Showing papers in "Journal of Genetics in 1992"
TL;DR: Genetic evidence is presented to show that the products ofmutS andmutL genes negativelycontrol two pathways of Cairnsian mutagenesis.
Abstract: The phenomenon of Cairnsian mutagenesis was studied inEscherichia coli mutants bearing mutations inmutS,mutL,recA andlexA genes. It is shown that development of resistance to exogenous valine could be used as an example of Cairnsian response. Strains defective inmutS andmutL show a high frequency of Cairnsian mutagenesis to valine resistance. The response inmutS mutants is dependent upon cleavability of the LexA protein whereas that inmutL is not. The latter is independent ofrecA also. The need for LexA protein cleavage inmutS mutants can be bypassed by over-production of the RecA protein due to arecA operator constitutive mutation. Genetic evidence is presented to show that the products ofmutS andmutL genes negativelycontrol two pathways of Cairnsian mutagenesis. Cairnsian response is also elicited whenmutS ormutL strains are grown under conditions wherein a required nutrient is present in sub-optimal concentrations. Random, unselected mutagenic events are likely to occur during or after Cairnsian mutagenesis provided the cells are SOS inducible.
24 citations
TL;DR: These Drosophila populations contained a polymorphism for a major factor on chromosome III controlling elevated mixed function oxidase activity together with associated organophosphorus resistance, which provided the immediate response to insecticide selection.
Abstract: Natural variation inDrosophila melanogaster populations for mixed function oxidase activity and organophosphorus resistance was studied by sampling iso-chromosomal lines and laboratory selection. A 20-fold variation in malathion LC50 was found among a sample of 25 third chromosomes from a Raleigh, North Carolina, population. These chromosomes were combined in a population that was selected for malaoxon (a toxic metabolite of malathion) resistance over 12 generations. Response to selection was rapid—within three generations—but small, less than two-fold increase in malathion LC50. Mixed function oxidase activity, as assayed by 7-ethoxycoumarin-O-deethylase, increased in parallel with malathion resistance in the selected population. In spite of the fact that this population was initially formed from strains which were homozygous for chromosome III, after 12 generations of selection for malaoxon resistance only a minority of third chromosomes could be isolated as homozygous combinations. This suggests that selection favoured heterozygous combinations of alleles with decreased fitness in the homozygous state. In a second study, a sample of 39 iso-female lines were collected from a Vineland, Ontario, population. Imidan™ (phosmet) LC50 varied 20-fold among these iso-female lines and was strongly correlated with increased 7-ethoxycoumarin-O-deethylase activity. The distribution of 7-ethoxycoumarin-O-deethylase activity was bimodal and estimates of the effective number of segregating factors by Wright’s formula were consistent with a single gene controlling extreme 7-ethoxycoumarin-O-deethylase activity differences. Vineland flies responded rapidly to selection for imidan resistance, but as with malaoxon selection only to a small degree. The 7-ethoxycoumarin-O-deethylase activity increased in imidan-selected flies to the level of the most resistant iso-female line from the sampled population. The major part of selected imidan resistance and all of the increased 7-ethoxycoumarin-O-deethylase activity were attributed to third chromosomal genes. The results suggest that theseDrosophila populations contained a polymorphism for a major factor on chromosome III controlling elevated mixed function oxidase activity together with associated organophosphorus resistance. This polymorphism provided the immediate response to insecticide selection. Other genes have minor effects and combine to give a multifactorial response to selection over longer periods of time.
8 citations
TL;DR: External supplementation of the plant growth substrate with purines or their biosynthetic intermediates fails to restore symbiosis, and the failure of complementation of these auxotrophs with the known symbiotic genes demonstrates that these mutants perhaps define a new set of genes influencing the symbiotic process in Rhizobium meliloti.
Abstract: Several purine auxotrophs were isolated inRhizobium meliloti and characterized for their nutritional requirements. They were found to produce small, irregular nodules lacking any detectable nitrogenase activity onMedicago sativa. The symbiotic aberration manifests itself only in the late developmental stage, for, (i) these purine auxotrophs infect theMedicago sativa root hairs by forming normal infection threads, and (ii) the mutants are recovered from the root nodules induced by them. External supplementation of the plant growth substrate with purines or their biosynthetic intermediates fails to restore symbiosis. This, and the failure of complementation of these auxotrophs with the known symbiotic genes, demonstrates that these mutants perhaps define a new set of genes influencing the symbiotic process inRhizobium meliloti.
6 citations
TL;DR: An interesting outcome is that plasticity can be favoured in a homogeneous environment, and it is selected against in one particular case of environmental heterogeneity: when two environments are equally likely to occur.
Abstract: The evolutionary dynamics of dominance, drift, selection and probability of environmental change is explored in the case of a single-locus two-allele model for the genetic control of phenotypic plasticity. The model represents a situation similar to the real case of the pennant/vestigial phenotype inDrosophila melanogaster. The aim of the simulation is to analyse the contribution of the four factors, of their quadratic effects, and of the two-way interactions on the equilibrium frequencies of the two alleles and on the genotypic constitution of the population. Selection turned out to be the only factor whose linear component significantly affects the system (73% of the variance explained); on the other hand, the cumulative effect of the nonlinear terms is strong (20% of the variance), and most of the interactions are highly significant. Some counter-intuitive effects of the interaction between selection and dominance or selection and frequency of the two environments are shown by means of contour plots from a multidimensional regression surface analysis. An interesting outcome is that plasticity can be favoured in a homogeneous environment, and it is selected against in one particular case of environmental heterogeneity: when two environments are equally likely to occur.
4 citations
TL;DR: A genetic model is discussed for recessively inherited disorders that do not follow a single-locus Mendelian pattern of inheritance and methods of statistical analysis of family data using the likelihood principle are described for such complex disorders.
Abstract: A genetic model is discussed for recessively inherited disorders that do not follow a single-locus Mendelian pattern of inheritance. Further complexity arising from variable age of onset is also discussed. Methods of statistical analysis of family data using the likelihood principle are described for such complex disorders. The methods are exemplified using data on families of prelingual deafness and vitiligo.
3 citations
TL;DR: It is shown that mouse-rat divergence occurred around 20 million years ago and the between-species relationships of Rattus rattus rufescens, Bandicota indica andBandicota bengalensis have been assessed and the time of divergence of the two bandicoot rats estimated.
Abstract: The interrelationships of murids and other rodent families as well as the evolutionary descent of multiple β-globins of murines are deduced from parsimony trees of relevant globin sequences. Our results show that Caviidae arises first, followed by Sciuridae which joins Muridae. In the murid line of descent Spalacinae arises first followed by two branches, one representing Cricentinae and Arvicolinae and the other Murinae. Although the rates of evolution of globin genes in the different rodent families are different, the murid branches show more or less a uniform rate of evolution of β globins. We have used this information to show that mouse-rat divergence occurred around 20 million years ago. The evolutionary rationale for the presence and the expression of different β-globin genes in murid populations is also discussed. Based on mitochondrial DNA restriction fragment analysis, the between-species relationships ofRattus rattus rufescens, Bandicota indica andBandicota bengalensis have been assessed and the time of divergence of the two bandicoot rats estimated.
3 citations
TL;DR: It will be shown that what was most important about Haldane's contributions to population genetics was a clear exposition of the general structure of genetic models of natural selection that made it possible for such models to be constructed in any context.
Abstract: It is well known that R. A. Fisher, J. B. S. Haldane and S. Wright were primarily responsible for laying down the foundations of theoretical population genetics in the 1920s (Sarkar 1992a). There were others such as S. Chetverikov (see Adams 1968), who were no doubt important for the conceptual innovations that they introduced but, nevertheless, were not remotely as influential as the canonical triumvirate in the period 1918-1932 when theoretical population genetics came of age. What is far less clear is the exact nature of the individual contributions of Fisher, Haldane and Wright, that is, the differences between, and the relative importance of, these contributions. For Fisher and Wright, at least part of such an analysis has been previously attempted (see, e.g., Provine 1985, 1986) but Haldane's role has largely been ignored probably because of his comparatively lesser influence on theoretical population genetics since 1935. The purpose of this paper is to use the occasion of Haldane's birth centenary to .begin to remedy this lacuna. It will first be shown (section 2) that what was most important about Haldane's contributions to population genetics was a clear exposition of the general structure of genetic models of natural selection that made it possible for such models to be constructed in any context. Some of the more important models that Haldane constructed in the 1920s will then be briefly discussed (section 3). Finally (section 4), it will be observed that Haldane's contributions to population genetics after the mid-1930s was much more episodic than the systematic work of the 1920s and, although individual insights continue to be relevant today, from the historical point of view, this later work is less important than what he achieved in the 1920s.
2 citations
2 citations
TL;DR: Competition between seeds within a fruit for parental resources is described using one-locus-two-allele models, with results seen to be most intense when there are only two seeds, and decreases with increasing number of seeds, suggesting that two-seeded fruits would be rarer than one- seeded or many-seeding ones.
Abstract: Competition between seeds within a fruit for parental resources is described using one-locus-two-allele models. While a i?½normali?½ allele leads to an equitable distribution of resources between seeds (a situation which also corresponds to the parental optimum), the i?½selfishi?½ allele is assumed to cause the seed carrying it to usurp a higher proportion of the resources. The outcome of competition between i?½selfishi?½ alleles is also assumed to lead to an asymmetric distribution of resources, the i?½winneri?½ being chosen randomly. Conditions for the spread of an initially rare selfish allele and the optimal resource allocation corresponding to the evolutionarily stable strategy, derived for species with n-seeded fruits, are in accordance with expectations based on Hamiltoni?½s inclusive fitness criteria. Competition between seeds is seen to be most intense when there are only two seeds, and decreases with increasing number of seeds, suggesting that two-seeded fruits would be rarer than one-seeded or many-seeded ones. Available data from a large number of plant species are consistent with this prediction of the model.
2 citations
TL;DR: The results suggest the presence of some major genes influencing fickle locomotion in both sexes on chromosome 3.
Abstract: Genetic analysis was performed to identify chromosomal regions carrying genes affecting the “fickle” behaviour observed during a study on locomotor activity inD. melanogaster (Costaet al. 1989). The experiments were carried out using a wild-type strain and 13 morphological markers on chromosomes X and 3. The results suggest the presence of some major genes influencing fickle locomotion in both sexes on chromosome 3. Sex-controlled genes affecting this behavioural trait also appear to be present on the X chromosome.
1 citations