Homologues Of Chromosome Pair Research Articles

Chromosomal study of Khawia abbottinae (Cestoda: Caryophyllidea): karyotype and localization of telomeric and ribosomal sequences after fluorescence in situ hybridization (FISH).

An original cytogenetic study combining classical karyotype analysis and modern fluorescence in situ hybridization using telomeric (TTAGGG)n and ribosomal sequences (18S rDNA) was performed in Khawia abbottinae (Cestoda, Caryophyllidea), a parasite of Chinese false gudgeon (Abbottina rivularis) from China. Analyses based on conventional Giemsa staining, DAPI, YOYO-1 dye, and silver (Ag) staining were also carried out. The karyotype is composed of eight pairs of metacentric and telocentric chromosomes (2n = 16, n=5m + 3t). Constitutive heterochromatin was mainly positioned at pericentromeric regions, and telomeric sequences (TTAGGG)n were restricted to the end of all chromosomes. In mitotic preparations stained with Giemsa, both homologues of chromosome pair 4 showed a distinct secondary constriction. FISH with rDNA probe confirmed that this secondary constriction contains a nucleolar organizer region (NOR). The process of spermatocyte meiosis and the dynamics of nucleolus degradation in dividing cell were scrutinized. The present study and its results enhance the limited knowledge on basic karyotype characteristics and 18S rDNA clusters location in caryophyllidean tapeworms.

Chromosome evolution in Cophomantini (Amphibia, Anura, Hylinae).

The hylid tribe Cophomantini is a diverse clade of Neotropical treefrogs composed of the genera Aplastodiscus, Boana, Bokermannohyla, Hyloscirtus, and Myersiohyla. The phylogenetic relationships of Cophomantini have been comprehensively reviewed in the literature, providing a suitable framework for the study of chromosome evolution. Employing different banding techniques, we studied the chromosomes of 25 species of Boana and 3 of Hyloscirtus; thus providing, for the first time, data for Hyloscirtus and for 15 species of Boana. Most species showed karyotypes with 2n = 2x = 24 chromosomes; some species of the B. albopunctata group have 2n = 2x = 22, and H. alytolylax has 2n = 2x = 20. Karyotypes are all bi-armed in most species presented, with the exception of H. larinopygion (FN = 46) and H. alytolylax (FN = 38), with karyotypes that have a single pair of small telocentric chromosomes. In most species of Boana, NORs are observed in a single pair of chromosomes, mostly in the small chromosomes, although in some species of the B. albopunctata, B. pulchella, and B. semilineata groups, this marker occurs on the larger pairs 8, 1, and 7, respectively. In Hyloscirtus, NOR position differs in the three studied species: H. alytolylax (4p), H. palmeri (4q), and H. larinopygion (1p). Heterochromatin is a variable marker that could provide valuable evidence, but it would be necesserary to understand the molecular composition of the C-bands that are observed in different species in order to test its putative homology. In H. alytolylax, a centromeric DAPI+ band was observed on one homologue of chromosome pair 2. The band was present in males but absent in females, providing evidence for an XX/XY sex determining system in this species. We review and discuss the importance of the different chromosome markers (NOR position, C-bands, and DAPI/CMA3 patterns) for their impact on the taxonomy and karyotype evolution in Cophomantini.

Karyological study of Ololygon tripui (Lourenço, Nascimento and Pires, 2009), (Anura, Hylidae) with comments on chromosomal traits among populations.

To increase the number of cytogenetic characters used in Ololygon tripui systematics, we applied some cytogenetic techniques such as Giemsa, C- and NOR-banding, and fluorescence in situ hybridization (FISH) with 18S rDNA and repetitive microsatellite DNA probes to the study of four populations from Minas Gerais State (southeastern Brazil). All populations showed 2n = 24 and FN = 48, and chromosomal formula 8m + 10sm + 6st. Nucleolar organizing regions (NORs) were located on chromosome pair 6 in all populations, although in the Tripuí locality additional markings were observed on one homologue of chromosome pair 3. These patterns were partially congruent with results obtained using the 18S rDNA FISH probe. The microsatellites repetitive DNA (GA)15 and (CAT)10 probes accumulated predominantly in the terminal region of all chromosomes. Chromosome morphology and Ag-NOR were conserved among populations, a conserved pattern in Ololygon Fitzinger, 1843. Repetitive DNA FISH probes patterns were similar among populations, but they revealed species-specific differences when compared with other species of the genus Ololygon, suggesting that molecular cytogenetics are potentially more informative in karyologically conservative taxa.

Classical and molecular cytogenetics of Khawia sinensis (Cestoda: Caryophyllidea), invasive parasite of carp, Cyprinus carpio

Chromosomes of the invasive tapeworm Khawia sinensis (Caryophyllidea), the specific parasite of common carp, were analyzed by means of conventional Giemsa staining and using fluorescent DAPI and YOYO-1 dyes, silver staining, and fluorescent in situ hybridization (FISH) with 18S rDNA probe. The karyotype is composed of eight pairs of metacentric and telocentric chromosomes (2n = 16, n = 3m + 5t, TCL = 42.54 μm). Constitutive heterochromatin was located at pericentromeric regions of all pairs, except for the largest metacentric pair (no. 1), which possessed no DAPI-positive band. FISH with rDNA probe revealed that both homologues of chromosome pair no. 6 carry a cluster of ribosomal arrays, which were located interstitially close to the centromere. Present results are compared with previous cytogenetic data on Khawia spp., and comments are made on the karyotypes with respect to their phylogenetic links.

Karyotypes of Rana tagoi Okada with diploid number 28 in the Chausu Mountains of the Minamishinshu district of Nagano Prefecture, Japan (Anura: Ranidae)

Karyotypes of Tago’s brown frog Rana tagoi from the Chausu mountains in Minamishinshu of Nagano Prefecture were examined by conventional Giemsa staining, C-banding and late replication (LR)-banding. Chromosome number was 2n = 28 in all cases. The 28 chromosomes consisted of four pairs (1–4) of large biarmed chromosomes, two pairs (5–6) of telocentric chromosomes and eight pairs (7–14) of small biarmed chromosomes. Chromosome pair 11 had a secondary constriction on the long arm. In females, the C-band on the long arm of chromosome pair 6 was detected in both homologs, but was absent from the arms of the homologs of chromosome pairs 5 and 9. In males, C-bands were found in the long arms of both homologs of chromosome pairs 5 and 6, were present only in one homolog of chromosome pair 5 for certain male specimens and found in only one homolog of chromosome pair 9. Specimens of R. tagoi (2n = 28) should thus have two pairs of telocentric chromosomes to provide the same number of chromosome arms, these originating quite likely from chromosome pair 1 in the 26-chromosome specimens by centric fission. Heteromorphic sex chromosomes of the XX-XY type in R. tagoi (2n = 28) in the Chausu mountains were identified. Karyotypes of tail-tip cells from a hybrid tadpole between female R. tagoi (2n = 26) from the Hinohara village in Tokyo and male R. tagoi (2n = 28) from the Chausu mountain population were examined by squash preparation. Chromosome number was 2n = 27 in all tadpoles. The 27 chromosomes consisted of one chromosome set of R. tagoi (2n = 28) and one of R. tagoi (2n = 26).

Genetic length of a human chromosomal segment measured by recombination between two fragile sites

Two families were studied in which the same homolog of chromosome pair 10 expressed both the fragile sites on the long (q) arm at 10q23 and 10q25. Recombination between the fragile sites was observed in 3 of the 27 offspring in whom it could occur. The genetic length of chromosome between the fragile sites was 11 female centimorgans within a 95 percent probability interval of 4 to 28 centimorgans. This estimate of genetic length is comparable to those obtained with other methods.

Heteromorphic X chromosomes in 46,XX males: evidence for the involvement of X-Y interchange.

G- and R-banded chromosome preparations from eight of twelve 46,XX males, with no evidence of mosaicism or a free Y chromosome, were distinguished in blind trials from preparations from normal 46,XX females by virtue of heteromorphism of the short arm of one X chromosome. Photographic measurements on X chromosomes and on chromosome pair 7 in cells from twelve 46,XX males, eight 46,XX females, and four 46,XY males revealed a significant increase in the size of the p arm of one X chromosome in the group of XX males, independently characterised as being heteromorphic for Xp. No such differences were observed between X chromosomes of normal males and females or between homologues of chromosome pair 7 in all groups. The heteromorphism in XX males is a consequence of an alteration in shape (banding profile) and length of the tip of the short arm of one X chromosome, and the difference in size of the two Xp arms in these 46,XXp+ males ranged from 0.4% to 22.9%. From various considerations, including the demonstration of a Y-specific DNA fragment in DNA digests from nuclei of one of three XX males tested, it is concluded that the Xp+ chromosome is a product of Xp-Yp exchange. These exchanges are assumed to originate at meiosis in the male parent and may involve an exchange of different amounts of material. The consequences of such unequal exchange are considered in terms of the inheritance of genes located on Yp and distal Xp. No obvious phenotypic difference was associated with the presence or absence of Xp+. Thus, some males diagnosed as 46,XX are mosaic for a cryptic Y-containing cell line, and there is now excellent evidence that maleness in others may be a consequence of an autosomal recessive gene. The present data imply that in around 70% of 46,XX males, maleness is a consequence of the inheritance of a paternal X-Y interchange product.