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Results for “vertebrate karyotype”

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PubMed2024

Comparative genomics illuminates karyotype and sex chromosome evolution of sharks.

Chondrichthyes is an important lineage to reconstruct the evolutionary history of vertebrates. Here, we analyzed genome synteny for six chondrichthyan chromosome-level genomes. Our comparative analysis reveals a slow evolutionary rate of chromosomal changes, with infrequent but independent fusions observed in sharks, skates, and chimaeras. The chondrichthyan common ancestor had a proto-vertebrate-like karyotype, including the presence of 18 microchromosome pairs. The X chromosome is a conversed microchromosome shared by all sharks, suggesting a likely common origin of the sex chromosome at least 181 million years ago. We characterized the Y chromosomes of two sharks that are highly differentiated from the X except for a small young evolutionary stratum and a small pseudoautosomal region. We found that shark sex chromosomes lack global dosage compensation but that dosage-sensitive genes are locally compensated. Our study on shark chromosome evolution enhances our understanding of shark sex chromosomes and vertebrate chromosome evolution.

Animals↗

PubMed1977

Rapid speciation and chromosomal evolution in mammals.

To test the hypothesis that population subdivision into small demes promotes both rapid speciation and evolutionary changes in gene arrangement by inbreeding and drift, we estimated rates of speciation and rates of chromosomal evolution in 225 genera of vertebrates. Rates of speciation were estimated by considering the number of living species in each genus and the fossil record of each genus as well as information about extinction rates. Speciation rate was strongly correlated with rate of chromosomal evolution and average rates of speciation in lower vertebrate genera were one-fifth those in mammalian genera. Genera with high karyotypic diversity and rapid speciation rates may generally have small effective population size (Ne), whereas large Ne values may be associated with karyotypically uniform genera and slow rates of speciation. Speciation and chromosomal evolution seem fastest in those genera with species organized into clans or harems (e.g., some primates and horses) or with limited adult vagility and juvenile dispersal, patchy distribution, and strong individual territoriality (e.g., some rodents). This is consistent with the above hypothesis regarding the evolutionary importance of demes.

Animals↗

PubMed1976

Studies on the organisation of the chicken genome and its expression during myogenesis in vitro.

DNA from the chicken genome was analysed both by isopycnic centrifugation in cesium salt density gradients and by reassociation analysis using hydroxyapatite (HAP) chromatography. Centrifugation in neutral CsCl revealed a single non-Gaussian band skewed toward the heavy side, but no discrete satellite components. In heavy metal (Ag+ or Hg++)-Cs2SO4 gradients, 4-8 satellite bands were revealed, comprising 5-9% of the total DNA. Purification of the satellites and recentrifugation in neutral CsCl demonstrated that 80-90% of this DNA would band in the shoulder, with the remainder in the main band. These satellites can account at most for 30% of the heavy shoulder DNA, thus most of the heavy shoulder DNA must be of lower repetition frequencies. Reassociation analyses of chicken DNA demonstrated that the complexity of the non-repetitive DNA is 9.49 X 10(8) nucleotide pairs, equivalent to about 90% of the haploid genome. Repetitive DNA comprises only 8-10% of the genome and has the following composition, relative to total DNA: 3.7% intermediate repetitive, 1.9% highly repetitive, and 3.9% "zero-time binding" DNA. This unusually low repetitive DNA content may be related to the small genome size of chickens, relative to other vertebrates, and to the presence of many microchromosomes in the chicken karyotype. Total cell RNA extracted from perfusion myoblasts, post-fusion myotubes, and myoblasts grown in BrdU was incubated in large excess with 3H-TdR labelled non-repetitive DNA and the resulting hybrids assayed by HAP chromatography. The amount of non-repetitive DNA represented in the RNA was found to increase from 7-8% in the myoblast stage to 10-11% in myotubes. An even smaller proportion, about 5%, is represented in the RNA of myoblasts prevented from differentiating by growth in BrdU.

Animals↗

PubMed1978

A case of partial 9p monosomy with some unusual clinical features.

A patient is described with a karyotype 46,XX,del(9)(qter leads to p22:) and having the main clinical characteristics of pure monosomy for part of the short arm of chromosome No 9, among which craniosynostosis and trigonocephaly. She has also a few atypical features: a clearly advanced osseous maturation, marked congenital vertebral anomalies and unusual dermatoglyphics.

Abnormalities, Multiple↗

PubMed1976

The relationship of a specific chromosomal region to the development of the acrosome.

In early spermatids of Urodeles the chromosome segments bearing constitutive heterochromatin are localized in one half of the round nucleus; this region becomes the basal part of the long nucleus of the spermatozoon. The euchromatic chromosome segments extend toward the anterior nuclear pole in a bouquet configuration (Macgregor and Walker, 1973). In the course of spermiohistogenesis, one of the heterochromatic regions (the acrosomal chromocenter) migrates from the basal part to the anterior half of the spermatid nucleus. This heterochromatic block is identical with a species-specific, definite C-band in the karyotype. This relationship between the acrosomal chromocenter and a specific chromosomal C-band was established in Triturus cristatus, T. marmoratus, T. alpestric and Cynops pyrrhogaster. In closely related species this particular C-band lies on similar chromosomes. - While the spermatid nucleus still retains its round shape the acrosomal chromocenter despiralizes into a long heterochromatic thread (acrosomal thread). Precisely at the position of this thread the nucleus evaginates and acquires a pear-like shape. During the elongation of the nuclear protrusion the acrosomal thread remains associated with the anterior end. At termination of spermiogenesis it lies closely below the acrosome in the tip of the spermatozoon. Spontaneous aberrations which affect the acrosomal chromocenter or the thread lead to the development of spermatozoa with defective tips. - Several euchromatic segments, interspersed between the heterchromatic segments, can be recognized in the completely despiralized acrosomal thread. Genes responsible for the morphogenetic activities of both, the acrosomal chromocenter and the acrosomal thread, in the development of the spermtip, might be localized in these interspersed euchromatic segments. The existence in higher vertebrates of an acrosomal chromocenter or an equivalent chromosomal region is discussed.

Acrosome↗

PubMed2026

Highly Contiguous Is Not Chromosomally Accurate: Integrated Cytogenetic and Genomic Mapping in Two Turtle Genome.

High-quality genome assemblies are essential for robust research across biological and medical fields. Assembly errors can have far-reaching consequences for downstream analyses, including gene annotation and the inference of synteny. In contrast to the rapid growth of genomic data volume, there is a notable lag in the integration of chromosome-level assemblies with cytogenetic data. We conducted the first direct genome-to-genome comparison, integrating comparative chromosome painting, the alignment of chromosome-specific probes to available genome assemblies, and synteny-based comparison of independent chromosome-level assemblies of the loggerhead sea turtle (Caretta caretta, 2n = 56) and the red-eared slider (Trachemys scripta elegans, 2n = 50). Using two independent sets of flow-sorted chromosome-specific probes in cross-species hybridizations, together with the sequencing and mapping of chromosome-derived DNA libraries, we assigned assembled scaffolds to all physical chromosomes of both species. In C. caretta, chromosomal assignments and genome-wide synteny were fully consistent with the published assembly, except for the reduced sizes of two microchromosome scaffolds, which we attribute to under-representation of repetitive DNA. In contrast, in T. s. elegans, cytogenetic validation of the assemblies revealed a false rearrangement compared to a missed one. Our results show that even highly contiguous vertebrate genome assemblies can misrepresent chromosome structure. When cytogenetic analyses reveal such inaccuracies, updated reference genomes should be generated for widely studied species to enable accurate inference of karyotype evolution and downstream comparative genomic analyses.

FISH↗

PubMed2026

Molecular divergence and genomic composition of B chromosomes in the fish Cyphocharax modestus (Characiformes, Curimatidae).

B chromosomes are supernumerary elements that evolve from standard A chromosomes and are primarily composed of repetitive DNAs, yet their origin, diversification, and molecular composition remain poorly understood in most vertebrates. We investigated two allopatric populations of Cyphocharax modestus (Curimatidae) combining classical cytogenetics, comparative genomic hybridization (CGH), and comparative satellitomics to characterize the repetitive DNA landscape of its B chromosomes. While both populations exhibited a conserved karyotype of 2n=54 biarmed chromosomes, five individuals from the Batalha River (BR) carried supernumerary chromosomes, comprising two distinct variants: a C-positive B1 and an C-negative B2. Comparative satellitome analysis between 3B-carrying and B-lacking individuals identified 116 satellite DNAs (CmoSatDNAs), with the 3B library showing higher abundances of specific sequences. Fluorescence in situ hybridization (FISH) revealed that both B variants share two centromeric satellites (CmoSat01-192 and CmoSat02-108) with the A complement, while CmoSat58-47 was exclusively to B2. Minimum spanning tree analysis of CmoSat58-47 revealed B-exclusive haplotypes alongside haplotypes shared with B-lacking individuals, suggesting a recent origin for these chromosomes. CGH experiments further confirm the sequence sharing between the A and B chromosomes, supporting an intraspecific origin, and revealing substantial genomic differentiation among B variants.

Animals↗

PubMed1978

Malignant neoplasms of genetic origin in Drosophila melanogaster.

Malignant neoplasms that develop in 12 recessive-lethal, larval mutants of Drosophila melanogaster are discussed. These mutations affect the adult optic neuroblasts and ganglion-mother cells in the larval brain, the imaginal discs, and the hematopoietic organs. The malignant neoplasms exhibit fast, autonomous growth, loss of the capacity for differentiation, increased mobility and invasiveness, lethality in situ and after transplantation, and histological, fine structural, and karyotypic abnormalities. Intermediate neoplasms are also found. These combine both benign and malignant qualities. They grow in a noninvasive, compact fashion, typical of benign tumors, yet they also exhibit malignant qualities such as fast, autonomous, and lethal growth, loss of differentiation capacity, changes in cellular morphology, and lethal growth after transplantation into wild-type hosts. Thus Drosophila and vertebrate neoplasms show striking similarities.

Animals↗