Metacentric Chromosomes Research Articles

Aneuploidy across individual chromosomes at the embryonic level in trophectoderm biopsies: changes with patient age and chromosome structure.

To characterize each chromosome's risk for being involved in embryonic aneuploidy. This is a retrospective cohort study conducted at a single, academic center. The cohort consisted of 15,169 consecutive trophectoderm biopsies which then underwent comprehensive chromosome screening utilizing validated real-time polymerase chain reaction (RT-PCR) or single nucleotide polymosphism (SNP) array platforms. Analysis was done to determine probability of aneuploidy by chromosome, changes in that risk with increasing maternal age, and in relationship of aneuploidy to chromosomal structure as classified by prior cytogenetic literature. The highest prevalence of imbalances leading to aneuploidy was seen for chromosomes 13, 15, 16, 18, 19, 21, and 22. While elevated in all age groups, there was a disproportionate rise in aneuploidy rates for these chromosomes with increasing maternal age. When classic cytogenetic karyotype groups were compared, the overall smaller groups D, E, and G were associated with the highest rates. Similarly, when grouped based upon structure, acrocentric chromosomes exhibited the highest rates of aneuploidy, followed by the metacentric chromosomes, with the lowest prevalence of error in those with submetacentric structures. The highest rates of chromosomal aneuploidy were found in chromosomes known to be involved in clinically detectable, abnormal pregnancies, not just simply implantation failure. The rate of aneuploidy in these chromosomes rises disproportionately with age when compared to the other chromosomes which may provide information about chromosomal susceptibility to aging. The biological structure groupings did show varied aneuploidy rates which may provide insight into the biology of aneuploidy.

Chromosome errors involving large metacentric and submetacentric chromosomes are more common in young infertility patients

Advanced maternal age (AMA) is the most significant risk factor associated with oocyte aneuploidy. Women at 40 years of age have a 50% reduction in fecundity compared to women a decade younger, including a significant increase in pregnancy loss. Chromosome analysis of pre-implantation embryos has revealed that all 23 pairs of chromosomes are involved in both chromosome gains and losses. The aim of this study was to evaluate the classification of blastocyst chromosome errors in association with maternal age at the time of infertility treatment.

Sex chromosomes and karyotype of the (nearly) mythical creature, the Gila monster, Heloderma suspectum (Squamata: Helodermatidae).

A wide variety of sex determination systems exist among squamate reptiles. They can therefore serve as an important model for studies of evolutionary transitions among particular sex determination systems. However, we still have only a limited knowledge of sex determination in certain important lineages of squamates. In this respect, one of the most understudied groups is the family Helodermatidae (Anguimorpha) encompassing the only two venomous species of lizards which are potentially lethal to human beings. We uncovered homomorphic ZZ/ZW sex chromosomes in the Gila monster (Heloderma suspectum) with a highly heterochromatic W chromosome. The sex chromosomes are morphologically similar to the ZZ/ZW sex chromosomes of monitor lizards (Varanidae). If the sex chromosomes of helodermatids and varanids are homologous, female heterogamety may be ancestral for the whole Anguimorpha group. Moreover, we found that the karyotype of the Gila monster consists of 2n = 36 chromosomes (14 larger metacentric chromosomes and 22 acrocentric microchromosomes). 2n = 36 is the widely distributed chromosomal number among squamates. In his pioneering works representing the only previous cytogenetic examination of the family Helodermatidae, Matthey reported the karyotype as 2n = 38 and suggested a different chromosomal morphology for this species. We believe that this was probably erroneously. We also discovered a strong accumulation of telomeric sequences on several pairs of microchromosomes in the Gila monster, which is a trait documented relatively rarely in vertebrates. These new data fill an important gap in our understanding of the sex determination and karyotype evolution of squamates.

Insight into genomic changes accompanying divergence: genetic linkage maps and synteny of Lucania goodei and L. parva reveal a Robertsonian fusion.

Linkage maps are important tools in evolutionary genetics and in studies of speciation. We performed a karyotyping study and constructed high-density linkage maps for two closely related killifish species, Lucania parva and L. goodei, that differ in salinity tolerance and still hybridize in their contact zone in Florida. Using SNPs from orthologous EST contigs, we compared synteny between the two species to determine how genomic architecture has shifted with divergence. Karyotyping revealed that L. goodei possesses 24 acrocentric chromosomes (1N) whereas L. parva possesses 23 chromosomes (1N), one of which is a large metacentric chromosome. Likewise, high-density single-nucleotide polymorphism−based linkage maps indicated 24 linkage groups for L. goodei and 23 linkage groups for L. parva. Synteny mapping revealed two linkage groups in L. goodei that were highly syntenic with the largest linkage group in L. parva. Together, this evidence points to the largest linkage group in L. parva being the result of a chromosomal fusion. We further compared synteny between Lucania with the genome of a more distant teleost relative medaka (Oryzias latipes) and found good conservation of synteny at the chromosomal level. Each Lucania LG had a single best match with each medaka chromosome. These results provide the groundwork for future studies on the genetic architecture of reproductive isolation and salinity tolerance in Lucania and other Fundulidae.

Cytogenetic and identification of the nucleolus organizer region in Heliconia bihai (L.) L.

The genus Heliconia is not much studied and the number of existing species in this genus is still uncertain. It is known that this number relies between 150 to 250 species. In Brazil, about 40 species are native and known by many different names. The objective of this paper was to characterize morphometrically and to identify the NOR (active nucleolus organizer regions) by Ag-NOR banding of chromosomes of Heliconia bihai (L) L. Root meristems were submitted to blocking treatment in an amiprofos-methyl (APM) solution, fixed in methanol-acetic acid solution for 24 hours, at least. The meristems were washed in distilled water and submitted to enzymatic digestion with pectinase enzyme. The slides were prepared by dissociation of the root meristem, dried in the air and also on hot plate at 50°C. Subsequently, some slides were submitted to 5% Giemsa stain for karyotype construction and to a solution of silver nitrate (AgNO3) 50% for Ag-NOR banding. The species H. bihai has 2n = 22 chromosomes, 4 pairs of submetacentric chromosomes and 7 pairs of metacentric chromosomes, and graded medium to short (3.96 to 0.67 μM), with the presence of active NOR in pairs 1 and 2 and interphase cells with 2 nucleoli. These are the features of a diploid species.

Chromatin organization and remodeling of interstitial telomeric sites during meiosis in the Mongolian gerbil (Meriones unguiculatus).

Telomeric DNA repeats are key features of chromosomes that allow the maintenance of integrity and stability in the telomeres. However, interstitial telomere sites (ITSs) can also be found along the chromosomes, especially near the centromere, where they may appear following chromosomal rearrangements like Robertsonian translocations. There is no defined role for ITSs, but they are linked to DNA damage-prone sites. We were interested in studying the structural organization of ITSs during meiosis, a kind of cell division in which programmed DNA damage events and noticeable chromatin reorganizations occur. Here we describe the presence of highly amplified ITSs in the pericentromeric region of Mongolian gerbil (Meriones unguiculatus) chromosomes. During meiosis, ITSs show a different chromatin conformation than DNA repeats at telomeres, appearing more extended and accumulating heterochromatin markers. Interestingly, ITSs also recruit the telomeric proteins RAP1 and TRF1, but in a stage-dependent manner, appearing mainly at late prophase I stages. We did not find a specific accumulation of DNA repair factors to the ITSs, such as γH2AX or RAD51 at these stages, but we could detect the presence of MLH1, a marker for reciprocal recombination. However, contrary to previous reports, we did not find a specific accumulation of crossovers at ITSs. Intriguingly, some centromeric regions of metacentric chromosomes may bind the nuclear envelope through the association to SUN1 protein, a feature usually performed by telomeres. Therefore, ITSs present a particular and dynamic chromatin configuration in meiosis, which could be involved in maintaining their genetic stability, but they additionally retain some features of distal telomeres, provided by their capability to associate to telomere-binding proteins.

Dynamics of Rye Telomeres in a Wheat Background during Early Meiosis

Migration of the telomere of the short arm of rye chromosome 5R (5RS) during bouquet organization is dependent on the conformation that this chromosome adopts in its intact, submetacentric, or truncated, metacentric, form. In order to establish whether the telomere migration dependence on chromosome conformation is a common feature of all rye chromosomes, the behavior of the telomeres of 2 other rye chromosomes, 1R and 6R, with apparent differences in the arm ratio, has been studied at the bouquet stage and compared with that of 5R. The presence of subtelomeric heterochromatic chromomeres in both arms of 1R and 6R, which were visualized by FISH, revealed the position of the adjacent telomeres in the bouquet. While the end of the long arms of both chromosomes was, with some exceptions, always included in the telomere cluster, the end of the short arms failed to migrate to the telomere pole. Disturbed telomere migration was more often observed in the short arm of the submetacentric chromosome 6R than in the short arm of the almost metacentric chromosome 1R. Thus, the chromosomal conformation effect on telomere mobility is a common feature of all rye chromosomes. Incomplete telomere clustering is followed by failure of synapsis and chiasma formation in chromosomes 5R and 6R. Chromosome arm 1RS, which carries the NOR, completes synapsis earlier than 5RS or 6RS, facilitated by the nucleolar fusion that occurs during early zygotene.

Meiotic recombination analyses of individual chromosomes in male domestic pigs (Sus scrofa domestica).

For the first time in the domestic pig, meiotic recombination along the 18 porcine autosomes was directly studied by immunolocalization of MLH1 protein. In total, 7,848 synaptonemal complexes from 436 spermatocytes were analyzed, and 13,969 recombination sites were mapped. Individual chromosomes for 113 of the 436 cells (representing 2,034 synaptonemal complexes) were identified by immunostaining and fluorescence in situ hybridization (FISH). The average total length of autosomal synaptonemal complexes per cell was 190.3 µm, with 32.0 recombination sites (crossovers), on average, per cell. The number of crossovers and the lengths of the autosomal synaptonemal complexes showed significant intra- (i.e. between cells) and inter-individual variations. The distributions of recombination sites within each chromosomal category were similar: crossovers in metacentric and submetacentric chromosomes were concentrated in the telomeric regions of the p- and q-arms, whereas two hotspots were located near the centromere and in the telomeric region of acrocentrics. Lack of MLH1 foci was mainly observed in the smaller chromosomes, particularly chromosome 18 (SSC18) and the sex chromosomes. All autosomes displayed positive interference, with a large variability between the chromosomes.

Distribution and heterogeneity of heterochromatin in the European huchen (Hucho hucho Linnaeus, 1758) (Salmonidae).

The chromosomal characteristics, locations and variations of the heterochromatin were studied in the European huchen (Hucho hucho, Linnaeus, 1758) karyotype using conventional C- banding, endonuclease digestion banding, silver nitrate (AgNO3), chromomycin A3 (CMA3) and DAPI staining techniques. The karyotype consists of 82 chromosomes: 13 pairs of metacentric chromosomes, 2 pairs of submetacentric chromosomes and 26 pairs of subtelo-acrocentric chromosomes (NF = 112). Original data on the chromosomal distribution of segments resistant to Alu I, Dde I and Mbo I restriction endonucleases and identification of the C-banded heterochromatin presented here have been used to characterize the huchen karyotype. On the basis of the banding patterns provided in the course of restriction enzyme digestion, AgNO3/CMA3 staining and C-banding we distinguished twelve types of heterochromatin grouped in four areas of the European huchen chromosomes. One pair of NOR-bearing chromosomes was found to be polymorphic in size and displayed two distinct forms. A combination of various staining techniques provided original data concerning heterochromatin distribution and heterogeneity in the European huchen which enabled better karyotypic definition of this fish species.

Chromosome counts and karyotypic study of Stachys lavandulifolia Vahl

Stachys lavandulifolia grows wild in Iran and is claimed to be effective for the treatment of infection, asthma, inflammatory diseases, and especially rheumatism. Thus, four populations of this species were studied karyologically. The basic chromosome number, the ploidy level, the total length of the chromosomes, and five different measures of karyotype asymmetry were investigated. The basic chromosome number of the studied populations was obtained as x = 15. The presence of 60 chromosomes in all of populations corresponds to tetraploidy (2n = 4x = 60) levels. The size of mitotic chromosomes was small and the mean length varied from 1.30 to 1.48 μm. The smallest chromosomes were observed in Manbar population and the largest in Angoran population. In all of the populations, metacentric chromosomes were the most common, whereas sub-metacentric chromosomes were rare. Karyotypic indices obtained for all populations revealed that the karyotypes were slightly asymmetrical. The intrachromosomal asymmetry index (A1) index varied from 0.16 to 0.25, interchromosomal asymmetry index (A2) ranged between 0.05 and 0.14, and Paszko’s asymmetry index (AI) ranged from 0.08 to 0.44. Gachsar population showed the highest levels of karyotypic heterogeneity. Finally, the results of the present study are important for breeding programs and for understanding the taxonomic position of this species.

Karyotype analysis of ten draught resistant cultivars of Indian taro - Colocasia esculenta cv. antiquorom Schott

Somatic chromosome number, detailed karyotype and genome size analysis were made to assess genetic diversity in ten drought resistant cultivars of Indian Taro (Colocasia esculenta var antiquorom Schott.). Karyotype analysis revealed genotype specific chromosomal characteristics and structural alterations in chromosomes of the genome, with variations of ploidy from 2n = 2 × = 28 (cv. Mothan, cv. Muktakeshi, cv. Sree Kiran, cv. Sree Pallavi, cv. Sunajhili) to 3n = 3 × = 42 (cv. Banky, cv. DP-25, cv. Duradin, cv. H-3, cv. Telia). Highly significant variations in the genomic length, volume and total form (TF) % were noted at variety level. Total genomic chromosome length varied from 46.96 μm in cv. Sree Kiran to 100.49 μm in cv. Duradin. Total genomic chromosome volume varied from 18.22 μm3 in cv. Sunajhili to 38.22 μm3 in cv. Duradin. Total form percentage was varied from 24.94 % in cv. Sree Kiran to 39.04 % in cv. H-3 confirming mostly of near metacentric to metacentric chromosomes in the karyotype. Significant variations in the 4C DNA content noted among the cultivars that ranged from 7.24 pg in cv. Sree Kiran to 18.24 pg in cv. Duradin; accordingly, genome size varied from ~7,095 to 17,875 Mbp. High genome size in all the triplod varieties with 3 x = 42 chromosomes could be due to the presence of extra set of chromosomes in the genome or high amount of repetitive DNA. The variation in the genome size at the cultivar level may be attributed to loss or addition of highly repetitive sequences in the genome. Detailed chromosomal analysis of ten drought resistant cultivars could help breeders to choose the diverse parents for breeding programme along with high yielding drought susceptible varieties for future crop improvement programme.

Cytological and Karyotypic Analyses in Some Populations of Leonurus cardiaca

Leonurus cardiaca (Motherwort) is one of the most resistant plants to biotic and abiotic stresses with a number of medicinal properties. In order to investigate the karyotypic variation between six populations of motherwort, this experiment was performed. Root-tip meristems were used for karyotypic evaluation. 8-hydroxy quinoline and ethanol–acetic acid (3:1 V/V) solution were used as pretreatment and fixative solutions, respectively. Chromosomes were stained by 2 % aceto-orcein. Long arm length (L), short arm length (S), total chromosome length (TL), L/S and S/L, overall genome length, the ratio of the longest to the shortest chromosome, and centromeric index were recorded. Result showed that the best root size for chromosome study of this species is 0.50–1.50 cm long and the best time for cutting the roots is about noon time. All the six studied populations were diploid (2n = 2x = 18), and metacentric chromosomes were dominant in all population. In some populations, a few submetacentric chromosomes were also observed. Cluster analysis based on karyotype traits revealed four groups of populations using Euclidean distance.

Comparative cytogenetics of Physalaemusalbifrons and Physalaemus cuvieri species groups (Anura,Leptodactylidae).

Recently, Physalaemus albifrons (Spix, 1824) was relocated from the Physalaemus cuvieri group to the same group as Physalaemus biligonigerus (Cope, 1861), Physalaemus marmoratus (Reinhardt & Lütken, 1862) and Physalaemus santafecinus Barrio, 1965. To contribute to the analysis of this proposition, we studied the karyotypes of Physalaemus albifrons, Physalaemus santafecinus and three species of the Physalaemus cuvieri group. The karyotype of Physalaemus santafecinus was found to be very similar to those of Physalaemus biligonigerus and Physalaemus marmoratus, which were previously described. A remarkable characteristic that these three species share is a conspicuous C-band that extends from the pericentromeric region almost to the telomere in the short arm of chromosome 3. This characteristic is not present in the Physalaemus albifrons karyotype and could be a synapomorphy of Physalaemus biligonigerus, Physalaemus marmoratus and Physalaemus santafecinus. The karyotype of Physalaemus santafecinus is also similar to those of Physalaemus marmoratus and Physalaemus biligonigerus owing to the presence of several terminal C-bands and the distal localization of the NOR in a small metacentric chromosome. In contrast, the Physalaemus albifrons karyotype has no terminal C-bands and its NOR is located interstitially in the long arm of submetacentric chromosome 8. The NOR-bearing chromosome of Physalaemus albifrons very closely resembles those found in Physalaemus albonotatus (Steindachner, 1864), Physalaemus cuqui Lobo, 1993 and some populations of Physalaemus cuvieri Fitzinger, 1826. Additionally, the Physalaemus albifrons karyotype has an interstitial C-band in chromosome 5 that has been exclusively observed in species of the Physalaemus cuvieri group. Therefore, we were not able to identify any chromosomal feature that supports the reallocation of Physalaemus albifrons.

Incomplete pole orientation of kinetochores in complex meiotic metaphase I configurations delays metaphase-anaphase transition in Secale.

To prevent unbalanced chromosome segregation, meiotic metaphase I - anaphase I transition is carefully regulated by delaying anaphase until all kinetochores are well oriented (anaphase checkpoint) in mammals and insects. In plants this has not yet been established. In heterozygotes of two reciprocal translocations of Secale cereale, with one chromosome replaced by its two telocentric arms, anaphase delay was correlated with the orientation of the kinetochores of the complex of five chromosomes. The terminal kinetochores of the half chromosomes were readily elongated and pole oriented. Chains of five chromosomes with all five kinetochores orienting on alternate poles where the first to start anaphase. Kinetochores of two adjacent chromosomes when oriented on the same pole were partly shielded and less well pole directed. Anaphase was delayed. Cells with this configuration accumulated during anther development. Kinetochores in metacentric chromosomes lacking chiasmata in one arm (in trivalents and bivalents) were slightly better pole oriented and delayed anaphase less. Release of chromatid cohesion as triggered by kinetochore stretch is apparently delayed by inadequate exposition and pole orientation of the kinetochores. It is a mild form of an anaphase checkpoint, in normal material synchronizing bivalent segregation.

Cytogenetic characterization of ten araneomorph spiders (Araneae): Karyotypes and meiotic features

Karyotypes, sex chromosome systems and meiotic characteristics are reported for ten spider species belonging to the families Gnaphosidae, Philodromidae, Salticidae, Oxyopidae and Sicariidae by using standard Giemsa staining. The male diploid numbers (2n) and sex chromosome systems are as follows: Berinda hakani 2n = 22 (X1X2), Berinda ensigera 2n = 22 (X1X2), Trachyzelotes lyonneti 2n = 22 (X1X2), Trachyzelotes malkini 2n = 22 (X1X2), Zelotes caucasius 2n = 22 (X1X2) (Gnaphosidae); Thanatus pictus 2n = 28 (X1 X2), Tibellus macellus 2n = 24 (X1 X2) (Philodromidae); Neon reticulatus 2n = 21 (X0) (Salticidae); Peucetia virescens 2n = 28 (X1X2) (Oxyopidae) and Loxosceles rufescens 2n = 21 (X1 X2Y) (Sicariidae). All species have monoarmed chromosomes with the exception of L. rufescens that has biarmed (metacentric and submetacentric) chromosomes. The obtained data are the first results for the genera Berinda, Trachyzelotes and Neon. Additionally, with the exception of L. rufescens, all species are being chromosomally analyzed for the first time.

BILATERAL SUBCLAVIAN STENOSIS AS A CAUSE OF UNEXPLAINED HYPOTENSION

The centromere is the DNA region of the eukaryotic chromosome that determines kinetochore formation and sister chromatid cohesion. Centromeres interact with spindle microtubules to ensure the segregation of chromatids during mitosis and of homologous chromosomes in meiosis. The origin of centromeres, therefore, is inseparable from the evolution of cytoskeletal components that distribute chromosomes to offspring cells. Although the origin of the nucleus has been debated, no explanation for the evolutionary appearance of centromeres is available. We propose an evolutionary scenario: The centromeres originated from telomeres. The breakage of the ancestral circular genophore activated the transposition of retroelements at DNA ends that allowed the formation of telomeres by a recombination-dependent replication mechanism. Afterward, the modification of the tubulin-based cytoskeleton that allowed specific subtelomeric repeats to be recognized as new cargo gave rise to the first centromere. This switch from actin-based genophore partition to a tubulin-based mechanism generated a transition period during which both types of cytoskeleton contributed to fidelity of chromosome segregation. During the transition, pseudodicentric chromosomes increased the tendency toward chromosomal breakage and instability. This instability generated multiple telocentric chromosomes that eventually evolved into metacentric or holocentric chromosomes.

B GENOME-RELATED KARYOTYPIC VARIATION IN CERTAIN BANANAS IN THAILAND

Many of edible bananas (Kluai in Thai) associated with Musa balbisiana are diversified in Southeast Asia, and their genomes vary from diploid to tetraploid. This research aimed to examine the chromosome number and karyotype of certain local bananas for their classification and crop improvement. Root tips of 20 banana accessions were collected from the banana germplasm collection at Pak Chong Research Station and Department of Horticulture, Kasetsart University, stained with Feulgen and then observed under light microscope. The results revealed that the bananas classified as BB group (2n=22) were ‘Tani Dam’, ‘Tani I-san’ and ‘Tani Nuea’. The banana in BBB group (2n=33) was ‘Thepphanom’. The bananas in AAB group (2n=33) were ‘Roi Wi’, ‘Nom Sao’, ‘Sam Duean’ (Phichit), ‘Nam Lek’ (Songkhla) and ‘Nam Phat’. The bananas in ABB group (2n=33), were ‘Namwa Dam’, ‘Namwa Ngoen’, ‘Namwa Ubon’, ‘Namwa Mali Ong’, ‘Namwa Sai Daeng’, ‘Hin’, ‘Namwo’, ‘Nang Phaya’, ‘Hak Muk Khiao’ and ‘Hak Muk Thong’. The banana in ABBB group (2n=44) was ‘Theppharot’. These genomes were varied in chromosome size ranging from 0.83 to 3.79 microns. The karyotypes in all groups were composed of metacentric and submetacentric chromosomes. The satellite was found on the first chromosomal pair in all genomic groups, but found on the second chromosomal pair only in ‘Roi Wi’, ‘Nang Phaya’, ‘Hak Muk Khiao’, ‘Hak Muk Thong’. There was no satellite observed in ‘Tani I-san’ and ‘Tani Nuea’. Our results suggested that karyotypic variation is related to B genome.

Preliminary cytogenetic study and report of ZZ/ZW sex chromosomes in the bullfrog, Hoplobatrachus tigerinus (Anura, Amphibia) from high altitude area of Jammu and Kashmir, India

Cytogenetic study of the Indian Bullfrog, Hoplobatrachus tigerinus was carried out using both conventional staining and banding methods, from Jammu and Kashmir. Karyotypes prepared by conventional staining in both male and female specimens showed diploid chromosome number as 2n = 26 and fundamental arm number as NF = 52. Karyotypes of both the sexes comprised of 13 pairs of biarmed chromosomes divided into two groups: first group of five pairs of larger metacentric or submetacentric chromosomes and second group of eight pairs of smaller metacentric or submetacentric chromosomes. Pair number 2, 3, and 4 among the first group and 8 and 9 among the second group were submetacentric chromosomes. All the other chromosomes in both the groups were metacentric. Meiotic stages observed were leptotene, diakinesis, metaphase-I and metaphase- II, from testicular cells of males. C-banding analysis of the species showed presence of centromeric C-bands in all the chromosomes of both male and female karyotypes. Female karyotype showed presence of completely heterochromatic homologue of the pair no. 8, which represented ZZ/ZW sex chromosome system in the species. NOR-banding showed presence of a pair of nucleolar organizer regions on the long arm of 6th pair in both the sexes.

Molecular cytogenetic study in Octopus (Amphioctopus) areolatus from Japan

Octopus (Amphioctopus) areolatus is an important marine cephalopod in Japan. We examined its diploid chromosome number, karyotype, and genome size (C value), and performed fluorescence in situ hybridization (FISH) using a vertebrate telomeric probe. The diploid chromosome number was 60 in embryonic cells, with 24 pairs of metacentric chromosomes, four pairs of metacentric/submetacentric chromosomes, and two pairs of submetacentric chromosomes. The mean C value was estimated to be 5.47 pg. From these findings, and those reported previously for other octopus species, we suggest that the factor causing the quantum change of C value in O. (A.) areolatus was genome duplication, and not polyploidy. In telomeric FISH analysis, hybridization signals were clearly observed in the telomeric regions of the chromosomes. This is the first report of FISH analysis of cephalopod chromosomes, and our findings suggest that the telomere sequence of O. (A.) areolatus is (TTAGGG)n, which may allow gene mapping in the future.

Dynamic Chromosome Reorganization in the Osprey (Pandion haliaetus, Pandionidae, Falconiformes): Relationship between Chromosome Size and the Chromosomal Distribution of Centromeric Repetitive DNA Sequences

The osprey (Pandion haliaetus) has a diploid number of 74 chromosomes, consisting of a large number of medium-sized macrochromosomes and relatively few microchromosomes; this differs greatly from the typical avian karyotype. Chromosome painting with chicken DNA probes revealed that the karyotype of P. haliaetus differs from the chicken karyotype by at least 14 fission events involving macrochromosomes (chicken chromosomes 1-9 and Z) and at most 15 fusions of microchromosomes, suggesting that considerable karyotype reorganization occurred in P. haliaetus in a similar manner previously reported for Accipitridae. A distinct difference was observed, however, between Accipitridae and Pandionidae with respect to the pattern of chromosome rearrangements that occurred after fissions of macrochromosomes. Metacentric or submetacentric chromosomes 1-5 in P. haliaetus appear to have been formed by centric fusion of chromosome segments derived from macrochromosomal fissions. By contrast, many pairs of bi-armed chromosomes in Accipitridae species seem to result from pericentric inversions that occurred in the fission-derived chromosomes. Two families of repetitive sequences were isolated; the 173-bp PHA-HaeIII sequence occurred on all chromosomes, whereas intense signals from the 742-bp PHA-NsiI sequence were localized to all acrocentric chromosomes, with weak signals on most of the bi-armed chromosomes. Two repetitive sequences cohybridized in the centromeric heterochromatin; however, the sequences differed in unit size, nucleotide sequence and GC content. The results suggest that the 2 sequence families originated from different ancestral sequences and were homogenized independently in centromeres, and that a chromosome size-dependent compartmentalization may have been lost in P. haliaetus.