bluuebunny/crossref_metadata_2025_split huggingface dataset:
STUDIES ON THE MECHANISM OF TRANSDUCTION BY BACTERIOPHAGE ϕγ. II. FORMATION OF TRANSDUCING ELEMENTS
Authors: Gratia Jean-Pierre 
Published: April 2021

ABSTRACT
The formation of the transducing elements (TE) of bacteriophage ɸγ, analyzed in lysogens of the thermo-inducible derivative ɸγhyI, has been found to parallel the formation of plaque-forming particles with a frequency of 2 × 10-2 TE/PFU, but is more sensitive to temperature and to UV. Deletion of one of the prophage termini (attR) prevents normal excision and formation of plaque-forming particles, but does not affect the formation of transducing elements, which arise at a rate of nearly 10-1 TE per induced bacterium. Transducing elements would be formed by in situ encapsulation of a hybrid segment from a specific point in the induced prophage, possibly the presumed packaging initiation site of the normal phage genome, before excision of the latter has occurred. Analysis of the mechanism of transduction to partly heterologous lysogens has revealed the participation of a co-infecting genome arranged in a linear fashion and has given evidence for a permutation in the sequence of transducing and nontransducing genomes. The data are consistent with a mechanism of encapsidation distinct from the Ter system even for hybrids inheriting part of the ɸ80 genome, but endowed with the property to form transducing elements like those of ɸγ. Upon infection, transducing elements are formed after one cycle of lytic development with the same characteristics as those resulting from induction, but with a frequency 50 to 100 times lower. This process is dependent on the efficiency of Int promoted recombination. Superinfection experiments performed under conditions preventing Int promoted recombination reveal that any superinfecting ɸγ can promote the formation of transducing particles, depending on the presence within the host prophage of a site from which transducing genome packaging initiates.
ULTRAVIOLET MUTAGENESIS STUDIES OF [psi], A CYTOPLASMIC DETERMINANT OF SACCHAROMYCES CEREVISIAE
Authors: Tuite M F , Cox B S 
Published: April 2021

ABSTRACT
UV mutagenesis was used to probe the molecular nature of [psi], a nonmitochondrial cytoplasmic determinant of Saccharomyces cereuisiae involved in the control of nonsense suppression. The UV-induced mutation from [psi +] to [psi -] showed characteristics of forward nuclear gene mutation in terms of frequency, induction kinetics, occurrence of whole and sectored mutant clones and the effect of the stage in the growth cycle on mutation frequency. The involvement of pyrimidine dimers in the premutational lesion giving the [psi -] mutation was demonstrated by photoreactivation. UV-induced damage to the [psi] genetic determinant was shown to be repaired by nuclear-coded repair enzymes that are responsible for the repair of nuclear DNA damage. UV-induced damage to mitochondrial DNA appeared to be, at least partly, under the control of different repair processes. The evidence obtained suggests that the [psi] determinant is DNA.
GENETIC ANALYSIS OF THE RELATIONSHIPS BETWEEN THE CELL SURFACE AND THE NUCLEI IN PARAMECIUM TETRAURELIA
Authors: Cohen Jean , Beisson Janine 
Published: April 2021

ABSTRACT
In Paramecium tetraurelia, a number of mutations have been shown to affect simultaneously cortical organization (attachment of trichocysts to the cortex) and nuclear divisions (RUIZ et al. 1976). In order to analyze the genetic and physiological basis of this correlation, we have isolated new mutations affecting the properties of the trichocysts and studied their genetic relationships with other previously known mutations. Of 24 to 28 loci controlling the biogenesis and properties of the trichocysts, mutations only in the 16 to 20 loci that control trichocyst attachment to the cortex result in nuclear defects. Cytological observations show that all of these mutants display the same set of nuclear abnormalities: in particular, rounded shape of the resting macronucleus, mispositioning and defective elongation of the dividing macronucleus and unequal repartition of the macro- and micronuclei. This common syndrome is independent of both the mutagenic origin and the mutated locus. Furthermore, by microinjection, it is possible to localize the site of action of the mutations in either the trichocyst compartment or the nontrichocyst compartment. It was found by this technique that the nuclear syndrome is also independent of the site of action of the mutation. All the genetic and physiological data support the conclusion that the nuclear defects are the consequence of the lack of trichocyst attachment to the cortex: in wild-type cells, trichocyst attachment would induce a membranar or perimembranar state necessary for correct nuclear positioning during cell division. In the absence of trichocyst attachment, the cortical control of nuclear division would be abolished. The possible involvement of cytoskeletal links between surface and nuclei is discussed.
DEFECTIVE KERNEL MUTANTS OF MAIZE. I. GENETIC AND LETHALITY STUDIES
Authors: Neuffer M G , Sheridan William F 
Published: April 2021

ABSTRACT
A planting of 3,919 M1 kernels from normal ears crossed by EMS-treated pollen produced 3,461 M1 plants and 3,172 selfed ears. These plants yielded 2,477 (72%) total heritable changes; the selfed ears yielded 2,457 (78%) recessive mutants, including 855 (27%) recessive kernel mutants and 8 (0.23%) viable dominant mutants. The ratio of recessive to dominant mutants was 201:l. The average mutation frequency for four known loci was three per 3,172 genomes analyzed. The estimated total number of loci mutated was 535 and the estimated number of kernel mutant loci mutated was 285. Among the 855 kernel mutants, 432 had a nonviable embryo, and 59 germinated but had a lethal seedling. A sample of 194 of the latter two types was tested for heritability, lethality, chromosome arm location and endosperm-embryo interaction between mutant and nonmutant tissues in special hyper-hypoploid combinations produced by manipulation of B-A translocations. The selected 194 mutants were characterized and catalogued according to endosperm phenotype and investigated to determine their effects on the morphology and development of the associated embryo. The possibility of rescuing some of the lethal mutants by covering the mutant embryo with a normal endosperm was investigated. Ninety of these 194 mutants were located on 17 of the 18 chromosome arms tested. Nineteen of the located mutants were examined to determine the effect of having a normal embryo in the same kernel with a mutant endosperm, and vice versa, as compared to the expression observed in kernels with both embryo and endosperm in a mutant condition. In the first situation, for three of the 19 mutants, the mutant endosperm was less extreme (the embryo helped); for seven cases, the mutant endosperm was more extreme (the embryo hindered); and for nine cases, there was no change. In the reverse situation, for four cases the normal endosperm helped the mutant embryo; for 14 cases there was no change and one case was inconclusive.
INCIPIENT GENOME DIFFERENTIATION IN GOSSYPIUM. II. COMPARISON OF 12 CHROMOSOMES IN G. HIRSUTUM, G. MUSTELINUM AND G. TOMENTOSUM USING HETEROZYGOUS TRANSLOCATIONS
Authors: Hasenkampf Clare A , Menzel Margaret Y 
Published: April 2021

ABSTRACT
Eight homozygous translocation lines (TT) of G. hirsutum marking 3 chromosomes of the A genome and 9 chromosomes of the D genome were crossed with G. hirsutum, G. mustelinum and G. tomentosum, all homozygous for the standard end arrangements (tt). Chiasma frequencies in the G. hirsutum Tt controls were compared with those in the G. hirsutum × G. mustelinum and the G. hirsutum × G. tomentosum Tt hybrids. Both nucleus-wide and regionspecific chiasma frequencies were compared.—Some genome differentiation appears to have arisen between G. hirsutum and G. mustelinum. The G. hirsutum × G. mustelinum hybrids had a 1.8 to 1.9% reduction in the nucleus-wide chiasma frequency. Four of the eight TT lines showed a 3.4 to 10.5% reduction in chiasmata in the hybrid translocation quadrivalents, suggesting that chromosomes 1, 21, 23 and 24 may have undergone localized genome differentiation. The two species may differ naturally in the end arrangement of two chromosomes, since a quadrivalent not due to experimentally introduced translocations was observed in 13% of the PMC's of two G. hirsutum × G. mutelinum hybrids.—Very little genome differentiation has occurred between G. hirsutum and G. tomentosum. In the G. hirsutum × G. tomentosum hybrids, the nucleus-wide estimates showed only a very small (0.1 to 0.2%), though statistically significant, lowering of the chiasma frequency, and there was no reduction in chiasma frequency in the more sensitive readings for specific translocation quadrivalents.
MAPABILITY OF VERY CLOSE MARKERS OF BACTERIOPHAGE Λ
Authors: Gussin Gary N , Rosen Elliott D , Wulff Daniel L 
Published: April 2021

ABSTRACT
Recombinant frequency was compared with nucleotide distance in crosses involving markers in either the P RM or the cy region of phage λ. For each pair of markers, we performed reciprocal four-factor crosses of the following types: (I) A + m 1 + m 2 - B - × A - m 1 - m 2 + B +; and (II) A + m 1 - m 2 + B - × A - m 1 + m 2 - B +. In crosses of type I, the frequency of A + m 1 + m 2 + B + recombinants among total (selected) A + B + progeny was directly proportional to nucleotide distance between m 1 and m 2 in the range from 3 to 160 nucleotides. When less than three nucleotides separated m 1 and m 2, the measured yields of m 1 + m 2 + recombinants were significantly depressed.
MATERNAL-ZYGOTIC LETHAL INTERACTIONS IN DROSOPHILA MELANOGASTER: THE EFFECTS OF DEFICIENCIES IN THE ZESTE-WHITE REGION OF THE X CHROMOSOME
Authors: Robbins Leonard G 
Published: April 2021

ABSTRACT
The possibility that essential loci in the zeste-white region of the Drosophila melanogaster X chromosome are expressed both maternally and zygotically has been tested. Maternal gene activity was varied by altering gene dose, and zygotic gene activity was manipulated by use of position-effect variegation of a duplication. Viability is affected when both maternal and zygotic gene activity are reduced, but not when either maternal or zygotic gene activity is normal. Tests of a set of overlapping deficiencies demonstrate that at least three sections of the zeste-white region yield maternal zygotic lethal interactions. Single-cistron mutations at two loci in one of these segments have been tested, and maternal heterozygosity for mutations at both loci give lethal responses of mutant-duplication zygotes. Thus, at least four of the 13 essential functions coded in the zeste-white region are active both maternally and zygotically, suggesting that a substantial fraction of the genome may function at both stages. The normal survival of zygotes when either maternal gene expression or zygotic gene expression is normal, and their inviability when both are depressed, suggests that a developmental stage exists when maternally determined functions and zygotically coded functions are both in use.
HIGH NEGATIVE INTERFERENCE AND RECOMBINATION IN BACTERIOPHAGE T5
Authors: Beck Barbara North 
Published: April 2021

ABSTRACT
The process of close recombinant formation in bacteriophage T5 crosses has been studied by examining the structure of internal heterozygotes (HETs), the immediate products of recombination events. The T5 system was chosen because it permits the study of internal heterozygotes exclusively, thus avoiding the ambiguities inherent in previous studies with T4. The heterozygotes were obtained by the nonselective screening of progeny phage in a prematurely lysed sample from an eight-factor cross. The molecular structure of each HET was inferred from the strand genotypes displayed among its progeny. This investigation presents unequivocal evidence that both overlap and insertion HETs are intermediates in recombinant formation and that insertion HETs are a significant source of close double recombinants. There is evidence suggesting that mismatch repair of overlap HETs could be the source of close triple exchanges. Thus, a significant part, and perhaps all, of the high negative interference for close-marker recombination observed in this system is a direct consequence of the fine structure of the recombinational intermediates. These findings are compatible with recombination models proposed by others, in which a single branched intermediate can give rise to HETs of both the overlap and insertion types.
SELECTION IN FINITE POPULATIONS. III. AN EXPERIMENTAL EXAMINATION
Authors: Hedrick Philip W 
Published: April 2021

ABSTRACT
The theory determining the probability of fixation of new mutants in a population that allows increased adaptation has been developed by Kimura. Two experimental systems were used to examine this theory. First, alleles were introduced at low frequencies into populations and their fate observed. The second approach was to follow populations with closely linked mutants that were introduced on different chromosomes and to follow the fate of favorable recombinants. These experiments allowed the investigation of the appropriateness of the mathematical model for the particular biological system. In the experiments reported here using two X-linked Drosophila mutants, y and w, the predictions of the theory were reasonably fulfilled in the first experimental system (introduction of new alleles), but not in the second system (favorable recombinants). However, the theoretical framework seems quite robust in that it allowed a satisfactory explanation of the experimental results for the second system as well. The probability of, and the time until, production of a favorable recombinant is discussed.
THE EFFECTS OF LETHAL SELECTION ON THE EST-6 TO PGM REGION OF CHROMOSOME 3 IN DROSOPHILA MELANOGASTER
Authors: Cochrane Bruce J , Richmond Rollin C 
Published: April 2021

ABSTRACT
A powerful means of studying the effects of selection on chromosome segments in Drosophila melanogaster has been described by Clegg et al. (1976, 1978). This method utilizes a recessive lethal, dominant visible allele whose selection dynamics can be accurately modelled to predict the fates of nonlethal alleles at linked loci. Results of these experiments indicate that strong epistatic interactions among loci occur that affect fitnesses associated with gametic types in the basal region of chromosome 3. We have used similar methods in studying a different segment of chromosome 3, that spanned by Est-6 (3—36.8) and Pgm (3—43.4), with the aim of determining whether the results of Clegg and his colleagues could be reproduced when a different region was studied. Our experiment showed that selection did operate on a region of the chromosome marked by Pgm, but that no evidence of selection at loci marked by Est-6 was apparent. Weak evidence for epistatic interactions among loci within the marked region was also found. Three possible explanations for the discrepancies between our experiments and those of Clegg et al. are suggested. First, the geographically homogeneous origin of our populations may preclude selectively significant changes as a result of recombination. Second, the results seen by Clegg et al. may have been unique to the regions they studied, which included the basal heterochromatin of the chromosome. Finally, the three loci employed may not adequately mark the unit of selection, so that actual departures from predictions of selective neutrality may not have been apparent.
MULTILOCUS STRUCTURE OF NATURAL POPULATIONS OF HORDEUM SPONTANEUM
Authors: Brown A H D , Feldman M W , Nevo E 
Published: April 2021

ABSTRACT
The association of alleles among different loci was studied in natural populations of Hordeum spontaneum, the evolutionary progenitor of cultivated barley. The variance of the number of heterozygous loci in two randomly chosen gametes affords a useful measure of such association. The behavior of this statistic in several particular models is described. Generally, linkage (gametic phase) disequilibrium tends to increase the variance above the value expected under complete independence. This increase is greatest when disequilibria are such as to maximize the sum of squares of the two-locus gametic frequencies.—When data on several loci per individual are available, the observed variance may be tested for its agreement with that expected under the hypothesis of complete interlocus independence, using the sampling theory of this model. When applied to allozyme data from 26 polymorphic populations of wild barley, this test demonstrated the presence of geographically widespread multilocus organization. On average, the variance was 80% higher than expected under random association. Gametic frequencies for four esterase loci in both of these populations of wild barley and two composite crosses of cultivated barley were analyzed. Most generations of the composites showed less multilocus structure, as measured by the indices of association, than the wild populations.
ISOLATION OF SPO12–1 AND SPO13–1 FROM A NATURAL VARIANT OF YEAST THAT UNDERGOES A SINGLE MEIOTIC DIVISION
Authors: Klapholz Sue , Esposito Rochelle Easton 
Published: April 2021

ABSTRACT
ATCC4117 is a strain of S. cerevisiae that undergoes a single nuclear division during sporulation to produce asci containing two diploid ascospores (Grewal and Miller 1972). All clones derived from these spores are sporulation-capable and, like the parental strain, form two-spored asci. In this paper, we describe the genetic analysis of ATCC4117. In tetraploid hybrids of vegetative cells of the ATCC4117 diploid and a/a or α/α diploids, the production of two-spored asci is recessive. From these tetraploids, we have isolated two recessive alleles, designated spo12–1 and spo13–1, each of which alone results in the production of asci with two diploid or near-diploid spores. These alleles are unlinked and segregate as single nuclear genes. spo12–1 is approximately 22 cM from its centromere; spo13–1 has been localized to within 1 cM of arg4 on chromosome VIII. This analysis also revealed that ATCC4117 carries a diploidization gene allelic to or closely linked to HO, modifiers that reduce the number of haploid spores per ascus and alleles affecting the total level of sporulation.
GENETIC ORGANIZATION OF THE REGION AROUND UNC-15 (I), A GENE AFFECTING PARAMYOSIN IN CAENORHABDITIS ELEGANS
Authors: Rose A M , Baillie D L 
Published: April 2021

ABSTRACT
In the nematode Caenorhabditis elegans mutants in the gene unc-15 (I) affect the muscle protein paramyosin (Waterston, Fishpool and Brenner 1977). We have characterized 20 ethyl methanesulfonate-induced mutations in essential genes closely linked to unc-15. These lethals defined 16 new complementation groups. In the 0.65 map-unit interval around unc-15 defined by dpy-14 and unc-56, seven newly identified genes have been mapped relative to five existing genes. At present, the average distance between genes in this region is approximately 0.05 map units. Two genes, unc-15 and unc-13, are only 0.025 map units apart. Partial fine-structure maps of alleles of these two genes have been constructed. This analysis of unc-15 and genes adjacent to it is the first in a series of genetic and biochemical studies directed towards understanding the control of unc-15 expression.
ON THE OPPORTUNITY FOR POLYMORPHISM WITH SEX-LINKAGE OR HAPLODIPLOIDY
Authors: Curtsinger James W 
Published: April 2021

ABSTRACT
This paper addresses the assertion that X-linked and haplodiploid genetic systems are inherently limited with respect to the potential for selectively maintained genetic polymorphisms. Using a variation of Haldane and Jayakar's (1964) parameterization of selection on an X-linked locus, analytical expressions are derived for the proportion of the total parameter space (P) in which stable diallelic polymorphism is attained. P is a function of the ratio of selection coefficients (r) associated with homozygous and hemizygous genotypes, and the intensity of selection (s). Analytical expressions for the opportunity for polymorphism at an autosomal locus (Pa) are also derived for comparison to the X-linked case. P and Pa are maximal and equal if the ratios of selection coefficients are -1 and selection is intense. Otherwise, P is slightly less than Pa, but the difference between autosomal and sex-linked loci is less than the range of values of P obtained over the range of r. Several arguments are presented suggesting that polymorphism arising from differential selection in the sexes (r &lt; 0) is probabilistically and biologically feasible.
DOUBLED HAPLOIDS FOR ESTIMATING MEAN AND VARIANCE OF RECOMBINATION VALUES
Authors: Choo T M 
Published: April 2021

ABSTRACT
In a diallel cross analysis using doubled haploids, both additive and additive x additive genetic variances can be estimated. In addition, mean and variance of recombination values can also be estimated. Linkage affects the covariance between half-sibs the most, the covariance between grandparent and grand offspring to an intermediate degree and the covariance between full sibs the least. The covariance of parent and offspring is not affected by linkage.
GENETICS OF LIFE HISTORY IN DROSOPHILA MELANOGASTER. I. SIB ANALYSIS OF ADULT FEMALES
Authors: Rose Michael R , Charlesworth Brian 
Published: April 2021

ABSTRACT
A sib analysis of adult life-history characters was performed on about twelve hundred females from a laboratory Drosophila melanogaster population that had been sampled from nature and cultured so as to preserve its genetic variability. The following results were found. There was no detectable trend with age in additive or dominance genetic variances for age-specific fecundity. Environmental variance for age-specific fecundity increased with age. The genetic variance for fecundity characters was primarily additive. The genetic variance for longevity was primarily dominance variance. There were negative genetic correlations between early fecundity and lifespan, as well as between mean egg-laying rate and longevity.
POLYMORPHISM AT THE REF(2)P LOCUS IN DROSOPHILA MELANOGASTER: PRELIMINARY EXPERIMENTS CONCERNING THE SELECTION MECHANISMS INVOLVED IN ITS MAINTENANCE
Authors: Fleuriet Annie 
Published: April 2021

ABSTRACT
It has been shown previously that a polymorphism for two alleles of the ref(2)P locus is a regular feature of French natural populations of Drosophila melanogaster and that this is maintained in laboratory populations raised in cages. In this paper, an experimental population and egg-collection experiments are reported. Differential survival of the three genotypes would be the main factor leading to the equilibrium frequencies, working only in drastic conditions of larval competition.
A THEORETICAL AND NUMERICAL ASSESSMENT OF GENETIC VARIABILITY
Authors: Karlin Samuel , Feldman Marcus W 
Published: April 2021

ABSTRACT
The equilibrium behavior of one-locus viability selection models is studied numerically. The selection schemes include randomly chosen viabilities, viabilities chosen to measure a hypothetical distance between the alleles making up the genotype and viabilities that obey various allelic dominance relations. From 3 to 8 alleles are considered. Among the key conclusions are (1) equilibria that are most polymorphic do not usually have the highest mean fitness, (2) the more structure there is in the choice of the viability model, the greater is the level of polymorphism at equilibrium, and (3) for the numbers of alleles chosen here, the equilibrium reached by iteration from the centroid of the allele frequency simplex is the best predictor of the equilibrium attainable from randomly chosen starting vectors. Preliminary evidence shows that this is not the case for 16 alleles.