bluuebunny/crossref_metadata_2025_split huggingface dataset:
RECOMBINATION IN RELATION TO ULTRAVIOLET SENSITIVITY IN CHLAMYDOMONAS REINHARDI
Authors: Rosen Howard , Ebersold W T 
Published: January 2021

ABSTRACT
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

ABSTRACT
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

Abstract
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

Abstract
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

Abstract
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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.