Search results for "USA"

2006

Understanding evolutionary processes that drive genome reduction requires determining the tempo (rate) and the mode (size and types of deletions) of gene losses. In this study, we analysed five endosymbiotic genome sequences of the gamma-proteobacteria (three different Buchnera aphidicola strains, Wigglesworthia glossinidia, Blochmannia floridanus) to test if gene loss could be driven by the selective importance of genes. We used a parsimony method to reconstruct a minimal ancestral genome of insect endosymbionts and quantified gene loss along the branches of the phylogenetic tree. To evaluate the selective or functional importance of genes, we used a parameter that measures the level of ad…

Boris Ephrussi and the Synthesis of Genetics and Embryology

1991

The career of Boris Ephrussi (1901–1979) presents a series of fascinating perspectives on the intellectual and sociological difficulties that plagued those who wished to reconcile genetics and embryology during the middle of this century (2–8). Ephrussi was born in a suburb of Moscow, but spent much of his working career in France, with important periods in the United States. He made major contributions to the rapprochement between genetics and developmental biology. His work, which we believe has been undervalued both by historians of biology and by subsequent generations of biologists, is worth studying for at least three reasons: 1. Throughout his long career, he sought an adequate causa…

Can Extensive Reticulation and Concerted Evolution Result in a Cladistically Structured Molecular Data Set?

2001

Hierarchy is the main criterion for informativeness in a data set, even if no explicit reference to evolution as a causal process is provided. Sequence data (nuclear ribosomal DNA ITS) from Armeria (Plumbaginaceae) contains a certain amount of hierarchical structure as suggested by data decisiveness (DD) and distribution of tree lengths (DTL). However, ancillary evidence suggests that extensive gene flow and biased concerted evolution in these multi-copy regions have significantly shaped the ITS data set. This argument is discussed using parsimony analysis of four data sets, constructed by combining wild sequences with those from different generations of artificial hybrids (wild + F1, F2, a…

Codon usage in the siliceous sponge Geodia cydonium: highly expressed genes in the simplest multicellular animals prefer C- and G-ending codons

2001

Among a sample of 39 Geodia cydonium (Demospongiae, Porifera) genes, with an average Gh+hC content of 51.2%, extensive structural heterogeneity and considerable variations in synonymous codon usage were found. The G + C content of coding sequences and G + C content at silent codon positions (GC3S) varied from 42.4 to 59.2% and from 35.6 to 76.5%, respectively. Correspondence analysis of 39 genes revealed that putative highly expressed genes preferentially use a limited subset of codons, which were therefore defined as preferred codons in G. cydonium. A total of 22 preferred codons for 18 amino acids with synonyms in codons were identified and they all (with one exception) end with C or G. A…

Recovery of Fusarium oxysporum Fo47 mutants affected in their biocontrol activity after transposition of the Fot1 element

2002

Trouvelot, S., Olivain, C., Recorbet, G., Migheli, Q., and Alabouvette, C. 2002. Recovery of Fusarium oxysporum Fo47 mutants affected in their biocontrol activity after transposition of the Fot1 element. Phytopathology 92:936-945. To investigate the biocontrol mechanisms by which the antagonistic Fusarium oxysporum strain Fo47 is active against Fusarium wilt, a Fot1 transposon-mediated insertional mutagenesis approach was adopted to generate mutants affected in their antagonistic activity. Ninety strains in which an active Fot1 copy had transposed were identified with a phenotypic assay for excision and tested for their biocontrol activity against F. oxysporum f. sp. lini on flax in greenho…

Recovery of mutants impaired in pathogenicity after transposition of Impala in Fusarium oxysporum f.sp. melonis

2000

The ability of transposon impala to inactivate genes involved in pathogenicity was tested in Fusarium oxysporum f. sp. melonis. Somatic excision of an impala copy inserted in the nitrate reductase-encoding niaD gene was positively selected through a phenotypic assay based on the restoration of nitrate reductase activity. Independent excision events were analyzed molecularly and shown to carry reinsertedimpala in more than 70% of the cases. Mapping of reinserted impala elements on large NotI-restriction fragments showed that impala transposes randomly. By screening 746 revertants on plants, a high proportion (3.5%) of mutants impaired in their pathogenic potential was recovered. According t…

Genome-Based Examination of Chlorophyll and Carotenoid Biosynthesis in Chlamydomonas reinhardtii    

2005

Abstract The unicellular green alga Chlamydomonas reinhardtii is a particularly important model organism for the study of photosynthesis since this alga can grow heterotrophically, and mutants in photosynthesis are therefore conditional rather than lethal. The recently developed tools for genomic analyses of this organism have allowed us to identify most of the genes required for chlorophyll and carotenoid biosynthesis and to examine their phylogenetic relationships with homologous genes from vascular plants, other algae, and cyanobacteria. Comparative genome analyses revealed some intriguing features associated with pigment biosynthesis in C. reinhardtii; in some cases, there are additiona…

Approche géoarchéologique sur la nécropole monumentale d'Escolives-Ste-Camille (Yonne): un site en bordure d'un chenal de l'Yonne à l'époque néolithi…

2006

Die Herausbildung des Mittelneolithikums I Cerny wird im Südosten des Pariser Beckens von dem Auftauchen monumentaler Nekropolen in den Sohlen von Flusstälern begleitet. Die Eingliederung dieser Bestattungsplätze in die Landschaft lässt eine ausdrückliche Absicht erkennen und tradiert möglicherweise den Anspruch einer Gruppe, ihr Gebiet deutlich als das ihre auszuweisen. Vor diesem Hintergrund waren die Ausgrabungen der Nekrolpole von Escolives-Sainte-Camille ‘La Pièce de l'Étang’ von Untersuchungen begleitet, welche die Umgebung des Fundplatzes in neolithischer Zeit bestimmen sollten. Es ging darum, die Einfügung des Platzes zwischen zwei Paläorinnen in ihrem hydrographischen Milieu zu rek…

Centres and peripheries in Finland: Granger causality tests using panel data

2009

Abstract Despite their importance from a policy point of view, empirical studies on the effects of growth centres in their regions are rare. This paper analyses mutual relationships between growth processes in centres and their surrounding hinterlands in 19 Finnish regions. Annual population data from the period 1970–2004 are used. A novel testing procedure based on an extension of the Granger causality definition in a panel data context is applied. Heterogeneity between regions is allowed. Both the homogeneous non-causality hypothesis and the homogeneous causality hypothesis are rejected. Causal processes prove to be heterogeneous. Causality from centres to peripheries is found for nine re…

Characteristics and definition and characterization of new Valencian urban areas

2014

La expansión urbanística, junto con la generalización de los procesos de descentralización residencial y económica, ha conducido a un nuevo modelo de ciudad dispersa caracterizado por la dificultad de establecer sus límites precisos. Utilizando un índice de densidad de ejes viarios procedente de una fuente comercial, y por tanto fácilmente actualizable, se ha delimitado el fenómeno urbano en la Comunidad Valenciana. Se discute la utilidad de la metodología y su capacidad para captar el hecho urbano a partir del contraste con la cartografía de usos del suelo de Corine. Urban expansion, along with the generalization of the processes of residential and economic decentralization has led to a ne…