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A Atlan

Publications and source records attributed to A Atlan.

6 recordsLinked to original sources
PubMed1998

Capillary zone electrophoresis in normal or reverse polarity separation modes for the analysis of hydroxy acid oligomers in neutral phosphate buffer.

Capillary zone electrophoresis (CZE) with neutral phosphate buffer as the background electrolyte was used to analyse water-soluble oligomers obtained by polycondensation of racemic lactic acid. Two CZE separation modes were tested. The first mode was based on normal separation (injection at the anodic side) using a fused-silica capillary. Eight peaks were observed within a 60-min migration time range. They were ascribed to dimer and higher water-soluble oligomers. Peaks from dimer to tetramer were split due to sensitivity for the fine structures at the level of the distribution of chiral lactic acid moieties in oligomer chains. The second mode was based on reverse separation (injection at the cathodic side) using a fused-silica capillary modified by adsorption of a polycation on its inner wall. Under these conditions, oligomers were rapidly separated without peak splitting. Considering the forces which are involved in CZE, data were plotted as a function of 1/t scale, according to the equation [signal]=f((-1)(k)/t) where k=0 and k=1 for normal and reverse separation modes, respectively. Such a plot allowed direct comparison between the various runs after a simple translation along the 1/t axis, regardless of the separation mode and the variation of electroosmotic flow. The second separation mode allowed separation of 3-hydroxybutyric acid and 6-hydroxyhexanoic acid oligomers. For the former series of oligomers, a side reaction generating crotyl bonds was observed due to the high sensitivity of CZE. It was shown that separation was governed by the ratio charge/mass of the oligoesters whatever their structure.

Buffers↗
PubMed1996

Genetic conflicts.

Self-promoting elements (also called ultraselfish genes, selfish genes, or selfish genetic elements) are vertically transmitted genetic entities that manipulate their "host" so as to promote their own spread, usually at a cost to other genes within the genome. Examples of such elements include meiotic drive genes and cytoplasmic sex ratio distorters. The spread of a self-promoting element creates the context for the spread of a suppressor acting within the same genome. We may thus say that a genetic conflict exists between different components of the same genome. Here we investigate the properties of such conflicts. First we consider the potential diversity of genomic conflicts and show that every genetic system has potential conflicts. This is followed by analysis of the logic of conflicts. Just as Evolutionarily Stable Strategy (ESS) terminology provides a short cut for discussion of much in behavioral ecology, so the language of modifier analysis provides a useful terminology on which to base discussions of conflicts. After defining genetic conflict, we provide a general analysis of the conflicting parties, and note a distinction between competing and conflicting genes. We then provide a taxonomy of possible short- and long-term outcomes of conflicts, noting that potential conflict in an unconstrained system can never be removed, and that the course of evolution owing to conflict is often unpredictable. The latter is most particularly true for strong conflicts in which suppressors may take surprising forms. The possibility of extended conflicts in the form of "arms races" between element and suppressor is illustrated. The peculiar redundancy of these systems is one possible trace of conflict, and others are discussed. That homologous conflicts may find highly different expression is discussed by referring to the mechanistic differences that are thought to underlie the action of the two best-described meiotic drive genes, and by the multiplicity of forms of cytoplasmic sex ratio distorters. The theoretical analysis establishes a logical basis for thinking about conflicts, but fails to establish the importance of conflict in evolution. We illustrate this contentious issue through consideration of some phenomena for whose evolution conflict has been proposed as an important force: the evolution of sex, sex determination, species, recombination, and uniparental inheritance of cytoplasmic genes. In general, it is proposed that conflict may be a central force in the evolution of genetic systems. We conclude that an analysis of conflict and its general importance in evolution is greatly aided by application of the concept of genetic power. We consider the possible components of genetic power and ask whether and how power evolves.

Animals↗
PubMed1996

Dynamics of plant mitochondrial genome: model of a three-level selection process.

The plant mitochondrial genome is composed of a set of molecules of various sizes that generate each other through recombination between repeated sequences. Molecular observations indicate that these different molecules are present in an equilibrium state. Different compositions of molecules have been observed within species. Recombination could produce deleted molecules with a high replication rate but bearing little useful information for the cell (such as "petite" mutants in yeast). In this paper we use a multilevel model to examine selection among rapidly replicating incomplete molecules and relatively slowly replicating complete molecules. Our model simulates the evolution of mitochondrial information through a three-level selection process including intermolecular, intermitochondrial, and intercellular selection. The model demonstrates that maintenance of the mitochondrial genome can result from multilevel selection, but maintenance is difficult to explain without the existence of selection at the intermitochondrial level. This study shows that compartmentation into mitochondria is useful for maintenance of the mitochondrial information. Our examination of evolutionary equilibria shows that different equilibria (with different combinations of molecules) can be obtained when recombination rates are lower than a threshold value. This may be interpreted as a drift-mutation balance.

Genome, Plant↗
PubMed1995

Variability within the Seychelles cytoplasmic incompatibility system in Drosophila simulans.

In Drosophila simulans, we described a cytoplasmic incompatibility (CI) system (Seychelles) restricted to insular populations that harbor the mitochondrial type SiI. Since then, these populations have been shown to be heterogeneous, some being infected by one Wolbachia genetic variant only (wHa), while others are infected simultaneously by wHa and by another variant (wNo) always found in association with wHa. We have experimentally obtained two D. simulans strains only infected by the wNo variant. This variant determines its own cytoplasmic incompatibility type. In particular, the cross between wNo-bearing flies and wHa-bearing ones is bidirectionally incompatible. The Seychelles CI type, stricto sensu, is distinguished by being determined by the simultaneous presence of two Wolbachia variants that we found to be mutually incompatible. In addition, we observed incomplete maternal transmission of the Wolbachia.

Animals↗
PubMed1993

A model simulating the dynamics of plant mitochondrial genomes.

Molecular evolution of the plant mitochondrial genome involves rearrangements due to the presence of highly recombining repeated sequences. As a result, this genome is composed of a set of molecules of various sizes that generate each other through recombination. The model presented simulates the evolution of various frequencies of the different types of molecules over successive cell cycles. It considers the mitochondrial genome as a population of circular molecules evolving through recombination, replication and random segregation. The model parameters are the rates of recombination of each sequence, the frequency of each type of recombination, the replication rates of the circles and the total amount of mitochondrial DNA per cell. This model demonstrates that high recombination rates lead to rapid deletions of sequences in the absence of selection. The frequency of deletion is dependent on the simulated reproductive mechanism. The conditions leading to reversible or irreversible rearrangements were also investigated.

Biological Evolution↗