bluuebunny/crossref_metadata_2025_split huggingface dataset:
ARE MITOTIC FUNCTIONS REQUIRED IN MEIOSIS?
Authors: Simchen G 
Published: January 2021

ABSTRACT
Sporulation of diploid yeasts (Saccharomyces cerevisiae), homozygous or heterozygous for temperature-sensitive mitotic cell-cycle mutations, was examined at the restrictive and permissive temperatures. Twenty genes, represented by 32 heterozygotes and 60 homozygotes, were divided into three groups, showing (i) normal sporulation, (ii) no sporulation at the restrictive temperature but normal sporulation at the permissive temperature, (iii) no sporulation at both temperatures. Group (i) as well as several other strains were tested for their meiotic behavior with regard to intragenic recombination and haploidization. The conclusion reached was that all the mitotic nuclear-division and DNA-synthesis functions were required in meiosis. The only cell-division mutations not to affect meiosis were in three cytokinesis loci and in one budemergence locus.
HAIRPIN-TAIL: A CASE OF POST-REDUCTIONAL GENE ACTION IN THE MOUSE EGG?
Authors: Johnson D R 
Published: January 2021

ABSTRACT
Hairpin-tail (Thp) is a new allele of brachyury on chromosome 17 (linkage group IX) of the mouse. The morphological effects in the heterozygote are on the notochord and the tail. The homozygous abnormal is unknown. Thp is unique in that the phenotype of the heterozygote seems to depend on the source of the Thp gene. If it is inherited via the egg the phenotype is extreme and death follows in utero. Embryos derived from a Thp sperm and a+egg are less abnormal and viable. This is not a simple maternal effect, as Thp×Thp matings produce two distinct types of heterozygous embryos.
COLD TEMPERATURE RESISTANCE, CHROMOSOMAL POLYMORPHISM AND INTERPOPULATION HETEROSIS IN DROSOPHILA PSEUDOOBSCURA
Authors: Jefferson Margaret C , Crumpacker David W , Williams James S 
Published: January 2021

ABSTRACT
Descendants of two Colorado, U.S.A., populations of D. pseudoobscura, Boulder and La Foret, were exposed to +2° and -2°. In third instar larvae from Boulder AR and PP third chromosome gene arrangements survived better than TL and others, while the reverse situation occurred for La Foret. Deleterious dominant effects were observed for AR from La Foret. In adults from Boulder there was a trend towards greater survival for AR and PP than for other gene arrangements, while AR from La Foret showed relatively poor cold resistance. Survival of Boulder and La Foret flies, and their interpopulation hybrid, was determined after exposure to -2° at two humidities. Order of survival of developmental stages was: adults &gt;&gt; third instar larvae &gt; mixture of first and second instar larvae. Adults survived better at low humidity, while larvae survived better at high humidity. Boulder adults and larvae survived better than those from La Foret. Advantage in survival of hybrids over the midparent ranged from 23% to 138%. Hybrid advantage over the higher parent ranged from 5% to 111%. Order of expression of heterosis was: mixture of first and second instar larvae &gt; third instar larvae &gt; adults. Relation of all results to the chromosomal polymorphisms at Boulder (seasonally constant) and La Foret (seasonally cyclic) is discussed.
A GENERAL MODEL TO ACCOUNT FOR ENZYME VARIATION IN NATURAL POPULATIONS
Authors: Gillespie John H , Langley Charles H 
Published: January 2021

ABSTRACT
Approximate conditions for genetic polymorphism in temporally and spatially varying environments are presented for loci which are intermediate at the level of fitness or at the level of gene function. The conditions suggest that polymorphism will be more likely in more variable environments while unlikely in constant environments. Biochemical evidence is presented to justify the assumption of heterozygote intermediacy. Observations on natural populations are cited which substantiate the claim that allozymic polymorphism is primarily due to selection acting on environmental variation in gene function.
LETHAL SECTORING AND THE DELAYED INDUCTION OF ANEUPLOIDY IN YEAST
Authors: James A P , Inhaber Elizabeth R , Préfontaine Gabrielle J 
Published: January 2021

ABSTRACT
Persistent lethal sectoring in a homothallic strain of yeast has been ascribed to tetrasomy for chromosome I. Such aneuploids can appear many generations after irradiati n. The data thus indicate that an induced predisposition towards aneuploidy can be prolonged through successive post-irradiation cell divisions. Sporadic cell death in tetrasomics for chromosome I was found to result from a metabolic imbalance and not from a genetic instability conseqent to aneuploidy. This imbalance may be due to a dosage effect involving cistrons for ribosomal RNA since many of these are known to be located on chromo ome I. Tetrasomy is not the only cause of persistent lethal sectoring; the phenomenon has been initiated through genetic recombination involving normal diploids. It has also been concluded that, in trisomics, equational division of the supernumerary chromosome sometimes occurs at the first meiotic division.
THE PERTINENCE OF THE PERIODIC SELECTION PHENOMENON TO PROKARYOTE EVOLUTION
Authors: Koch Arthur L 
Published: January 2021

ABSTRACT
A quarter of a century ago, it was pointed out that evolution can act in an important conservative way, in addition to its normal progresssive mode. Evolution to a fitte form via changes at one locus means that the descendants of an individual with an improved locus or set of loci will supplant the previous population and carry with them the ulk of the total genotype of that original individual in asexual populations. Inasmuch as that individual is most likely to be wild type at most other loci, neutral and even other positively selected mutations will be reduced or eliminated from the population, if they are rare at the time of the evolutionary advance. In the present paper this problem has been set up for a computer simulation. The computations show the limits within which this effect functions and the conditions under which it does not. The conclusion is that it is likely tliat evoluticn at a locus proceeds in the course of many population re lacements or revolutions, mostly via the rare occasions when the revolution carries a previously infrequent mutational type into abundance.
ISOZYME ALLELIC FREQUENCIES RELATED TO SELECTION AND GENE-FLOW HYPOTHESES
Authors: Schaffer Henry E , Johnson F M 
Published: January 2021

ABSTRACT
Significant correlations between allelic frequencies and environmental variables in a number of insect species have been demonstrated by multivariate techniques. Since many environmental variables show a strong relationship to geographic location and since gene flow between populations can also produce patterns of gene frequencies which are related to the geographic location, both selection and gene-flow hypotheses are consistent with the observed correlations. The genetic variables can be corrected for geographic location and so for linear gene-flow patterns. If, after correction, the genetic variables still show significant correlations with similarly corrected environmental variables, then these correlations are consistent with hypotheses of selection but not of gene flow. The data of JOHNSON and SCHAFFER (1973) have been reanalyzed using the method of canonical correlation after correction for geographical location by means of multiple regression. Five of the nine loci studied exhibit significant canonical correlations. These results, under the assumption of linear gene flow, support hypotheses of selective action of environmental variables in the genotype-environment relationships observed.
GENETIC CONTROL OF ALKALINE PHOSPHATASE SYNTHESIS IN NEUROSPORA: THE USE OF PARTIAL DIPLOIDS IN DOMINANCE STUDIES
Authors: Metzenberg Robert L , Gleason Mary K , Littlewood Barbara S 
Published: January 2021

ABSTRACT
In wild-type Neurospora, alkaline phosphatase is made under conditions of phosphate limitation, but not conditions of phosphate sufficiency. Mutants at two unlinked loci, nuc-1 and nuc-2, do not make alkaline phosphatase under any conditions, while mutants at two quite closely linked loci, pcon and preg, make alkaline phosphatase even under conditions of phosphate sufficiency. pcon is extremely closely linked to nuc-2. nuc-2 and pregc (constitutive) mutants are recessive to their wild-type alleles in partial diploids as well as in heterokaryons, while pconc mutants are dominant or co-dominant. nuc-1 is epistatic to both pconc and pregc mutants. The implications of these findings for theories of metabolic control in eukaryotes are briefly discussed.
A NOVEL DITERTIARY TETRASOMIC IN TOMATO
Authors: Gill Bikram S 
Published: January 2021

ABSTRACT
Cytogenetic studies were carried out on a ditertiary tetrasomic, 2n + 2 (5L.7S), of tomato (Lycopersicon esculentum Mill.). In studies of transmission of the 5L.7S chromosome, male and female rates of 57.1% and 74.5%, respectively, were found—the highest yet reported for any tomato aneuploid. Additionally, two 5L.7S tertiary chromosomes were transmitted through the female gametophyte, the maximum duplication known to be tolerated by this developmental stage. Monotertiary tetrasomics of a novel type, 2n + 5L.5S + 5L.7S, were recovered in the selfed progeny of 2n + 2(5L.7S). The usefulness of the ditertiary tetrasomic for the production of double trisomics and for dosage and experimental evolutionary studies is elaborated.
SELECTION FOR HIGH MUTATION RATES IN CHEMOSTATS
Authors: Cox Edward C , Gibson Thomas C 
Published: January 2021

ABSTRACT
Competition experiments in chemostats show that mutator populations of Escherichia coli are more fit than wild type. The increased fitness can be explained by the appearance of new mutants better adapted to the chemostat environment. Fitness values vary between chemostats and are strongly correlated (P &lt; 0.001) with fluctuations in population density.
PHENETHYL ALCOHOL RESISTANCE IN ESCHERICHIA COLI. III. A TEMPERATURE-SENSITIVE MUTATION (dnaP) AFFECTING DNA REPLICATION
Authors: Wada Chieko , Yura Takashi 
Published: January 2021

ABSTRACT
A temperature-sensitive DNA replication mutant of E. coli K-12 was isolated among the mutants selected for phenethyl alcohol resistance at low temperatures. This mutation, designated as dnaPl8, affects sensitivity of the cell to phenethyl alcohol, sodium deoxycholate and rifampicin, presumably due to an alteration in the membrane structure. At high temperatures (e.g., 42°), synthesis of DNA, but not RNA or protein, is arrested, leading ta the formation of "filaments" in which no septum formation is apparent. Nucleoids observed under electron microscope seem to become dispersed and DNA fibrils less condensed, which may explain the loss of viability under these conditions. Genetic analyses, including reversion studies, indicate that a recessive dnaP mutation located between cya and metE on the chromosome is responsible for both alterations of the membrane properties and temperature sensitivity. The dnaPl8 mutation does not affect growth of phage T4 or lambda under conditions where host DNA replication is completely inhibited. Kinetic studies of DNA replication and cell division in this mutant after the temperature shift from 30 to 42°, and during the subsequent recovery at 30°, accumulated evidence suggesting that DNA replication comes to a halt at 42° upon completion of a cycle already initiated before the temperature shift. Since the recovery of DNA synthesis after exposure to 42° does not depend on protein or RNA synthesis or other energy-requiring processes, the product of the mutant dnaP gene appears to be reversibly inactivated at 42°. Taken together with the recessive nature of the present mutation, it was suggested that one of the membrane proteins involved in initiation of DNA replication is affected in this mutant.
DIFFERENTIATION BETWEEN AMBER AND OCHRE MUTANTS OF YEAST BY REVERSION WITH 4-NITROQUINOLINE-1-OXIDE
Authors: Prakash Louise , Sherman Fred 
Published: January 2021

ABSTRACT
4-nitroquinoline-1-oxide (NQO) induces high frequencies of intragenic revertants of amber (UAG) but not ochre (UAA) mutants of yeast. Distinction of the amber and ochre codons was made with well-characterized nonsense mutants of the iso-1-cytochromc c gene (cycl mutants) as well as with nonsense mutants having nutritional requirements. Thus the NQO-induced reversion frequencies corroborated the assignments that wece based on the pattern of amino acid replacements in intragenic revertants and on the speficity of suppression. It was concluded from these results and from the results of a previous investigation with other cycl mutants (PRAKASH, STEWART and SHERMAN 1974) that NQO induces transversions of G:C base pairs at many sites and that the specificity is not strongly influenced by neighboring base pairs in at least the strains examined in these studies. NQO was previously shown to induce G: C → A: T transitions at least at one site and this and the previous study established that it does not significantly mutate A:T base pairs at numerous sites. Thus NQO can be used to selectively mutate G:C base pairs and to determine if the pathways of reverse mutations involve G:C base pairs. Suppressors that act on either amber or ochre mutants were induced with NQO, indicating that they can arise by mutations of G:C base pairs.
MUTANTS OF YEAST DEFECTIVE IN ISO-1-CYTOCHROME c
Authors: Sherman Fred , Stewart John W , Jackson Mary , Gilmore Richard A , Parker John H 
Published: January 2021

ABSTRACT
A medium containing chlorolactate has been devised to enrich for mutants that are unable to utilize lactate for growth, and therefore that may be defective in cytochrome c. Complementation tests of 6,520 chlorolactate-resistant mutants that were obtained spontaneously or induced with UV, ICR-170, or nitrosoimidazolidone resulted in the identification of 195 mutations at the cycl locus, which controls the primary structure of iso-1-cytochrome c. These 195 mutants, with 16 cycl mutants previously isolated, were examined for total cytochrome c by spectroscopic methods, growth on lactate medium, suppressibility by defined nonsense suppressor, mutational sites by x-ray-induced recombination, ability to revert, and in 86 cases, whether intragenic revertants contain altered iso-1-cytochrome c. Except for the deletion mutant cycl-1, all of thb mutants appeared to contain single-site mutdons that could be assigned to at least 35 different sites within the gene. The cycl mutants either completely lacked iso-1-cytochrome c or contained iso-1-cytochromes c that were completely or partially nonfunctional. In spite of the fact that the cyd mutants obtained by the chlorolactate procedure were selected on the basis of defective function, 68% appeared to completely lack iso-1-cytochrome c. The remaining cycl mutants contained below normal amounts of iso-1-cytochromes c. Studies at several incubation temperatures indicated that these nonfunctional iso-1-cytochromes c were thermolabile. It is suggested that the predominant means for abolishing iso-1-cytochrome c by mutations are either through a complete loss, such as produced by chain terminating codons, or impairments through drastic changes of tertiary structure which lead to instability and thermolability.
THE NUCLEOLUS ORGANIZER REGION OF MAIZE (ZEA MAYS L.): TESTS FOR RIBOSOMAL GENE COMPENSATION OR MAGNIFICATION
Authors: Phillips R L , Weber D F , Kleese R A , Wang S S 
Published: January 2021

ABSTRACT
Ribosomal gene compensation and magnification that might be detected on a whole-plant basis was not found in maize. Plants monosomic for chromosome 6 (the NOR chromosome) were compared with monosomic-8 and monosomic-10 plants, disomic sibs, and parental lines. Assuming no rDNA compensation, monosomic-6 plants showed approximately the decrease expected in rRNA cistron number. Monosomic-8 had a normal ribosomal gene number, while monosomic-10 showed a decrease; but further documentation is needed. Besides demonstrating the absence of gene compensation, the results document our previous conclusion that maize chromosome 6 carries DNA complementary to ribosomal RNA. Further documentation was provided from studies with trisomic chromosome 6 plants showing proportional increases in ribosomal gene number. Progeny of the monosomic plants crossed as males to a standard singlecross hybrid possessed expected ribosomal gene numbers suggesting the lack of ribosomal gene magnification.—The ragged (rgd) mutant of maize, suspected of being deficient in rRNA cistrons, had a normal number.
AN EFFECT OF CENTROMERE FUNCTION ON THE BEHAVIOR OF RING-X CHROMOSOMES IN DROSOPHILA MELANOGASTER
Authors: Sandler L , Romans Patricia , Figenshow Jan 
Published: January 2021

ABSTRACT
It is shown that under the influence of an autosomal meiotic mutant that causes abnormalities in meiotic centromere function (mei-S332), ring-X chromosomes are frequently nonrecoverable. Evidence is presented that this nonrecoverability is caused by a failure of sister ring-chromatids to successfully effect an equational separation with resultant dominant lethality. Because mei-S332 results in meiotic abnormalities only after replication has been completed, and because ring chromosomes are normally transmitted with approximately the same efficiency as rod chromosomes, it is suggested that during replication in normal meioses, sister ring-chromatids form mutually interlocked ring complexes that are resolved without genetic consequences at anaphase II, with the resolution owing at least in part to normal centromere function.
COMPARISON OF THE FREQUENCIES OF SPONTANEOUS AND CHEMICALLY-INDUCED 5-BROMODEOXYURIDINE-RESISTANCE MUTATIONS IN WILD-TYPE AND REVERTANT BHK-21/13 CELLS
Authors: Caboche Michel 
Published: January 2021

ABSTRACT
5-bromodeoxyuridine resistance mutations induced by mutagenesis were studied. The average expression time for induced mutations vaned with the concentration of the mutagen ethyl methanesulfonate (EMS). However, a constant number of two generation times was necessary for half maximal expression of induced mutations. Also, induced mutation rates were compared under optimal expression conditions for bromodeoxyuridine, fluorodeoxy-uridine and azaguanine resistance markers. Ten independent bromodeoxy-uridine-resistant clones were tested for reversion. Two clones reverted—one spontaneously and the other after mutagenesis. The spontaneous rate of mutation to bromodeoxyuridine resistance, estimated by the fluctuation test, was high in revertant clones (4 × 10-6 / cell / generation) and low in the wild-type cells (&lt; 3.5 × 10-8 / cell / generation). A comparison of induced mutation frequencies at variable EMS concentrations showed a single-hit curve for revertant clones and a multihit curve for the wild-type cells. Thymidine kinase activities of resistant clones were usually less than 2% of that of the wild-type clone. Inducibility, thermal stability and intracellular localization of the thymidine kinases of the wild-type cells and of a revertant clone were identical. A low, but significant (P &lt; 0.10), Km discrepancy was observed between enzyme extracts of these lines. The genetic implications of these results are discussed.
GENETIC VARIATION IN NATURAL POPULATIONS OF FIVE DROSOPHILA SPECIES AND THE HYPOTHESIS OF THE SELECTIVE NEUTRALITY OF PROTEIN POLYMORPHISMS
Authors: Ayala Francisco J , Tracey Martin L , Barr Lorraine G , McDonald John F , Pérez-Salas Santiago 
Published: January 2021

ABSTRACT
We have studied genetic variation at 30-32 loci coding for enzymes in natural populations of five species of Drosophila. The average proportion of heterozygous loci per individual is 17.7 ± 0.4%. The average proportion of polymorphic loci per population is 69.2 ± 2.6% or 49.8 ± 2.2%, depending on what criterion of polymorphism is used. The following generalizations are advanced: (1) The amount of genetic polymorphism varies considerably from locus to locus. (2) At a given locus, populations of the same species are very similar in the amount and pattern of genetic variation. (3) However, at some loci large differences sometimes occur between local populations of the same species. (4) The amount of variation at a given locus is approximately the same in all five species. (5) When different species are compared, the pattern of the variation is either essentially identical or totally different at a majority of loci. We have tested the hypothesis that protein polymorphisms are selectively neutral by examining four predictions derived from the hypothesis. Our results are at variance with every one of the predictions. We have measured the amount of genetic differentiation, D, between taxa of various degrees of evolutionary divergence. The average value of D is 0.033 for local populations, 0.228 for subspecies, 0.226 for semispecies, 0.538 for sibling species, and 1.214 for morphologically distinguishable species. Our results indicate that a substantial degree of genetic differentiation (22.8 allelic substitutions for every 100 loci) occurs between allopatric populations that have diverged to the point where they might become different species if they were to become sympatric. However, very little additional genetic change is required for the development of complete reproductive isolation. After the speciation process is completed, species continue to diverge genetically from each other.
REC-MEDIATED RECOMBINATIONAL HOT SPOT ACTIVITY IN BACTERIOPHAGE LAMBDA. I. HOT SPOT ACTIVITY ASSOCIATED WITH SPI-DELETIONS AND bio SUBSTITUTIONS
Authors: McMilin Kenneth D , Stahl Mary M , Stahl Franklin W 
Published: January 2021

ABSTRACT
In order to survey the distribution along the bacteriophage λ chromosome of Rec-mediated recombination events, crosses are performed using conditions which block essentially all DNA synthesis. One parent is density-labeled and carries a genetic marker in the left terminal λ gene (A), while the other parent is unlabeled and carries a genetic marker in the right terminal λ gene (R). Both parents are deleted for the λ recombination genes int and red, together with other recombination-associated genes, by virtue of either (1) a pure deletion or (2) a bio insertion-deletion. The distribution in a cesium density gradient of the resulting A+R+ recombinant phage reflects the chromosomal distribution of the recombination events which gave rise to those phage.
FINE STRUCTURE MAPPING, COMPLEMENTATION, AND PHYSIOLOGY OF ESCHERICHIA COLI hfl MUTANTS
Authors: Gautsch James W , Wulff Daniel L 
Published: January 2021

ABSTRACT
Six of seven hfl mutations of Escherichia coli K12, characterized by high frequencies of lysogenization by phage lambda and λcIII mutants, are shown to be tightly linked to, but not within, the purA locus. All six hfl mutations are recessive to wild type in hfl+/hfl merodiploids and all lie in a single complementation group, located just counterclockwise from the purA locus. All six mutations confer a slightly increased resistance to penicillin and rifamycin and a slightly increased sensitivity to sodium dodecyl sulfate. Some cases of intragenic complementation and intragenic recombination were observed. It is argued that the hfl+ gene determines the synthesis of a protein which antagonizes lysogenization by phage lambda. It is further argued that the function of the λcIII gene product is to negate the antagonistic effect of this hfl+ protein.