Showing papers on "Mutation (genetic algorithm) published in 1974"

IS2, a genetic element for turn-off and turn-on of gene activity in E. coli.

Abstract: Genetic analysis of the constitutive revertants of the IS2 mutation 308 located in the control region of the gal operon on the bacterial chromosome suggests that the constitutive expression of the gal genes might be due to inversion of IS2.

How do antibiotic-producing microorganisms avoid suicide?

Abstract: Because antibiotics are among the most potent compounds made by living organisms, it is remarkable that producing strains can remain metabolically active and viable in their own soups, which in some cases contain a concentration of antibiotic as high as 50 mM. Despite this apparent insensitivity, when a producing strain is inoculated into a fresh medium that contains an even lower concentration of antibiotic, adverse effects on growth are observed. In this contribution, I shall examine this apparent contradiction and present some possible answers to the question of how antibiotic-producing microorganisms manage to stay alive. I shall also examine the possible functions of antibiotics in the lives of the producing microorganisms.

Further observations on the hairpin-tail (Thp) mutation in the mouse

Abstract: The hairpin-tail allele (Thp) of brachyury (T) on chromosome 17 of the mouse is unique in that the phenotype of heterozygous offspring depends on which parent contributed the Thp.The present paper offers formal proof of this fact using the th2 allele of T as a marker, and discusses possible modes of action of the hairpin allele.

The Decay of Genetic Variability in Geographically Structured Populations

Abstract: The ultimate rate and pattern of approach to equilibrium of a diploid, monoecious population subdivided into a finite number of equal, large, panmictic colonies are calculated. The analysis is restricted to a single locus in the absence of selection, and every mutant is assumed to be new to the population. It is supposed that either the time-independent backward migration pattern is symmetric in the sense that the probability that an individual at position x migrated from y equals the probability that one at y migrated from x, or it depends only on displacements and not on initial and final positions. Generations are discrete and nonoverlapping. Asymptotically, the rate of convergence is approximately (I-u)2t[I-(2NT)-1]t, where u, NT, and t denote the mutation rate, total population size, and time in generations, respectively; the transient part of the probability that two homologous genes are the same allele is approximately independent of their spatial separation. Thus, in this respect the population behaves as if it were panmictic.

A population birth-and-mutation process, I: explicit distributions for the number of mutants in an old culture of bacteria

Abstract: Luria and Delbruck (1943) have observed that, in old cultures of bacteria that have mutated at random, the distribution of the number of mutants is extremely long-tailed. In this note, this distribution will be derived (for the first time) exactly and explicitly. The rates of mutation will be allowed to be either positive or infinitesimal, and the rate of growth for mutants will be allowed to be either equal, greater or smaller than for non-mutants. Under the realistic limit condition of a very low mutation rate, the number of mutants is shown to be a stable-Levy (sometimes called “Pareto Levy”) random variable, of maximum skewness s, whose exponent α is essentially the ratio of the growth rates of non-mutants and of mutants. Thus, the probability of the number of mutants exceeding the very large value m is proportional to m –α–1 (a behavior sometimes referred to as “asymptotically Paretian” or “hyperbolic”). The unequal growth rate cases α ≠ 1 are solved for the first time. In the α = 1 case, a result of Lea and Coulson is rederived, interpreted, and generalized. Various paradoxes involving divergent moments that were encountered in earlier approaches are either absent or fully explainable. The mathematical techniques used being standard, they will not be described in detail, so this note will be primarily a collection of results. However, the justification for deriving them lies in their use in biology, and the mathematically unexperienced biologists may be unfamiliar with the tools used. They may wish for more details of calculations, more explanations and Figures. To satisfy their needs, a report available from the author upon request has been prepared. It will be referred to as Part II.

The role of genetic drift in the differentiation of icelandic and norwegian cattle.

Abstract: Gene frequency differences between populations can arise from (1) random genetic drift, the accumulation of sampling variance over several generations, (2) selective forces acting differentially on the populations, (3) differential migration from a population with different gene frequencies, and/or (4) distinct mutation histories, resulting in the chance occurrence of a particular allele in one population, but not in others in the absence of migration equalizing such effect. If differential gene flow from outside has not occurred and no unique mutations are present, the problem of deciding between drift and selection as the cause of observed differences still remains difficult. The effects of selective forces can be predicted only if the selection coefficients are known, an exceedingly rare circumstance, but the expected magnitude of difference due to random genetic drift can be predicted on the basis of demographic data which are relatively easy to obtain. However, little is known about the historical demography of most species, man being the major exception. Another species for which both genetic and demographic data are available is domestic cattle. The genetic data on cattle comes mostly from blood typing. Cattle blood typing has a long history (Stormont, 1962), and is routinely done in many countries as the best method of parentage control. The specific demographic (“bosographic”) data we have analyzed come from Iceland and Norway. Comparable genetic data are also available on these breeds, providing a uniquely suitable material for comparing the expected genetic change due to drift with observed gene frequency differences: (1) they have been separated from each other, and probably all other breeds as well, for about 1000 years, a sizable length of time; (2) they are very likely to share a common origin in Norway; (3) there are some historical demographic data available on both Icelandic and Norwegian breeds, and (4) there are good genetic data available on the present day populations. With this material we shall study whether random genetic drift alone can account for the observed differences among Norse cattle breeds.

Accurate repair of ultraviolet-induced damage in Micrococcus radiodurans.

Abstract: UV-induced mutation in the very radiation-resistant bacterium Micrococcus radiodurans was investigated. Forward mutation of the wild type to resistance to trimethoprim and reversion of a temperature-sensitive mutant were studied. Both the wild type and the temperature-sensitive mutant were found to be non-mutable by UV-radiation, but were sensitive to mutation by N -methyl- N ′-nitro- N -nitrosoguanidine (NTG). The wild type was also resistant to mutation by 4-nitroquinoline- N -oxide (4NQO). Neither strain was sensitized to UV-induced mutation by exposure to caffeine after irradiation. It is concluded that, unlike other bacteria in which high resistance to UV-induced killing is associated with sensitivity to UV-induced mutation, repair of UV-induced damage in M. radiodurans is accurate.

Suppression of methionine mutants in Coprinus

Abstract: The met-1-1 mutation in Coprinus lagopus is known to be suppressed by five recessive non-allelic suppressor genes (sup-1 to sup-5). Two of these genes complement normally in heterozygotes but the other three fail to complement each other in any combination. Four of the suppressor genes, sup-1, sup-2, sup-3 and sup-5, were tested for ability to suppress met-1-2 a second met-1 mutation. Non-identity of the two met-1 alleles was first confirmed by demonstrating intragenic recombination. The complementing suppressors, sup-1 and sup-2, proved to be allele unspecific and suppressed both met-1 mutations. The non-complementing suppressors, sup-3 and sup-5, were allele specific and could only suppress the met-1-1 mutation. This is interpreted to mean that sup-1 and sup-2 act indirectly to circumvent the metabolic lesion caused by any met-1 mutation whereas sup-3 and sup-5 are missense informational suppressors involving modified tRNA species which specifically mistranslate the met-1-1 mutant codon.

Misrepair mutagenesis in bacteriophage T4.

Abstract: The T4 mutations px, y and 1206 inactivate an error-prone recombination-like repair system, reducing or abolishing mutagenesis by UV irradiation, MMS, and white light irradiation in the presence of the photosensitizer 8MOP. Both px and y increase some spontaneous mutation rates and slightly enhance proflavin mutagenesis; neither mutation affects thymineless or 2AP mutagenesis appreciably, but both mildly enhance 5BU mutagenesis. The mutation hm promotes UV, MMS, photodynamic, thymineless, and base analog mutagenesis, in addition to spontaneous base pair substitution mutation. It does not, however, markedly affect proflavin mutagenesis. The px mutation maps in the vicinity of genes 41-56, and the hm mutation maps in the vicinity of genes rI-v.

Morphological mutants of Escherichia coli K12. Mapping of the env C mutation.

Abstract: Morphological env C mutation affects the septum and leads to chain formation. Genetic analysis of a non-conditional env C mutant is performed; the gene order found is xyl-mtl-env C-pyr E.

Fosfomycin-resistant mutant of Escherichia coli.

Abstract: Fosfomycin ( 1,2-epoxypropylphosphonic acid, or phosphonomycin) is a bactericidal antibiotic isolated from strains of Streptomyces.l, 2 The elegant work of Kahan and colleagues has led to the following conclusions: this antibiotic enters the bacterial cell via either of at least two inducible transport systems for phosphate esters, namely, the L-a-glycerophosphate transport system (glpT) and the hexose phosphate transport system ( u h p ) in Escherichia coli; it irreversibly inhibits the activity of phosphoenolpyruvate (PEP) :uridine diphospho-N-acetylglucosamine ( UDPGlcN Ac ) enolpyruvyl transferase, the first unique enzyme in the biosynthesis of uridine diphospho-N-acetylmuramyl peptides.3, 1 We were interested in the studies of fosfomycin-resistant mutants of E. coli, especially those in which the drug resistance is either due to a derepression in the synthesis of this enzyme or to a decreased affinity of the mutant enzyme toward this antibiotic. Wild-type E . coli K-12 strains (AB1157 and HfrH) were mutagenized with ethyl methanesulfonate or nitrosoguanidine and allowed to grow in enriched media at 30\" C overnight for phenotypic expression. Fosfomycin t was added to a final concentration of 0.3 mM. After incubation at 30\" C in the presence of this antibiotic for 5-6 hr, the remaining viable cells were washed and grown at 30\" C overnight. The survivors were found to belong to the following three classes :

The in vivo production of hemoglobin C in ruminants.

Abstract: The first indication for the production of a hemoglobin type in an anemic sheep that is different from that of the nonanemic animal was obtained in the late 1950's when changes in the relative quantities of the two hemoglobins A and B were observed in a sheep that was infected with Strongylus larvae causing a mild, chronic anemia.' These data are presented in FIGURE 1. Independent studies by three groups of investigators, namely Blunt and Evans,2 van W e t and Huisman,3 and Braend, Efremov and Helle,j have later shown that Hb C may completely replace Hb A in severely anemic animals but not Hb B. This phenomenon is illustrated in FIGURE 2; Hb A is partially replaced by Hb C in the anemic AB sheep whereas the percentage of Hb B is not altered.

Directed mutation in Streptomyces lipmanii.

Abstract: Streptomyces lipmanii produces two β-lactam antibiotics, penicillin N and 7-(5-carboxyvaleramido)-7-methoxycephalosporanic acid. A method has been developed whereby mutation can be directed toward ...

Genes controlling chromosome activity. An X-linked mutation affecting Y-lampbrush loop activity in Drosophila hydei.

Abstract: Normal propagation of Y chromosome lampbrush loops was used as a screening tool in order to recover X-linked mutations controling Y chromosome activation. The nature of the most extreme mutationthus recovered, sterile (1) XL2, is described. It is a recessive gene mutation, readily mapped 2 cross over units distally to white. The mutation exerts its sterilizing effect by blocking normal unfolding of all Y lampbrush loops, but does not affect the unique shape of each diminutive loop. The degree to which a loop forming site is developed is partially temperature sensitive. It is independent however, on its map location or the dose of homologous as well as heterologous sites. It was provisionally concluded therefore that site response to the XL2 effect is a stage specific and not a quantitative one. The possible ways by which non homologous genes control Y chromosome activity are discussed.