ABSTRACT
The class Bdelloidea of the phylum Rotifera is the largest well studied eukaryotic taxon in which males and meiosis are unknown, and the only one for which these indications of ancient asexuality are supported by cytological and molecular genetic evidence. We estimated the rates of synonymous and nonsynonymous substitutions in the hsp82 heat shock gene in bdelloids and in facultatively sexual rotifers of the class Monogononta, employing distance based and maximum likelihood methods. Relative-rate tests, using acanthocephalan rotifers as an outgroup, showed slightly higher rates of nonsynonymous substitution and slightly lower rates of synonymous substitution in bdelloids as compared with monogononts. The opposite trend, however, was seen in intraclass pairwise comparisons. If, as it seems, bdelloids have evolved asexually, an equality of bdelloid and monogonont substitution rates would suggest that the maintenance of sexual reproduction in monogononts is not attributable to an effect of sexual reproduction in limiting the load of deleterious nucleotide substitutions.
Subject(s)
Heat-Shock Proteins/genetics , Mutation , Rotifera/physiology , Acanthocephala/genetics , Acanthocephala/physiology , Animals , Base Sequence , HSP90 Heat-Shock Proteins , Molecular Sequence Data , Phylogeny , Reproduction , Rotifera/genetics , Saccharomyces cerevisiae ProteinsABSTRACT
A neutral cleanup method for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in milk and animal tissue was developed involving solvent extraction and liquid adsorption chromatography on magnesia-Celite 545, alumina, and Florisil. Cleaned up extracts were subjected to dual-ion analysis in a direct probe high resolution mass spectrometer, interfaced to a multi-channel analyzer for signal averaging. Calibration experiments were carried out with bovine milk and beef fat samples containing added TCDD. The 37CI isotopic isomer of TCDD was added as an internal standard. The response was linear for concentrations in the ppt range, with recoveries about 80%. Milk from a cow fed TCDD was cleaned up by the neutral procedure or, alternatively, a base-acid extraction procedure. The TCDD recoveries for both procedures were essentially the same. Recoveries of TCDD from liver samples of a rat given 14C-TCDD intraperitoneally, subjected to neutral cleanup and radioactive counting, were about 70%.
Subject(s)
Adipose Tissue/analysis , Dioxins/analysis , Milk/analysis , Polychlorinated Dibenzodioxins/analysis , Animals , Cattle , Hydrogen-Ion Concentration , Liver/analysis , Mass Spectrometry , Methods , Rats , SolventsABSTRACT
A general model is proposed for genetic recombination. Its essential new feature is the hypothesis that recombination is initiated by a single-strand (or asymmetric) transfer, which may, after isomerization, become a two-strand (or symmetric) exchange. The likelihood of this transition from asymmetric to symmetric strand exchange determines certain characteristic features of recombination in any particular organism.
