bluuebunny/crossref_metadata_2025_split huggingface dataset:
A deterministic model of cyclical selection
Authors: Hoekstra Rolf F. 
Published: September 2009

SUMMARYA deterministic model of cyclical selection in randomly mating populations is studied. Sufficient conditions for a protected polymorphism, which are for the special case of alternating selection also necessary conditions, are obtained using a simple graphical approach. The most important condition requires ‘marginal overdominance’ (Wallace, 1968); the other conditions seem hard to satisfy in a natural situation. Furthermore it is shown that the cyclical selection model can be regarded as a special case of a frequency-dependent selection model (Cockerhamet al.1972). Using this property, a mean fitness function for the cyclical selection model is derived. Generally, the mean fitness will not be maximized under cyclical selection. The relevance of the model to the problem of the role of cyclical selection in the maintenance of genetic polymorphism in natural populations is discussed. It is concluded that this relevance is probably rather limited with regard to the creation of protected polymorphism, but that the influence of cyclical selection on transient polymorphisms might be more significant. An approximate formula for the time needed for a given change in gene frequency under cyclical selection is derived. It appears that cyclical selection can extend considerably the time during which a transient polymorphism persists, especially if the selective differences in the different environments are of the same order of magnitude and of opposite sign.
The effect of different selection intensities on selection response in egg-laying ofTribolium castaneum
Authors: Ruano R. G. , Orozco F. , López-Fanjul C. 
Published: September 2009

SUMMARYAn experiment was carried out to test the effect of varying selection intensity on the response to individual selection with a fixed number of individuals scored per generation. The selected trait was egg laying of virgin females ofTribolium castaneumscored from the 7th to the 1 lth day after adult emergence. Five different selected proportions of females were considered (5, 10, 20, 33 and 50%) and each treatment was represented by two replicate lines. Control lines were maintained throughout the experiment. The lines selected at the lowest proportions (5 and 10%) led to the largest initial gains, but the largest final gains were achieved, by the lines where the proportions selected were 10 and 20%, in agreement with theory. Lines where the proportion selected was 50% gave the lowest rate of response over the period considered (32 generations). A good agreement was found between predicted and realized short-term responses to selection. Prediction at later stages of selection deteriorated in the most strongly selected lines mainly due to the levels of inbreeding attained.
The dominance ofexrBoverexrB+in heterodiploids ofEscherichia coli
Authors: Greenberg Joseph , Donch John , Berends Leonard 
Published: September 2009

SUMMARYTo test whetherexrB, a mutation inEscherichia coliB making this strain sensitive to ultraviolet radiation and unable to divide normally, is dominant toexrB+, merodiploids were constructed by crossing HfrexrB metA+his× F−malB met A thr proA recA. metA+recombinants were fertile (F′) and sensitive to UV. One of these, F′exrB proA, was crossed with an F−metA malB thr, selecting formetA+proA+. All such progeny acquiringmalB+were UV-sensitive, fertile and segregatedmet malUV-resistant progeny. They were, therefore, meriodiploids, F′exrB/exrB+.exrBis dominant toexrB+, in which respect it resemblesexrA(lex).
Protein variation in strains of mice differing in body size
Authors: Garnett I. , Falconer D. S. 
Published: September 2009

SUMMARYNine (41%) of the 22 enzymic and non-enzymic loci examined in a strain of mice divergently selected for six-week body weight (six lines selected in each direction and six controls) were found to be polymorphic. The degree of polymorphism varied between the replicates from a maximum of 38% to a minimum of 14% with an average individual heterozygous at 7·7% of its loci. There was no obvious association between any of the isozyme variants and body size. The frequency distribution among the 18 lines was adequately accounted for by random genetic drift. However, an association was observed between body size and theHbblocus; theHbbsallele was found to be fixed in all of the six Large lines. An examination of the variance of gene frequencies at this locus excluded random genetic drift as an explanation for the fixation.
Location of genes for the utilization of acetamide, histidine and proline on the chromosome ofPseudomonas aeruginosa
Authors: Day Martin , Potts J. Rowland , Clarke Patricia H. 
Published: September 2009

SUMMARYInterrupted mating methods were used to map the positions on thechromosomeof genes for the utilization of acetamide, histidine and proline. An entry time of 22 min was found for aputmarker determining the utilization of proline. Two groups ofhutmutants were studied. Mutationhut-109 was located at 18 min and mutationhutU108, which results in a defect in urocanase activity, mapped at 28 min.hutUwas shown by transduction with bacteriophage F116 to be linked toser-3 but not tomet-28 andilv-202, giving a map order ofhutU-ser-3-ilv-202-met-28.The amidase genes were assigned an entry time of 65–75 min. A method is described for examining late entry markers by interrupted mating.
Extensions to the model of an infinite number of selectively neutral alleles in a finite population
Authors: Avery P. J. 
Published: September 2009

SUMMARYThe model, suggested by Ohta & Kimura, of an infinite number of selectively neutral alleles, in which alleles can only mutate to neighbouring alleles, has been extended to include a migratory pattern. The stepping-stone and island models of migration have been considered. In the latter case, it has been found that as the number of colonies becomes large, the expected number of alleles,ne, becomes approximately equal towheremis the migration rate,vis the mutation rate andNeis the effective size of each population. This solution tends to that of Ohta & Kimura asm→ 0 but one can see that for any appreciable value ofNem, a large increase inneis obtained. In order to check the validity of iterative results, models with a finite number of alleles have been considered, and their solutions have been found to converge quickly to those of the infinite case. The results exemplify the great power of migratory structure and neutral alleles to maintain a large amount of heterozygosity. Double step mutation and the finite time solution have also been considered.
Cytofluorimetric evidence for meiosis in gametangial nuclei of Phytophthora drechsleri
Authors: Mortimer A. Martin , Shaw David S. 
Published: September 2009

SUMMARYRelative DNA contents of samples of nuclei from hyphal tips and from gametangia at different stages of development have been obtained by cytofluorimetry. The occurrence of nuclei with 4C, 2C and 1C DNA complements in gametangia and mainly 2C complements in hyphae indicates that meiosis takes place in the gametangia of Phytophthora drechsleri.
Trimethoprim-resistant mutants ofE. coliK12: preliminary genetic mapping
Authors: Breeze A. S. , Sims P. , Stacey K. A. 
Published: September 2009

SUMMARYTrimethoprim-resistant mutants ofE. coliK12 have been isolated by-serial subculture in progressively higher concentrations of trimethoprim. High-level resistance depends on the accumulation of several mutational changes. Transduction with bacteriophage P1 has shown that all the mutations involved in resistance are associated with a locus, to be calledtmr, betweenpyr AandpdxAand closely linked topdxA. Resistance is accompanied by, and presumably due to, an increased activity of the target enzyme, dihydrofolate reductase. Thetmrlocus may include the structural gene for dihydrofolate reductase but the only mutations that have so far been observed are concerned with regulation.
The replication of the chromosome of Pseudomonas aeruginosa strain 1: II. Sequential mutagenesis of synchronized cultures
Authors: Booker R. J. , Loutit J. S. 
Published: September 2009

SUMMARYThe order of replication of a series of genes in Pseudomonas aeruginosa has been studied in synchronized cultures using a method based on the technique of sequential mutagenesis. This technique relies on the increased susceptibility of the replication point of the bacterial chromosome to mutagenesis by N-methyl-N′-nitro-N-nitrosoguanidine. The genes studied were those previously mapped by conjugation and whose order of replication had been studied by an investigation of gene frequencies in exponential populations. The results are consistent with the idea that there is two-way replication of the chromosome of P. aeruginosa starting at a point near trp-1 and arg-6. They also confirm that the two linkage groups which have been found by conjugation replicate at different times. If the assumption is made that there is only one chromosome in P. aeruginosa, the results can be used to show how the two linkage groups may possibly be joined together and the order is such that there would have to be two sites of attachment for the sex factor FP2.
Drift variances of heterozygosity and genetic distance in transient states
Authors: Li Wen-Hsiung , Nei Masatoshi 
Published: September 2009

SUMMARYUsing the moments of gene frequencies, the drift variances of heterozygosity and genetic distance in transient states have been studied under the assumption that all mutations are selectively neutral. Interestingly, this approach provides a simple derivation of Stewart's formula for the variance of heterozygosity at steady state. The results obtained indicate that if all alleles in the initial population are equally frequent, the standard derivation of heterozygosity is very small and increases linearly with time in the early generations. On the other hand, if the initial allele frequencies deviate appreciably from equality, then the standard deviation in the early generations is much larger but increases linearly with the square root of time. Under certain conditions, the standard deviation of genetic distance also increases linearly with time. Numerical computations have shown that the standard deviations of heterozygosity and genetic distance relative to their means are so large that a large number of loci must be used in estimating the average heterozygosity and genetic distance per locus.
Evidence for a new kind of regulatory gene controlling expression of genes for morphogenesis during the cell cycle inUstilago violacea
Authors: Day A. W. , Cummins J. E. 
Published: September 2009

SUMMARYThe first part of the paper provides strong supportive evidence for the previous findings (Cummins & Day, 1973; Day & Cummins, 1973) that the two alleles of the mating-type locus of the basidiomyceteUstilago violaceahave different periods of inducibility during a cell cycle, and that the cell cycle characteristics of each allele are maintained in freshly isolated diploids. This difference in temporal properties of the alleles appears to be the basis of the dominance of allele a2as it is inducible during a phase of the cell cycle when allele a1is non-inducible. During G1both alleles appear to be inducible and apparently ‘neutralize’ each other so that the cell cannot mate.The second part of the paper provides evidence for a unique genetic control mechanism. The evidence suggests that the period of cell cycle inducibility of a locus governing a morphogenetic pathway may be regulated by a separate control gene thecclocus, with two known allelesccstr(a stringent or restricted period of inducibility) andccrel(a relaxed or non-restricted period of inducibility). This hypothesis stems from analysis of a diploid that wasa1·ccstr/a2·ccreland showed dominance of allelea2during the S and G2phases when freshly isolated, but which became incapable of mating after a period of subculturing. Analysis of haploids derived from this diploid strain showed that both mating-type alleles were functional but that it was now homozygous forccstr, i.e. of genotypea1·ccstr/a2·ccstr· Thus the temporal and functional aspects of the mating type alleles are determined by different loci. It is postulated that cell cycle control loci may be widespread and serve to regulate the action of genes concerned with morphogenesis in relation to other cell cycle events.
The genetics ofPhycomyces blakesleeanus
Authors: Cerdá-Olmedo E. 
Published: September 2009

SUMMARYThe genetic relationship between germspores and parental mycelia has been investigated in crosses involving multiply-marked heterokaryons and in simple difactor crosses.It is concluded that for each zygospore the number of different diploid nuclei undergoing meiosis is often more than one, but generally not more than two. The meiotic products divide to produce the nuclei in the usually uninucleate germspore primordia and then continue dividing to produce germspores. Unmated nuclei do not pass directly from parents to progeny.Each germsporangium contains differing numbers of viable germspores, with an average of about 7000; different genotypes are represented by varied numbers of germspores and often expected genotypes are missing. When the results of several germsporangia are added together or germspore stocks from many germsporangia are analysed, reciprocal genotypes appear in equal numbers and reliable recombination frequencies may be calculated.
The effect of selected linked locus on heterozygosity of neutral alleles (the hitch-hiking effect)
Authors: Ohta Tomoko , Kimura Motoo 
Published: September 2009

SUMMARYA diffusion model was developed to investigate the effect of a mutant substitution by natural selection on heterozygosity at a linked neutral locus. Using this theory, we made extensive numerical analyses to compute the expected total heterozygosity (i.e. the sum of the fraction of heterozygotes over all generations until fixation or loss) at the neutral locus. It was shown that the hitch-hiking effect is generally unimportant as a mechanism for reducing heterozygosity. The effect becomes significant only when the recombination fraction between the selected and the neutral marker loci is smaller than the selection coefficient. In order to check the validity of the mathematical theory, Monte Carlo experiments were performed, and the results were in agreement. It has been suggested that linkage is important only in transient small populations such as at the time of speciation.
The probability of survival of a mutant gene in an age-structured population and implications for the evolution of life-histories
Authors: Charlesworth Brian , Williamson John A. 
Published: September 2009

SUMMARYAn expression is derived for determining the probability of survival of a new favourable mutation in a large random-mating population with overlapping generations. For a gene of small effect, in a near-stationary population, an approximate formula similar to the usual one for discrete generations is obtained. The implications of these results for the evolution of life histories are discussed, using the partial derivatives of the chance of survival of a gene, with respect to changes in age-specific fecundities and survival probabilities. The properties of these derivatives are very similar to those of the derivatives of the intrinsic rate of increase, analysed by Hamilton (1966), thus providing a genetical basis for his conclusions concerning the evolution of life histories.
Manganese mutagenesis in yeast: II. Conditions of induction and characteristics of mitochondrial respiratory deficientSaccharomyces cerevisiaemutants induced with manganese and cobalt
Authors: Prazmo Wieslawa , Balbin Ewa , Baranowska Hanna , Ejchart Anna , Putrament Aleksandra 
Published: September 2009

SUMMARYManganese and cobalt are capable of inducing ρ−mutations* in non-growing cells ofSaccharomyces cerevisiae, but their mutagenic action is much stronger in growing cells. At a given concentration cobalt and manganese can be either strongly mutagenic or non-mutagenic, depending on the cell density.Most of the ρ−mutants induced with manganese and a considerable proportion of those induced with cobalt are suppressive and/or transmit drug resistance markers, so they must still carry mitochondrial DNA. Cobalt can decrease suppressiveness with low efficiency and eliminate drug resistance markers from established ρ−clones.
The distributions of the combinations of the sexes in mammalian litters
Authors: James William H. 
Published: September 2009

SUMMARYThere is subnormal dispersion in the distributions of the combinations of the sexes in some samples of litters of pigs, rabbits and mice. For instance, consider litters of exactly size 8. As contrasted with binomial expectation, there are too many with exactly 4 males and 4 females, and too few unisexual litters. It is argued that this supports the hypothesis (independently proposed by the author and by Guerrero) that P, the probability that a zygote will be male, varies with the time at which it is formed within the cycle. It is noted that data of Kaufman seem to support the hypothesis.
Cell lineage analysis of kynurenine producing organs inDrosophila melanogaster
Authors: Nissani Moti 
Published: September 2009

SUMMARYSix hundred and ten gynandromorphs were produced in which anXchromosome loss uncovered the vermilion mutation. The mosaic patterns observed indicate that wild type ocelli are incapable of kynurenine production and that, in addition to the eyes, postembryonic kynurenine producing cells originate from two separate regions of the blastoderm. The positions of these regions on the genetic fate map ofDrosophila melanogastercorrespond to the embryonic precursors which give rise to the kynurenine producing cells of the larval fat body and Malpighian tubes.
A factor on a wild third chromosome (IIIRa) that modifies the Segregation Distortion phenomenon inDrosophila melanogaster
Authors: Trippa G. , Loverre A. 
Published: September 2009

SUMMARYIIIRais a genetic modifier of Segregation Distortion (SD) inDrosophila melanogaster, which was discovered in the same natural population from Ranna (Sicily) that carriedSDRa. It is located at 49·7 ± 0·8 on chromosome III.IIIRawas found to have a dominant effect on segregation distortion which varied with the origin of theSDchromosome tested. Thus it enhanced the level of distortion caused by 14SDchromosomes from seven natural populations in Southern Italy and Sicily, but decreased the level of distortion caused bySDR−1, a chromosome from a natural population near Rome. Moreover,IIIRadetermined or enhanced the distorting effect ofSDRain males heterozygous forSDRaand variousSD+wild chromosomes differently sensitive toSDRa. The frequency of chromosomes having an effect likeIIIRachromosome was very high (around 70%) in samples from two natural populations of Southern Italy tested-those of Ranna and Corato. No effects ofIIIRaother than its ability to modify SD have been detected.
Use of isozymes as chromosome markers in wheat-rye addition lines and in triticale
Authors: Tang K. S. , Hart G. E. 
Published: September 2009

SUMMARYThe alcohol dehydrogenase (ADH), glutamate oxaloacetate transaminase (GOT), acid phosphatase (ACPH), endopeptidase (EP) and aminopeptidase (AMP) zymogram phenotypes of Chinese Spring wheat, Imperial rye, the Chinese Spring-Imperial triticale and the series of seven disomic Imperial chromosome additions to Chinese Spring were determined. It was found that the zymogram phenotypes produced for one or more of the enzymes by each of the Imperial chromosomes 3, 6, C and D differ sufficiently from that of Chinese Spring so as to provide evidence for the presence or absence of each of these chromosomes in addition lines and triticales. The structural genes Got-R2 and Got-R3 were located in Imperial chromosomes 6 and 3 respectively and other genes involved in the production of GOT in chromosomes C and D. By analysis of GOT alone, evidence for the presence or absence of Imperial chromosomes 3, 6, C and D in addition lines and triticales can be obtained. Adh-R1 was located in chromosome C and a gene(s) involved in the production of an ACPH was located in chromosome D.The linkages obtained for Got-R2, Got-R3 and Adh-R1 demonstrate homoeology between the Imperial chromosomes 3, 6 and C and the Chinese Spring chromosomes of groups 3, 6 and 4 respectively. The discovery that Adh-R1 is located in Imperial chromosome C also suggests that the 4R/7R and 7R/4R homoeologous groupings proposed elsewhere for the chromosomes of the rye cultivars Imperial, Dakold, and King II should be reassessed, since they are inconsistent with the known linkages of Adh-R1 in the three cultivars. The finding in King II of two forms of ADH and of two ADH genes has been reported. The results of our study of Imperial, King II, and Dakold indicate that rye possesses but one ADH and only one ADH structural gene.
Linkage relationships of markers on chromosome 17 of the house mouse
Authors: Hammerberg Graig , Klein Jan 
Published: September 2009

SUMMARYLinkage data for the following markers on chromosome 17 of the house mouse were obtained: centromere (marked by translocationR67),Brachyury(T),tufted(tf),H-2, andthin fur(thf). The markers were found to be arranged in that order in the genetic map and the combined genetic distances between individual markers were found to be as follows:Rb7…T, 4·5 cM;T…tf, 5·8 cM;tf…H-2, 5·0 cM;H-2…thf, 15·1 cM. The localization of thethflocus on the non-centromeric side of theH-2complex provides an important marker for this arm of chromosome 17. The map distances in the centromeric portion of chromosome 17 changed drastically in the presence of varioustfactors. These factors strongly reduce the recombination frequency in theT…tfandtf…H-2intervals and this crossing-over suppression is most likely responsible for the linkage disequilibrium betweentandH-2reported earlier. Recombinants involving atchromosome but occurring to the right of theH-2complex do not change the properties oftfactors suggesting that all determinants responsible for the t phenotype are located in the chromosomal region betweenTandtf(H-2).
Inheritance of the macrophage alloantigenic marker (Mph-1) in inbred mice
Authors: Archer James R. 
Published: September 2009

SUMMARYImprovements in cytotoxic technique allowed a determination to be made of the strain distribution and inheritance of Mph-1, the mouse peritoneal exudate cell alloantigen. Mph-lb, the allele in B10 lines, is inherited as a Mendelian co-dominant gene. In a 3-point backcross using the colour markers pink eye dilution (p) and chinchilla (cch) it was shown to map about 36 units from p in the order p-cch-Mph-l on chromosome 7. An alternative antigen, Mph-1.1, has been identified on strains F/St and I/StDa.
The maintenance of genetic variability by mutation in a polygenic character with linked loci
Authors: Lande Russell 
Published: September 2009

SUMMARYIt is assumed that a character under stabilizing selection is determined genetically bynlinked, mutable loci with additive effects and a range of many possible allelic effects at each locus. A general qualitative feature of such systems is that the genetic variance for the character is independent of the linkage map of the loci, provided linkage is not very tight. A particular detailed model shows that certain aspects of the genetic system are moulded by stabilizing selection while others are selectively neutral. With reference to experimental data on characters ofDrosophilaflies, maize, and mice, it is concluded that large amounts of genetic variation can be maintained by mutation in polygenic characters even when there is strong stabilizing selection. The properties of the model are compared with those of heterotic models with linked loci.