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Genetics. Dec 1980; 96(4): 801–817.
PMCID: PMC1219302

Selective Neutrality of 6pgd Allozymes in E. COLI and the Effects of Genetic Background

Abstract

We have used gluconate-limited chemostats to study selective differences between isogenic strains of Escherichia coli K12 into which four naturally occurring alleles coding for allozymes of 6-phosphogluconate dehydrogenase (6PGD) had been transferred. The limit of detectability of selection with our procedures is a selection coefficient of 0.5%. In the normal E. coli K12 genetic background, all alleles are selectively neutral or nearly neutral. The absence of detectable selection does, however, depend on genetic background and on such environmental factors as cell density. In a genetic background containing a mutation that cuts off the alternative metabolic route for 6-phosphogluconate, selection between allozymes can be detected, and the selection is in the direction expected from the measured apparent Km values of the allozymes. Even when the alternative metabolic route is not blocked by mutation, one of the 6PGD allozymes has a detrimental, but density-dependent, interaction with a mutation conferring resistance to bacteriophage T5. In all cases, the observed selection is due to the allozymes themselves (or to associated regulatory elements), as the selection disappears when the chemostats are limited by a different carbon source (ribose plus succinate). Nevertheless, the four alleles do seem to be selectively neutral or nearly neutral in the normal E. coli K12 genetic background. Moreover, the distribution of allele frequencies in natural populations of E. coli is in accord with the expectations of selective neutrality.

I am inclined to suspect that we see, at least in some [cases], variations which are of no service to the species, and which consequently have not been seized on and rendered definite by natural selection.... Variations neither useful nor injurious would not be affected by natural selection, and would be left either a fluctuating element, as perhaps we see in certain polymorphic species, or would ultimately become fixed.... We may easily err in attributing importance to characters, and in believing that they have been developed through natural selection;... many structures are now of no direct use to their possessors, and may never have been of any use to their progenitors.... [On the other hand,] we are much too ignorant in regard to the whole economy of any organic being to say what slight modifications would be of importance or not.

Charles Darwin, 1872

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.
  • Allard RW, Babbel GR, Clegg MT, Kahler AL. Evidence for coadaptation in Avena barbata. Proc Natl Acad Sci U S A. 1972 Oct;69(10):3043–3048. [PMC free article] [PubMed]
  • Bachmann BJ, Low KB. Linkage map of Escherichia coli K-12, edition 6. Microbiol Rev. 1980 Mar;44(1):1–56. [PMC free article] [PubMed]
  • Cavener DR, Clegg MT. Dynamics of correlated genetic systems. IV. Multilocus effects of ethanol stress environments. Genetics. 1978 Nov;90(3):629–644. [PMC free article] [PubMed]
  • Christiansen FB, Frydenberg O. Geographical patterns of four polymorphisms in Zoarces viviparus as evidence of selection. Genetics. 1974 Aug;77(4):765–770. [PMC free article] [PubMed]
  • Clegg MT, Allard RW. Patterns of Genetic Differentiation in the Slender Wild Oat Species Avena barbata. Proc Natl Acad Sci U S A. 1972 Jul;69(7):1820–1824. [PMC free article] [PubMed]
  • Day TH, Hillier PC, Clarke B. The relative quantities and catalytic activities of enzymes produced by alleles at the alcohol dehydrogenase locus in Drosophila melanogaster. Biochem Genet. 1974 Feb;11(2):155–165. [PubMed]
  • van Delden W, Boerema AC, Kamping A. The alcohol dehydrogenase polymorphism in populations of Drosophila melanogaster. I. Selection in different environments. Genetics. 1978 Sep;90(1):161–191. [PMC free article] [PubMed]
  • van Delden W, Kamping A, van Dijk H. Selection at the alcoholdehydrogenase locus in Drosophila melanogaster. Experientia. 1975 Apr 15;31(4):418–420. [PubMed]
  • De Jong G, Scharloo W. Environmental determination of selective significance or neutrality of amylase variants in Drosophila melanogaster. Genetics. 1976 Sep;84(1):77–94. [PMC free article] [PubMed]
  • Lewontin RC, Hubby JL. A molecular approach to the study of genic heterozygosity in natural populations. II. Amount of variation and degree of heterozygosity in natural populations of Drosophila pseudoobscura. Genetics. 1966 Aug;54(2):595–609. [PMC free article] [PubMed]
  • Milkman R. Electrophoretic variation in Escherichia coli from natural sources. Science. 1973 Dec 7;182(4116):1024–1026. [PubMed]
  • Selander RK, Levin BR. Genetic diversity and structure in Escherichia coli populations. Science. 1980 Oct 31;210(4469):545–547. [PubMed]
  • de Silva AO, Fraenkel DG. The 6-phosphogluconate dehydrogenase reaction in Escherichia coli. J Biol Chem. 1979 Oct 25;254(20):10237–10242. [PubMed]

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