13-bp palindrome sequence. The results of Southern blot hybridization suggest that the sequence of the GBH535 family is conserved in the genomic DNAs of Gryllus species, whereas the GBH542 family is a species-specific sequence.     

The distribution of repetitive DNAs between regular and supernumerary chromosomes in Species of Glossina (Tsetse): a two-step process in the origin of supernumeraries

Several species of tsetse fly within the Morsitans and Fusca subgenera of Glossina contain supernumerary (B) chromosomes. Previous studies on the meiotic behaviour of chromosomes (Southern and Pell, 1973) and the C-band patterns (Jordan et al., 1977) have indicated a close similarity between the Y chromosome and the supernumeraries. The distributions of the highly abundant families of DNA (satellite DNAs) between the autosomes, sex chromosomes and B chromosomes of G.m. morsitans, G. austeni and G. pallidipes have been examined by in situ hybridisation. In addition, the organisation and sequence homologies of satellite DNAs have been examined by restriction enzymes and heterologous hybridisations in in situ and Southern transfer conditions. The majority of satellite sequences that are homologous between species are distributed in several different arrangements between A and B chromosome telomeres with minority sequences at some centromeric and intercalary locations. There is no extensive satellite DNA similarity between the Y and B chromosomes. We suggest that the Y and B chromosome associations and synchronous allocycly during meiosis are the result of extensive heterochromatinisation of these two chromosome types, that is probably a reflection of two separate stages involved in the generation of the B chromosomes in the genus. The independent evolution of satellites and supernumeraries is discussed.     

Fundamentally different repetitive element composition of sex chromosomes in Rumex acetosa

Background and AimsDioecious species with well-established sex chromosomes are rare in the plant kingdom. Most sex chromosomes increase in size but no comprehensive analysis of the kind of sequences that drive this expansion has been presented. Here we analyse sex chromosome structure in common sorrel (Rumex acetosa), a dioecious plant with XY₁Y₂ sex determination, and we provide the first chromosome-specific repeatome analysis for a plant species possessing sex chromosomes.MethodsWe flow-sorted and separately sequenced sex chromosomes and autosomes in R. acetosa using the two-dimensional fluorescence in situ hybridization in suspension (FISHIS) method and Illumina sequencing. We identified and quantified individual repeats using RepeatExplorer, Tandem Repeat Finder and the Tandem Repeats Analysis Program. We employed fluorescence in situ hybridization (FISH) to analyse the chromosomal localization of satellites and transposons.Key ResultsWe identified a number of novel satellites, which have, in a fashion similar to previously known satellites, significantly expanded on the Y chromosome but not as much on the X or on autosomes. Additionally, the size increase of Y chromosomes is caused by non-long terminal repeat (LTR) and LTR retrotransposons, while only the latter contribute to the enlargement of the X chromosome. However, the X chromosome is populated by different LTR retrotransposon lineages than those on Y chromosomes.ConclusionsThe X and Y chromosomes have significantly diverged in terms of repeat composition. The lack of recombination probably contributed to the expansion of diverse satellites and microsatellites and faster fixation of newly inserted transposable elements (TEs) on the Y chromosomes. In addition, the X and Y chromosomes, despite similar total counts of TEs, differ significantly in the representation of individual TE lineages, which indicates that transposons proliferate preferentially in either the paternal or the maternal lineage.     

CENP-B binds a novel centromeric sequence in the Asian mouse Mus caroli.

Minor satellite DNA, found at Mus musculus centromeres, is not present in the genome of the Asian mouse Mus caroli. This repetitive sequence family is speculated to have a role in centromere function by providing an array of binding sites for the centromere-associated protein CENP-B. The apparent absence of CENP-B binding sites in the M. caroli genome poses a major challenge to this hypothesis. Here we describe two abundant satellite DNA sequences present at M. caroli centromeres. These satellites are organized as tandem repeat arrays, over 1 Mb in size, of either 60- or 79-bp monomers. All autosomes carry both satellites and small amounts of a sequence related to the M. musculus major satellite. The Y chromosome contains small amounts of both major satellite and the 60-bp satellite, whereas the X chromosome carries only major satellite sequences. M. caroli chromosomes segregate in M. caroli x M. musculus interspecific hybrid cell lines, indicating that the two sets of chromosomes can interact with the same mitotic spindle. Using a polyclonal CENP-B antiserum, we demonstrate that M. caroli centromeres can bind murine CENP-B in such an interspecific cell line, despite the absence of canonical 17-bp CENP-B binding sites in the M. caroli genome. Sequence analysis of the 79-bp M. caroli satellite reveals a 17-bp motif that contains all nine bases previously shown to be necessary for in vitro binding of CENP-B. This M. caroli motif binds CENP-B from HeLa cell nuclear extract in vitro, as indicated by gel mobility shift analysis. We therefore suggest that this motif also causes CENP-B to associate with M. caroli centromeres in vivo. Despite the sequence differences, M. caroli presents a third, novel mammalian centromeric sequence producing an array of binding sites for CENP-B.     

Evolution of satellite DNA sequences in two tribes of Bovidae: A cautionary tale

Two clones, Bt1 from Bos taurus and Om1 from Ovis orientalis musimon, were used as probes for hybridization on genomic DNA and on metaphase chromosomes in members of Bovini and Caprini tribes. Bt1 and Om1 are sequences respectively belonging to the 1.715 and 1.714 DNA satellite I families. Southern blots and fluorescence in situ hybridization experiments showed completely coherent results: the Bovini probe Bt1 hybridized only to members of the Bovini tribe and not to members of Caprini. Likewise, the Caprini probe Om1 hybridized only to members of the Caprini tribe and not to members of Bovini. Hybridization signals were detected in the heterochromatic regions of every acrocentric autosome, except for two pairs of autosomes from Capra hircus that did not show hybridization to probe Om1. No signal was detected on X and Y chromosomes or on bi-armed autosomes. Remarkably, probe Om1 showed almost 100% homology with a bacterial sequence reported in Helicobacter pylori.     

Cytogenetic analysis of the tamaraw (Bubalus mindorensis): a comparison of R-banded karyotype and chromosomal distribution of centromeric satellite DNAs, telomeric sequence, and 18S-28S rRNA genes with domestic water buffaloes

The karyotype of the tamaraw (Bubalus mindorensis, 2n = 46) was investigated by RBG-banding technique and compared with those of the river and the swamp cytotypes of domestic water buffalo (B. bubalis). The tamaraw karyotype consisted of 6 submetacentric and 16 acrocentric autosome pairs (NAA = 56), and X and Y chromosomes. The RBG-banded karyotype of the three taxa had a high degree of homology, and the tamaraw karyotype could be explained by a Robertsonian translocation between chromosomes 7 and 15 and by a telomere-centromere tandem fusion between chromosomes 4p and 12 of the standardized river buffalo cytotype (2n = 50, NAA = 58). The buffalo satellite I and II DNAs were localized to the centromeric regions of all the tamaraw chromosomes. The biarmed chromosome 2 of the tamaraw resulting from the fusion between chromosomes 7 and 15 of the standard contained much larger amounts of the satellite I DNA than the other biarmed chromosomes, suggesting that this chromosome was formed by a relatively recent Robertsonian fusion. The (TTAGGG)n telomeric sequence was specifically localized to the telomeric region of all the buffalo chromosomes. The 18S + 28S rDNA was localized to the telomeric regions of the chromosomes 5p, 7, 19, 21, and 22 of the tamaraw and of their homologous chromosomes in the river and swamp buffalo cytotypes.