Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “EVOLUTION”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9Linked to original sources
PubMed2004

Morphological evolution in sea urchin development: hybrids provide insights into the pace of evolution.

Hybridisations between related species with divergent ontogenies can provide insights into the bases for evolutionary change in development. One example of such hybridisations involves sea urchin species that exhibit either standard larval (pluteal) stages or those that develop directly from embryo to adult without an intervening feeding larval stage. In such crosses, pluteal features were found to be restored in fertilisations of the eggs of some direct developing sea urchins (Heliocidaris erythrogramma) with the sperm of closely (Heliocidaris tuberculata) and distantly (Pseudoboletia maculata) related species with feeding larvae. Such results can be argued to support the punctuated equilibrium model-conservation in pluteal regulatory systems and a comparatively rapid switch to direct development in evolution.1,2 Generation of hybrids between distantly related direct developers may, however, indicate evolutionary convergence. The 'rescue' of pluteal features by paternal genomes may require maternal factors from H. erythrogramma because the larva of this species has pluteal features. In contrast, pluteal features were not restored in hybridisations with the eggs of Holopneustes purpurescens, which lacks pluteal features. How much of pluteal development can be lost before it cannot be rescued in such crosses? The answer awaits hybridisations among indirect and direct developing sea urchins differing in developmental phenotype, in parallel with investigations of the genetic programs involved.

Animals↗
PubMed1996

Dynamic analysis of the evolution of a novel genetic system: the evolution of ciliate meiosis.

Many ciliates undergo a peculiar form of meiosis in which four haploid nuclei are produced, three are digested, and the single remaining nucleus undergoes mitosis. It is paradoxical that such a meiotic process occurs, since one could imagine several other less costly ways of producing two nuclei. Here we investigate a possible resolution of this paradox. It is shown that the spread of a selfish gene that kills the mate not containing it, provides the conditions for the spread of a costly modifier of the form of meiosis. We investigate the conditions under which the modifier can fixate.

Animals↗
PubMed1992

Evolution of the plastid ribosomal RNA operon in a nongreen parasitic plant: accelerated sequence evolution, altered promoter structure, and tRNA pseudogenes.

The nucleotide sequence of a 7.4 kb region containing the entire plastid ribosomal RNA operon of the nongreen parasitic plant Epifagus virginiana has been determined. Analysis of the sequence indicates that all four rRNA genes are intact and almost certainly functional. In contrast, the split genes for tRNA(Ile) and tRNA(Ala) present in the 16S-23S rRNA spacer region have become pseudogenes, and deletion upstream of the 16S rRNA gene has removed a tRNA(Val) gene and most of the promoter region for the rRNA operon. The rate of nucleotide substitution in 16S and 23S rRNAs is several times higher in Epifagus than in tobacco, a related photosynthetic plant. Possible reasons for this, including relaxed translational constraints, are discussed.

Base Sequence↗
PubMed1978

The evolution of the environment and its influence on the evolution of life.

Thermodynamic data and known paleogeological data were used to deduce when and what elements (compounds) were readily available during the whole history of the earth. On the basic assumption that available compounds would dictate the type of organisms to emerge, we attempted to derive a kind of evolutionary tree. This was then compared with the existing evolutionary trees derived from the sequences of proteins and polynucleotides.

Animals↗