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At least 37 records · Page 2Linked to original sources
PubMed1990

Evolution of the autosomal chorion cluster in Drosophila. IV. The Hawaiian Drosophila: rapid protein evolution and constancy in the rate of DNA divergence.

Autosomal chorion genes s18, s15, and s19 are shown to diverge at extremely rapid rates in closely related taxa of Hawaiian Drosophila. Their nucleotide divergence rates are at least as fast as those of intergenic regions that are known to evolve more extensively between distantly related species. Their amino acid divergence rates are the fastest known to date. There are two nucleotide replacement substitutions for every synonymous one. The molecular basis for observed length and substitution mutations is analyzed. Length mutations are strongly associated with direct repeats in general, and with tandem repeats in particular, whereas the rate for an average transition is twice that for an average transversion. The DNA sequence of the cluster was used to construct a phylogenetic tree for five taxa of the Hawaiian picture-winged species group of Drosophila. Assignment of observed base substitutions occurring in various branches of the tree reveals an excess of would-be homoplasies in a centrally localized 1.8-kb segment containing the s15 gene. This observation may be a reflection of ancestral excess polymorphisms in the segment. The chorion cluster appears to evolve at a constant rate regardless of whether the central 1.8-kb segment is included or not in the analysis. Assuming that the time of divergence of Drosophila grimshawi and the planitibia subgroup coincides with the emergence of the island of Kauai, the overall rate of base substitution in the cluster is estimated to be 0.8% million years, whereas synonymous sites are substituted at a rate of 1.2% million years.

Amino Acid Sequence↗
PubMed1978

Attempts at simulating evolution by a computer: I. evolution of proteins under prebiotic conditions.

The effect of random mutations of five identical pentapeptides that have been inserted arbitrarily along a 100 amino acid-long protein chain has been studied by computer simulation. The method used was the application of mutation probability matrix for 2 PAMs of Dayhoff (1972) repeatedly to obtain the desired length of time. The results indicated that, given sufficient length of time, even the identical peptides could become drastically altered and in order to recognise them as stemming from the same origin one has to use reasonable statistical significance thresholds.

Amino Acid Sequence↗
PubMed1978

Evolution of the nervous system: role of ontogenetic mechanisms in the evolution of matching populations.

Nervous systems are composed of populations of cells that are synaptically connected in a highly predictable manner, and we have called two interconnected populations a pair of matching populations. Heritable genetic changes that affect a pair of matching populations can be evolutionary only when this matching quality is not disrupted. We distinguish two types of heritable change. Concordant heritable changes autonomously preserve the match and are thus automatically candidates for what we call type I evolutionary change. Nonconcordant heritable changes, on the other hand, are those that do not autonomously preserve the match. Those nonconcordant heritable changes that can use other normally present ontogenetic mechanisms to preserve the match are candidates for what we call type II evolutionary change. One example of such an ontogenetic mechanism consists of the production of excess neuroblasts and the subsequent weeding out (via cell death) of those that do not successfully match. Because normal ontogeny is an integral part of type II evolutionary change, ontogenetic manipulations can give evolutionary insights. Embryonic graft experiments, in particular, can elucidate the nature of ontogenetic mechanisms that participate in type II changes. Thus, some developmental experiments can be considered to be evolutionary experiments.

Animals↗
PubMed1990

The pattern of mammalian evolution and the relative rate of molecular evolution.

The rates of nucleotide substitution at four genes in four orders of eutherian mammals are compared in relative rate tests using marsupial orthologs for reference. There is no evidence of systematic variation in evolutionary rate among the orders. The sequences are used to reconstruct the phylogeny of the orders using maximum likelihood, parsimony and compatibility methods. A branching order of rodent then ungulate then primate and lagomorph is overwhelmingly indicated. The nodes of the nucleotide based cladograms are widely separated in relation to the total lengths of the branches. The assumption of a star phylogeny that underlies Kimura's test for molecular evolutionary rate variation is shown to be invalid for eutherian mammals. Excess variance in nucleotide or amino acid differences between mammalian orders, above that predicted by neutral theory is explained better by variation in divergence time than by variation in evolutionary rate.

Animals↗
PubMed1979

Effect of pH on chloroplast photosynthesis. Inhibition of O2 evolution by inorganic phosphate and magnesium.

1. The pH optimum of CO2-dependent O2 evolution by barley (Hordeum vulgare L.) chloroplasts was found to be between 7.8 and 8.2. The addition of 1 mM MgCl2 in the dark inhibited O2 evolution over the entire pH range tested and resulted in a much sharper pH profile centered around pH 8.2. 2. The pH optimum for O2 evolution, in the presence and absence of 1 mM MgCl2, was acid-shifted 0.3--0.4 pH units by 2 mM NH4Cl. The pH optimum of O2 evolution, with and without 1 mM MgCl2, was base-shifted by 2 mM sodium acetate, approx. 0.5 pH units relative to the controls. 3. O2 evolution in the presence of bicarbonate plus 3-phosphoglycerate or ribose-5-phosphate was considerably less sensitive to pH than CO2-dependent O2 evolution in the absence of substrate. With these substrates, both in the presence and absence of 1 mM MgCl2, the pH optimum was broad and was centered around pH 7.8. 4. Inhibition of CO2-dependent O2 evolution by inorganic phosphate and magnesium increased as the pH of the reaction mixture was decreased below the optimum. Decreasing the pH from 8.2 to 7.6, reduced over 3-fold the concentration of inorganic phosphate required to inhibit O2 evolution completely. For magnesium, a similar change in pH reduced the concentration required to inhibit O2 evolution 50% approx. 5-fold. At pH 8.2, magnesium inhibition required inorganic phosphate. Magnesium was not required for inhibition of O2 evolution by inorganic phosphate, but incresaed the relative inhibition observed. 5. Illumination of intact barley chloroplasts increased the activity of NADP-glyceraldehyde-3-P dehydrogenase, phosphoribulokinase and fructose-1,6-diphosphatase. MgCl2 and inorganic phosphate prevented this increase in enzyme activity at concentrations that completely inhibited CO2-dependent O2 evolution. 6. The results obtained suggest that magnesium inhibition of O2 evolution may be caused by enhanced phosphate exchange across the chloroplast envelope.

Chloroplasts↗