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PubMed2004

Genome sequence of the Brown Norway rat yields insights into mammalian evolution.

The laboratory rat (Rattus norvegicus) is an indispensable tool in experimental medicine and drug development, having made inestimable contributions to human health. We report here the genome sequence of the Brown Norway (BN) rat strain. The sequence represents a high-quality 'draft' covering over 90% of the genome. The BN rat sequence is the third complete mammalian genome to be deciphered, and three-way comparisons with the human and mouse genomes resolve details of mammalian evolution. This first comprehensive analysis includes genes and proteins and their relation to human disease, repeated sequences, comparative genome-wide studies of mammalian orthologous chromosomal regions and rearrangement breakpoints, reconstruction of ancestral karyotypes and the events leading to existing species, rates of variation, and lineage-specific and lineage-independent evolutionary events such as expansion of gene families, orthology relations and protein evolution.

Animals↗
PubMed1995

Chromosomal evolution in bovids: a comparison of cattle, sheep and goat G- and R-banded chromosomes and cytogenetic divergences among cattle, goat and river buffalo sex chromosomes.

A G- and R-banding comparison of cattle (Bos taurus, 2n = 60), goat (Capra hircus, 2n = 60) and sheep (Ovis aries, 2n = 54) chromosomes at the 450 band level was made. The study revealed a large number of banding homologies among the autosomes of the three species and resolved some ambiguities in arranging some of their small disputed acrocentrics by direct and indirect comparisons with some bovid marker chromosomes. A loss of the subcentromeric G-positive band in sheep chromosome 2g was observed when the G-banding patterns of sheep 2q and homologous cattle and goat chromosome 2 were compared. The chromosomal divergences among cattle, goat and river buffalo (Bubalus bubalis, 2n = 50) sex chromosomes are shown to have occurred by pericentric and paracentric inversions with a loss (or acquisition of constitutive heterochromatin.

Animals↗
PubMed1975

Nature genetic basis and evolution of the haemoblobin polymorphism in Chironomus.

Chironomus larvae exhibit considerable haemoblobin polymorphism. Chironomus tnetans has 10 and C. pallidivittatus has 8 electrophoretically different Hb-chains. With the exception of one Hb-chain, all are species-specific. The hybrid which is fertile, shows the Hb-pattern of both parents. In the F2 and subsequent generations, considerable chromosome rearrangements occurs. Since the chromosomes of the parent species can be distinguished in the polytene state, Hb-patterns can be correlated with specific chromosomal constitutions. All the species-specific Hb-genes are located on one chromosome. This finding suggests that the Hb-genes have evolved through multiple gene duplications. Different mechanisms for gene duplication are discussed.

Biological Evolution↗
PubMed1997

Shared DNA sequences between the X and Y chromosomes in the tammar wallaby - evidence for independent additions to eutherian and marsupial sex chromosomes.

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.

Animals↗
PubMed1995

Chromosome evolution in retinoblastoma.

An attempt to reconstruct the chromosome evolution in 19 primary retinoblastoma tumors was made, taking into consideration the frequencies of the rearrangements for each case. The rearrangements were classified as early or late according to their frequency. Early chromosome rearrangements were +1q, +6p, -13/del(13q), -16/del(16q), -17/del(17p), and late rearrangements were (in decreasing order) -8, -17/del(17p), -22, +3/+3q, -4, -19, +1q, +7/+7q, -14, +21. Chromosome evolution was reconstructed by the analysis of parsimony using programs of phylogenetic inference, which belong to the computer package PHYLIP. Results of the reconstruction of chromosome evolution suggest that there are two types of retinoblastoma tumors which can be distinguished based on chromosome imbalance, and correlate with the presence or absence of additional copies of the short arm (p) of chromosome 6. Tumors with additional 6p chromosome had marked heterogeneity, with a high frequency of early as well as late chromosome changes. By contrast, tumors with a normal 6p complement had the fewest chromosome changes and, in particular, a lower frequency of late changes.

Biological Evolution↗
PubMed2003

Duplicate, decouple, disperse: the evolutionary transience of human centromeric regions.

Human centromeric regions are enriched for segmental duplications, which elsewhere in the genome precipitate both genetic disease and gene formation. Molecular cytogenetic analyses of primate chromosomes have established that centromeres frequently move without altering the surrounding gene order. Recently, the positions of two ancestral centromeres have been mapped to regions of the human genome that are both rich in segmental duplications and are associated with duplication-based clinical phenotypes. This suggests a model for the evolution of euchromatic segmental duplication families involving the localised elevation of recombination rates within the duplication-rich heterochromatin of recently inactivated centromeres, and raises the possibility that the distribution of duplication/deletion syndromes within our genome has been heavily influenced by such events. The relaxation of the heterochromatin environment that must accompany centromere inactivation would also increase the transcriptional activity within previously pericentromeric DNA, increasing the likelihood of chimaeric gene creation through pericentromeric-directed duplication events.

Centromere↗
PubMed1998

Localization of the repetitive telomeric sequence (TTAGGG)n in four sturgeon species.

We analysed the localization of the telomeric sequence (TTAGGG)n in four species of the genus Acipenser, namely A. naccarii (2n = 246 +/- 6), A. ruthenus (2n = 118 +/- 4), A. gueldenstaedti (2n = 256 +/- 6) and A. baeri (2n = 246 +/- 8). The hybridization signal was localized at the telomeres of all chromosomes in A. naccarii, A. ruthenus and A. baeri. In A. gueldenstaedti, two chromosomes were entirely marked with blocks of telomeric repeating sequences. The results are discussed in the light of their evolutionary inference.

Animals↗
PubMed2002

Higher-order organization and compartmentalization of satellite DNA PIM357 in species of the coleopteran genus Pimelia.

The PIM357 satellite DNA family is present in 26 Pimelia taxa (Tenebrionidae, Coleoptera) with endemic congeneric species from the Canary Islands showing higher interrepeat variability than continental ones. In this paper, we compare the repetitive DNA sequences of a Canarian species that has distinct subfamilies of repeat units, P. radula ascendens, with another without such subfamilies, P. sparsa sparsa. The chromosomal localization of the repeat units and the comparison of the variability of randomly cloned monomers to the one estimated by comparing repeat units from dimers and trimers suggest the absence of satellite subfamilies in P. sparsa sparsa. Hence, the repeat units of this species seem to be uniformly and randomly distributed throughout all chromosomes out of one chromosomal pair. On the contrary, P. radula ascendens shows four divergent subfamilies of repeat units supported by several diagnostic nucleotide substitutions. These subfamilies seem to form four distinct repeat units: monomer subfamily 1, monomer subfamily 4 and two higher-order units (dimer linking subfamily 1 and 4, and dimer linking subfamily 2 and 3). Moreover, monomers of subfamily 1 are present in three chromosomal pairs only. We discuss the effect of different potential factors acting in the concerted evolution and the genomic organization of stDNA sequences in these taxa.

Animals↗
PubMed2005

Ancestry of American polyploid Hordeum species with the I genome inferred from 5S and 18S-25S rDNA.

BACKGROUND AND AIMS: The genus Hordeum exists at three ploidy levels (2x, 4x and 6x) and presents excellent material for investigating the patterns of polyploid evolution in plants. Here the aim was to clarify the ancestry of American polyploid species with the I genome. * METHODS: Chromosomal locations of 5S and 18S-25S ribosomal RNA genes were determined by fluorescence in situ hybridization (FISH). In both polyploid and diploid species, variation in 18S-25S rDNA repeated sequences was analysed by the RFLP technique. * KEY RESULTS: Six American tetraploid species were divided into two types that differed in the number of rDNA sites and RFLP profiles. Four hexaploid species were similar in number and location of both types of rDNA sites, but the RFLP profiles of 18S-25S rDNA revealed one species, H. arizonicum, with a different ancestry. * CONCLUSIONS: Five American perennial tetraploid species appear to be alloploids having the genomes of an Asian diploid H. roshevitzii and an American diploid species. The North American annual tetraploid H. depressum is probably a segmental alloploid combining the two closely related genomes of American diploid species. A hexaploid species, H. arizonicum, involves a diploid species, H. pusillum, in its ancestry; both species share the annual growth habit and are distributed in North America. Polymorphisms of rDNA sites detected by FISH and RFLP analyses provide useful information to infer the phylogenetic relationships of I-genome Hordeum species because of their highly conserved nature during polyploid evolution.

Americas↗
PubMed2000

Chromosome fission associated with growth of ribosomal DNA in Neodiprion abietis (Hymenoptera: Diprionidae).

The haploid complement consists of seven metacentric chromosomes in most diprionid species but has evolved to n = 8 by fission in Neodiprion abietis. This fission generated a small telocentric chromosome and a large pseudoacrocentric chromosome with a short arm carrying a satellite. In situ hybridization indicated that the location of the rRNA gene cluster corresponds to the whole short arm. This suggests that (i) the breaking point was located close to an rRNA gene cluster, and (ii) fission was associated with growth of rDNA. These results suggest rDNA as a preferential breaking point but with a role in the healing of naked chromosome ends.

Animals↗