bluuebunny/crossref_metadata_2025 huggingface dataset:
SPECIFICITY OF INSERTION BY THE TRANSLOCATABLE TETRACYCLINE-RESISTANCE ELEMENT Tn10
Authors: Kleckner Nancy , Steele David A , Reichardt Katherine , Botstein David
Published: April 2021

Genetic analysis of 131 independent transpositions of the tetracycline-resistance element TnlO from a single site in phage P22 into the histidine operon of Salmonella typhimurium reveals that Tn1O insertions are not randomly distributed along this chromosomal target. The insertions occur in 22 different "clusters"; insertions within each cluster are very tightly linked in recombination tests. TnlO insertions are not evenly distributed among the identified clusters. The existence of these clusters suggests that this chromosomal target contains particular genetic signals that guide TnlO to particular preferred positions for insertion. Insertions within each cluster occur in both orientations with roughly equal frequency.——The relationship among different insertions within each cluster has been examined. The resolution of genetic mapping places an upper limit of about 50 basepairs on the distance between different insertions within a cluster. Different insertions within a cluster usually have the same reversion frequency; however, heterogeneity in reversion frequency has been detected in at least two clusters. For most clusters, the available data are consistent with the simple possibility that all insertions within a cluster are at identical positions; however, the data do not exclude other possibilities.
MEIOTIC-LIKE RECOMBINATION IN VEGETATIVE DIKARYONS OF SCHIZOPHYLLUM COMMUNE
Authors: Frankel Carl
Published: April 2021

A total of 65 Schizophyllum commune dikaryons of three different geno-types were synthesized, maintained on agar plates, prevented from fruiting, and macerated. The macerate was plated. Germlings of homokaryotic morphology were isolated using no chemical or genetic selection, grown, and tested for recombinant genotypes. Crossover types were plentiful among the homokaryons with recombinant genotypes, indicating that meiotic-like processes in vegetative dikaryons are common and may be as important as conventional basidial meiosis in the origin of recombinant strains.
HYBRID DYSGENESIS IN DROSOPHILA MELANOGASTER: STERILITY RESULTING FROM GONADAL DYSGENESIS IN THE P-M SYSTEM
Authors: Kidwell Margaret G , Novy Jill B
Published: April 2021

Crosses between two types of strains, called P and M, characteristically give high frequencies of F1 sterility and other aberrant traits. Previous studies indicated that, in addition to the direction of the parental cross, many factors influence the manifestation of this phenomenon known as "hybrid dysgenesis."—The present study is concerned with the characteristics of GD (gonadal dysgenesis) sterility associated with the P-M system and its temperature dependence. Female sterility is accompanied by a complete absence of egg-laying, and this is not attributable to an inability to mate. Thus, it seems likely that sterility results from a defect in gametogenesis of hybrid individuals. This conclusion is supported by the morphological and cytological observations presented in an accompanying paper (SCHAEFER, KIDWELL and FAUSTO-STERLING 1979).—A narrow, critical, developmental temperature range was found in which both female and male sterility rose sharply from a low level to a high maximum. The critical range was 27 to 29° for males, slightly higher than the range of 24 to 26° for females. Two other dysgenic traits, male recombination and transmission ratio distortion, were affected by developmental temperature, but temperature response curves were quite different from those for sterility. The temperature-sensitiye stage for female sterility occurs during embryonic and early larval development.——GD sterility is compared and contrasted with SF sterility, another specific type of nonMendelian sterility resulting from a different interstrain dysgenic interaction.
GENETIC DETERMINATION OF THE DEVELOPMENTAL PROGRAM FOR MOUSE LIVER β-GALACTOSIDASE: INVOLVEMENT OF SITES PROXIMATE TO AND DISTANT FROM THE STRUCTURAL GENE
Authors: Berger Franklin G , Breen Gail A M , Paigen Kenneth
Published: April 2021

The identification and mode of action of genetic loci that program gene expression during development are important for understanding differentiation in higher organisms. Previous work from this laboratory has identified two patterns for the postnatal development of liver β-galactosidase among inbred mouse strains: type I, where activity levels remain constant after about 30 days of age, is found in strains DBA/BJ, CBA/J, and BALB/cJ, among others; type 11, where activity levels increase between 25 and 50 days of age to reach a new adult level, is found in strain C57BL/6J and related strains. It has been shown that the type I vs. type II developmental difference between strains C57BL/6S and DBA/2J is due to variation at a locus, Bgl-t, that maps with the β-galactosidase complex, [Bgl], on chromosome 9. In the present study, we have confirmed the existence of Bgl-t as a temporal locus within [Bgl] by analysis of both a congenic strain carrying the β-galactosidase complex of strain CBA/J in the C57BL/6J genetic background and a cross of strains CBA/J and C57BL/6J. The existence of additional temporal loci for β-galactosidase that segregate independently of the structural gene and participate in determination of the type I vs. type II difference was revealed by analysis of: (1) a congenic strain containing the β-galactosidase complex of strain BALB/cJ in the C57BL/lOSn background; (2) recombinant inbred lines derived from progenitor strains C57BL/6ByJ and BALB/cByJ; and (3) a genetic cross between strains C57BL/6ByJ and BALB/cByJ. Thus, for these pairs of strains, the type I us. type II developmental difference is due to variation at a temporal locus (or loci) unlinked to the enzyme structural gene, and not at Bgl-t. These facts, together with information gathered from an examination of the distribution of β-galactosidase phenotypes among over 100 inbred strains (BREEN, LUSIS and PAIGEN 1977), have led us to conclude that the postnatal developmental pattern for liver β-galactosidase is determined by a set of interacting temporal genes. One of these, Bgl-t, is located within [Bgl], and one or more are separable from [Bgl] by recombination. A possible mode of interaction among the temporal and structural loci is suggested.
ON THE NATURE OF SISTER-CHROMATID EXCHANGES IN 5-BROMODEOXYURIDINE-SUBSTITUTED CHROMOSOMES
Authors: Schvartzman J B , Cortés F , González-Fernández A , Gutiérrez C , LÓpez-Sáez J F
Published: April 2021

Sister-chromatid exchanges (SCE) were studied in Allium cepa L. meristematic cells at the second and third divisions after BrdUrd-substitution during just the first or during the second and third cycles, respectively. The observed SCE nonreciprocal/reciprocal ratios detected at the third division in both experiments, as well as comparison of the lowest SCE frequency observed per cycle and expressed per picogram of DNA with data from different species expressed accordingly, strongly suggest that most of the exchanges detected in BrdUrd-substituted chromosomes are BrdUrd-dependent events. Hypotheses suggesting some different mechanisms are discussed to explain the formation of these BrdUrd-dependent SCEs.
ALLOZYMIC VARIATION AND LINKAGE DISEQUILIBRIUM IN SOME LABORATORY POPULATIONS OF DROSOPHILA MELANOGASTER
Authors: Laurie-Ahlberg C C , Weir B S
Published: April 2021

Nine laboratory populations of D. melanogaster were surveyed by starch gel electrophoresis for variation at 17 enzyme loci. A single-fly extract could be assayed for all 17 enzymes, so that the data consist of 17-locus genotypes.— Pairwise linkage disequilibria were estimated from the multilocus genotypic frequencies, using both BURROWS' and HILL'S methods. Large amounts of link-age disequilibrium were found, in contrast to the results reported for natural populations.—Knowledge of the approximate sizes of these populations was used to compare the observed heterozygosities and linkage disequilibria with predictions of the neutral allele hypothesis. The relatively large amount of linkage disequilibrium is consistent with the small sizes of the populations. However, the levels of heterozygosity in at least some populations suggest that some mechanism has been operating to retard the rate of decay by random drift. Several examples of significant deviation from Hardy-Weinberg frequencies and the large amount of linkage disequilibnim present in these populations indicate that a likely mechanism is selective effects associated with neutral alleles because of linkage disequilibrium with selected loci (e.g., "associative overdominance"). The results are therefore consistent with both neutralist, and selectionist hypotheses, but suggest the importance of considering linkage disequilibrium between neutral and selected loci when attempting to explain the dynamics of enzyme polymorphisms.
THE BAM H1 RESTRICTION SITE IN THE BACTERIOPHAGE T4 CHROMOSOME IS LOCATED IN OR NEAR GENE 8
Authors: Wilson Geoffrey G , Neve Rachael L , Edlin Gordon J , Konigsberg William H
Published: April 2021

Bacteriophage T4 cytosine-containing DNA is cleaved at a single site by the restriction endonuclease, Bam H1. The site lies within the late region of the T4 genome, close to, or within, gene 8, one of the structural genes of the phage particle baseplate.
GENETIC MODULATION OF RNA METABOLISM IN DROSOPHILA. III. REQUIREMENT FOR AN rDNA-DEFICIENT X CHROMOSOME IN YbbSuVar–5-MEDIATED INCREASES IN RNA SYNTHESIS
Authors: Strausbaugh Linda D , Kiefer Barry I
Published: April 2021

Males of the genotype car bb/YbbSuVar-5 have an approximately two-fold increase in the rate of accumulation of 4S, 5S, 18s + 28s and poly-A+ RNA molecules when compared to males of the genotype car bb/Ybb- (CLARK, STRAUSBAUGH and KIEFER 1977; CLARK and KIEFER 1977). Experiments were designed to determine if the modulation of RNA metabolism by YbbSuVar-5 requires an rDNA deficiency on the X chromosome. Synthetic rates for 4S, 5S, and 18s + 28s RNA's were measured in the genotypes Sam+iso/Ybb- and Sam+iso/Ybbsuvar-5 by injecting adult males with 3H-uridine, allowing them to incorporate label for two hours, fractionating extracted RNA by polyacrylamide gel electrophoresis and determining the specific activities of RNA's (dpm/μgRNA). The results of these determinations showed that the synthetic rates for 4S, 5S, and 18s + 28S RNA's are the same in these two genotypes, demonstrating that the YbbSuVar-5 chromosome does not increase transcription when paired with an X chromosome that is wild type for rDNA. Saturation hybridization was used to measure the rDNA content in several genotypes. These results showed that Sam+iso/YbbSuVar-5 males and Sam+iso/Ybb- males have equivalent amounts of rDNA.—These results are consistent with the suggestion that the Ybb- and YbbSuVar-5 chromosomes have similar amounts of rDNA. The nature of compensatory strategies in rDNA-deficient genotypes is discussed.
INTERCHROMOSOMAL EFFECTS OF HETEROCHROMATIC DELETIONS ON RECOMBINATION IN DROSOPHILA MELANOGASTER
Authors: Yamamoto Masatoshi
Published: April 2021

It is now known that partial deletions of the satellite sequences in X - chromosome heterochromatin result in a significant decrease in intrachromosoma1 recombination in the proximal region of the X chromosome of D. melanogaster (YAMAMOTO and MIKLOS 1978). It is important to ask then if the loss or gain of heterochromatin on the X also alters recombination in other chromosomes of the genome (interchromosomal effects). I have looked for such alterations by measuring recombination in chromosome 3. The results clearly indicate that the partial loss of X-chromosome heterochromatin not only decreases crossing over in the proximal region of the X chromosome itself, but also increases the frequency in chromosome 3. especially in the euchromatic regions around the centromere. Furthermore, the greater the deficiency of X heterochromatin, the higher is recombination in chromosome 3. This finding not only provides further evidence in support of the hypothesis that heterochromatin, in this case mainly composed of satellite DNA, regulates the recombination system, but it demonstrates that when the satellite content of one chromosome of the D. melanogasier genome is altered, there is an alteration in the crossover characteristics of other chromosomes in the same complement. If the amount of satellite DNA in a genome is being continuously altered, then one can predict that the recombination system is also being continually perturbed. Thus, the changing gene Combinations produced indirectly by increases or decreases of heterochromatin are among the components available to organisms to break up or form new gene combinations upon which se!ection can act.
FISSION MODELS OF POPULATION VARIABILITY
Authors: Thompson E A
Published: April 2021

Most models in population genetics are models of allele frequency, making implicit or explicit assumptions of equilibrium or constant population size. In recent papers, we have attempted to develop more appropriate models for the analysis of rare variant data in South American Indian tribes; these are branching process models for the total number of replicates of a variant allele. The spatial distribution of a variant may convey information about its history and characteristics, and this paper extends previous models to take this factor into consideration. A model of fission into subdivisions is superimposed on the previous branching process, and variation between subdivisions is considered. The case where fission is nonrandom and the locations of like alleles are initially positively associated, as would happen were a tribal cluster or village to split on familial lines, is also analyzed. The statistics developed are applied to Yanomama Indian data on rare genetic variants. Due to insufficient time depth, no definitive new inferences can be drawn, but the analysis shows that this model provides results consistent with previous conclusions, and demonstrates the general type of question that may be answered by the approach taken here. In particular, striking confirmation of a higher-than-average growth rate, and hence smaller-than-previously-estimated age, is obtained for the Yan2 serum albumen variant.
ISOLATION AND CHARACTERIZATION OF TEMPERATURE-SENSITIVE RESPIRATORY MUTANTS OF NEUROSPORA CRASSA
Authors: Pittenger Thad H , West David J
Published: April 2021

Filtration-enrichment and inositol-less death methods of mutant isolation, coupled with a screen for cyanide-insensitive respiration, proved to be highly efficient methods for isolating temperature-sensitive (ts) nuclear Neurospora mutants having defective respiration. Eighteen different ts respiratory mutants have been isolated. Most of them are pleiotropic and defective in one or more of the following phenotypes: cytochrome aa3, b, and c (individual or multiple defects); oligomycin inhibition of ATPase activity; respiration and its inhibition by KCN and salicyl hydroxamic acid; and growth rates in liquid and solid media at 25° and 38°. Among these mutants are the first cytochrome c mutant of Neurospora and an extranuclear ts ATPase mutant. An added bonus was the fact that aver half of the mutants were affected either in ribosome assembly or in protein synthesis in the mitochondrion. We have yet to find any mutants completely lacking activities associated with the respiratory chain. However, the wide spectrum of mutants isolated here, along with those currently available, constitutes a considerable resource for investigating respiration in obligate aerobes.
GENETICS OF ARGININE BIOSYNTHESIS IN NEUROSPORA CRASSA
Authors: Davis Rowland H
Published: April 2021

A large number of arginine-requiring mutants of Neurospora was isolated, using a strain already partially impaired in an enzyme of the pathway. Among the mutants, all previously described loci, except one, were represented, and several new loci were defined and mapped. Four groups of mutants were of particular interest. First, thc large group of arg-6 mutants, when tested for intragenic complementation, suggested a bifunctional gene, possibly controlling two steps in ornithine synthesis. This is consistent with the limited enzymic information about this locus. Second, the arg-13 locus was represented by 14 new mutants. All five tested were quite leaky. suggesting that the function controlled by this gene can be rarried out to a limited extent spontaneously or by another gene product. Third, a new locus, arg-14, was defined. It controls a step in ornithine synthesis. It lies in a 1 to 2 map-unit interval between arg-2 and pyr-3 on LG IVR, as shown by mapping in relation tG translocation breakpoints. Fourth, a second new locus whose mutants render the partial mutation in starting material auxotrophic was defined and mapped near the centromere of LG VIL. These new mutants are unable to derepress enzymes of the pathway and may qualify as regulatory mutants.
CYTOGENETIC BEHAVIOR OF SPORE KILLER GENES IN NEUROSPORA
Authors: Raju Namboori B
Published: April 2021

Crosses heterozygous and homozygous for Sk–1, Sk–2 and Sk–3 were examined by light microscopy. All three Spore killers behave similarly. In heterozygoua killer x sensitive crosses, meiosis and ascospore development are normal until after the second postmeiotic mitosis when four of the eight ascospores in each ascus stop developing and degenerate. The four surviving ascospores carry the killer. Death of sensitives thus occurs only after killer and sensitive alleles, SkK and SkS, have segregated into separate ascospores. Homozygous killer x killer crosses do not show such a pattern of degeneration. Either all ascospores are normal or, if some fail to mature, they do not resemble the degenerating sensitive ascospores in heterozygous asci.——With Sk–2, it was shown that SkS nuclei do not abort when both SkK and SkS are present in the same ascospore. Mutants affecting ascus development were used to obtain large ascospores enclosing both SkK and SkS meiotic products in a common cytoplasm. SkS nuclei do not then undergo the degeneration that would be seen if they werc sequestered into separate ascospores, and viable SkS progeny are recovered in undiminished numbers when the mixed multinucleate large ascospores are germinated. In a four-spored mutant, where each ascospore encloses a single nucleus following meiosis, degeneration of SkS ascospores nevertheless occurs, even though the third nuclear division is omitted. Cycloheximide and temperature treatments do not affect: the expression of SkK.
MOLECULAR EVOLUTION AND POLYMORPHISM IN A RANDOM ENVIRONMENT
Authors: Gillespie John H
Published: April 2021

A model of multi-allelic selection in a random environment, the SAS-CFF model, is examined for compatability with allele frequency and genetic distance data acquired by electrophoresis. The symmetric version of the model tends to predict higher than observed levels of polymorphism unless substantial positive autocorrelations in the environment are postulated. The actual allele frequency configurations observed in nature are in rough agreement with those predicted by the SAS-CFF model. An approximate analysis of the transient properties of the SAS-CFF model shows that, in broad outline, the behavior is quite similar to that of the neutral model.
EXCURSIONS ALONG THE INTERFACE BETWEEN DISRUPTIVE AND STABILIZING SELECTION
Authors: Felsenstein Joseph
Published: April 2021

When a polygenic character is exposed to natural selection in which the curve giving fitness as a function of phenotype is a mixture of two Gaussian (normal) curves, the population may respond either by evolving to a specialized phenotype near one of the two optimum phenotypes, or by evolving to a generalized phenotype between them. Using approximate multivariate normal distribution methods, it is demonstrated that the condition for selection to result in a specialized phenotype is that the curve of fitness as a function of breeding value be bimodal. This implies that a specialized phenotype is more likely to result the higher is the heritability of the character. Numerical iterations of four-locus models and algebraic analysis of a symmetric two-locus model generally support the conclusions of the normal approximation.
THE SENSITIVITY OF GEL ELECTROPHORESIS AS A DETECTOR OF GENETIC VARIATION
Authors: Ramshaw John A M , Coyne Jerry A , Lewontin R C
Published: April 2021

Three experiments based on an idea of YOUDERIAN have been performed to determine the proportions and kinds of amino acid substitutions that are detected by gel electrophoresis when applied to surveys of protein variation in populations. The experiments involved applying the sequential method of electrophoresis under sereral conditions of pH and gel concentration to a large sample of human hemoglobins with known amino acid substitutions. In the first experiment, a random sample of 20 different hemoglobin variants was studied, and these were separated into 17 distinct electrophoretic classes by three sequential gel conditions, thus giving a detectability of 85%. A single pass under standard conditions detected eight classes. The second experiment compared groups of substitutions that were chemically identical, but in different positions in the α and β chains, while the third experiment compared pairs of substitutions that were charge equivalent. but chemically different at the same chain position. The sequential method distinguished 90% of all chemically identical substitutions when they were at different chain locations, and four out of five charge equivalent but chemically different substitutions at the same site. Examination of the location of each substitution in the three-dimensional structure of hemoglobins showed that interior substitutions usually are less different from HbA than are surface substitutions and that local interactions with chain and spatial neighbors are sufficient to distinguish substitutions in very similar positions on the outside of the molecule. The "charge ladder" model of electrophoretic classes is clearly incorrect, and it appears that sequential gel electrophoresis as practiced in our Drosophila surveys has detected a substantial fraction of amino acid substitutions if hemoglobin is regarded as a model. This estimate may be modified as other molecules beside hemoglobin are subjected to similar calibration experiments.
RESTORATION OF NUCLEO-MITOCHONDRIAL COMPATIBILITY IN PARAMECIUM
Authors: Sainsard-Chanet Annie , Knowles Jonathan
Published: April 2021

In Paramecium, as previously described, the nuclear mutation cl1 is incompatible with wild-type mitochondria (M+); however, all cl1,/cl1,M+ cells eventually overcome this incompatibility (SAINSARD, CLAISSE and BALME-FREZOL 1974). We have studied the kinetics and genetic basis of the spontaneous restoration of harmony between nucleus and mitochondria. We also studied the modification of these kinetics following microinjection of compatible mutant mitochondria into cl1/cl1M+ cells. We demonstrate that nucleo-mitochondrial readjustment is always achieved by mitochondrial changes that fall into two classes. The first class corresponds to spontaneous mitochondrial mutations affecting the amount of cytochrome aa3 and is similar to the previously described Mcl and Msu mutations (SAINSARD-CHANET 1978; SAINSARD 1975). The nature of the second class of modification is not yet understood; it may correspond either to a mitochondrial "adaptation" or to an unusual type of mutation arising and reverting at high frequency.
CYTOGENETICS OF THE SOUTH AMERICAN DROSOPHILA MULLERI COMPLEX: THE MARTENSIS CLUSTER. MORE INTERSPECIFIC SHARING OF INVERSIONS
Authors: Wasserman Marvin , Koepfer H Roberta
Published: April 2021

Three Drosophila mulleri complex species have been found to be endemic to the cactus regions of northern South America. The three species are morphologically distinct, and no hybridization between species has been found in either the laboratory or nature. An analysis of their salivary gland chromosomes revealed that they evolved from a single cytological population, subspecies F of the ancestor of the D. mulleri complex, and comprise a cluster of sister species that are homozygous for inversions not found elsewhere. Within the martensis cluster are also found several inversions that are unique for these species, but have segregated out among the three species. Thus 2f2 is found in martensis and starmeri, but not in uniseta, while 2t6, 3v and 3w are found in starmeri and uniseta, but not in martensis. This is analogous to the situation found within the remainder of the mulleri complex species, all the members of which share homozygosity for six other inversions. An interpretation of the cytological evolution of the martensis cluster is proposed.
EFFECT OF TERMINAL ANEUPLOIDY ON EPIDERMAL CELL VIABILITY IN DROSOPHILA MELANOGASTER
Authors: Ripoll Pedro
Published: April 2021

In Drosophila melanogaster, individuals heterozygous for translocations between chromosomes Y and 3 can generate, by means of mitotic recombination, somatic cells bearing duplications and deletions. Using translocations with different breakpoints, I have studied the behavior of clones ofcells with increasing degrees of aneuploidy in the abdominal cuticle. Both hyper- and hypoploid cells can survive being duplicated or deficient even for large chromosome 3 fragments. While hyperploidy does not severely affect cell viability, the recovery of hypoploid clones decreases linearly as a function of the size of the deleted fragment. In this report, the quantitative and qualitative aspects of thiseffect are discussed.
DYNAMICS OF CORRELATED GENETIC SYSTEMS. V. RATES OF DECAY OF LINKAGE DISEQUILIBRIA IN EXPERIMENTAL POPULATIONS OF DROSOPHILA MELANOGASTER
Authors: Clegg M T , Kidwell J F , Horch C R
Published: April 2021

The dynamic behavior of four-locus gametic frequency distributions was studied in five replicate cage populations of Drosophila melanogaster for up to 50 generations. The joint frequency distributions were resolved into gene freqcencies and various disequilibrium measures. In addition, F statistics for marginal single-locus genotypic frequency distributions were followed through time. The gene frequency, disequilibrium and F statistics were obtained for four chromosome 3 enzyme marker loci [isocitrate dehydrogenase (3-27.1), esterase4 (3-36.8). phosphoglucomutase (343.4) and esterase-c (3-49.0)]. The initial structure of the experimental populations featured random mating proportions, and two complementary gametic types with respect to the marker loci, thus assuring complete pairwise linkage disequilibrium among the markers.—The experimental results indicate: (1) the between-replicate variance in gene frequency varied substantially among loci, with isocitrate dehydrogenase showing the greatest between-replicate variance, and esterase-C the least. (2) The F statistics initially were strongly negative but decayed to the neighborhood ofzero for all marker lociexcept esterase-C. The rate at which the F statistics approached zero varied among the marker loci, indicating substantial differences in the distribution of selective effects along the chromosome. The centromeric region, marked by esterase-C, shows the strongest selective effects. (3)The rate of decay 3flinkage disequilibrium was much faster than expected for pairs of neutral loci, averaging 1.82times the neutral rate over all replicates and pairs of loci. This acceleration, which was observed for all six pairwise combinations of loci, was interpreted asresulting from the interaction bctween selection and recombination. Our experimental results are consistent with many investigations of linkage disequilibrium in natural populations of Drosophila melanogasler that show little or no disequilibrium among enzyme loci. (4) Afortuitous contamination of two cages revealed an apparent regulatory interaction between the migrant and nonmigrant chromosomes at the esterase-C locus. The migrant chromosomes were very rapidly absorbed into the recipient populations, despite this interaction. This result suggests that the dynamics of migration in populations may be phenomenologically richer than anticipated by simple theory.
DEFINITION OF ADDITIONAL FLAGELLAR GENES IN ESCHERICHIA COLI K12
Authors: Komeda Yoshibumi , Kutsukake Kazuhiro , Iino Tetsuo
Published: April 2021

Twentynine flagellar genes in Escherichia coli K12 have previously been assigned to three regions of the genome. Flagellar region I is located between pyrC and ptsG, region I1 between aroD and uvrC, and region I11 between uvrC and his. In this study, flagellar mutants in EscherLchia coli K12 were obtained by selection for resistance to the flagellotropic phage, x. They were analyzed in complementation tests using PI phage-mediated transduction. In addition to the fla genes already described, eight more flagellar genes were identified. This analysis defined six more fla genes in region I (flaU, etc.), one more in region I1 (fZbB) and one more in region I11 (flbC) . Region I was shown to include at least 12 fla cistrons. Complementation analysis with polar Muphage-induced Fla- mutants and with λfla phage defined four transcriptional units in region I. These were: flaU, flbA-flaw-flav-flaK-flax-flaL-flay-flaM, fluz and flaS-flaT, with transcription proceeding from left to right. The flbB gene was found to be part of an operon: flbB-flal in region 11. In region 111, a previously unidentified gene flbC was located between hag and flaN.
THE MEIOTIC EFFECTS OF A DEFICIENCY IN DROSOPHILA MELANOGASTER: IDENTIFICATION OF TWO DOSAGE-SENSITIVE SITES
Authors: Robbins Leonard G
Published: April 2021

Heterozygosity for a deficiency for the entire zeste-white region of the X chromosome of Drosophila melanogaster females causes both reduced recombination and increased nondisjunction. The location of the dosage-sensitive sites responsible for these two meiotic defects has been studied by use of a set of deficiencies that subdivide the region. Recombination is reduced when the zw7-zwll region is present in one dose, while nondisjunction is increased only if the doses of both the zw8-zwl0 and zwb-zwll segments are reduced. Examination of truns heterozygotes of two deficiencies explicitly demonstrates the compound nature of the meiotic dose effect and further delimits the location of the proximal disjunctional site to the zwl2-zwll interval. In inversion/deficiency heterozygotes, reduced dose ofthe zw8-zwl0 region alone, without reduced dose of the proximal site, yields increased nondisjunction, suggesting that the proximal element that affects disjunction is the same as that which affects recombination. Thus, the zeste-white region contains at least two dosagesensitive loci that affect meiosis: reduced dosage of one locus, in the zw7-zwfl interval, causes reduced recombination; reduced dose of another, in the zw8-zw10 region, increases the probability that nonexchange chromosomes will nondisjoin. Aslight effect on the regional distribution of exchange may also be a property of the zw8-zwlO region locus, but could be an effect of yet another locus or of structural heterozygosity. The implications of these results for understanding meiotic control and the prospects for further analysis of the structure of the zeste-white interval are considered.
PLEIOTROPIC EFFECTS ON FITNESS OF MUTATIONS AFFECTING VIABILITY IN DROSOPHILA MELANOGASTER
Authors: Simmons Michael J , Preston Christine R , Engels William R
Published: April 2021

The relative viabilities and fitnesses of wild-type second chromosomes in heterozygous condition were determined. Joint analysis of these permitted an estimation of a parameter that relates the viability effect of a mutation to its effect on fitness as a whole. For newly arisen mutations, the estimate was slightly greater than one, indicating that the reductions in viability caused by these mutations are associated with reductions in other components of fitness. For mutations from an equilibrium population, the estimate of the parameter was near zero, implying that the deleterious viability effects of these mutations arc compensated by improvements in other aspects of fitness.
NUMERICAL ANALYSIS OF RANDOM DRIFT IN A CLINE
Authors: Nagylaki Thomas , Lucier Bradley
Published: April 2021

The equilibrium state of a diffusion model for random genetic drift in a cline is analyzed numerically. The monoecious organism occupies an unbounded linear habitat with constant, uniform population density. Migration is homogeneouq symmetric and independent of genotype. A single diallelic locus with a step environment is investigated in the absence of dominance and mutation. The flattening of the expected cline due to random drift is very slight in natural populations. The ratio of the variance of either gene frequency to the product of the expected gene frequencies decreases monotonically to a nonzero constant. The correlation between the gene frequencies at two points decreases monotonically to zero as the separation is increased with the average position fixed; the decrease is asymptotically exponential. The correlation decreases monotonically to a positive constant depending on the separation as the average position increasingly deviates from the center of the cline with the separation fixed. The correlation also decreases monotonically to zero if one of the points is fixed and the other is moved outward in the habitat, the ultimate decrease again being exponential. Some asymptotic formulae are derived analytically.—The loss of an allele favored in an environmental pocket is investigated by simulating a chain of demes exchanging migrants, the other assumptions being the same as above. For most natural populations, provided the allele would be maintained in the population deterministically, this process is too slow to have evolutionary importance.
HITCHHIKING: A COMPARISON OF LINKAGE AND PARTIAL SELFING
Authors: Hedrick Philip W
Published: April 2021

Genetic hitchhiking occurs when alleles at unselected loci are changed in frequency because of an association with alleles at a selected locus. This association may be mediated either by linkage or partial selfing (inbreeding) and can affect the gene frequency and gametic disequilibrium at the neutral loci. Hitchhiking from partial selfing (unlinked loci) occurs more quickly than linkage hitchhiking and generally has a greater effect. In addition, partial-selfing hitchhiking can cause increases or changes in sign in gametic disequilibrium between neutral loci. The effects of the two types of hitchhiking with different levels of dominance, zygotic frequencies and number of selected loci are also examined. The general conditions for linkage and partial-selfing hitchhiking are outlined and the implications of hitchhiking are discussed for marker or electrophoretic loci.
PLEIOTROPIC PROPERTIES OF A YEAST MUTANT INSENSITIVE TO CATABOLITE REPRESSION
Authors: Stark Helene Cherrick , Fugit Donna , Mowshowitz Deborah Bernhardt
Published: April 2021

The flk1 mutation, which was originally isolated in the yeast Saccharomyces cadsbergenesis, causes insensitivity to catabolite repression. This mutation has been further characterized and mapped. The gene flkl is located on chromosome III between thr4 and MAL2,14 centimorgans from MAL2. flk1 is shown to be allelic to the pleiotropic mutants tupl, cyc9, and umr7; and flk1 is shown to exhibit an array of pleiotropic properties common to tupl, cyc9 and umr7; These results suggest that the flkl mutation is not a specific lesion affecting catabolite repression.
GENETIC MAPPING OF THE pho2, PHO82–pho4 AND pho85 LOCI OF YEAST
Authors: Toh-E Akio
Published: April 2021

The PH082-pho4 (PHOO-phoD) locus was mapped on the right arm of chromosome VI,6.5 cM centromere-distal to met10. A pho85 (phoU) mutant was newly isolated, and its map location was determined on the left arm of chromosome XVI, 15 cM centromere-distal to rad1. Amutant gene that causes temperature-sensitive growth on nutrient medium was found very near (or at) the pho85 locus. The supertriploid method was successfully applied to locate the pho2 (phoB) locus on chromosome IV. The pho2 locus was 40 cM from rna11 on the left arm of chromosome IV.
COMPONENTS OF HYBRID DYSGENESIS IN A WILD POPULATION OF DROSOPHILA MELANOGASTER
Authors: Engels William R , Preston Christine R
Published: April 2021

Hybrid dysgenesis is a condition foand in certain interstrain hybrids of Drosophila melanogrrster caused by the interaction of chromosomal and cytoplasmic factors. Germ line abnormalities, including sterility, high mutability and male recombination, appear in the affected individuals. There are at least two distinct systems of hybrid dysgenesis. We examined a Wisconsin wild populetion in two consecutive years to determine the distribution of the chromosomal P factor and the extrachromosomal M cytotype that together cause one kind of hybrid dysgonic sterility. The P factor was found to be very common in the populetion, with all three major chromosomes heing polymorphic for it. This polymorphism was strongly correlated with variability for male recombination elements, suggesting that these two traits are part of the same system of hybrid dysgenesis. There was a slight tendency for the P factor to be lost in lines taken from this population and inbred in the laboratory for many generations. A large-scale search for the M cytotype, which causes susceptibility to the P factor, showed that it is present in the papulation at only very low frequencies. Further evidence that the population is mostly immune to the action of the P factor was our finding of a general lack of dysgenic sterility in the wild flies themselves. However, we were able to isolate several wild strains that consistently showed the M cytotype. In some cases, the frequency of the M cytotype could be maintained in these lines, but it could not usually be increased by artificial sclection. Some possible consequences of hybrid dysgenesis for the evolutional y Siology of Drosophila are suggested.
MAPPING OF THE polA LOCUS OF ESCHERICHIA COLI K12: GENETIC FINE STRUCTURE OF THE CISTRON
Authors: Kelley William S
Published: April 2021

The close linkage of the glnA gene with polA was exploited to construct a fine structure map of polA by means of generalized transduction with phage P1. Nine different polA- alleles were mapped by recombinational crosses. The results indicate a gene order consistent with previous observations (KELLEYand GRINDLEY 19 76a; MURRAY an d KELLEY 1979). Three mutations, polA5, polA6 and polA12 map within the "carboxy-terminal" or "large-fragment'' portion of the gene in unambiguous order. Four alleles, known to affect the "aminoterminal" portion of the gene, polA107, polA214, polA480ex and polA4113, appear to be closely linked with certain ambiguities in their exact order. All four of these mutations are known to alter the 5'→3' exonuclease activity of DNA polymerase I and three of them result in the conditional lethal polA- phenotype. The polA1 nonsense mutation maps between these two groups in a position consistent with its known effect, production of an amber fragment that includes the 5'→3' exonuclease. The final allele, resAl, is another nonsense mutation that maps at; the extreme "amino-terminus" of the cistron.—A number of control experiments were conducted to determine the effects of pol.A- mutatims on the PI-mediated recombinational event. These experiments indicated that abortive transduction occurs quite frequently, but the formation of abortive transductants and segregation of unselected transduced markers among daughter progeny is like that observed by other investigators. There was no evidence that any individual polA- allele behaved in an exceptional fashion during recombination.
MATHEMATICS OF CHROMOSOME PAIRING
Authors: Driscoll C J , Gordon G H , Kimber G
Published: April 2021

Analysis of frequencies of chromosome configurations in wheat-related species hybrids is extended to include cases involving homoeologous groups of size six. Further, the expected frequencies of the various configurations emanating from homologous and homoeologous pairing events have been determined for groups consisting of two and three homoeologous pairs of homologous chromosomes. Analysis of configuration frequencies of nullisomic 5B of wheat, in which both homologous and homoeologous pairing occurs, led to estimation of the relative frequencies of homologous and homoeologous pairing events as 17.9: 1. In the samples analyzed, slightly less than one homoeologous exchange occurred per gamete.
A METHOD FOR COMPLEMENTATION ANALYSIS OF NUCLEAR AND CHLOROPLAST MUTANTS OF PHOTOSYNTHESIS IN CHLAMYDOMONAS
Authors: Bennoun Pierre , Masson Arlette , Delosme Monique
Published: April 2021

The photosynthetic properties of young zygotes of Chlamydomonas reinhardi were analyzed. In heterozygotes for two nuclear or two chloroplast mutations affecting photosynthesis, recovery of photosynthetic activity was observed that is most likely the result of intergenic complementation.—We observed that chloramphenicol inhibited the recovery of activity in double heterozygotes for mutants lacking at least one thylakoid polypeptide of chloroplast origin, while it had no effect on wild-type homozygotes. This indicates that the recovery of activity in double heterozygotes could result from the repair of existing thylakoid membranes by de nouo synthesis of the missing polypeptides.
HETERODUPLEX REPAIR AS AN INTERMEDIATE STEP OF UV MUTAGENESIS IN YEAST
Authors: Eckardt Friederike , Teh Soo-Jeet , Haynes R H
Published: April 2021

We have measured UV-induced mutation frequencies in yeast in a forward, nonselective assay system by scoring white adex ade2 double auxotrophs among parental red-pigmented ade2 clones. The frequencies of sectored and pure mutant clones were determined separately. In excision-defective strains carrying the genes radl-1, rad3-2 and rad4-4, as well as in the double mutants, rad 1-1 rad 3-2 and rad 1-1 rad 4-4, considerably more sectored than pure clones are induced in the low-dose range; in repair-competent strains, pure mutant clones substantially outnumber the sectored clones. These results can be explained on the basis of known differences in the timing of error-prone repair during the cell division cycle; that is, we assume that error-prone repair occurs primarily before replication in RAD wild-type strains but after replication in excision-deficient mutants. It has been suggested that excision deficiency has a pleiotropic effect on heteroduplex repair and nucleotide excision repair; however, the high percentage (36.6%) of half-sectored clones found in the rad1-1 strain is hard to reconcile with this hypothesis. We propose that heteroduplex repair occurs subsequent to error-prone repair in both excisionproficient and excision-deficient strains.
REVERSION FROM SUPPRESSION TO NONSUPPRESSION IN SUQ5 [psi
+] STRAINS OF YEAST: THE CLASSIFICATION OF MUTATIONS
Authors: Cox B S , Tuite M F , Mundy C J
Published: April 2021

Reversion from the suppressed to nonsuppressed phenotype in strains of genotype SUQ5 [psi  +] ade2-1 his5-2 lys1-1 can1-100 ura3-1 has been induced by treatment with ethyl methanesulphonate, nitrosoguanidine or UV (254 nm) light. Spontaneously occurring revertants have also been selected by two different methods. Reversion has been shown to occur through a variety of nuclear mutations and through mutation of [psi  +] to [psi  -]. Nuclear mutations included back-mutation of SUQS, antisuppressor mutations that were recessive, semi-dominant or dominant, and dominant or recessive mutations of genes required for the maintenance of the [psi  +] factor. Complementation tests by which the various kinds of mutations could be distin guished from one another were designed. The spectra of spontaneously occurring and induced mutations have been described.
JOINT SEGREGATION OF BIOCHEMICAL LOCI IN SALMONIDAE. II. LINKAGE ASSOCIATIONS FROM A HYBRIDIZED SALVELINUS GENOME (S. NAMAYCUSH x S. FONTINALIS)
Authors: May Bernie , Stoneking Mark , Wright James E
Published: April 2021

The results of more than 300 parwise examinations of biochemical loci for joint segregation in brook trout (Salvelinus fontinalis) and in the hybridized genome of lake trout (S. namaycush) × brook trout are summarized. Nineteen loci have been assigned to the following eight linkage groupings on the basis of nonrandom assortment, including cases of both classical linkage and pseudolinkage: ODH with PMI with PGI-3, PGI-2 with SDH, ADA-1 with AGP-2, AAT-(1,2) with AGP-1 with MDH-I, MDH-3 with MDH-4, LDH-3 with LDH-4, IDH-3 with ME-2 and GUS with CPK-I. Pseudolinkage (an excess of nonparental progeny types) was observed only for male testcross parents. The results suggest that this phenomenon involves homeologous chromosome arms as evidenced by the de novo association of presumed duplicate loci in each case. Classical linkage has not been found for the five pairs of duplicate loci examined in Salvelinus, suggesting that not all of the eight metacentrics in the haploid complement involve fusions of homeologous chromosomes. Females consistently showed a greater degree of recombination.
FRAMESHIFT SUPPRESSION IN SACCHAROMYCES CEREVISIAE. II. GENETIC PROPERTIES OF GROUP II SUPPRESSORS
Authors: Culbertson Michael R , Underbrink Karen M , Fink Gerald R
Published: April 2021

Suppressors of ICR-induced mutations that exhibit behavior similar to bacterial frameshift suppressors have been identified in the yeast Saccharomyces cerevisiae. The yeast suppressors have been divided into two groups. One of these groups (Group II: SUFI, SUF3, SUF4, SUF5 and SUF6) appears to include a set of informational suppressors in which the vehicle of suppression is glycyl-tRNA. Some of the genetic properties of Group II suppressors are described in this communication.—Corevertants of the Group II frameshift mutations his4-519 and leu2-3 have been characterized to determine the spectrum of reversion events induced by the frameshift mutagen ICR-170. Seventythree ICR-induced corevertants were analyzed. With the exception of one corevertant, which carried an allele of SUF1, all carried alleles of SUF3 or SUF5, SUF1, SUF3, SUF4 and SUF6 were represented among spontaneous and UV-induced corevertants. In the course of these experiments one of the suppressors was mapped. SUF5, the probable structural gene for tRNAGLY1, is located between ade2 and ade9 on chromosome XV.—SUF1, SUF4 and SUF6 have novel properties and comprise a distinct subset of suppressors. Although these suppressors show no genetic linkage to each other, they share several common features including lethality in haploid pairwise combinations, reduced tRNAGLY3 isoacceptor activity and increased efficiency of suppression in strains carrying the cytoplasmically inherited [PSI] element. In addition, strains carrying SUFI, SUF4 or SUF6 are phenotypically unstable and give rise to mitotic Suf+ segregants at high frequency. These segregants invariably contain a linked, second-site mutation that maps in or adjacent to the suppressor gene itself. Strains carrying any of these suppressors also give rise to mitotic segregants that exhibit enhanced efficiency of suppression; mutations responsible for this phenotype map at two loci, upf1 and upf2. These genes show no genetic linkage to any of the Group II suppressors.—Methods that permit positive selection for mutants with decreased or enhanced efficiency of suppression have been devised in order to examine large numbers of variants. The importance of these interacting mutants is underscored by their potential utility in studying suppressor function at the molecular level.