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Chromosome Evolution (chromosome + evolution)
Selected AbstractsChromosome evolution in the genus Cicindela: physical mapping and activity of rDNA loci in the tiger beetle species Cicindela littoralis and C. flexuosaJOURNAL OF ZOOLOGICAL SYSTEMATICS AND EVOLUTIONARY RESEARCH, Issue 4 2003S. J. R. Proença Abstract Cicindela littoralis and Cicindela flexuosa were analysed at population level to determine the localization and activity of ribosomal genes. Fluorescence in situ hybridization (FISH), using a PCR-amplified 18S rDNA fragment as a probe, revealed the presence of polymorphism regarding the number of chromosomes with ribosomal genes as well as their localization within the genome. Nine populations of C. littoralis showed a consistent pattern of two loci located in an autosomal pair (active during spermatogenesis as shown by silver staining) and one locus located in one of the multiple X chromosomes (silent during spermatogenesis), whereas individuals from the population of Punta Entinas showed only signals in the autosomal pair, lacking the heterosomal locus. In C. flexuosa, two patterns were also observed. Nine populations showed two loci in an autosomal pair whereas individuals from the population of San Pedro del Pinatar showed the two loci located in the heterosomes (one of the multiple Xs and in the Y). The hypothesis that these two different populations may reflect a status of well-differentiated phylogenetic entities is not supported for C. littoralis after the phylogenetic analysis of a fragment of the cytochrome oxidase I gene. [source] Dynamic linkage relationships to the mating-type locus in automictic fungi of the genus MicrobotryumJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 8 2010J. L. ABBATE Abstract Regions of the chromosomes determining mating compatibility in some fungi, including Microbotryum lychnidis-dioicae and Neurospora tetrasperma, exhibit suppressed recombination similar to sex chromosomes in plants and animals, and recent studies have sought to apply basic theories of sex chromosome evolution to fungi. A phylogeny of the MTL1 locus in Microbotryum indicates that it has become part of the nonrecombining regions of the mating-type chromosomes in multiple independent events, and that recombination may have been subsequently restored in some cases. This illustrates that fungal mating-type chromosomes can exhibit linkage relationship that are quite dynamic, adding to the list of similarities to animal or plant sex chromosomes. However, fungi such as M. lychnidis-dioicae and N. tetrasperma exhibit an automictic mating system, for which an alternate theoretical framework exists to explain the evolution of linkage with the mating-type locus. This study encourages further comparative studies among fungi to evaluate the role of mating systems in determining the evolution of fungal mating-type chromosomes. [source] MicroReview: Divided genomes: negotiating the cell cycle in prokaryotes with multiple chromosomesMOLECULAR MICROBIOLOGY, Issue 5 2005Elizabeth S. Egan Summary Historically, the prokaryotic genome was assumed to consist of a single circular replicon. However, as more microbial genome sequencing projects are completed, it is becoming clear that multipartite genomes comprised of more than one chromosome are not unusual among prokaryotes. Chromosomes are distinguished from plasmids by the presence of essential genes as well as characteristic cell cycle-linked replication kinetics; unlike plasmids, chromosomes initiate replication once per cell cycle. The existence of multipartite prokaryotic genomes raises several questions regarding how multiple chromosomes are replicated and segregated during the cell cycle. These divided genomes also introduce questions regarding chromosome evolution and genome stability. In this review, we discuss these and other issues, with particular emphasis on the cholera pathogen Vibrio cholerae. [source] Cytogenetics of species of Chamaecrista (Leguminosae , Caesalpinioideae) native to southern BrazilBOTANICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2006ELAINE BIONDO Chromosome numbers, karyotypes, meiotic behaviour and pollen analysis are presented for species of Chamaecrista Moench (Leguminosae, Caesalpinioideae, Cassieae) native to southern Brazil: C. nictitans ssp. patellaria, C. nictitans ssp. disadena, C. repens, C. rotundifolia, C. flexuosa, C. vestita and C. desvauxii. Meiotic behaviour is reported for the first time for all the taxa and was very regular; only bivalents were formed at diakinesis and metaphase I, chromosome disjunction and segregation were regular at anaphases I and II, meiotic indexes were over 99% and pollen fertility was over 92%. Pollen grains were subprolate in C. flexuosa and C. vestita and prolate,spheroidal in the other taxa. Karyotypes were symmetrical in all six species and the data are original, except for C. nictitans ssp. patellaria. Chromosome number is presented for the first time for C. repens (2n = 16) and has been confirmed for the other taxa: 2n = 14 for C. desvauxii, 2n = 32 for the tetraploid C. nictitans ssp. patellaria and C. nictitans ssp. disadena, and 2n = 16 for the other species. These two basic numbers found in the genus, x = 7 and x = 8, point to chromosome evolution by dysploidy, which has also been accompanied by polyploidy. © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society, 2006, 150, 429,439. [source] | ||||||||||