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Supernumerary elements of the genome are often called B chromosomes. They usually consist of various autosomal sequences and, because of low selective pressure, are mostly pseudogenized and contain many repeats. There are numerous reports on B chromosomes in mammals, fish, invertebrates, plants, and fungi, but only a few of them have been studied using sequencing techniques. However, reptilian supernumerary chromosomes have been detected only cytogenetically and never sequenced or analyzed at the molecular level. One model squamate species with available genome sequence is Anolis carolinensis. The scope of the present article is to describe the genetic content of A. carolinensis supernumerary chromosomes. In this article, we confirm the presence of B chromosomes in this species by reverse painting and synaptonemal complex analysis. We applied low-pass high-throughput sequencing to analyze flow-sorted B chromosomes. Anole B chromosomes exhibit similar traits to other supernumerary chromosomes from different taxons: they contain two genes related to cell division control (INCENP and SPIRE2), are enriched in specific repeats, and show a high degree of pseudogenization. Therefore, the present study confirms that reptilian B chromosomes resemble supernumerary chromosomes of other taxons. [ABSTRACT FROM AUTHOR]

Pigeons and doves (Columbiformes) are one of the oldest and most diverse extant lineages of birds. However, the karyotype evolution within Columbiformes remains unclear. To delineate the synteny-conserved segments and karyotypic differences among four Columbidae species, we used chromosome painting from Gallus gallus (GGA, 2n = 78) and Leucopternis albicollis (LAL, 2n = 68). Besides that, a set of painting probes for the eared dove, Zenaida auriculata (ZAU, 2n = 76), was generated from flow-sorted chromosomes. Chromosome painting with GGA and ZAU probes showed conservation of the first ten ancestral pairs in Z. auriculata, Columba livia, and Columbina picui, while in Leptotila verreauxi, fusion of the ancestral chromosomes 6 and 7 was observed. However, LAL probes revealed a complex reorganization of ancestral chromosome 1, involving paracentric and pericentric inversions. Because of the presence of similar intrachromosomal rearrangements in the chromosomes corresponding to GGA1q in the Columbidae and Passeriformes species but without a common origin, these results are consistent with the recent proposal of divergence within Neoaves (Passerea and Columbea). In addition, inversions in chromosome 2 were identified in C. picui and L. verreauxi. Thus, in four species of distinct genera of the Columbidae family, unique chromosomal rearrangements have occurred during karyotype evolution, confirming that despite conservation of the ancestral syntenic groups, these chromosomes have been modified by the occurrence of intrachromosomal rearrangements. [ABSTRACT FROM AUTHOR]

Bats are distinct from other mammals in their small genome size as well as their high metabolic rate, possibly related to flight ability. Although the genome sequence has been published in two species, the data lack cytogenetic information. In this study, the size and GC content of each chromosome are measured from the flow karyotype of the mouse-eared bat, Myotis myotis (MMY). The smaller chromosomes are GC-rich compared to the larger chromosomes, and the relative proportions of homologous segments between MMY and human differ among the MMY chromosomes. The MMY genome size calculated from the sum of the chromosome sizes is 2.25 Gb, and the total GC content is 42.3 %, compared to human and dog with 41.0 and 41.2 %, respectively. The GC-rich small MMY genome is characterised by GC-biased smaller chromosomes resulting from preferential loss of AT-rich sequences. Although the association between GC-rich small chromosomes and small genome size has been reported only in birds so far, we show in this paper, for the first time, that the same phenomenon is observed in at least one group of mammals, implying that this may be a mechanism common to genome evolution in general. [ABSTRACT FROM AUTHOR]

We analyzed the meiotic behavior of the sex chromosomes of the bats Glossophaga soricina (XX/XY), Artibeus cinereus and Uroderma magnirostrum (neo-XX/XY) using multicolor FISH. The X chromosome and pair 15 autosome probes are from Phyllostomus hastatus and the Y from Carollia brevicauda. On both species with the neo-XX/XY system, the autosome translocated to the sex chromosomes is the pair 15 in P. hastatus, a synapomorphy. The analysis of meiosis confirms that the X and Y have a pseudo-autosomal region, with a typical end-to-end pairing. The autosomal regions of the neo-XX/XY shows different levels of condensation when compared to the original XX/XY. The compound system presented a characteristic shape, as if it was a closed ring with a tail. The ring represents the non-paired segments of the X and Y and the small pairing region of the original sex chromosomes. The tail corresponds to the pairing of the 15 P. hastatus autosomal bivalent, which are translocated to the sex chromosomes. Probably the non-pairing is responsible for the meiotic silencing of these segments. [ABSTRACT FROM AUTHOR]

The genus Microtus consists of 65 extant species, making it one of the rodentia genera with the highest number of species. The extreme karyotype diversification in Microtus has made them an ideal species group for comparative cytogenetics and cytotaxonomy. Conventional comparative cytogenetic studies in Microtus have been based mainly on chromosomal banding patterns; the number of Microtus species examined by molecular cytogenetics—cross-species chromosome painting—is limited. In this study, we used whole chromosome painting probes of the field vole Microtus agrestis to detect regions of homology in the karyotypes of eight Microtus species. For almost all investigated species, species-specific associations of conserved chromosomal segments were revealed. Analysis of data obtained here and previously published data allowed us to propose that the ancestral Microtus species had a 2 n = 54 karyotype, including two associations of field vole chromosomal segments (MAG 1/17 and 2/8). Further mapping of the chromosome rearrangements onto a molecular phylogenetic tree allows the reconstruction of a karyotype evolution pathway in the Microtus genus. [ABSTRACT FROM AUTHOR]

Evolutionary cytogenetics can take confidence from methodological and analytical advances that promise to speed up data acquisition and analysis. Drastic chromosomal reshuffling has been documented in birds of prey by FISH. However, the available probes, derived from chicken, have the limitation of not being capable of determining if breakpoints are similar in different species: possible synapomorphies are based on the number of segments hybridized by each of chicken chromosome probes. Hence, we employed FACS to construct chromosome paint sets of the white hawk ( Leucopternis albicollis), a Neotropical species of Accipitridae with 2n = 66. FISH experiments enabled us to assign subchromosomal homologies between chicken and white hawk. In agreement with previous reports, we found the occurrence of fusions involving segments homologous to chicken microchromosomes and macrochromosomes. The use of these probes in other birds of prey can identify important chromosomal synapomorphies and clarify the phylogenetic position of different groups of Accipitridae. [ABSTRACT FROM AUTHOR]

The laboratory mouse ( Mus musculus, 2 n = 40), the Chinese hamster (Cricetulus griseus, 2 n = 22), and the golden (Syrian) hamster ( Mesocricetus auratus, 2 n = 44) are common laboratory animals, extensively used in biomedical research. In contrast with the mouse genome, which was sequenced and well characterized, the hamster species has been set aside. We constructed a chromosome paint set for the golden hamster, which for the first time allowed us to perform multidirectional chromosome painting between the golden hamster and the mouse and between the two species of hamster. From these data we constructed a detailed comparative chromosome map of the laboratory mouse and the two hamster species. The golden hamster painting probes revealed 25 autosomal segments in the Chinese hamster and 43 in the mouse. Using the Chinese hamster probes, 23 conserved segments were found in the golden hamster karyotype. The mouse probes revealed 42 conserved autosomal segments in the golden hamster karyotype. The two largest chromosomes of the Chinese hamster (1 and 2) are homologous to seven and five chromosomes of the golden hamster, respectively. The golden hamster karyotype can be transformed into the Chinese hamster karyotype by 15 fusions and 3 fissions. Previous reconstructions of the ancestral murid karyotype proposed diploid numbers from 2 n = 52 to 2 n = 54. By integrating the new multidirectional chromosome painting data presented here with previous comparative genomics data, we can propose that syntenies to mouse Chrs 6 and 16 were both present and to hypothesize a diploid number of 2 n = 48 for the ancestral Murinae/Cricetinae karyotype. [ABSTRACT FROM AUTHOR]

Two centuries after the duck-billed platypus was discovered, monotreme chromosome systems remain deeply puzzling. Karyotypes of males, or of both sexes, were claimed to contain several unpaired chromosomes (including the X chromosome) that form a multi-chromosomal chain at meiosis. Such meiotic chains exist in plants and insects but are rare in vertebrates. How the platypus chromosome system works to determine sex and produce balanced gametes has been controversial for decades. Here we demonstrate that platypus have five male-specific chromosomes (Y chromosomes) and five chromosomes present in one copy in males and two copies in females (X chromosomes). These ten chromosomes form a multivalent chain at male meiosis, adopting an alternating pattern to segregate into XXXXX-bearing and YYYYY-bearing sperm. Which, if any, of these sex chromosomes bears one or more sex-determining genes remains unknown. The largest X chromosome, with homology to the human X chromosome, lies at one end of the chain, and a chromosome with homology to the bird Z chromosome lies near the other end. This suggests an evolutionary link between mammal and bird sex chromosome systems, which were previously thought to have evolved independently. [ABSTRACT FROM AUTHOR]

An examination of the synteny blocks between mouse and human chromosomes aids in understanding the evolution of chromosome divergence between these two species. We comparatively mapped the human (HSA) Chromosome (Chr) 14q11.2-q13 cytogenetic region with the intervals of orthologous genes on mouse (MMU) chromosomes. A lack of conserved gene order was identified between the human cytogenetic region and the interval of orthologs on MMU 12. The evolutionary breakpoint junction was defined within 2.5 Mb, where the conserved synteny of genes on HSA 14 changes from MMU 12 to MMU 14. At the evolutionary breakpoint junction, a human EST (GI: 1114654) with identity to the human and mouse BCL2 interacting gene, BNIP3, was mapped to mouse Chr 3. New gene homologs of LAMB1, MEOX2, NRCAM, and NZTF1 were identified on HSA 7 and on the proximal cytogenetic region of HSA 14 by mapping mouse genes recently reported to be genetically linked within the relevant MMU 12 interval. This study contributes to the identification of homology relationships between the genes of HSA 14q11.2-q13 and mouse Chr 3, 12, and 14. [ABSTRACT FROM AUTHOR]

We have established a series of highly specific painting probes for human acrocentric chromosomes. These chromosomes are involved in the formation of the nucleolar organizer region (NOR) and show DNA sequence homologies within their pericentric heterochromatin. To date, these chromosomes have shown considerable cross hybridization in chromosome painting experiments. Our probe set has been established from primate homologues that are not involved in the NOR in that particular species or from species in which highly repetitive sequences have undergone rapid sequence divergence. The new painting probes should be of particular value for automated microscopy, for which highly specific signals are required as they are recorded at low magnification, e.g. when scoring chromosome 21 domains in interphase nuclei. [ABSTRACT FROM AUTHOR]

Marsupial sex chromosomes are smaller than their eutherian counterparts and are thought to reflect an ancestral mammalian X and Y. The gene content of this original X is represented largely by the long arm of the human X chromosome. Genes on the short arm of the human X are autosomal in marsupials and monotremes, and represent a recent addition to the eutherian X and Y. The marsupial X and Y apparently lack a pseudoautosomal region and show only end-to-end pairing at meiosis. However, the sex chromosomes of macropodid marsupials (kangaroos and wallabies) are larger than the sex chromosomes of other groups, and a nucleolus organizer is present on the X and occasionally the Y. Chromosome painting using DNA from sorted and microdissected wallaby X and Y chromosomes reveals homologous sequences on the tammar X and Y chromosomes, concentrated on the long arm of the Y chromosome and short arm of the X. Ribosomal DNA sequences were detected by fluorescence in situ hybridization on the wallaby Xp but not the Y. Since no chiasmata have been observed in marsupial sex chromosomes, it is unlikely that these shared sequences act as a pseudoautosomal region within which crossing over may occur, but they may be required for end-to-end associations. The shared region of wallaby X and Y chromosomes bears no homology with the recently added region of the eutherian sex chromosomes, so we conclude that independent additions occurred to both sex chromosomes in a eutherian and macropodid ancestor, as predicted by the addition-attrition hypothesis of sex chromosome evolution. [ABSTRACT FROM AUTHOR]