bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of pulsed magnetic field on density reduction of high flow velocity plasma sheath
Authors: XU Jiahao , LI Xiaoping , LIU Donglin , WANG Yuan
Published: April 2021

A three-dimensional model is proposed in this paper to study the effect of the pulsed magnetic field on the density distribution of high flow velocity plasma sheath. Taking the typical parameters of plasma sheath at the height of 71 km as an example, the distribution characteristics and time evolution characteristics of plasma density in the flow field under the action of pulsed magnetic field, as well as the effect of self-electric field on the distribution of plasma density, are studied. The simulation results show that pulsed magnetic field can effectively reduce the density of plasma sheath. Meanwhile, the simulation results of three-dimensional plasma density distribution show that the size of the density reduction area is large enough to meet the communication requirements of the Global Position System (GPS) signal. Besides, the location of density reduction area provides a reference for the appropriate location of antenna. The time evolution of plasma density shows that the effective density reduction time can reach 62% of the pulse duration, and the maximum reduction of plasma density can reach 55%. Based on the simulation results, the mechanism of the interaction between pulsed magnetic field and plasma flow field is physically analyzed. Furthermore, the simulation results indicate that the density distributions of electrons and ions are consistent under the action of plasma self-electric field. However, the quasi neutral assumption of plasma in the flow field is not appropriate, because the self-electric field of plasma will weaken the effect of the pulsed magnetic field on the reduction of electron density, which cannot be ignored. The calculation results could provide useful information for the mitigation of communication blackout in hypersonic vehicles.
Integration in reproducing kernel Hilbert spaces of Gaussian kernels
Authors: Karvonen Toni , Oates Chris , Girolami Mark
Published: April 2021

The Gaussian kernel plays a central role in machine learning, uncertainty quantification and scattered data approximation, but has received relatively little attention from a numerical analysis standpoint. The basic problem of finding an algorithm for efficient numerical integration of functions reproduced by Gaussian kernels has not been fully solved. In this article we construct two classes of algorithms that use

N
N

evaluations to integrate

d
d

-variate functions reproduced by Gaussian kernels and prove the exponential or super-algebraic decay of their worst-case errors. In contrast to earlier work, no constraints are placed on the length-scale parameter of the Gaussian kernel. The first class of algorithms is obtained via an appropriate scaling of the classical Gauss–Hermite rules. For these algorithms we derive lower and upper bounds on the worst-case error of the forms

exp
⁡
(
−

c
1

N

1

/

d

)

N

1

/

(
4
d
)

\exp (-c_1 N^{1/d}) N^{1/(4d)}

and

exp
⁡
(
−

c
2

N

1

/

d

)

N

−
1

/

(
4
d
)

\exp (-c_2 N^{1/d}) N^{-1/(4d)}

, respectively, for positive constants

c
1

>

c
2

c_1 > c_2

. The second class of algorithms we construct is more flexible and uses worst-case optimal weights for points that may be taken as a nested sequence. For these algorithms we derive upper bounds of the form

exp
⁡
(
−

c
3

N

1

/

(
2
d
)

)

\exp (-c_3 N^{1/(2d)})

for a positive constant 

c
3

c_3

.
Uniformly branching trees
Authors: Bonk Mario , Meyer Daniel
Published: April 2021

A quasiconformal treeTTis a (compact) metric tree that is doubling and of bounded turning. We callTTtrivalent if every branch point ofTThas exactly three branches. If the set of branch points is uniformly relatively separated and uniformly relatively dense, we say thatTTis uniformly branching. We prove that a metric spaceTTis quasisymmetrically equivalent to the continuum self-similar tree if and only if it is a trivalent quasiconformal tree that is uniformly branching. In particular, any two trees of this type are quasisymmetrically equivalent.
Adapting Mizoguchi’s Ugetsu in Kazuo Ishiguro’s The Buried Giant
Authors: Shen Anni
Published: April 2021

The Ishiguro archive in the Harry Ransom Center in Austin houses Ishiguro’s extensive research on Japanese ghost stories and films from his early film writing, revealing his fascination with Kenji Mizoguchi’s Ugetsu Monogatari and Sansho Dayu. This article explores Kazuo Ishiguro’s references to Ugetsu in The Buried Giant to reflect on the realistic portrayal of ghosts as a way to reveal a suppressed pagan narrative. Using materials from the Ishiguro archive, I argue that Ishiguro borrows tactics from Ugetsu and then incorporates the Japanese Buddhist myth and folklore underlying Sansho Dayu to build a hidden discourse of the dead that subverts the dominant discourse of God, creating an implicit supernatural plot that parallels the novel’s explicit realistic plot and that decentres Britain’s national beliefs.
The Utility of Unsupervised Machine Learning in Anatomic Pathology
Authors: McAlpine Ewen D , Michelow Pamela , Celik Turgay
Published: April 2021

Objectives

Developing accurate supervised machine learning algorithms is hampered by the lack of representative annotated datasets. Most data in anatomic pathology are unlabeled and creating large, annotated datasets is a time consuming and laborious process. Unsupervised learning, which does not require annotated data, possesses the potential to assist with this challenge. This review aims to introduce the concept of unsupervised learning and illustrate how clustering, generative adversarial networks (GANs) and autoencoders have the potential to address the lack of annotated data in anatomic pathology.

Methods

A review of unsupervised learning with examples from the literature was carried out.

Results

Clustering can be used as part of semisupervised learning where labels are propagated from a subset of annotated data points to remaining unlabeled data points in a dataset. GANs may assist by generating large amounts of synthetic data and performing color normalization. Autoencoders allow training of a network on a large, unlabeled dataset and transferring learned representations to a classifier using a smaller, labeled subset (unsupervised pretraining).

Conclusions

Unsupervised machine learning techniques such as clustering, GANs, and autoencoders, used individually or in combination, may help address the lack of annotated data in pathology and improve the process of developing supervised learning models.
The Influence of Abdominal Obesity on Endothelial Function of the Tibial Artery in the Elderly Essential Hypertensives of Different Sex
Authors: Cai Xiao-qi , Huang He-ling , Shen Yi-hua , Zhang Ling-yu , Xu Guo-yan , Xie Liang-di
Published: April 2021

Background

To investigate the relationship between abdominal obesity and endothelial function of the tibial artery in the elderly essential hypertensives of different sex.

Methods

A total of 658 elderly patients (≥60 years old) with essential hypertension and 64 elderly subjects without clinical evidence of hypertension were recruited from the department of geriatrics from August 2000 to May 2016. The dilatation of anterior tibial artery induced by reactive hyperemia was examined by high-resolution vascular ultrasound and was defined as endothelium-dependent dilatation (EDD). All the participants were divided into 4 groups based on blood pressure (≥140/90 mm Hg) and waist circumference (male ≥90 cm, female ≥85 cm): normotensive without abdominal obesity (n = 34), normotensive with abdominal obesity (n = 30), hypertensive without abdominal obesity (n = 287), and hypertensive with abdominal obesity (n = 371).

Results

A gradual decline in EDD was observed from normotensive without abdominal obesity (9.37 ± 1.11%), normotensive with abdominal obesity (8.59 ± 0.99%), hypertensive without abdominal obesity (7.70 ± 0.30%) to hypertensive with abdominal obesity (6.75 ± 0.26%) (P < 0.05). There was no significant difference in EDD between the male and female elderly hypertensives with or without abdominal obesity. In male elderly hypertensives, EDD in those with central obesity was more blunted compared with those without central obesity (6.31 ± 0.38% vs. 7.46 ± 0.38%, P < 0.05). Whereas, in female elderly hypertensives, EDD in those with abdominal obesity was similar to those without abdominal obesity. In male elderly hypertensives, EDD was correlated with waist circumference (r = −0.194, P < 0.05) while such association was not shown in females. Multivariate linear regression analysis revealed that waist circumference was associated with EDD (β = −0.161, P < 0.05) in the male elderly hypertensives, but not in females.

Conclusions

Waist circumference is an influencing factor of EDD in male elderly essential hypertension patients. However, abdominal obesity has little effect on EDD of the tibial artery in female elderly hypertensives.
Bacterial biosilicification: a new insight into the global silicon cycle
Authors: Ikeda Takeshi
Published: April 2021

Biosilicification is the process by which organisms incorporate soluble, monomeric silicic acid, Si(OH)4, in the form of polymerized insoluble silica, SiO2. Biosilicifying eukaryotes, including diatoms, siliceous sponges, and higher plants, have been the targets of intense research to study the molecular mechanisms underlying biosilicification. By contrast, prokaryotic biosilicification has been less well studied, partly because the biosilicifying capability of well-known bacteria was not recognized until recently. This review summarizes recent findings on bacterial extracellular and intracellular biosilicification, the latter of which has been demonstrated only recently in bacteria. The topics discussed herein include bacterial (and archaeal) extracellular biosilicification in geothermal environments, encapsulation of Bacillus spores within a silica layer, and silicon accumulation in marine cyanobacteria. The possible contribution of bacterial biosilicification to the global silicon cycle is also discussed.
COMPOUND AUTOSOMES IN DROSOPHILA MELANOGASTER: THE MEIOTIC BEHAVIOR OF COMPOUND THIRDS
Authors: Holm David G , Chovnick Arthur
Published: April 2021

Studies of the meiotic distribution of compound-3 chromosomes in males and females of Drosophila melanogaster provided the following results. (1) From females homozygous for the standard arrangement of all chromosomes other than C(3L) and C(3R), less than 5% of the gametes recovered were nullosomic or disomic for compound-3 chromosomes. The frequency of nonsegregation differed between strains, but within a given strain it remained relatively constant. (2) According to egg-hatch frequencies, C(3L) and C(3R) segregate independently during spermatogenesis. (3) In females, structurally heterozygous second chromosomes occasion a marked increase in the recovery of nonsegregational progeny; in males, rearranged seconds have no apparent influence on the distribution of compound thirds. (4) The highest frequencies of nonsegregational progeny were recovered from C(3L);C(3R) females carrying compound-X (plus free Y) chromosomes. (5) In comparing the recovery of nonsegregating compound thirds to the recovery of rearranged heterologs, a definite nonrandom distribution was realized in several crosses. These results are examined in reference to the concepts of distributive pairing (Grell 1962). Moreover, considering the structural nature of compound autosomes, we propose that nonhomologous (distributive) pairing is a property of the centromeric region and suggest that rearrangements involving breaks in this region possibly alter the effectiveness of distributive pairing forces.
ELEMENTS CAUSING MALE CROSSING OVER IN DROSOPHILA MELANOGASTER
Authors: Slatko Barton E , Hiraizumi Yuichiro
Published: April 2021

A second chromosome line of Drosophila melanogaster (Symbol: T-007) has previously been shown to be responsible for the induction of male recombination. In the present investigation, the genetic elements responsible for this phenomenon have been partially identified and mapped. A major element (Symbol: Mr, for M ale recombination) locates on the second chromosome between the pr (2L-54.4) and c (2R-75.5) loci and is responsible for the large majority of male recombination. In addition, there appear to be "secondary elements" present which have the ability to induce male recombination in much reduced frequencies and which are diluted out through successive backcross generations when Mr is removed by recombination. The possible nature of these "secondary elements" is discussed.
DIALLEL ANALYSIS OF GROWTH TRAITS IN MICE
Authors: Jamison M G , White J M , Vinson W E , Hinkelmann K
Published: April 2021

Two replications of a complete diallel cross experiment were performed among four partially inbred lines of mice. These inbred lines originated from a random-bred ICR strain and were produced by 12 generations of full sibbing (F ≃ 92%). Individual body weight was recorded for each animal at 12, 21, 42 and 56 days of age. Body weight gain traits were examined for intervals 12-21, 21-42 and 42-56 days. Simultaneous least squares analyses of inbred and linecrossed groups were used. Sex differences were highly significant for all traits. Replicate differences were significant but made a small contribution to the total variation. Inbred lines differed greatly. Crosses showed growth trends similar to their contemporary maternal and paternal inbreds. Heterosis was highly significant for all traits except 21-day weight. Inbreds were heavier at 12 days of age, but linecrossed progeny were superior to inbreds for all post-weaning weights. General combining ability was highly significant for 12- and 56-day weights and 21-42-day gain. Specific combining ability was highly significant for 21-day weight, 12-21- and 42-56-day gain. Significant maternal effects were found for all individual weights but not for 12-21- and 21-42-day gain. Residual reciprocal effects were significant for all traits. Estimated variances among linecrossed groups contained a large maternal component, a fluctuating additive genetic component and consistent non-additive genetic influence on all growth parameters measured.
INDUCTION AND TRANSMISSION OF A MERODIPLOID CONDITION NEAR THE TERMINAL AREA OF THE CHROMOSOME OF BACILLUS SUBTILIS
Authors: Jamet-Vierny C , Anagnostopoulos C
Published: April 2021

A small fraction (about 0.5%) of the transformants for a particular marker of B. subtilis (ilvA4; most probably a deletion) were found to be relatively unstable merodiploids. They possess a redundancy of the metB–ilvA chromosome segment. When their DNA is used as donor in transformation a merodiploid condition for the whole of this segment is created in all ilvA4+ transformants. For several of the duplicated loci both copies often are of recipient strain origin. Markers originally belonging to different copies of the diploidized region can be contransferred in PBS1-mediated transduction. The data are well in agreement with the hypothesis that the merodiploids carry a tandem duplication. An alternative hypothesis which does not call for integration of the exogenote within the recipient chromosome was also considered. Models are proposed for interpreting the segregation of the merodiploids, the transmission of the diploid state and its generation during transformation of the ilvA4 marker by wild-type DNA.
SEX DETERMINATION IN BEES. IV. GENETIC CONTROL OF JUVENILE HORMONE PRODUCTION IN MELIPONA QUADRIFASCIATA (APIDAE)
Authors: Kerr Warwick Estevam , Akahira Yukio , Camargo Conceição A
Published: April 2021

Cell number and volume of corpora allata was determined for 8 phases of development, the first prepupal stage to adults 30 days old, in the social Apidae Melipona quadrifasciata. In the second prepupal stage a strong correlation was found between cell number and body weight (r=0.651**), and cell number and corpora allata volume in prepupal stage (r=0.535*), which indicates that juvenile hormone has a definite role in caste determination in Melipona. The distribution of the volume of corpus allatum suggest a 3:1 segregation between bees with high volume of corpora allata against low and medium volume. This implies that genes xa and xb code for an enzyme that directly participates in juvenile hormone production. It was also concluded that the number of cells in the second prepupal stage is more important than the weight of the prepupa for caste determination. A scheme summarizing the genic control of sex and caste determination in Melipona bees in the prepupal phase is given.
THE GENETIC STRUCTURE OF A TRIBAL POPULATION, THE YANOMAMA INDIANS. XIV. CLINES AND THEIR INTERPRETATION
Authors: Ward R H , Neel James V
Published: April 2021

The Yanomama Indians are a South American tribe distributed over an irregular area approximately 200 × 300 miles. The gene frequencies observed at 12 loci in 47 villages within this area have been analyzed for the occurrence of clines. Apparently significant clines are observed for alleles of the Rh, MNSs, Kidd, Gm, Inv and serum albumin system. Available data concerning recent tribal expansion and admixture permit a tentative analysis of the causes of these clines. Although the action of selection cannot be rigorously excluded, it seems unlikely to be the major cause. Admixture with surrounding tribes plays a role which can be quantified because of the fortuitous circumstance of two genetic markers for admixture. It is suggested that an important factor in the origin of these clines is the manner in which the tribe has recently expanded through successive village fissionings and a predominantly centrifugal pattern of village migration.
TWO-WAY SELECTION FOR GROWTH RATE IN THE COMMON CARP (CYPRINUS CARPIO L.)
Authors: Moav R , Wohlfarth G
Published: April 2021

The domesticated European carp was subjected to a two-way selection for growth rate. Five generations of mass selection for faster growth rate did not yield any response, but subsequent selection between groups (families) resulted in considerable progress while maintaining a large genetic variance. Selection for slow growth rate yielded relatively strong response for the first three generations. Random-bred control lines suffered from strong inbreeding depression and when two lines were crossed, the F1 showed a high degree of heterosis. Selection was performed on pond-raised fish, but growth rate was also tested in cages. A strong pond-cage genetic interaction was found. A theoretical explanation was suggested involving overdominance for fast growth rate and amplification through competition of intra-group but not inter-group variation.
ISOLATION AND CHARACTERIZATION OF AMBER SUPPRESSORS IN YEAST
Authors: Liebman Susan W , Sherman Fred , Stewart John W
Published: April 2021

Nonsense suppressors were obtained in a haploid yeast strain containing eight nutritional mutations, that are assumed to be amber or ochre, and the cyc1-179 amber mutation that has a UAG codon corresponding to position 9 in iso-1-cytochrome c. Previous studies established that the biosynthesis and function of iso-1-cytochrome c is compatible with replacements at position 9 of amino acids having widely different structures (Stewart and Sherman 1972). UV-induced revertants, selected on media requiring the reversion of one or two of the amber nutritional markers, were presumed to contain a suppressor if there was the unselected reversion of at least one other marker. The 1088 suppressors that were isolated could be divided into 78 phenotypic classes. Only 43 suppressors of three classes caused the production of more than 50% of the normal amount of iso-1-cytochrome c in the cyc1-179 strain. Genetic analyses indicated that all of these highly efficient amber suppressors are allelic to one or another of the eight suppressors which cause the insertion of tyrosine at ochre (UAA) codons (Gilmore, Stewart and Sherman 1971). Furthermore, only tyrosine has been identified at position 9 in iso-1-cytochrome cin cyc1-179 strains suppressed with these efficient amber suppressors.
LINKAGE RELATIONSHIPS AND CHROMOSOME ASSIGNMENT OF FOUR ESTERASE LOCI IN THE MOSQUITO ANOPHELES ALBIMANUS
Authors: Vedbrat Sharanjit S , Whitt Gregory S
Published: April 2021

Although anopheline mosquitoes are important vectors of malaria, their genetic makeup has not yet been extensively investigated. The present studies concentrate on the genetic basis of esterases in Anopheles albimanus. Nine zones of esterase activity have been resolved by gel electrophoresis. Four of these esterases: EST-2, EST-4, EST-6, and EST-8 are present throughout all developmental stages and also possess allelic variation. Mass matings were carried out with homozygous males and females heterozygous for two or more loci. The analyses of progeny from single egg batches revealed that the four esterase systems mentioned above are encoded in separate loci with codominant alleles. Analyses of two-point and three-point crosses have indicated the following linkage relationship: Est-8 — 12% — Est-4 — 22% — Est-2 — 9% — Est-6. The assignment of this linkage group to chromosome 3 has been accomplished by the use of a Y-2 chromosome translocation.
SUPPRESSION OF THE KILLER PHENOTYPE IN USTILAGO MAYDIS
Authors: Koltin Y , Day P R
Published: April 2021

Nineteen sensitive cell lines of U. maydis were crossed with three killer strains and sample progenies were screened for killer segregation patterns. Crosses involving 11 lines gave killer frequencies ranging from 71%-100% of the progeny and 4:0 segregations in tetrads. Segregations in some crosses involving each of the remaining 8 lines gave killer frequencies from 0%-58% and mixed tetrads containing both non-killer and killer meiotic products. Many of the killers were unstable on further culture. Killer suppression showed varying degrees of specificity, appeared to be cytoplasmically determined for at least one strain, and was associated with possession of dsRNA in this strain and one other. No dsRNA was detected in two other suppressive strains. There was no evidence for segregation of nuclear maintainer genes for any of the killer determinants.
SYNAPTONEMAL COMPLEXES DURING PREMEIOTIC DNA SYNTHESIS IN OOCYTES OF DROSOPHILA MELANOGASTER
Authors: Day John W , Grell Rhoda F
Published: April 2021

Well-synchronized populations of oocytes obtained by means of the "pupal system" (Grell, 1973a) have been examined to determine the time of appearance of the synaptonemal complex. The complex first appears in the most advanced oocytes between 132 and 138 hr of female development. Between 138 and 156 hr the complex apparently undergoes a fourfold increase in length. At 150 and 156 hr the complex system is extensive and present in virtually all oocytes. Previous studies using the pupal system have placed the period of premeiotic DNA synthesis between 132 and 162 hr. Thus, indirect evidence indicates that a significant portion of synaptonemal complex formation is coextensive with the main DNA replication in the oocyte. Direct evidence that DNA synthesis and complex formation occur simultaneously in oocytes has been obtained by electron microscope autoradiography. By definition, then, the stage of synaptonemal complex formation in Drosophila must include premeiotic interphase.
SPECIALIZED TRANSDUCING PHAGES DERIVED FROM PHAGE P22 THAT CARRY THE proAB REGION OF THE HOST, SALMONELLA TYPHIMURIUM: GENETIC EVIDENCE FOR THEIR STRUCTURE AND MODE OF TRANSDUCTION
Authors: Jessop Adrienne P
Published: April 2021

Two independently isolated specialized transducing phages, P22pro-1 and P22pro-3, have been studied. Lysates of P22pro-1contain a majority of transducing phages which can go through the lytic cycle only in mixed infection; these defective phages transduce by lysogenization in mixed infection and by substitution in single infection. A few of the transducing phages in P22pro-1 lysates appear to be non-defective, being able to form plaques and to transduce by lysogenization in single infection. Transduction by P22pro-3 lysates is effected by non-defective transducing phages, which transduce by lysogenization; these lysates also contain a majority of defective phages which do not co-operate in mixed infection.

The P22pro-1 genome is thought to contain an insertion of bacterial DNA longer than the terminal repetition present in P22 wild type, so that at maturation a population of differently defective phages is produced. The exact structure of the P22pro-3 genome is open to conjecture, but it seems clear that the insertion of bacterial DNA is smaller than that in P22pro-1. Both P22pro-1 and P22pro-3 are defective in integration at ataA under non-selective conditions, although both integrate on medium that lacks proline.
MUTATIONAL ANALYSIS OF NATURAL ALLELES AT THE B INCOMPATIBILITY FACTOR OF SCHIZOPHYLLUM COMMUNE: α2 AND β6
Authors: Raudaskoski Marjatta , Stamberg Judith , Bawnik Nurit , Koltin Y
Published: April 2021

The B incompatibility factor of the fungus Schizophyllum commune having allelic specificity α2–β6 was subjected to mutagenesis by X-irradiation. Five types of mutations were recovered, four of them new types previously unreported. All lead to loss of the B-factor regulatory function; three of the five have retained their allelic specificity. The mutations map in three closely linked sites: Bα, Bβ, and between Bα and Bβ.
REMARKS ON THE EVOLUTIONARY EFFECT OF NATURAL SELECTION
Authors: Ewens W J
Published: April 2021

The so-called "Fundamental Theorem of Natural Selection", that the mean fitness of a population increases with time under natural selection, is known not to be true, as a mathematical theorem, when fitnesses depend on more than one locus. Although this observation may not have particular biological relevance, (so that mean fitness may well increase in the great majority of interesting situations), it does suggest that it is of interest to find an evolutionary result which is correct as a mathematical theorem, no matter how many loci are involved. The aim of the present note is to prove an evolutionary theorem relating to the variance in fitness, rather than the mean: this theorem is true for an arbitrary number of loci, as well as for arbitrary (fixed) fitness parameters and arbitrary linkage between loci. Connections are briefly discussed between this theorem and the principle of quasi-linkage equilibrium.
THIALYSINE-RESISTANT MUTANT OF SALMONELLA TYPHIMURIUM WITH A LESION IN THE thrA GENE
Authors: Jegede Victor A , Spencer Friederica , Brenchley Jean E
Published: April 2021

A mutant of Salmonella typhimurium was selected for its spontaneous resistance to the lysine analog, thialysine (S-2-aminoethyl cysteine). This strain, JB585, exhibits a number of pleiotropic properties including a partial growth requirement for threonine, resistance to thiaisoleucine and azaleucine, excretion of lysine and valine, and inhibition of growth by methionine. Genetic studies show that these properties are caused by a single mutation in the thrA gene which encodes the threonine-controlled aspartokinase-homoserine dehydrogenase activities. Enzyme assays demonstrated that the aspartokinase activity is unstable and the threonine-controlled homoserine dehydrogenase activity absent in extracts prepared from the mutant. These results explain the growth inhibition by methionine because the remaining homoserine dehydrogenase isoenzyme would be repressed by methionine, causing a limitation for threonine. The partial growth requirement for threonine during growth in glucose minimal medium may also, by producing an isoleucine limitation, cause derepression of the isoleucine-valine enzymes and provide an explanation for both the valine excretion, and azaleucine and thiaisoleucine resistance. The overproduction of lysine may confer the thialysine resistance.
TEMPERATURE-SENSITIVE YEAST MUTANTS DEFECTIVE IN MEIOTIC RECOMBINATION AND REPLICATION
Authors: Roth Robert
Published: April 2021

A system is described for isolating temperature-sensitive mutants of Saccharomyces cerevisiae with defects in early meiotic events. We used an otherwise haploid strain disomic (n+1) for chromosome III, and heteroallelic at the leucine-2 locus. Meiotic development was initiated by exposure of the strain to acetate sporulation medium, and monitored by the appearance of leucine-independent intragenic recombinants. Mutant isolation was based on the recovery of thermally induced defects in recombination. The temperature-sensitive characteristic was included to allow eventual characterizations of the temporal period during meiosis when each gene performs its essential function. Following mutagenesis with either ethyl methane sulfonate or nitrosoguanidine individual clones were tested at 34° and 24° for acetate-induced recombination. Starting with 2700 clones, derived from cells that survived mutagenic treatment, we isolated 48 strains with thermally induced lesions in recombination. In the majority of mutants premeiotic replication occurred normally, or nearly normally, at the restrictive temperature, indicating that the meiotic cycle was initiated and that there was a defect in an event required for intragenic recombination. We also detected mutants where the thermally induced lesion in recombination resulted from temperature-sensitive premeiotic DNA synthesis.
MUTAGENESIS OF CULTURED PLANT CELLS
Authors: Sung Z Renee
Published: April 2021

Experiments were designed to study the effectiveness of the chemical mutagens ethylmethane sulfonate and nitrosoguanidine on plant cells growing in liquid suspensions. Mutation frequency was defined as the number of colonies appearing on selective plates divided by the number of colonies growing on non-selective plates. The compounds tested usually increased mutation frequency by one order of magnitude over the spontaneously occurring rate, although the increase ranged from one to 140-fold. Cell killing was found to be directly correlated with mutation frequency.
ENVIRONMENTAL DETERMINATION OF SELECTIVE SIGNIFICANCE OR NEUTRALITY OF AMYLASE VARIANTS IN DROSOPHILA MELANOGASTER
Authors: De Jong G , Scharloo W
Published: April 2021

Strains homozygous at the amylase locus were derived from a polymorphic laboratory population of Drosophila melanogaster. The Amy 4,6 strain has higher enzyme activity than the Amy1 strain.—Maltose has the same nutritional value as starch.—The effect of starch in pure culture depends on the yeast level. At low yeast level increasing starch increases survival, at high yeast level increasing starch increases mean dry weight. The strains do not differ in survival or mean dry weight in pure culture.—In mixed cultures at 50% input of Amy 4,6 and Amy1 as larvae the percentage Amy4,6 in adults increases with increasing starch at low yeast levels, but equals input frequency at high yeast levels. No increase in percentage Amy4,6 in adults is present with increasing maltose at low yeast levels in mixed culture. The increase in percentage Amy4,6 with increasing starch must be due to selection on the amylase locus working by competition for food in the larval stage. The single locus selection coefficient is determined by the environment and can reach quite high values.—Viability selection in the presence of starch is in the direction indicated by the enzyme activities.
THE STRUCTURAL GENE FOR α-MANNOSIDASE-1 IN DICTYOSTELIUM DISCOIDEUM
Authors: Free S J , Schimke R T , Loomis W F
Published: April 2021

We have isolated 4 independent mutations affecting α-mannosidase-1, a a developmentally regulated activity in Dictyostelium discoideum. Three of these result in a thermolabile α-mannosidase-1 activity. One mutation also affects the substrate affinity (Km) of the activity. In diploids these mutations show a gene dosage effect and are all alleles. The structural gene for α-mannosidase-1, as defined by these mutations, defines a new linkage group, linkage group VI. α-Mannosidase-1 is probably a homopolymer with subunits of 54,000 daltons.
REGULATION OF PHOSPHATE METABOLISM IN NEUROSPORA CRASSA: IDENTIFICATION OF THE STRUCTURAL GENE FOR REPRESSIBLE ACID PHOSPHATASE
Authors: Nelson Robert E , Lehman John F , Metzenberg Robert L
Published: April 2021

A mutant of Neurospora crassa with an altered repressible acid phosphatase has been isolated. The enzyme is much more thermolabile than that of wild type, and has an increased Michaelis constant. Tests of allelic interactions (in partial diploids) and in vitro mixing experiments were consistent with the mutation being in the structural gene for the enzyme. This gene, pho-3, was found to be located in the right arm of Linkage Group IV (LG IV). Thus, pho-3 and the structural gene for repressible alkaline phosphatase, pho-2 (LG V), map in separate linkage groups and cannot be part of the same operon. Neither of these structural genes is linked to the known regulatory genes, nuc-1 (LG I), nuc-2 (LG II), and preg (LG II).
THE GENETICS OF DOPA DECARBOXYLASE IN DROSOPHILA MELANOGASTER I. ISOLATION AND CHARACTERIZATION OF DEFICIENCIES THAT DELETE THE DOPA-DECARBOXYLASE-DOSAGE-SENSITIVE REGION AND THE α-METHYL-DOPA-HYPERSENSITIVE LOCUS
Authors: Wright Theodore R F , Hodgetts Ross B , Sherald Allen F
Published: April 2021

A detailed cytogenetic investigation of 16 overlapping deficiencies in the 36C-40A region on the left arm of the second chromosome (2L) in Drosophila melanogaster is reported. These deficiencies permit a localization of both the dopa-decarboxylase-dosage-sensitive region and the α-methyl-dopa-hypersensitive locus, l(2)amd, to the same region, 37B10-37C7.
ENZYMES AND REPRODUCTION IN NATURAL POPULATIONS OF DROSOPHILA EURONOTUS
Authors: Stalker Harrison D
Published: April 2021

Populations of Drosophila euronotus, one from southern Louisiana (3 samples), and one from Missouri (2 samples), were classified for allele frequencies at alkaline phosphatase (APH) and acid phosphatase (ACPH) loci. The two populations differed consistently in allele frequencies at both loci. The APH locus is on the inversion-free X chromosome; the chromosomal locus of the autosomal ACPH is unknown, and could involve inversion polymorphism. Wild females from Missouri and Louisiana populations heterozygous at the APH locus carried more sperm at capture than did the corresponding homozygotes. This heterotic association was significant for the combined samples, and whether it was the result of heterosis at the enzyme locus studied, or due to geographically widespread close linkage with other heterotic loci, it should help to maintain heterozygosity at the APH locus. In a Louisiana collection which included large numbers of sperm-free females, simultaneous homozygosity at both enzyme loci was significantly associated with lack of sperm. It is suggested that the latter association is the result of young heterozygous females achieving sexual maturity earlier than do the double homozygotes. The average effective sperm load for 225 wild females was only 29.4, suggesting the necessity for frequent repeat-mating in nature to maintain female fertility. A comparison of the sex-linked APH genotypes of wild females with those of their daughters indicated that among 295 wild-inseminated females from five populations, 35% had mated more than once, and of this 35%, six females had mated at least three times. Because of ascertainment difficulties, it is clear that the true frequency of multiple-mating in nature must have been much higher than the observed 35%. Laboratory studies indicate that multiple-mating in this species does not involve sperm displacement, possibly due to the small number of sperms transmitted per mating, and the fact that the sperm receptacles are only partially filled by a given mating.
CHARACTERIZATION OF POSTREPLICATION REPAIR IN MUTAGEN-SENSITIVE STRAINS OF DROSOPHILA MELANOGASTER
Authors: Boyd J B , Setlow R B
Published: April 2021

Mutants of Drosophila melanogaster, with suspected repair deficiencies, were analyzed for their capacity to repair damage induced by X-rays and UV radiation. Analysis was performed on cell cultures derived from embryos of homozygous mutant stocks. Postreplication repair following UV radiation has been analyzed in mutant stocks derived from a total of ten complementation groups. Cultures were irradiated, pulse-labeled, and incubated in the dark prior to analysis by alkaline sucrose gradient centrifugation. Kinetics of the molecular weight increase in newly synthesized DNA were assayed after cells had been incubated in the presence or absence of caffeine. Two separate pathways of postreplication repair have been tentatively identified by mutants derived from four complementation groups. The proposed caffeine sensitive pathway (CAS) is defined by mutants which also disrupt meiosis. The second pathway (CIS) is caffeine insensitive and is not yet associated with meiotic functions. All mutants deficient in postreplication repair are also sensitive to nitrogen mustard. The mutants investigated display a normal capacity to repair single-strand breaks induced in DNA by X-rays, although two may possess a reduced capacity to repair damage caused by localized incorporation of high specific activity thymidine-3H. The data have been employed to construct a model for repair of UV-induced damage in Drosophila DNA. Implications of the model for DNA repair in mammals are discussed.
VARIATION IN THE NUMBER OF GENES CODING FOR SALIVARY AMYLASE IN THE BANK VOLE, CLETHRIONOMYS GLAREOLA
Authors: Nielsen Jørn Tønnes
Published: April 2021

A Danish population of bank voles is polymorphic for three electrophoretically different salivary amylases, A, H and S, of which A is the most common. Both single-, double- and triple banded phenotypes were observed, and in several crosses two electrophoretic forms cosegregated. In addition to the qualitative variation, some individuals show consistent quantitative variation in the relative activities of their amylase bands. This variation has been qualified by spectrophotometrical measurements of the relative amounts of amylase protein in the various bands.—Seventy wild chromosomes were analyzed by determining the amounts of amylase they produced when heterozygous with a laboratory stock chromosome known to carry two closely linked amylase genes, both coding for a fourth electrophoretic variant, B. The amount of A-protein divided by half the amount of B-protein was used as an estimate of the number of A-genes on the tested chromosomes. The wild chromosomes fell into three clearly distinguishable classes: 9 clustered around a gene number estimate of one, 45 chromosomes yielded estimates around two genes, and the gene number estimate of the remaining 16 was close to three. The integer values of the gene number estimates and the cosegregation of electrophoretically different salivary amylases are consistent with the model that the population is polymorphic for chromosomes with either one, two, or three closely linked amylase genes. It is suggested that such gene number variation may be more common than generally recognized, and some other reported cases of quantitative enzyme variation, for instance that of human red cell acid phosphatase, are interpreted in terms of variation in the number of genes involved.
MUTAGEN SPECIFICITY IN THE INDUCTION OF CHROMOSOMAL ABERRATIONS IN SOMATIC CELLS OF DROSOPHILA MELANOGASTER
Authors: Pimpinelli S , Pignone D , Santini G , Gatti M , Olivieri G
Published: April 2021

The distribution of chromosomal aberrations between and within chromosomes of male D. melanogaster somatic cells after treatment with UV has been analyzed.—Distribution of the breaks between chromosomes was largely nonrandom since we found a higher aberration frequency than that expected on the Y chromosome. Moreover, within the chromosomes the aberrations are clustered in the pericentromeric heterochromatic regions. The above distribution is compared with that of the breaks induced by X rays and methyl-methane-sulphonate (MMS) which were distributed in a different pattern.
INFLUENCE OF GENE DUPLICATION AND X-INACTIVATION ON MOUSE MITOCHONDRIAL MALIC ENZYME ACTIVITY AND ELECTROPHORETIC PATTERNS
Authors: Eicher Eva M , Coleman Douglas L
Published: April 2021

We have investigated, with and without the influence of X-inactivation, the relationship between autosomal gene-dosage and gene-product in a mammalian system, the mouse. The gene was mitochondrial malic enzyme (Mod-2), shown to lie on Chromosome 7 between the albino (c) and shaker-1 (sh-1) loci, and the enzyme was its product, mitochondrial malic enzyme (MOD-2). Gene duplication, with and without the influence of X-inactivation, was achieved using a translocation that involves the insertion of a portion of Chr 7, including Mod-2, into the X, T(X;7)1Ct. A 1:1 relationship for Mod-2 dosage and MOD-2 activity was found in heart mitochondria. Evidence of X-inactivation of Mod-2 was noted in heart and kidney preparations from females carrying a Mod-2 duplication (one copy of Mod-2 in the X and two copies of Mod-2 on Chr 7). We conclude that the expression of an autosomal locus attached to X-chromatin depends upon whether the translocation is in a balanced or unbalanced state.
IDENTIFICATION OF A MAJOR LOCUS CONTRIBUTING TO ERYTHROCYTE 2,3-DIPHOSPHOGLYCERATE VARIABILITY IN HOODED (LONG-EVANS) RATS
Authors: Noble N A , Brewer G J
Published: April 2021

The erythrocyte glycolytic intermediate 2,3-diphosphoglycerate (DPG) and adenosine triphosphate (ATP) play an important role in oxygen transport and delivery by binding to hemoglobin (Hb) and reducing its affinity for oxygen. Considerable quantitative variability in the levels of DPG and ATP exists in human populations and in a population of hooded (Long-Evans) rats we have studied. This paper presents the results of studies on the genetic component of DPG-level variation in an outbred population of hooded rats. Beginning with about 100 rats, a two-way selection experiment was initiated. Pairs of rats with the highest DPG levels were mated to produce a High-DPG rat strain and animals with the lowest DPG levels were mated to produce a Low-DPG strain. Mean DPG levels responded rapidly to selection and, from generation 3 on, the differences between strain means were highly significant. Ten High-DPG strain rats were intercrossed with 10 Low-DPG strain rats of generation 10 to produce an F1 generation in which the DPG levels were almost as high as those of High-DPG animals. This indicates partial dominance of High-DPG alleles. The F2 DPG-level distribution showed two distinct subpopulations. The high DPG subpopulation contained three times as many animals as the low DPG subpopulation. From these results and the statistical analyses performed, it was concluded that the DPG differences between strains were due to an allelic difference at one major locus, the allele carried by the High-DPG strain showing partial dominance over the allele carried by the Low-DPG strain. It appears that this locus may also effect ATP levels to a large extent and is polymorphic in hooded rat populations. Identification of this locus gives us a useful tool for studies of the physiological effects of DPG variability, as well as providing an example of a major gene effect in a quantitatively varying trait.
MICROGEOGRAPHIC DIFFERENTIATION OF CHROMOSOMAL AND ENZYME POLYMORPHISMS IN DROSOPHILA PERSIMILIS
Authors: Taylor Charles E , Powell Jeffrey R
Published: April 2021

We studied microgeographic and temporal genetic differentiation in natural populations of Drosophila persimilis with respect to chromosome inversion and enzyme polymorphisms. Both inversion frequencies and allozyme frequencies varied significantly over short distances. Neither differed significantly between morning and evening collections. Because several studies of the dispersal behavior of this species have been performed, we attempt to fit the observed data to mathematical models which relate dispersion to random genetic drift and to spatially varying selection coefficients. We conclude that the observations are due at least partly to behavioral differences among genotypes. i.e., habitat preferences. These results have implications for genetic load theory and models of selection in heterogeneous environments.
FURTHER STUDIES ON GENE POLYMORPHISM IN THE MAINBODY AND GEOGRAPHICALLY ISOLATED POPULATIONS OF DROSOPHILA PSEUDOOBSCURA
Authors: Prakash Satya
Published: April 2021

We have examined polymorphism at 22 additional loci in the populations from the mainbody of Drosophila pseudoobscura and an isolated population from Bogotá, Colombia, which also shows partial reproductive isolation from mainbody populations. These studies extend our previous observations of reduced gene polymorphism and apparent lack of unique allele in the Bogotá population.
CENTROMERIC EFFECT ON THE DEGREE OF NONRANDOM DISJUNCTION IN THE FEMALE DROSOPHILA MELANOGASTER
Authors: Mark Hon Fong Louie , Zimmering Stanley
Published: April 2021

From crosses of females possessing a heteromorphic X-chromosome bivalent, FR1/+, the shorter crossover products were recovered on the average more frequently than the longer reciprocals as predicted by Novitski's (1951) hypothesis of nonrandom disjunction (NRD). The present study stemmed from an unexpected result of these crosses. Evidence for a centromeric effect on NRD was obtained, suggested by a negative correlation between the degree of NRD, c, and the distance between the region of exchange and the centromere as inferred from SET's (single exchange tetrads). Studies on sex chromosome systems other than FR1 confirmed these results. An analogous centromeric effect on preferential segregation had been clearly demonstrated in maize (Kikudome 1958, 1959; Rhoades and Dempsey 1966). However, prior to the present investigation, no such effect of the centromere on NRD in Drosophila had been described, although reanalysis of part of the data of Novitski (1951) and Novitski and Sandler (1956) suggests some evidence of a seriation of increasing c values extending from the most distal region of the chromosome toward the centromere. A suggestion that the effect in Drosophila may be related in some way to the time required for chiasma terminalization, i.e., those terminalizing earlier (distally located crossovers) permitting more random disjunction of the chromatids from the asymmetric dyad and those terminalizing later, progressively less random, is considered and rejected since in general the expected pattern of c values for the various double exchange tetrads (DET's) is inconsistent with that prediction and provides evidence suggesting the possibility of reversals, in part, of c values obtained for SET's.
EFFECTS OF SELFING ON SELECTION FOR RECOMBINATION
Authors: Charlesworth D , Charlesworth B , Strobeck C
Published: April 2021

This paper describes the results of computer simulations of selection on a locus which affects the rate of recombination between a pair of loci under selection. Four different models of selection for increased recombination were examined. In our first two models, which involve hitchhiking effects, increased levels of selfing can lead to increased selection for recombination, but need not always do so. With two models of selection for recombination caused by fluctuations in the environment, increased selfing always led to increased selection for recombination. Constant-environment models with nonadditive fitnesses at the two selected loci were also studied. Selfing increased selection for modifiers decreasing recombination, compared with random-mating populations in which indeed there might be no selection for decreased recombination. At high levels of selfing, the intensity of selection against recombination was sometimes found to weaken again.
MUTATOR MUTATIONS IN BACTERIOPHAGE T4 GENE 42 (dHMC HYDROXYMETHYLASE)
Authors: Williams Warren E , Drake John W
Published: April 2021

Temperature-sensitive mutations of bacteriophage T4 gene 42 produce diverse effects upon spontaneous mutation rates. G:C → A:T transition rates are increased, often strongly; frameshift mutation rates are weakly increased; A:T → G:C transition rates (and perhaps also A:T → Py:Pu transversion rates) are decreased; and one G:C → Py:Pu transversion rate is also decreased. These results, together with certain interactions between gene-42 mutator effects and both base analogue mutagenesis and the viral error-prone repair system, suggest that the dHMC hydroxymethylase coded by gene 42 affects mutation rates in a more complex manner than by the simple regulation of the concentration of the DNA precursor dHMCTP.