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Showing papers in "Journal of Genetics in 1985"


Journal ArticleDOI
TL;DR: It is concluded that compensatory neutral mutants may play an important role in molecular evolution.
Abstract: A pair of mutations at different loci (or sites) which are singly deleterious but restore normal fitness in combination may be called compensatory neutral mutations. Population dynamics concerning evolutionary substitutions of such mutants was developed by making use of the diffusion equation method. Based on this theory and, also, by the help of Monte Carlo simulation experiments, a remarkable phenomenon was disclosed that the double mutants can easily become fixed in the population by random drift under continued mutation pressure if the loci arc tightly linked, even when the single mutants are definitely deleterious. More specifically, I consider two loci with allelesA andA’ in the first locus, and allelesB andB’in the second locus, and assign relative fitnesses 1, 1-s’, 1-s’ and 1 respectively to the four gene combinationsAB, A’B, AB’ andA’B’, wheres’ is the selection coefficient against the single mutants (s’ > 0). Letv be the mutation rate per locus per generation and assume that mutation occurs irreversibly fromA toA’ at the first locus, and fromB toB’ at the second locus, whereA andB are wild type genes, andA’ andB’ are their mutant alleles. In a diploid population of effective size N e (or a haploid population of 2N e breeding individuals), it was shown that the average time (T) until joint fixation of the double mutant (A’B’) starting from the state in which the population consists exclusively of the wild type genes (AB) is not excessively long even for large 4N e s’ values. In fact, assuming2N e v = 1 we have -T = 54Ne for 4Nes’ = 400, and -T = 128Ne for 4N e s’ = 1000. These values are not unrealistically long as compared with -T~ 5N e obtained for 4N e s’ = 0. The approximate analytical treatment has also been extended to estimate the effect of low rate crossing over in retarding fixation. The bearing of these findings on molecular evolution is discussed with special reference to coupled substitutions at interacting amino acid (or nucleotide) sites within a folded protein (orrna) molecule. It is concluded that compensatory neutral mutants may play an important role in molecular evolution.

271 citations


Journal ArticleDOI
TL;DR: Hitch-hiking models provide an adequate explanation for the maintenance of sex and recombination in eukaryotes and the main selective force favouring recombination isdna repair.
Abstract: The selective forces responsible for the evolution of genes mediating recombination are discussed. These genes originated because of their role indna repair. In eukaryotes, their role in repair is not sufficient to account for the evolution of meiosis and syngamy. Therefore, a “hitch-hiking” explanation is required, according to which a recombination gene gets a lift in frequency from the high-fitness genes to which it is linked. Such hitch-hiking models are reviewed: collectively they provide an adequate explanation for the maintenance of sex and recombination in eukaryotes. In prokaryotes, the main selective force favouring recombination isdna repair: the cross-overs caused by recombination may occasionally have important evolutionary effects, but they are the consequences, rather than the causes, of the evolution of recombination in prokaryotes. In both prokaryotes and eukaryotes, recombination genes also cause specific, repeatable and adaptive rearrangements of the genetic material.

67 citations


Journal ArticleDOI
TL;DR: Resistance to brown planthopper in rice cultivar ARC 10550 was found to be governed by a single recessive gene which was designatedbph 5.0, and it should be possible to combine this gene with any of the other four genes to develop rice cultivars with a broad spectrum of resistance.
Abstract: Resistance to brown planthopper in rice cultivar ARC 10550 was found to be governed by a single recessive gene which was designatedbph 5. It conveys resistance to brown planthopper populations in South Asia but not to the populations in East and Southeast Asia. This gene segregated independently of four other known genes for brown planthopper resistance. It should be possible to combine this gene with any of the other four genes to develop rice cultivars with a broad spectrum of resistance.

49 citations


Journal ArticleDOI
TL;DR: The four genera, Clarkia, Nicotiana, Lathyrus andAllium have widely different geographical distributions and evolutionary patterns, but the nucleardna amounts of species within each genus occur in groups at intervals of approximately 2 or 4 picograms, implying there are favoured, discontinuous, DNA amounts, either arisingde novo or subsequently within a continuously varying distribution.
Abstract: The four genera,Clarkia, Nicotiana, Lathyrus andAllium have widely different geographical distributions and evolutionary patterns, but the nucleardna amounts of species within each genus occur in groups at intervals of approximately 2 or 4 picograms. Diploids with different basic chromosome numbers, and polyploids, can occur in the same group. When anydna group of one genus is paired with the nearestdna group of another genus all other groups of both genera pair exactly in so far as they have a common range of DNA amounts. Hence thedna groups of the four genera are associated in larger groups, or nodes, separated by 2 or 4 picograms forming a progression over all four genera, implying there are favoured, discontinuous,dna amounts, either arisingde novo or subsequently within a continuously varying distribution.

36 citations


Journal ArticleDOI
TL;DR: ThisBal-X-l carries the marker mutationlon-2(e678) and can be detected cytologically and proved useful for rnaimaining a number of X-linked lethal mutations and deficiencies inC. elegans.
Abstract: A single X-chromosome balancer-bearingCelegans ♂+, as a founder of a strain (AF1), was isolated directly from Fl progeny of irradiated+dpy-8unc-3/lon-2++ hermaphrodites on the basis of the absence of recombinant F2 categories. The balancer chromosome (Bal-X-1) suppresses recombination over a two-thirds section of the X chromosome (between genesdpy-8 andlet-2) and is associated with a reciprocal translocation between linkage groups (LG) X and I. Animals homozygous for the translocation (szT1(X:1)) are nonviable. Hermaphrodites heterozygous for the translocation segregate male selfprogeny at a frequency of 0.08-0.12.Bal-X-l carries the marker mutationlon-2(e678) and can be detected cytologically. This balancer chromosome proved useful for rnaimaininga number of X-linked lethal mutations and deficiencies inC. elegans.

23 citations


Journal ArticleDOI
TL;DR: There were no significant differences between the various inbreeding classes in the number of liveborn or living children, nor was a significant consanguinity-related effect on the proportion of survivors detectable.
Abstract: Consanguineous marriages have been favoured throughout South India for many generations. On theoretical grounds it was proposed that long-term inbreeding would have resulted in the elimination of deleterious, recessive lethal and sub-lethal genes. As part of a newborn screening programme for amino acidopathies, data were collected on the level of inbreeding in the current populations of the cities of Bangalore and Mysore, and on the relationship between consanguinity and mean numbers of liveborn and living children. Mean cnonsanguinity was 32.24%, equivalent to a cuoefficient of inbreeding in the newborns,F = 00271. There were no significant differences between the various inbreeding classes in the number of liveborn or living children, nor was a significant consanguinity-related effect on the proportion of survivors detectable. In the light of these findings, the effects on the gene pool of multiple generations of inbreeding are discussed.

17 citations


Journal ArticleDOI
TL;DR: A model of selection (local selection) in which successive favorable alleles enter into a population by displacing a random fraction of each of the preexisting alleles is examined, leading to a convenient algorithm for simulating random equilibrium frequencies of alleles within samples.
Abstract: We have examined a model of selection (local selection) in which successive favorable alleles enter into a population by displacing a random fraction of each of the preexisting alleles. When the distribution of fitness among newly arising favorable mutations is given by a power law, then the distribution of allele frequencies in the population converge to a Poisson-Dirichlet limit, and the sampling distribution of alleles is a Ewens distribution. This property leads to a convenient algorithm for simulating random equilibrium frequencies of alleles within samples. The model can also be interpreted in terms of species abundances when each invading species displaces a random fraction of each pre-existing species, or in terms of age structures in populations subjected to random catastrophes.

13 citations


Journal ArticleDOI
TL;DR: Flowering time was closely associated with plant form, inflorescence development, and numerous other traits which differentiate the crop and weed species, providing interesting insights into evolutionary changes under domestication and dispersal from lower to higher latitudes.
Abstract: The inheritance of flowering time was studied in a cross between an early flowering weedy species,Amaranthus retroftexus L., and a late flowering related crop species,A. cruentus L. Segregation ratios were scored in four successive backcrosses of the hybrid to the crop species (BC1 to BC4) and in backcross-derived generations (BC2F2, BC2F3) grown under 8-hr and 16-hr photoperiods and 30/20°C day/night temperatures in growth chambers, and under field and greenhouse environments during summer months at Davis. One major gene for earliness (Ea), dominant over late flowering, was identified conclusively under the 8-hr regime and in some genetic backgrounds under field conditions. Based on segregation patterns within individual progenies and the observed transgressive segregation, a model of three genes seemed to explain all of the ratios consistently. Evidence of segregation distortion at theEa locus, resulting in the deficiency of early individuals, and some role of epistatic interactions among the three postulated major genes requires further testing based on more isogenic and specific progeny materials. Flowering time was closely associated with plant form, inflorescence development, and numerous other traits which differentiate the crop and weed species. This association provides interesting insights into evolutionary changes under domestication and dispersal from lower to higher latitudes.

12 citations


Journal ArticleDOI
TL;DR: In replication-blocked crosses in phage λ,cos, λ’s packaging origin, provokes Red-mediated recombination in its neighborhood, and it is found that the complementary crossover products are not produced in equal numbers.
Abstract: In replication-blocked crosses in phage λ,cos, λ’s packaging origin, provokes Red-mediated recombination in its neighborhood. In crosses of wild-type x mutantcos, cosstimulated crossover products can be packaged fromcos sites cloned medially in the two parents (Stahl F W, Kobayashi I and Stahl M M 1985J. Mol. Biol. 181: 199–209). We find that the complementary crossover products are not produced in equal numbers. In agreement with the model presented earlier (ibid), most of the recombinants inherit λ’ s right arm (R arm) from thecos +parent and λ’s left arm (A arm) from the parent with the mutantcos.

11 citations


Journal ArticleDOI
TL;DR: It is shown that kin recognition resulting in the ability to invest in full but not in half sisters reverts the sex ratio back to that in the case of single mating and thus completely overcomes the hurdles for the operation of kin selection.
Abstract: A model is constructed to study the effects of local mate competition and multiple mating on the optimum allocation of resources between the male and female reproductive brood in social hymenopteran colonies from the 'points of view' of the queen (parental manipulation theory) as well as the workers (kin selection theory). Competition between pairs of alleles specifying different sex investment ratios is investigated in a game theoretic frame work. All other things being equal, local mate competition shifts the sex allocation ratio in favour of females both under queen and worker control. While multiple mating has no effect on the queen's optimum investment ratio, it leads to a relatively male biased investment ratio under worker control. Under queen control a true Evolutionarily Stable Strategy (ESS)does not exist but the 'best' strategy is merely immune from extinction. A true ESS exists under worker control in colonies with singly mated queens but there is an asymmetry between the dominant and recessive alleles so that for some values of sex ratio a recessive allele goes to fixation but a dominant allele with the same properties fails to do so. Under multiple mating, again,a true ESS does not exist but a frequency dependent region emerges. The best strategy here is one that is guaranteed fixation against any competing allele with a lower relative frequency. Our results emphasize the need to determine levels of local mate competition and multiple mating before drawing any conclusions regarding the outcome of queen-worker conflict in social hymenoptera. Multiple mating followed by sperm mixing, both of which are known to occur in social hymenoptera, lower average g netic relatedness between workers and their reproductive sisters. This not only shifts the optimum sex ratio from the workers 'point of view' in favour of males but also poses problems for the kin selection theory. We show that kin recognition resulting in the ability to invest in full but not in half sisters reverts the sex ratio back to that in the case of single mating and thus completely overcomes the hurdles for the operation of kin selection.

9 citations


Journal ArticleDOI
TL;DR: A simple and analytically solvable model for the spread of a transposable element which has deleterious effects on fitness and proves that a polymorphism is impossible unless the copy number decreases fitness in a more-than-muitiplicative fashion.
Abstract: We consider a simple and analytically solvable model for the spread of a transposable element which has deleterious effects on fitness. Two possible modes are treated, one in which transposition occurs in the newly fertilized zygote, and another in which transposition takes place only in the germ line. In effect, transposition precedes selection in the first case and follows it in the second. This has different long-term consequences depending on the rate of transposition and the values of the selection coefficients. Conditions are derived for the existence of a stable polymorphism with respect to element copy number; the conditions are more stringent in the first case than in the second. It is proved that a polymorphism is impossible unless the copy number decreases fitness in a more-than-muitiplicative fashion.

Journal ArticleDOI
TL;DR: The results have been interpreted to mean that esterase-6 does not have a direct role in malathion resistance, and that theEst-6 polymorphism in the experimental population was maintained by balancing selection.
Abstract: The effects of selection for resistance to the organophosphate insecticide malathion on esterase-6 polymorphism was studied in laboratory populations ofD. melanogaster. A genetically well-mixed population was constructed from 40 locally-caught, iso-female lines, divided into control and malathion-selected lines and the frequency of the majorEst-6 alleles was followed for more than 100 generations. The main findings were: (1) The allele frequency in control replicates remained stable for over one hundred generations; (2) the allele frequency in the populations exposed to malathion changed dramatically and in the opposite direction between replicates during the early generations of the selection experiment; (3) all selected populations eventually returned to the controlEst-6 allele frequencies. This return was more rapid in populations exposed to lower selection intensity compared to those exposed to higher selection intensity; (4) the convergence ofEst-6 allele frequencies to control values was also observed in three populations obtained by mixing flies of appropriate genotypes from the control population to give different initial frequencies. These results have been interpreted to mean that esterase-6 does not have a direct role in malathion resistance, and that theEst-6 polymorphism in our experimental population was maintained by balancing selection.

Journal ArticleDOI
TL;DR: The story of the development of molecular biology, and particularly the molecular basis of inheritance (molecular genetics), is outlined, and how the two revolutions in physics and biology became linked historically through the life and work of Max Delbrfick is shown.

Journal ArticleDOI
TL;DR: Developments in techniques of chromosome analysis and the integration of tumor cytogenetics with immunology and molecular genetics have permitted extraordinary insights into the nature of the perturbations that gene structure and function undergo in cancer cells.
Abstract: The significance of germ-line and somatic genetic changes to the etiology of cancer has been a subject of continuing interest for cancer cell biologists Recognition of certain basic principles of cancer cell genetics such as the clonal nature of tumors and their dynamic genetic systems were the early results of these studies, which mainly related to chromosomes in tumor cells Recent advances in techniques of chromosome analysis and the integration of tumor cytogenetics with immunology and molecular genetics have permitted extraordinary insights into the nature of the perturbations that gene structure and function undergo in cancer cells These developments have been reviewed here in so far as they address the central issue of cancer genetics, namely, the role of somatic and gerrn-line chromosome change in the origin and evolution of neopolastic cells