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  • Neutral theory  (3)
  • Amino acid code  (2)
  • AT/GC pressure  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Amino acid codes in mitochondria as possible clues to primitive codes (1981)
    Springer
    Journal of molecular evolution 18 (1981), S. 15-17 
    Details
    ISSN: 1432-1432
    Keywords: Amino acid code ; Evolution ; Primitive codes ; Mitochondria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Differences between mitochondrial codes and the universal code indicate that an evolutionary simplification has taken place, rather than a return to a more primitive code. However, these differences make it evident that the universal code is not the only code possible, and therefore earlier codes may have differed markedly from the previous code. The present universal code is probably a “frozen accident.” The change in CUN codons from leucine to threonine (Neurospora vs. yeast mitochondria) indicates that neutral or near-neutral changes occurred in the corresponding proteins when this code change took place, caused presumably by a mutation in a tRNA gene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01733206
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  • 2
    Electronic Resource
    Electronic Resource
    Evolution of the amino acid code: Inferences from mitochondrial codes (1983)
    Springer
    Journal of molecular evolution 19 (1983), S. 219-225 
    Details
    ISSN: 1432-1432
    Keywords: Amino acid code ; Molecular evolution ; Mitochondrial code ; Anticodons ; Archetypal code
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The amino acid code is usually presented as a table of 64 codons. Actually the code results from the action of tRNA molecules that carry amino acids to codons in mRNA by means of codon-anticodon pairing. The tRNA molecules are transcribed from genes that undergo evolution and the number of anticodons can therefore increase during evolution, but the number of codons is fixed at 64. Mammalian mitochondrial codes contain only 22 anticodons for 20 amino acids as compared with 54 anticodons for 20 amino acids in the universal code. It is proposed that an archetypal code containing 16 anticodons for 15 amino acids evolved into the universal code by gene duplication, followed by mutations that modified the anticodons and amino acid acceptor sites. In substantiation of this proposal, it is noted that the mammalian mitochondrial code, is simplified by comparison with the universal code. For example, single anticodons are used for each of eight amino acids in the mammalian mitochondrial code. This simplification may represent an evolutionary retrogression towards the proposed archetypal code.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02099969
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  • 3
    Electronic Resource
    Electronic Resource
    Evolutionary constraints and the neutral theory (1984)
    Springer
    Journal of molecular evolution 21 (1984), S. 90-92 
    Details
    ISSN: 1432-1432
    Keywords: Neutral theory ; Codon usage ; Synonymous condons ; Pseudogenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The neutral theory of molecular evolution postulates that nucleotide substitutions inherently take place in DNA as a result of point mutations followed by random genetic drift. In the absence of selective constraints, the substitution rate reaches the maximum value set by the mutation rate. The rate in globin pseudogenes is about 5 × 10−9 substitutions per site per year in mammals. Rates slower than this indicate the presence of constraints imposed by negative (natural) selection, which rejects and discards deleterious mutations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02100633
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  • 4
    Electronic Resource
    Electronic Resource
    Codon reassignment (codon capture) in evolution (1989)
    Springer
    Journal of molecular evolution 28 (1989), S. 271-278 
    Details
    ISSN: 1432-1432
    Keywords: Genetic code ; Codon reassignment ; Codon capture ; Directional mutation pressure ; AT/GC pressure ; Wobble rules ; Mitochondria ; Mycoplasma ; Ciliated protozoa
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The genetic code, once thought to be “frozen”, show variations from the universal code. Variations are found in mitochondria,Mycoplasma, and ciliated protozoa. The variations results from reassignment of codons, especially stop codons. The ressignments take place by disappearance of a codon from coding sequences, followed by its reappearance in a new role. Simultaneously, a changed anticodon must appear. We discuss the role of directional mutation pressure in the pressure in the events, and we also describe the possibility that such events have taken place during early evolution of the genetic code and can occur during its present evolution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02103422
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  • 5
    Electronic Resource
    Electronic Resource
    Silent nucleotide substitutions and G+C content of some mitochondrial and bacterial genes (1986)
    Springer
    Journal of molecular evolution 24 (1986), S. 39-44 
    Details
    ISSN: 1432-1432
    Keywords: G+C content of DNA ; Codon usage ; Mitochondrial genes ; Tryptophan synthase ; Neutral theory ; Silent changes ; D loop
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The G+C content of DNA varies widely in different organisms, especially microorganisms. This variation is accompanied by changes in the nucleotide composition of silent positions in codons. (Silent positions are defined and explained in the text.) These changes are mostly neutral or near neutral, and appear to result from mutation pressure in the direction of increasing either A+T (AT pressure) or G+C(GC pressure) content. Variations in G+C content are also accompanied by substitutions at replacement positions in codons. These substituions produce changes in the amino acid content of homologous proteins. The examples studied were genes for 13 mitochondrial proteins in five species, and A and B genes for bacterial tryptophan synthase in four species. In microorganisms, varying AT and GC mutational pressures, presumably resulting from shifts in the DNA polymerase system, exert strong effects on molecular evolution by changing the G+C content of DNA. These effects may be greater than those of random drift. The effects of GC pressure on silent substitutions in the systems examined are several times as great as the effects on replacement substitutions. GC pressure is exerted on noncoding as well as coding regions in mitochondrial DNA. This is shown by the close correlation (correlation coefficient, 0.99) of the G+C content of the noncoding D loop of mitochondria with the G+C content of silent positions in the corresponding mitochondrial genes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02099949
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  • 6
    Electronic Resource
    Electronic Resource
    Relationship between G + C in silent sites of codons and amino acid composition of human proteins (1993)
    Springer
    Journal of molecular evolution 36 (1993), S. 201-213 
    Details
    ISSN: 1432-1432
    Keywords: G + C content ; Silent sites ; GC pressure ; Directional mutation pressure ; Human genome ; Codon usage ; Amino acid composition ; Neutral theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have investigated the relationship between the G + C content of silent (synonymous) sites in codons and the amino acid composition of encoded proteins for approximately 1,600 human genes. There are positive correlations between silent site G + C and the proportions of codons for Arg, Pro, Ala, Trp, His, Gln, and Leu and negative ones for Tyr, Phe, Asn, Ile, Lys, Asp, Thr, and Glu. The median proteins coded by groups of genes that differ in silent-site G + C content also differ in amino acid composition, as do some proteins coded by homologous genes. The pattern of compositional change can be largely explained by directional mutation pressure, the genetic code, and differences in the frequencies of accepted amino acid substitutions; the shifts in protein composition are likely to be selectively neutral.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00160475
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