bluuebunny/crossref_metadata_2025_split huggingface dataset:
GENE CONVERSION OF THE MATING-TYPE LOCUS IN SACCHAROMYCES CEREVISIAE
Authors: Klar Amar J S , Fogel Seymour , Lusnak Karin 
Published: April 2021

ABSTRACT
Tetrad analysis of MAT a/MATα diploids of Saccharomyces cerevisiae generally yields 2 MATa:2MATα meiotic products. About 1 to 1.8% of the tetrads yield aberrant segregations for this marker. Described here are experiments that determine whether the aberrant meiotic segregations at the mating-type locus are ascribable to gene conversions or to MAT switches, that is, to mating-type interconversions. Diploid strains incapable of switching MAT a to MATα, or the converse, nevertheless display changes of MAT a to MATα, or the reverse. These events must be attributed to gene conversion. Further, we suggest that MAT a and MATα alleles may represent nonhomologous sequences of DNA since they fail to display postmeiotic segregations.
THE EFFECTS OF MUTAGEN-SENSITIVE MUTANTS OF DROSOPHILA MELANOGASTER IN NONMUTAGENIZED CELLS
Authors: Baker Bruce S , Smith David A 
Published: April 2021

ABSTRACT
The effects of 13 mutagen-sensitive (mus) mutants (representing seven loci) on mitotic chromosome stability in nonmutagenized cells have been examined genetically. To do this, mus-bearing flies heterozygous for the recessive somatic-cell marker, multiple wing hairs (mwh), were examined for increased frequencies of mwh clones in the wing blade. Mutants at the mus-103, mus-104 and mus-106 loci do not affect the frequency of mwh clones, while mus-101, mus-102, mus-105 and mus-109 alleles cause increases in the frequency of mwh clones. These data show that the wild-type alleles of latter four loci specify functions that are required for chromosome stability in nonmutagenized cells. Analysis of the size distribution of mwh clones produced by these mutants suggests that most chromosome instability caused by these mutants is the consequence of chromosome breakage; in the presence of mus-105 and mus-109 alleles a small fraction of the mwh clones are produced by an event (mitotic recombination, mutation, nondisjunction) that produces euploid clones. To inquire whether any of the extant alleles of the mus-101, mus-102, mus-105 and mus-209 loci might be leaky alleles of loci that carry out essential mitotic functions, chromosome stability in females homozygous for alleles of these loci has been compared to that of females carrying one dose of a mutant over a deficiency for that mus locus. These comparisons show that the extant alleles at the mus-102, mus-1O9 and mus-105 loci are all leaky mutants. It is suggested that all three of these loci may specify essential mitotic functions.
THE EFFECT OF ABO PHENOTYPIC EXPRESSION ON RIBOSOMAL DNA INSTABILITIES IN DROSOPHILA MELANOGASTER
Authors: Krider Hallie M , Yedvobnick Barry , Levine Bryan I 
Published: April 2021

ABSTRACT
The recessive maternal-effect mutation, abnormal oocyte (abo:2-38), reduces viability in the offspring of homozygous mutant females. Zygotes lacking specific heterochromatic segments of the X or Y chromosomes are most severely affected. We have shown that abo/abo lines can lose the capacity to express the mutant phenotype, and that elevated rDNA redundancies can be observed in such stocks (KRILIER and LEVINE 1975). In this study, we describe a microhybridization procedure that facilitates the measurement of rDNA redundancy, using a small number of adult Drosophila. We show that instability of the rDNA content persists in an abo/abo line after loss of the capacity to express the phenotype, and that changes in rDNA amounts occur between successive generations of the stock. Further, we show that the rDNA content of XO progeny from abo/abo females is elevated. The effect is directly correlated with the expression of the abo phenotype, and it is not observed in the XO progeny of abo heterozygous females or abo homozygotes from lines that do not show abo expression.
ISOLATION AND CHARACTERIZATION OF dnaX AND dnaY TEMPERATURE-SENSITIVE MUTANTS OF ESCHERICHIA COLI
Authors: Henson Joan M , Chu Herman , Irwin Carleen A , Walker James R 
Published: April 2021

ABSTRACT
Escherichia coli mutants with temperature-sensitive (ts) mutations in dnaX and dnaY genes have been isolated. Based on transduction by phage PI, dnaX and Y have been mapped at minutes 10.4-10.5 and 12.1, respectively, in the sequence dnaX purE dnaY. Both dnaXts36 and YtslO are recessive to wild-type alleles present on episomes. F13 carries both dnaX + and Y +; the shorter F210 carries dnaY +, but not X +. Lambda transducing phages that carry dnaX + or Y + have been isolated, and hybrid plasmids of Col E1 and E. coli DNA from the CLARKE and CARBON (1976) collection also carry portions of the dnaX purE dnaY region. Results obtained with the λ transducing phages and the hybrid plasmids suggest that dnaX is a different gene from the previously characterized dnaZ gene, which is also near minute 10.5.—The dnaXts36 mutant, after a shift to 42°, stopped DNA synthesis gradually, and the total amount of DNA increased two-fold. When this mutant was shifted to M°, the rate of DNA synthesis dropped immediately and the final increment of DNA was only 10% of the initial amount. Replicative DNA synthesis in toluene-treated cells was completely inhibited at 42° and was partially in-hibited even at 30°.—When the dnaYtslO mutant was shifted to 42°, DNA synthesis gradually stopped, and the amount of DNA increased 3.6-fold. At 44°, residual DNA synthesis amounted to a two-fold increase. Replicative DNA synthesis in vitro in toluene-treated cells was inactivated after 20 minutes at 42° or by "preincubation" of cells at 42° before toluene treatment.— The dnaX and dnaY products probably function in polymerization of DNA, although participation also in initiation cannot be excluded.
AN ENRICHMENT FOR TEMPERATURE-SENSITIVE MUTANTS IN TETRAHYMENA THERMOPHILA
Authors: Martindale Duane W , Pearlman Ronald E 
Published: April 2021

ABSTRACT
The parameters for the killing of Tetrahymena by 5-bromodeoxyuridine (BUdR) and near-ultraviolet light have been determined. Significant preferential killing by UV* of cells that have incorporated BUdR was obtained when the cells were irradiated in a nonnutrient buffer. UV alone was found to be toxic to cells irradiated in growth medium. Mutants defective in division at a restrictive temperature were isolated from mutagenized cultures that had been treated with BUdR and UV and from mutagenized cultures that had no such treatment. Results indicate that the number of temperature sensitive (ts) growth mutants can be increased five to six times using the BUdR/UV treatment. Data are presented that indicate differences in the frequency of occurrence of various types of ts mutants, with and without enrichment. A mutant that immediately stopped macromolecular synthesis and cell division upon being placed at the restrictive temperature was more resistant to BUdR/UV treatment than wild type by 1000-fold. Using the above techniques, BUdR-resistant mutants altered in the phosphorylation of thymidine have been isolated.
A NEUROSPORA MUTATION THAT ARRESTS PERITHECIAL DEVELOPMENT AS EITHER MALE OR FEMALE PARENT
Authors: Johnson Thomas E 
Published: April 2021

ABSTRACT
A mutant of Neurospora crassa fails to produce perithecia when crossed as either the male (fertilizing) parent or the female (protoperithecial) parent. This mutant is unique in that it appears to be due to a single mutation that blocks sexual development when crossed as either parent. As either a male or female parent, the mutant, fmf-1, produces perithecia blocked at a diameter of 120 microns and containing no meiotic figures; normal perithecia are over 4.00 microns in diameter. The mutant maps to linkage group IL near arg-1. Forced heterokaryons have been made between fmf-1 and fmf-1 + nuclei. These heterokaryons are fertile when crossed, and fmf-1 can participate as either the male or female component; the mutation is thus heterokaryon recessive and nuclear nonautonomous. Homokaryotic fmf-1 conidia were purified from a mixed conidial population derived from such a heterokaryon; these conidia failed to function as the male parent, suggesting that the fmf-1 + gene product is not contained in the conidium. In mixed mating-type heterokaryons, formed using tol, fmf-1 participates in ascospore formation and triggers perithecial development. Moreover, to1 suppreses the action of fmf-1 if present in both components of a cross.——These data suggest that (1) fmf-1 acts in the perithecium at some time between fusion of the conidium with the trichogyne and the onset of meiosis; (2) the fmf-1 gene product is not contained in conidia; and (3) both mating types may enter the protoperithecium when a mixed mating-type heterokaryon is used as the male parent.
THE Ah LOCUS: BIOCHEMICAL BASIS FOR GENETIC DIFFERENCES IN BRAIN TUMOR FORMATION IN MICE
Authors: Levitt Roy C , Fysh Jacquelene M , Jensen Nancy M , Nebert Daniel W 
Published: April 2021

ABSTRACT
Allelic differences at the Ah locus are shown to exist in the mouse brain. This finding probably explains inbred mouse strain differences in polycyclic hydrocarbon tumorigenesis of the brain described more than 35 years ago and may be important in understanding the etiology of genetic differences in certain human intracranial neoplasms.
SOME PROPERTIES OF SITE-SPECIFIC AND GENERAL RECOMBINATION INFERRED FROM INT-INITIATED EXCHANGES BY BACTERIOPHAGE LAMBDA
Authors: Echols Harrison , Green Linda 
Published: April 2021

ABSTRACT
The site-specific recombination at the attachment site for prophage integration might proceed by two general mechanisms: (1) a concerted reaction with-out a free intermediate; (2) a sequential mechanism differing from typical general recombination only by an inability of the cross-strand intermediate structure to migrate into the region of nonhomology adjacent to the attachment site. The blocked-migration, sequential model predicts frequent genetic exchange in the int xis region near the attachment site if Int-mediated recombination occurs between λ phage with homologous attachment sites. We fiid such additional int xis exchanges, but only at very low frequency (1% of the Int-mediated recombination). We conclude that the resolution point only rarely moves away from the initial crossover point specified by Int and, therefore, that the Int reaction is mainly concerted. We interpret the rare additional int xis recombinants as indicative of occasional branch migration from an initial Int-mediated crossover. The frequency of the rare int xis recombinants is not simply related to distance from thp attachment site to an int - or xis - mutation, suggesting that the heteroduplex distance is often at least a gene in length. The frequency of these additional exchanges is also not a strong function of distance between two mutations; from this we conclude that the resolution to the observed recombinant structure in the sequential cases occurs often by mismatch repair. We have found no marked effect of mutations in the bacterial recA, recB, recC, recF, or recL genes on the frequency of the int xis recombinants; this may indicate that none of these genes specifies a product uniquely required for resolution of a cross-strand intermediate.
ESTIMATION OF GENETIC COVARIANCE FROM JOINT OFFSPRING-PARENT AND SIB-SIB STATISTICS
Authors: Gianola Daniel 
Published: April 2021

ABSTRACT
Formulae for calculating the variances and covariances of estimates of genetic variance or covariance from offspring-parent and sib covariance data are presented. The model consists of a one-way classification of families with unequal numbers of offspring, where normally distributed traits x (a parental measure), y and z (offspring measures) are recorded. Procedures for pooling offspring-parent and sib covariance estimators are discussed. An application of the results to estimating genetic variance is presented, and the offspring-parent and sib covariance estimators and a pooled statistic are compared in terms of exact and asymptotic formulae. Implications for experimental design and allocation of experimental resources are also reported.
REARRANGEMENT OF THE BACTERIAL CHROMOSOME USING Tn10 AS A REGION OF HOMOLOGY
Authors: Chumley Forrest G , Roth John R 
Published: April 2021

ABSTRACT
The transposable tetracycline resistance element, TnlO, can serve as a region of homology to promote rec-dependent deletion, duplication and directed transposition of bacterial genes. TnlO insertions in regions of the chromosome near the histidine operon (his) have been isolated and characterized in Salmonella typhimurium. When strains are constructed containing two TnlO insertions flanking the his operon in the same orientation (TniO-his-TnZO), recombination can occur between TnZO sequences resulting in the deletion of the intervening his region. The sites of the TnZO insertions determine the endpoints of the deletion. In crosses designed toconstruct strains carrying Tn10-his-TnZO, another class of unstable recombinants arises in which the his region exists in tandem duplication, with a TnlO insertion joining the duplicated copies (his-TnlO-his). The sites of the parental TnZO insertions mark the endpoints of the duplication. When a strain carrying TnIO-his-TnZO is used as a donor of his+ in conjugation or P22-mediated transduction, recombinants can arise in which the his region has been transposed to the site of any Tn1O insertion, far from the normal location of his in the recipient chromosome. In this manner, the his operon has been moved to the site of a pyrB::TdO insertion and has been placed on F' plasmids. At these new locations, the his+ character shows the rec-dependent deletion of his+ expected for a TnZO-his-TnlO duplication. These methods should be generally useful for the manipulatioo of bacterial genes.
A MUTANT OF E. COLI THAT RESTRICTS GROWTH OF BACTERIOPHAGE T4 AT ELEVATED TEMPERATURES
Authors: Jensen Jean L , Susman Millard 
Published: April 2021

ABSTRACT
After nitrosoguanidine mutagenesis, a Phage Host Defective (phd) mutant of E. coli HfrH was isolated that supported the growth of T4D wild-type bacteriophage at 30",but not at 40"or higher. Eleven independent spontaneous mutants of T4 (go mutants) were isolated that overcame the growth restriction at high temperature. All of these mutants were located within three percent recombination of a gene 39 amber mutation in the clockwise direction on the standard map. In mixed infections, the representative go mutant chosen for further study seems to be recessive to its wild-type allele. Temperature-shift experiments suggested that the mutated host function involved in phage growth is a "late" function, beginning in mid-eclipse.—Electrophoresis of phage proteins labelled early and late in infection showed that under restrictive conditions early protein synthesis was normal, but that certain late proteins were absent. However, measurements ofDNA synthesis showed that under restrictive conditions the amount of phage DNA synthesized, and especially the amount of DNA sedimenting as high molecular weight replicative intermediate, was reduced. Pulse-chase experiments showed that the phage DNA made under restrictive conditions was not rapidly degraded.
THE POPULATION BIOLOGY OF BACTERIAL PLASMIDS: A PRIORI CONDITIONS FOR THE EXISTENCE OF MOBILIZABLE NONCONJUGATIVE FACTORS
Authors: Levin Bruce R , Stewart Frank M 
Published: April 2021

ABSTRACT
A mathematical model for the population dynamics of nonconjugative plasmids that can be mobilized by conjugative factors is presented. In the analysis of the properties of this model, primary consideration is given to the conditions under which these nonself-transmissible extrachromosomal elements could become established and would be maintained in bacterial populations. The results of this analysis demonstrate the existence of conditions where, as a consequence of infectious transmission via mobilization, nonconjugative plasmids could become established and be maintained even when the bacteria carrying them have lower reproductive fitnesses than plasmid-free members of the population. However, these existence conditions are stringent and suggest, therefore, that it is highly unlikely that plasmids of this type would become established and maintained without some direct selection favoring their carriage. The general implications of these results and limitations of the model are discussed. Brief consideration is also given to the implications of these theoretical findings to the problems of the spread of multiple antibiotic resistance plasmids (R-factors) and the risk of contaminating natural populations of bacteria with chimeric plasmids produced by work with recombinant DNA.
MATING-TYPE FUNCTIONS FOR MEIOSIS AND SPORULATION IN YEAST ACT THROUGH CYTOPLASM
Authors: Klar Amar J S 
Published: April 2021

ABSTRACT
Given a nutritional regime marked by a low nitrogen level and the absence of fermentable carbon sources, conventional a/α diploid cells of Saccharomyces cerevisiue exhibit a complex developmental sequence that includes a round of premeiotic DNA replication, commitment to meiosis and the elaboration of mature tetrads containing viable ascospores. Ordinarily, haploid cells and diploid cells af genotype a/a and α/α fail to display these reactions under comparable conditions. Here, we describe a simple technique for sporulation of α/α and a/a cells. Cells of genotype α/α are mated to haploid a cells carrying the karl (karyogamy defective) mutation to yield heterokaryons containing the corresponding diploid and haploid nuclei. The karl strains mate normally, but nuclei in the resultant zygotes do not fuse. When heterokaryotic cells are inoculated into sporulation media, they produce asci with six spores. Four spores carry genotypes derived from the diploid nucleus and the other two posses the markers originating from the haploid nucleus, i.e., the diploid nucleus divides meiotically while the haploid nucleus apparently divides mitotically. Similarly, the a/a genome is "helped" to sporulate as a consequence of mating with α karl strains. The results allow us to conclude that the mating-type functions essential for meiosis and sporulation are communicated and act through the cytoplasm and that sporulation can be dissociated from typical meiosis. This procedure will facilitate the genetic analysis of strains that are otherwise unable to sporulate.
THE CYTOGENETIC LOCALIZATION OF THE ALCOHOL DEHYDROGENASE-1 LOCUS IN MAIZE
Authors: Birchler James A 
Published: April 2021

ABSTRACT
The alcohol dehydrogenase-I (Adh) locus in maize has been positioned relative to thirteen reciprocal translocations that have breakpoints in the long arm of chromosome I (1L). The methods of GOPINATH and BURNHAM (1956) to produce interstitial segmental trisomy with overlapping translocations and of RAKHA and ROBERTSON (1970) to produce compound B-A translocations were coupled with the co-dominant nature of the ADH isozymes to allow the cytological placement. The results of several crosses are consistent with Adh being in the region of 0.80-0.90 of 1L.—The duplication that results from the overlap of translocations 1-3 (5267) and 2-3 (5242) and that includes Adh was studied with respect to meiotic segregation and pollen transmission. When heterozygous with normal chromosomes, a low level of recombination within the duplicated regions is detectable and the duplication and normals are recovered with equal frequencies through the female. In the pollen, the hyperploid grains cannot compete equally with the euploids in achieving fertilization.—The use of co-dominant heteromultimeric isozymes as genetic markers for the development of a series of interstitial segmental trisomics in maize is discussed.
ANALYSIS OF SOME TWO-LOCUS SYSTEMS FOR TRAITS EXHIBITING CONTINUOUS VARIATION
Authors: Carmelli Dorit 
Published: April 2021

ABSTRACT
Some generalized two-locus, major-gene models for traits exhibiting continuous expression are investigated. Conditions of gametic equilibria are stated as functions of the parameters characterizing the within phenotypic-genotypic distributions. Selection is stabilizing in favor of an optimum phenotype. It is established that an increase in the phenotypic variance facilitates stability of a central polymorphic state with tighter linkage. Also, with increased phenotypic variance in an additive two-locus selection model, a HARDY-WEINBERG type of equilibrium will be less central. The rate d convergence, in this case, is slowed down with an augmented environmental background.
STATISTICAL STUDIES ON PROTEIN POLYMORPHISM IN NATURAL POPULATIONS. III. DISTRIBUTION OF ALLELE FREQUENCIES AND THE NUMBER OF ALLELES PER LOCUS
Authors: Chakraborty Ranajit , Fuerst Paul A , Nei Masatoshi 
Published: April 2021

ABSTRACT
With the aim of understanding the mechanism of maintenance of protein polymorphism, we have studied the properties of allele frequency distribution and the number of alleles per locus, using gene-frequency data from a wide range of organisms (mammals, birds, reptiles, amphibians, Drosophila and non-Drosophila invertebrates) in which 20 or more loci with at least 100 genes were sampled. The observed distribution of allele frequencies was U-shaped in all of the 138 populations (mostly species or subspecies) examined and generally agreed with the theoretical distribution expected under the mutation-drift hypothesis, though there was a significant excess of rare alleles (gene frequency, 0 ~ 0.05) in about a quarter of the populations. The agreement between the mutation-drift theory and observed data was quite satisfactory for the numbers of polymorphic (gene frequency, 0.05 ~ 0.95) and monomorphic (0.95 ~ 1.O) alleles.—The observed pattern of allele-frequency distribution was incompatible with the prediction from the overdominance hypothesis. The observed correlations of the numbers of rare alleles, polymorphic alleles and monomorphic alleles with heterozygosity were of the order of magnitude that was expected under the mutation-drift hypothesis. Our results did not support the view that intracistronic recombination is an important source of genetic variation. The total number of alleles per locus was positively correlated with molecular weight in most of the species examined, and the magnitude of the correlation was consistent with the theoretical prediction from mutation-drift hypothesis. The correlation between molecular weight and the number of alleles was generally higher than the correlation between molecular weight and heterozygosity, as expected.
SELECTION-MIGRATION REGIMES CHARACTERIZED BY A GLOBALLY STABLE EQUILIBRIUM
Authors: Karlin Samuel , Campbell R B 
Published: April 2021

ABSTRACT
The principle that a subdivided population subject to overdominance viability selection in each habitat will manifest a unique, globally attractng polymorphic equilibrium is posited. This follows as a corollary to the stronger principle that, if haploid selection or submultiplicative diploid selection (definition: the geometric mean of the homozygote viabilities is less than or equal to the heterozygote viability) is operating in each habitat,there is a unique, globally attracting stable equilibrium that may be monomorphic or polymorphic. These principles are proven for a broad spectrum of migration patterns. In all such migration selection systems, multiple fixation states cannot be simultaneously stable under submultiplicative viability regimes. Contrasting examples where sub-multiplicative viabilities are not in force are given.