bluuebunny/crossref_metadata_2025 huggingface dataset:
THE α-GLYCEROPHOSPHATE IN DROSOPHILA MELANOGASTER II. GENETIC ASPECTS
Authors: O'Brien Stephen J , Macintyre Ross J
Published: January 2021

Seven alleles of the α-Glycerophosphate dehydrogenase-1 (αGpdh-1) locus of Drosophila melanogaster have been described. These include two naturally occurring electrophoretic variants, one EMS-induced electrophoretic variant, and four EMS-induced "null" or "zero" mutants. With the electrophoretic variants, the locus was mapped to II-20.5 ± 2.5. A complementation matrix was prepared utilizing the null mutants. Three of the four mutants and a deletion of the locus (Grell 1967) exhibit dosage dependency. The dosage independent mutant exhibits complementation with two of the other null alleles. Flies genetically deficient in α-glycerophosphate dehydrogenase are fertile, but their relative viability is severely diminished. Such flies also lose the ability to sustain flight, an observation consistent with the enzyme's function in energy production. The levels of mitochondrial α-glycerophosphate oxidase, measured in flies genetically deficient in the cytoplasmic enzyme, were normal.
ON SOME GENETIC ASPECTS OF PHAGE Λ RESISTANCE IN E. COLI K12
Authors: Thirion J P , Hofnung M
Published: January 2021

Most mutations rendering E. coli K12 resistant to phage λ, map in two genetic regions mal A and mal B.—The malB region contains a gene lamB specifically involved in the λ receptor synthesis. Twenty-one independent lamB mutations studied by complementation belonged to a single cistron. This makes it very likely that lamB is monocistronic. Among the lamB mutants some are still sensitive to a host range mutant of phage λ. Mutations mapping in a proximal gene essential for maltose metabolism inactivate gene lamB by polarity confirming that both genes are part of the same operon. Because cases of intracistronic complementation have been found, the active lamB product may be an oligomeric protein.—Previously all λ resistant mutations in the malA region have been shown to map in the malT cistron. malT is believed to be a positive regulatory gene necessary for the induction of the "maltose operons" in the malA region and in the malB region of the E. coli K12 genetic map. No trans dominant malT mutation have been found. Therefore if they exist, they occur at a frequency of less than 10–8, or strongly reduce the growth rate of the mutants.
RECOMBINATION IN RELATION TO ULTRAVIOLET SENSITIVITY IN CHLAMYDOMONAS REINHARDI
Authors: Rosen Howard , Ebersold W T
Published: January 2021

A mutant strain of Chlamydomonas reinhardi which is UV sensitive as a result of a single-gene chromosomal mutation has also been found to exhibit reduced recombination. In crosses homozygous for the mutant allele, a reduction in recombination frequency was demonstrated in two different linkage groups and in three different genetic backgrounds. Thus a single mutation affecting UV sensitivity also has a possible effect on recombination. Such a mutant could be analogous to the rec  - mutants discovered in E. coli and as such be useful in the study of recombination mechanisms. Three additional UV-sensitive isolates were tested. Recombination was not altered in these mutant strains.
A METHOD FOR DETECTING AND MEASURING CONCEALED VARIABILITY IN THE MOSQUITO, CULEX TRITAENIORHYNCHUS
Authors: Sakai Richard K , Baker Richard H
Published: January 2021

A natural population of Culex tritaeniorhynchus was sampled to test the efficacy of a proposed method to detect and measure concealed variability. Thirty-nine lethals and ten recessive visible mutations were uncovered out of a total of 125 chromosomes tested.
GENETICAL AND BIOCHEMICAL EVIDENCE FOR FURTHER INTER-RELATIONSHIPS BETWEEN THE POLYAROMATIC SYNTHETIC AND THE QUINATE-SHIKIMATE CATABOLIC PATHWAYS IN NEUROSPORA CRASSA
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Authors: Case Mary E , Giles Norman H , Doy Colin H
Published: January 2021

Studies have been performed with a special class of revertants occurring with a high spontaneous frequency as suppressor mutations in mutants of the arom-1  + gene, which encodes the enzyme dehydroshikimate reductase in the constitutive, polyaromatic, biosynthetic pathway in Neurospora crassa. Combined genetical and biochemical evidence indicates that these reversions to prototrophy result from mutations in the unlinked qa-4  + gene, which encodes the enzyme dehydroshikimate dehydrase in the inducible, quinate-shikimate catabolic pathway. Additional evidence indicates that such revertants can occur only if a qa-3  + gene (which encodes shikimate, and quinate, dehydrogenase) is present. These results support the hypothesis that prototrophic arom-1 qa-4 double mutants accumulate high levels of dehydroshikimate which lead to the induction of high levels of shikimate dehydrogenase (the enzyme normally degrading shikimate to dehydroshikimate) and by mass action cause a net conversion of dehydroshikimate to shikimate. Thus, shikimate dehydrogenase effectively replaces dehydroshikimate reductase and supplies the aromatic amino acid requirements of arom-1 mutants. In this situation, a mutation leading to the loss of a biochemically distinct second enzyme activity acts as a special type of suppressor mutation——not by restoring the first activity as is true of nonsense suppressor mutations——but by causing the enzymic activity originally missing to be replaced by a catalytically related but otherwise physically distinct enzyme encoded in an unlinked gene.
CHROMOSOME SEGREGATION INFLUENCED BY TWO ALLELES OF THE MEIOTIC MUTANT c(3)G IN DROSOPHILA MELANOGASTER
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Authors: Hall Jeffrey C
Published: January 2021

c(3)G is a gene in Drosophila melanogaster defined by two independently isolated mutants on the third chromosome. When homozygous in females, the mutants—c(3)G  17 or c(3)G  68—result in the elimination of meiotic crossing over and a great increase in nondisjunction at the first meiotic division. The gametic frequency of X-, second-, or third-chromosome nondisjunction is approximately .3 in c(3)G  17  , and .4 in c(3)G  68  ; for the fourth chromosome, the frequency is .2 in c(3)G  17 and .3 in c(3)G  68  . These values are at least two hundred fold greater than for spontaneous nondisjunction, though not high enough to indicate that chromosomes are distributed at random to the first meiotic division poles. Chromosomes loss is inferred from an excess of nullo-exceptional over diplo-exceptional ova. Loss is more frequent in c(3)G  68. If c(3)G females mate at low temperature, crossing over is still absent, but nondisjunction is decreased. c(3)G  17 is more temperature sensitive than c(3)G  68  .—Nonhomologous chromosomes tend to undergo nondisjunction in the same meiotic cells in c(3)G. Moreover, there is substantial nonhomologous pairing involving the larger chromosomes of the genome, inferred from the tendency for nonhomologs to disjoin from each other. Nonhomologous segregation is not observed between chromosome 4 and any other chromosome. c(3)G  68 exhibits more nonhomologous segregation than does c(3)G  17  , and, for either allele, the degree of nonhomologous segregation is directly proportional to the similarity in length of the two nonhomologs being considered. The degree of nonhomologous segregation is increased at low temperature.—Heterozygosity for inversions tends to increase c(3)G-mediated nondisjunction, and to alter the patterns of nonhomologous segregations. The effects are observed even if the inversion does not disrupt centromeric heterochromatin, and even though the inversions do not change the lengths of the chromosomes involved. In XXY females, c(3)G  17 shows more separation of the two X’s from the Y chromo-some than does c(3)G  68  . Fourth-chromosome nondisjunction is increased by the presence of a Y chromosome in both kinds of mutant females. But in XXY;c(3)G females which are also heterozygous for an X inversion, frequencies of fourth-chromosome nondisjunction are little different from those in XX; c(3)G females, while the degrees of XX-from-Y disjunction are increased.—The chromosome behavior of the two alleles of c(3)G is readily rationalized by a model which assumes that c(3)G+ controls a stage of meiosis prior to synapsis and crossing over. If exchange is directly disrupted in c(3)G homozygotes, disjunctional consequences should be the same in c(3)G  17 and c(3)G  68  . They are not. If, however, c(3)G+ controls a precondition to crossing over—such as the association of homologous and nonhomologous chromosomes—then the two alleles could each abolish crossing over, but lead to different amounts and patterns of nondisjunction.
DYNAMICS OF POLYMORPHISMS: I. SELECTION COMPONENTS IN AN EXPERIMENTAL POPULATION OF DROSOPHILA MELANOGASTER
Authors: Bundgaard Jørgen , Christiansen Freddy Bugge
Published: January 2021

The total dynamics of a fourth chromosome polymorphism in Drosophila melanogaster is studied in an experimental population in which it is possible to measure various selection components simultaneously in each generation. It is demonstrated that although zygotic selection operates in the system, the component of major importance for the dynamics is sexual selection, and it is this component that is responsible for the stability of the polymorphism. Fecundity selection is of very minor importance. Both zygotic and sexual selection components behave in a frequency-dependent way. The results are discussed in relation to genetic load and the detection of selection in natural and experimental populations.
DELETION MAPPING OF zwf, THE GENE FOR A CONSTITUTIVE ENZYME, GLUCOSE 6-PHOSPHATE DEHYDROGENASE IN ESCHERICHIA COLI
Authors: Fraenkel D G , Banerjee Santimoy
Published: January 2021

Genes for three enzymes of intermediary sugar metabolism in E. coli, zwf (glucose 6-phosphate dehydrogenase, constitutive), edd (gluconate 6-phosphate dehydrase, inducible), and eda (2-keto-3-deoxygluconate 6-phosphate aldolase, differently inducible) are closely linked on the E. coli genetic map, the overall gene order being man… old… eda. edd. zwf… cheB… uvrC… his. One class of apparent revertants of an eda mutant strain contains a secondary mutation in edd, and some of these mutations are deletions extending into zwf. We have used a series of spontaneous edd-zwf deletions to map a series of point mutants in zwf and thus report the first fine structure map of a gene for a constitutive enzyme (zwf).
STABILIZING AND DISRUPTIVE SELECTION ON A MUTANT CHARACTER IN DROSOPHILA. IV. SELECTION ON SENSITIVITY TO TEMPERATURE
Authors: Scharloo W , Zweep A , Schuitema K A , Wijnstra J G
Published: January 2021

Individual selection on temperature sensitivity was applied to the relative length of the 4th vein of the mutant ciD-G in four selection lines according to different selection schemes indicated in Figure 1. These selection systems include, besides the selection on temperature, disruptive selection. In all lines the disruptive component causes an increase of the phenotypic variance, but there are large differences in its composition. The selection changed temperature sensitivity in the expected direction in all lines. In one line (C-D-) however, the change in temperature sensitivity and the increase in variance were only small because the disruptive component and the canalizing component of the selection scheme restricted each others' effect. The results are discussed in relation to earlier results obtained by disruptive selection at one temperature.
INSTABILITY OF S MALE-STERILE CYTOPLASM IN MAIZE
Authors: Singh Arjun , Laughnan John R
Published: January 2021

A number of S male-sterile plants from several shrunken-2 inbred lines were crossed initially with an R138-TR inbred line pollinator carrying the nonrestoring genotype for S sterile cytoplasm. One such cross, involving a male-sterile female parent from inbred line M825, produced, unexpectedly, a number of male-fertile F1 progeny, along with the expected male-sterile off-spring. Pollen records of plants in F2, F3 and F4 progenies in the exceptional pedigree, and of a variety of testcross and backcross progenies from these male-fertile exceptions, indicate that the exceptional male fertility is not attributable to the action of either dominant or recessive nuclear restorer genes. They are, however, consistent with the hypothesis that the event responsible for the appearance of exceptional male-fertile offspring among progeny of the original cross involved a change from male-sterile to male-fertile condition in the cytoplasm of the male-sterile M825 plant involved as the female parent in this cross. It appears that this plant bore an ear in which there was a relatively early mutational event at the cytoplasmic level resulting in a chimera involving some kernels which carried S male-sterile cytoplasm, and others which carried the mutated fertile cytoplasmic condition. The finding of a number of additional ear chimeras supports this contention.—The evidence suggests that the change from sterile to fertile cytoplasm has occurred in a number of other instances. The male-sterile line M825 is especially prone to this change. These findings are of particular interest because it has heretofore been considered that both S and T types of male-sterile cytoplasm are highly stable.—The data presented here are not sufficient to support the notion that the exceptional event involves a qualitative change, analogous to gene mutation, in a cytoplasmic entity governing the expression of male fertility. It is equally plausible that the exceptional male fertility is the result of occasional transfer of normal cytoplasm through the male germ cells of maintainer parents.
ORIGIN OF REPRODUCTIVE ISOLATION IN THE ABSENCE OF APPARENT GENIC DIFFERENTIATION IN A GEOGRAPHIC ISOLATE OF DROSOPHILA PSEUDOOBSCURA
Authors: Prakash Satya
Published: January 2021

F1 males obtained from the cross of D. pseudoobscura females from Bogotá (Colombia) × males of this species from mainland, i.e. populations from various locations in the United States and from Guatemala, are sterile. This sterility is due to genes located on the X chromosome and the autosomes; the Y chromosome is not involved. The percentage of sterile males in backcrosses can be explained by assuming an interaction between two loci on the Bogotá X chromosome and probably two loci, one each on two of the mainland autosomes. The role of founder events, inbreeding and geographic isolation in the development of reproductive isolation and the magnitude of gene differences responsible for the origin of reproductive isolation is discussed. It is concluded that founder events, inbreeding and geographic isolation play a major role in the development of reproductive isolation and that major adaptive incorporation of new alleles at a large number of structural loci is not necessary for the origin of reproductive isolation.
ON TREATING THE CHROMOSOME AS THE UNIT OF SELECTION
Authors: Slatkin Montgomery
Published: January 2021

A simple method is presented for approximating the behavior of a multiple genetic system under the action of selection and linkage. The effects of genetic drift and mutation are left out. It is found that the results are close to those obtained from a computer simulation of the same problem by Franklin and Lewontin (1970). It is possible to describe the system in terms of a correlation length on the chromosome which measures the degree to which the different parts are bound by linkage. There is also a brief discussion about the higher order correlation coefficients as a measure of the interaction effects.
CLONAL VARIATION IN PARAMECIUM III. HETEROGENEITY WITHIN CLONES OF IDENTICAL SEROTYPES
Authors: Finger Irving , Heller Carol , Magers Stephen
Published: January 2021

Clones of genetically uniform paramecia differ in the extent to which they retain the antigenic type of a common ancestor. Some are faithful and are considered stable. Others are unstable. Apparently there are two kinds of "unstable" clones. One is composed of cells all of which tend to produce subclones with some cells which have transformed to new serotypes. Other "unstable" clones apparently are really composed of two or more kinds of cells, each of which tends to yield subclones which are made up almost exclusively of cells of one serotype, although some of these subclones are not of the original serotype. Support for the existence of such heterogeneous unstable clones is presented, and several possible mechanisms to account for their existence are discussed.
POLYNUCLEOTIDE LIGASE IN BACTERIOPHAGE T4D RECOMBINATION
Authors: Krisch H M , Hamlett Nancy V , Berger Hillard
Published: January 2021

Following infection of E. coli B with ligase-deficient rII bacteriophage T4D recombination between linked markers is increased 4.2 fold and heterozygote frequency increased 2.3 fold. In such infection recombination occurs at a rapid rate for an extended period. This is in contrast to the time course of recombination observed in wild-type, lysis-inhibited, or lysis-defective (gene t defective) infection. In all of these cases recombination under standard cross conditions occurs early in the vegetative cycle. The increased recombination in ligase-deficient rII infection is reduced in a bacterial strain which produces greater than normal levels of host ligase. These results indicate that ligase has a crucial role not only in the replication of DNA but also in recombination. The level of ligase may determine whether DNA replication occurs with or without concomitant recombination.
SEX CHROMOSOME TRANSLOCATIONS IN THE EVOLUTION OF REPRODUCTIVE ISOLATION
Authors: Tracey Martin L
Published: January 2021

Haldane's rule states that in organisms with differentiated sex chromosomes, hybrid sterility or inviability is generally expressed more frequently in the heterogametic sex. This observation has been variously explained as due to either genic or chromosomal imbalance. The fixation probabilities and mean times to fixation of sex-chromosome translocations of the type necessary to explain Haldane's rule on the basis of chromosomal imbalance have been estimated in small populations of Drosophila melanogaster. The fixation probability of an X chromosome carrying the long arm of the Y(X.YL) is approximately 30% greater than expected under the assumption of no selection. No fitness differences associated with the attached YL segment were detected. The fixation probability of a deficient Y chromosome is 300% greater than expected when the X chromosome contains the deleted portion of the Y. It is suggested that sex-chromosome translocations may play a role in the establishment of reproductive isolation.
TETRAZOLIUM OXIDASE POLYMORPHISM IN RAINBOW TROUT
Authors: Cederbaum Stephen D , Yoshida Akira
Published: January 2021

Tetrazolium oxidase from the blood and liver of rainbow trout was found to be genetically polymorphic. The inheritance pattern of the liver enzyme was compatible only with a one locus-two allele hypothesis. The enzymes in the blood while having an electrophoretically identical polymorphism could differ genotypically from that of the liver in a given fish. The significance of these findings to the understanding of the evolution of the salmonid genome is discussed.
A STUDY OF THE GENETIC BASIS OF THE SEXUAL DIMORPHISM FOR WING LENGTH IN DROSOPHILA MELANOGASTER
Authors: Bird Margaret A , Schaffer H E
Published: January 2021

The genetic basis of a sexually dimorphic quantitative character in Drosophila melanogaster was investigated by means of two-way directional selection for increased and decreased differences between male and female wing length. The sex dimorphism (SD), defined as the mean wing length difference between the sexes, within families, provided the criterion for selection.—The two lines (High SD, Low SD) diverged rapidly during the 15 generations of selection, indicating the presence of extensive genetic variability for the genotype-sex interaction underlying the observed sexual dimorphism. There was evidence that genetic variability persisted in both lines when selection was relaxed. Most of the divergence between the two lines remained after 10 generations of relaxed selection.—The change in the level of sex dimorphism in the High line was due primarily to a decrease in male wing length; in the Low line most of the change in SD was the result of a decrease in female wing length. An overall reduction in wing length in both sexes in both lines is interpreted as an effect of inbreeding.—The distribution and nature of the genetic control underlying the SD characteristic of the two selection lines was investigated by chromosome substitution between selection lines using a marked inversion technique. The two lines differed by factors located on each of the three major chromosome pairs. Chromosome III had the greatest effect on the difference in SD level between lines, and showed an overall additive effect when present in homozygous versus heterozygous combination. Chromosome II had the least effect, with a significant dominance effect of the High II being evident when heterozygotes were compared with homozygotes. The effect of the X chromosome was intermediate. There was some evidence of interaction between non-homologous chromosomes.
TERMINAL SYNTHESIS OF XANTHOMMATIN IN DROSOPHILA MELANOGASTER. III. MUTATIONAL PLEIOTROPY AND PIGMENT GRANULE ASSOCIATION OF PHENOXAZINONE SYNTHETASE
Authors: Phillips John P , Forrest Hugh S , Kulkarni Anil D
Published: January 2021

Phenoxazinone synthetase, which catalyzes the condensation of 3-hydroxykynurenine to xanthommatin, the brown eye pigment of Drosophila, is shown to exist in association with a particle which resembles the cytologically defined Type I pigment granule. Several classical eye color mutants (v, cn, st, ltd, cd, w), including two which effect other enzymes in the xanthommatin pathway (v, cn), have low levels of phenoxazinone synthetase activity and disrupt the normal association of the enzyme with the pigment granule. A model is proposed depicting several structural and enzymatic interrelationships involved in the developmental control of xanthommatin synthesis in Drosophila.
GENETIC CONSERVATION: OUR EVOLUTIONARY RESPONSIBILITY
Authors: Frankel O H
Published: January 2021

The conservation of the crop varieties of traditional agriculture in the centers of genetic diversity is essential to provide genetic resources for plant improvement. These resources are acutely threatened by rapid agricultural development which is essential for the welfare of millions. Methodologies for genetic conservation have been worked out which are both effective and economical. Urgent action is needed to collect and preserve irreplaceable genetic resources.

Wild species, increasingly endangered by loss of habitats, will depend on organized protection for their survival. On a long term basis this is feasible only within natural communities in a state of continuing evolution, hence there is an urgent need for exploration and clarification of the genetic principles of conservation. Gene pools of wild species are increasingly needed for various uses, from old and new industries to recreation. But the possibility of a virtual end to the evolution of species of no direct use to man raises questions of responsibility and ethics.
THE X CHROMOSOMES OF MAMMALS: KARYOLOGICAL HOMOLOGY AS REVEALED BY BANDING TECHNIQUES
Authors: Pathak Sen , Stock A Dean
Published: January 2021

A comparison of the Giemsa-banding patterns of the X chromosomes in various mammalian species including man indicates that two major bands (A and B), which are resistant to trypsin and urea-treatments, are always present irrespective of the gross morphology of the X chromosomes. This is true in all mammalian species with the "original or standard type" X chromosomes (5-6% of the haploid genome) thus far analyzed. In the unusually large-sized X chromosomes the extra chromosomal material may be due either to the addition of genetically inert constitutive heterochromatin or to an X-autosome translocation. In these X chromosomes two major bands are present in the actual X-chromosome segment. Our data on C and G band patterns also support Ohno's hypothesis that the mammalian X chromosome is extremely conservative in its genetic content, in spite of its cytogenetic variability.
GENETIC VARIATION IN A HETEROGENEOUS ENVIRONMENT. I. TEMPORAL HETEROGENEITY AND THE ABSOLUTE DOMINANCE MODEL
Authors: Hedrick Philip W
Published: January 2021

The conditions for a stable polymorphism and the equilibrium gene frequency in an infinite population are compared when there is spatial or temporal environmental heterogeneity for the absolute dominance model. For temporal variation the conditions for stability are more restrictive and the equilibrium gene frequency is often at a low gene frequency. In a finite population, temporal environmental heterogeneity for the absolute dominance model was found to be quite ineffective in maintaining genetic variation and is often less effective than no selection at all. For comparison, the maximum maintenance for temporal variation is related to the overdominant model. In general, cyclic environmental variation was found to be more effective at maintaining genetic variation than where the environment varies stochastically. The importance of temporal environmental variation and the maintenance of genetic variation is discussed.
CYTOLOGICAL DETECTION OF THE c
25H DELETION INVOLVING THE ALBINO (c) LOCUS ON CHROMOSOME 7 IN THE MOUSE
Authors: Miller D A , Dev V G , Tantravahi R , Miller O J , Schiffman M B , Yates R A , Gluecksohn-Waelsch S
Published: January 2021

A deletion of the albsino (c) locus on mouse chromosome 7 has been demonstrated using Q- and G-banding methods in a mouse heterozygous for the radiation-induced lethal albino allele, c 25H . The deletion, which is thought to be 1-6 cM long, represents about 7.6% of the length of the metaphase chromosome.
THE DIRECTION OF LINKAGE DISEQUILIBRIUM
Authors: Langley Charles H , Crow James F
Published: January 2021

The previous paper (LANGLEYT,O BARanId KOJIMA 1974) reports that the directional linkage disequilibria, Dw = PABPab-PAbPaB, tend to be negative for data between allozymes and linked to inversions. A and B stand for the two alleles with the greatest frequency in the population. In this paper we show that linkage disequilibrium in this direction is produced at equilibrium when double homozygotes have fitnesses that are a constant fraction of the product of the two component single homozygote fitnesses, a pattern that is frequently observed in experimental data.
GENE FLOW AND GENETIC DIFFERENTIATION
Authors: Spieth P T
Published: January 2021

A brief analysis is presented for the effects of gene flow upon genetic differentiation within and between populations generated by mutation and drift. Previous results obtained with the "island" model are developed into a form that lends itself to biological interpretation. Attention is focused upon the effective local population size and the ratio of the genetic identity of two genes in different populations to that of two genes in the same population. The biological significance of this ratio, which is independent of population size, is discussed. Similarities between the results of this model and those of the "stepping-stone" model are noted.
LACK OF CHEMICALLY INDUCED MUTATION IN REPAIR-DEFICIENT MUTANTS OF YEAST
Authors: Prakash Louise
Published: January 2021

Two genes, rad6 and rad9, that confer radiation sensitivity in the yeast Saccharomyces cerevisiae also greatly reduce the frequency of chemically-induced reversions of a tester mutant cyc1-131, which is a chain initiation mutant in the structural gene determining iso-1-cytochrome c. Mutations induced by ethyl methanesulfonate (EMS), diethyl sulfate (DES), methyl methanesulfonate (MMS), dimethyl sulfate (DMS), nitroquinoline oxide (NQO), nitrosoguanidine (NTG), nitrogen mustard (HN2), β-propiolactone, and tritiated uridine, as well as mutations induced by ultraviolet light (UV) and ionizing radiation were greatly diminished in strains homozygous for either the rad6 or rad9 gene. Nitrous acid and nitrosoimidazolidone (NIL), on the other hand, were highly mutagenic in these repair-deficient mutants, and at low doses, these mutagens acted with about the same efficiency as in the normal RAD strain. At high doses of either nitrous acid or NIL, however, reversion frequencies were significantly reduced in the two rad mutants compared to normal strains. Although both rad mutants are immutable to about the same extent, the rad9 strains tend to be less sensitive to the lethal effect of chemical mutagens than rad6 strains. It is concluded that yeast requires a functional repair system for mutation induction by chemical agents.
THE LOCUS FOR HUMAN ADENINE PHOSPHORIBOSYLTRANSFERASE ON CHROMOSOME NO. 16
Authors: Kahan Brenda , Held Karsten R , DeMars Robert
Published: January 2021

Evidence for assigning the locus determining the structure of adenine phosphoribosyltransferase (APRT) to human chromosome No. 16 is presented. Hybrids of APRT-deficient mouse cells and of human fibroblasts having normal APRT were isolated by fusing the parental cells with Sendai virus, blocking de novo purine nucleotide synthesis with azaserine and selecting for hybrids that could use exogenous adenine. The hybrid clones that were studied had only APRT activity that was indistinguishable from human APRT with regard to electrophoretic migration and reaction with antibodies against the partially purified human enzyme. No. 16 was the only human chromosome consistently present in all of the clones, and in one clone, it was the only human chromosome detected. Selection against hybrid cells with 2,6-diaminopurine (DAP) yielded DAP-resistant survivors that lacked chromosome No. 16. One hybrid that originally had an intact No. 16 yielded adenine-utilizing subclones that lacked No. 16 but had a new submetacentric chromosome. The distribution of centromere-associated heterochromatin and the fluorescence pattern indicated that this chromosome consisted of a mouse telocentric chromosome and the long arm of No. 16. Cells having the submetacentric chromosome had human APRT. Both the enzyme and the chromosome were absent in DAP-resistant derivatives. These results suggest that the structure of APRT is defined by a locus on the long arm of human chromosome No. 16.
THE RIBOSOMES OF DROSOPHILA II. STUDIES ON INTRASPECIFIC VARIATION
Authors: Berger Edward M , Weber Lee
Published: January 2021

Electrophoretic comparisons of 40S and 55S ribosomal subunit proteins from 18 strains of Drosophila melanogaster revealed the virtual absence of allelic variation. More detailed two-dimensional studies on the large subunit proteins in 6 of the strains demonstrated additional complexity but still no interstrain variation. The significance of these results is discussed with respect to present estimates of genic heterozygosity in natural populations.
GENETIC BACKGROUND AND THE FITNESS OF ALLOZYMES
Authors: Jones J S , Yamazaki T
Published: January 2021

Experimental perturbations of gene frequency at the esterase-5 locus in Drosophila pseudoobscura were carried out in a series of population cages started with differing numbers of founder chromosomes. Cages founded with few chromosomes showed changes in gene frequency at the allozyme locus. Such changes were less marked in cages founded with a larger sample of chromosomes. These experiments show the importance of linkage disequilibrium in affecting allozyme frequencies, and emphasize the necessity of careful experimental design when studying fitness differences between allozymes in laboratory populations.
CONCURRENT MULTIPLE PATERNITY IN NATURAL AND LABORATORY POPULATIONS OF DROSOPHILA MELANOGASTER
Authors: Milkman Roger , Zeitler Rodney R
Published: January 2021

Electrophoretic analysis of two or three linked enzyme loci in progenies of homozygous females from cage and natural populations demonstrates frequent concurrent multiple paternity in both cases.
THE GENETIC VARIANCE FOR VIABILITY AND ITS COMPONENTS IN A LOCAL POPULATION OF DROSOPHILA MELANOGASTER
Authors: Mukai Terumi , Cardellino Ricardo A , Watanabe Takao K , Crow James F
Published: January 2021

Two hundred and ninety second chromosomes extracted from a natural population of Drosophila melanogaster were analyzed to estimate the genetic variance of viability and its components by means of a partial diallel cross (Design II of Comstock and Robinson 1952). The additive and dominance variances are estimated to be 0.009 and 0.0012. Using the dominance variance and the inbreeding depression, the effective number of overdominant loci contributing to the variance in viability is estimated to be very small, a dozen or less. Either the actual number of loci is small, or the distribution of viabilities is strongly skewed with a large majority of very weakly selected loci. The additive variance in viability appears to be too large to be accounted for by recurrent harmful mutants or by overdominant loci at equilibrium with various genetic parameters estimated independently. The excess might be due to frequency-dependent selection, to negative correlations between viability and fertility, or possibly to the presence of a mutator. The selection for viability and fertility, or possibly to the presence of a mutator. The selection for viability at the average polymorphic locus must be very slight, of the order of 10-3 or less.
PARTIAL EXCLUSION BETWEEN T-EVEN BACTERIOPHAGES; AN INCIPIENT GENETIC ISOLATION MECHANISM
Authors: Russell Richard L , Huskey Robert J
Published: January 2021

Conditional lethal mutant systems developed in T-even bacteriophages T2, T4 and T6 have been used to study the partial exclusion which characterizes mixed infections of these phages. In bacteria mixedly infected with T2 and T4, the dominant phage (T4) acts against localized exclusion sensitivity determinants in the genome of the excluded phage (T2). These determinants are clustered near genes controlling early functions; the determinants themselves do not appear among the progeny, but markers located close to them appear infrequently, by recombination. The excluding action of T4 does not depend on the action of any gene so far identified by conditional lethal mutations, nor does it depend on differences in DNA glucosylation between infecting phages. Regardless of mechanism, the genetic consequence of this partial exclusion is to limit genetic exchange between T2 and T4 in the region of the genome controlling early functions, while retaining the capacity for extensive exchange in other regions; in short, partial exclusion constitutes a localized genetic isolating mechanism. Related forms of partial exclusion characterize mixed infections of other T-even phages, including those of some phages newly isolated from nature.
FITNESS OF KARYOTYPES IN DROSOPHILA PSEUDOOBSCURA
Authors: Wasserman Marvin , Koepfer Helen Roberta
Published: January 2021

In the dynamics of the survival of chromosomal polymorphism selection may be operating at the genic level, at the chromosomal level or at the supergene level. Tests designed to distinguish between these levels were run on Drosophila pseudoobscura. There was no evidence for heterosis, a necessary requirement for gene-determined chromosomal polymorphism. A strong chromosmal selection was observed. No evidence was found for the presence within one locality of more than a single superallele for each supergene (= gene order). These results are compared to those found by others.
THE WAXY LOCUS IN MAIZE III. EFFECT OF STRUCTURAL HETEROZYGOSITY ON INTRAGENIC RECOMBINATION AND FLANKING MARKER ASSORTMENT
Authors: Nelson Oliver E
Published: January 2021

The effect of heterozygosity for structural rearrangements on recombination between two wx heteroalleles (C and 90) and the pattern of flanking markers in the resultant Wx gametes has been examined. The rearrangements are Tp9, an insertional translocation in which a segment of chromosome 3 has been inserted into the short arm of chromosome 9 close to the wx locus; In9a, a long pericentric inversion with wx in the inverted segment; and Rearr 9, a complex rearrangement of chromosome 9. Heterozygosity for rearrangements decreases the frequency of Wx gametes to varying degrees.—Heterozygosity for Tp9 enhances the proportion of Wx gametes that are apparent convertants and allows the conclusion that such gametes do not normally arise from an exchange in the wx locus plus a second exchange distal to wx. Heterozygosity for In9a markedly decreases the frequency of Wx gametes that are recombinant for outside markers but does not decrease the frequency of convertants.—Heterozygosity for Rearr 9 permits a low frequency of Wx gametes, all of which are apparent convertants.—A high proportion of the convertants have the flanking markers that entered the cross with C so recombination is polarized in normal homologs and in heterozygotes for all rearrangements.
THE MOLECULAR BASIS FOR ALLELIC COMPLEMENTATION OF ALCOHOL DEHYDROGENASE MUTANTS OF MAIZE
Authors: Schwartz Drew
Published: January 2021

Studies on interallelic complementation with two temperature-sensitive alcohol dehydrogenase mutants in maize are described. The data suggest that the phenomenon results from instability or abnormal maturation of the mutant homodimer rather than correction of configurational defects in mutant heterodimers.
THE INFLUENCE OF CHROMOSOME CONTENT ON THE SIZE AND SHAPE OF SPERM HEADS IN DROSOPHILA MELANOGASTER AND THE DEMONSTRATION OF CHROMOSOME LOSS DURING SPERMIOGENESIS
Authors: Hardy Robert Walter
Published: January 2021

The volumes of sperm heads were estimated from three-dimensional reconstructions of serially sectioned bundles of nearly mature spermatid nuclei. Cysts from males in which all sperm are expected to have comparable amounts of chromatin (X/Y and In(3LR)/+) show unimodal frequency distributions of nuclear volumes, whereas cysts from males in which meiotic segregation is expected to deliver unequal amounts of chromatin material to spermatid nuclei show two (XY/O and XY/Y) or more (T(2;3)/+ and C(2L);C(2R)) modes. The mean volumes of the subpopulations in these cases are related in the same proportions as the metaphase lengths of their chromosomal complements. Thus the volumes of sperm nuclei are proportional to their DNA content. Sperm head shape, on the other hand, does not appear to be very sensitive to chromosomal constitution, as heads of different size do not vary greatly in shape.—The numbers of sperm heads in the various size classes in a cyst depart from mendelian expectations; these departures are caused by the elimination, during individualization, of chromosomes contained within micronuclei that are formed in spermatids at the end of the second meiotic division. The effect of this chromosome loss is to increase the proportion of nullosomic gametes in the sperm pool.—The relative frequencies of XY-bearing and nullo-X, nullo-Y sperm in XY/O males were estimated from the volume measurements. Taking this estimate as a measure of the fertilizing population, it is possible to infer from the change in sex ratio over time following insemination, that XY-bearing sperm have an advantage of 1.5 over nullo-X, nullo-Y sperm in leaving the seminal receptacle of the female for fertilization of ova.
SELECTION IN COMPLEX GENETIC SYSTEMS III. AN EFFECT OF ALLELE MULTIPLICITY WITH TWO LOCI
Authors: Feldman Marcus W , Lewontin Richard C , Franklin Ian R , Christiansen Freddy B
Published: January 2021

A two-locus model with three alleles at one locus and two at the other is studied. The viability system is such that all double heterozygotes have fitness unity, all single heterozygotes have fitness w < 1 and all double homozygotes have fitness w2. The following are the major findings: 1. There are more stable equilibria for tight linkage than in the corresponding three-locus model, even though the number of chromosomes is lower. 2. The equilibria stable for tight linkage do not belong to a unique high complementarity class, as is the case for two alleles at each locus. Instead the strength of selection determines the structure of the equilibrium. 3. The increase in number of alleles seems to reduce the possible extent of assocation between the loci. 4. The measure of this association is not well defined, although we have suggested a statistically standard way of getting over this. 5. A mutation introduced while a population is in linkage disequilibrium may, per medium only of the change in number of alleles, destroy the linkage disequilibrium.
GENIC HETEROZYGOSITY AND PROTEIN POLYMORPHISM AMONG LOCAL POPULATIONS OF OENOTHERA BIENNIS
Authors: Levin Donald A
Published: January 2021

Twenty enzyme loci were studied in 44 Illinois populations of Oenothera biennis; four were polymorphic. Most of the variation was distributed between populations. Fifty-nine percent of the populations had one genotype, 27% two genotypes and the remaining 16% from three to five genotypes; the average was 1.50. The proportion of genetic diversity present in single populations is.38 of that present in the state. Members of single populations were uniformly heterozygous for 1 to 4 loci. The mean heterozygosity per population ranged from 0 to 20%. For Illinois populations collectively, heterozygosity averaged 4.5%. There was much gene frequency heterogeneity between populations. The true standardized genetic variance among populations for alleles at polymorphic loci varied from.40 to.78. Populations from Cook County were much more similar inter se than those downstate, had fewer genotypes and polymorphic loci, and had less heterozygosity than downstate populations. The mean normalized genetic identity among Cook County populations was.987 versus.947 for downstate populations. The mean number of genotypes per population in Cook County was 1.06 versus 2.40 in downstate populations. There was only one polymorphic locus in Cook County, VLP. The genetic structure of Oe. biennis suggests that single populations are colonized by one, or at best a few individuals. Cook County populations are judged to be less variable than downstate populations because the mean age of the populations probably is less than that of those downstate.
GENETIC POLYMORPHISM AND EVOLUTION IN PARTHENOGENETIC ANIMALS. II. DIPLOID AND POLYPLOID SOLENOBIA TRIQUETRELLA (LEPIDOPTERA: PSYCHIDAE)
Authors: Lokki Juhani , Suomalainen Esko , Saura Anssi , Lankinen Pekka
Published: January 2021

Genic polymorphism at sixteen enzyme loci of four different chromosomal races of Solenobia triquetrella (bisexual, two diploid parthenogenetic races and tetraploid parthenogenetic) has been studied by starch gel electrophoresis. Isolated small diploid bisexual populations have rather uniform allele frequencies at all loci which we have studied. Diploid and tetraploid parthenogenetic individuals of this species are in general as heterozygous as bisexual ones. All parthenogenetic local populations are different from each other in the Alps. These parthenogenetic genotypes cannot be derived from a common ancestor through single mutations but rather bear evidence for a polyphyletic origin of parthenogenesis in Solenobia triquetrella. In the marginal distribution areas of the species in northern Europe single genotypes are spread over far larger areas than in the mountain regions of central Europe. This may be due to the old origin of parthenogenesis and polyploidy in northern Europe. No new parthenogenetic and polyploid strains have lately arisen in the regions outside of the Alps.
THE DETERMINISTIC BEHAVIOR OF SELF-INCOMPATIBILITY ALLELES
Authors: Nagylaki Thomas
Published: January 2021

For a system of n self-incompatibility alleles, neglecting mutation and random drift, it is shown that the completely symmetric equilibrium is locally stable, and any allelic frequency less than q = 1+a-(see PDF), where a = [2(n - 1)]-1, will increase. For all n, q > (2n)-1, but if n > > 1, q ≈ (2n)-1.
COMPLEMENTATION ANALYSIS OF METHYL METHANE-SULFONATE-INDUCED RECESSIVE LETHAL MUTATIONS IN THE ZESTE-WHITE REGION OF THE X CHROMOSOME OF DROSOPHILA MELANOGASTER
Authors: Liu C P , Lim J K
Published: January 2021

Recessive lethal mutations in the 3A1 to 3C2 region of the X chromosome of Drosophila melanogaster were detected in 113 of 33,544 sperm treated by feeding 5 mM methyl methanesulfonate in 1% sucrose for 22 hours. Seven of the 113 lethals were sterile, leaving 106 for analysis by complementation tests. With only one exception, these mutants were found to have lesions restricted to single loci. One of these single-site mutations was in gt, 2 in tko, 18 in zw-1, 12 in zw-8, 6 in zw-4, 3 in zw-10, 3 in zw-13, 21 in zw-2, 7 in zw-3, 5 in zw-6, 6 in zw-12, 1 in zw-7, 12 in zw-5, 5 in zw-11, and 3 in zw-9, One of the lethals, m69, was non-complementary to two adjacent loci, zw-2 and zw-3, possibly indicating a deletion encompassing two loci. The results confirm that there are at least 15 recessive lethal loci in the region and are consistent with the hypothesis of Lim and Snyder (1968 and 1974) that inability of monofunctional alkylating chemicals to induce deletion-associated mutations is a characteristic of the compounds.
MUTATOR GENES AND SELECTION FOR THE MUTATION RATE IN BACTERIA
Authors: Painter P R
Published: January 2021

Gene frequencies in populations of haploid, asexual organisms are described by linear recurrence equations. Several models in which the mutation rate is controlled by one locus and the fitness is controlled at one or more other loci are developed. It is shown that good approximations can be introduced to give explicit solutions for the course of selection in these models. It is shown that a strong non-equilibrium selection for mutator genes is possible even when the presence of such a gene decreases the fitness of an individual. Experiments that corroborate these conclusions are discussed along with the effects of population size that determine the applicability of these results to natural populations.
Solving the frequency-domain acoustic VTI wave equation using physics-informed neural networks
Authors: Song Chao , Alkhalifah Tariq , Waheed Umair Bin
Published: January 2021

Frequency-domain wavefield solutions corresponding to the anisotropic acoustic wave equation can be used to describe the anisotropic nature of the Earth. To solve a frequency-domain wave equation, we often need to invert the impedance matrix. This results in a dramatic increase in computational cost as the model size increases. It is even a bigger challenge for anisotropic media, where the impedance matrix is far more complex. In addition, the conventional finite-difference method produces numerical dispersion artefacts in solving acoustic wave equations for anisotropic media. To address these issues, we use the emerging paradigm of physics-informed neural networks (PINNs) to obtain wavefield solutions for an acoustic wave equation for transversely isotropic (TI) media with a vertical axis of symmetry (VTI). PINNs utilize the concept of automatic differentiation to calculate their partial derivatives, which are free of numerical dispersion artefacts. Thus, we use the wave equation as a loss function to train a neural network to provide functional solutions to the acoustic VTI form of the wave equation. Instead of predicting the pressure wavefields directly, we solve for the scattered pressure wavefields to avoid dealing with the point-source singularity. We use the spatial coordinates as input data to the network, which outputs the real and imaginary parts of the scattered wavefields and auxiliary function. After training a deep neural network, we can evaluate the wavefield at any point in space almost instantly using this trained neural network without calculating the impedance matrix inverse. We demonstrate these features on a simple 2-D anomaly model and a 2-D layered model. Additional tests on a modified 3-D Overthrust model and a 2-D model with irregular topography further validate the effectiveness of the proposed method.