bluuebunny/crossref_metadata_2025_split huggingface dataset:
AN ANALYSIS OF FREQUENCIES OF CHROMOSOME CONFIGURATIONS IN WHEAT AND WHEAT HYBRIDS
Authors: Driscoll C J , Bielig L M , Darvey N L 
Published: April 2021

ABSTRACT
Presynaptic association of homologous chromosomes is a prerequisite to the sequence of events that lead to chiasma formation. This association of homologous chromosomes, as entire units, occurs with probability a, and chiasma formation occurs independently in opposite chromosome arms with probability c. a and c have been estimated from frequencies of different chromosome configurations at metaphase I of euhexaploid wheat and several derived lines. In the euploid, a is essentially unity and c is of the order of 95%. All changes in the aneuploidy studied involved c rather than a, whereas the change induced by colchicine application primarily involved a.—Observed and expected frequencies of configurations were compared in wheat hybrids in which only homoeologues were present. The expected frequencies of configurations were estimated from the data, based on a being unity for entire groups of homoeologues and c being the probability of chiasma formation between random homoeologous arms. Observed and expected frequences of configurations were in general agreement; however, an excess of observed closed bivalents at the expense of multivalents is interpreted to mean that not all homoeologues are effectively associated in all cells.—In euhexaploid wheat, we suggest that homologues associate with almost certainty, whereas homoeologous pairs of chromosomes associate less efficiently. The aneuploidy examined in this study does not appear to affect the association of chromosomes, but rather the number of chiasmata that eventuate and, in the case of deficiency of chromosome 5B the distribution of chiasmata within homoelogues, perhaps by way of rendering sites for chiasma formation of homoelogues more similar.
TEMPERATURE-SENSITIVE VARIANTS OF NICOTIANA TABACUM ISOLATED FROM SOMATIC CELL CULTURE
Authors: Malmberg Russell L 
Published: April 2021

ABSTRACT
Temperature-sensitive variants of Nicotiana tabacum were isolated from a liquid suspension culture of somatic cells by a negative selection procedure, using bromodeoxyuridine and light. A total of nine such variants have been recovered, with an estimated rate of 2 × 10-7 per cell division. The appearance of the variants at the permissive temperature varied from nearly wild type, white and friable, to brown, compact and slow growing. Two of the variants adapted from growth on solid medium to growth in a liquid suspension culture; these were further characterized for chromosome number, growth rate, cell death rate at the restrictive temperature, growth on nutritionally modified media, and RNA and protein synthesis. The variants have been placed on regeneration media, and one of them has produced plantlets. Leaves from a plantlet have been placed on callus-inducing media, and the resulting callus displayed the temperature-sensitive phenotype.
EVOLUTION OF POLYPYRIMIDINES IN DROSOPHILA
Authors: Cseko Y M T , Dower N A , Minoo P , Lowenstein L , Smith G R , Stone J , Sederoff R 
Published: April 2021

ABSTRACT
We surveyed 101 different Drosophila species for the presence of a particular highly repetitive DNA sequence containing long tracts of polypyrimidine/ polypurine DNA, first found in D. melanogaster. Out of 55 tested species in the melanogaster group, only the sibling species D. simulans and D. mauritiana, as well as one distant relative in the ananassae subgroup, D. varians, contained the same sequence. All four of these species have long pyrimidine tracts as shown by acid hydrolysis of labelled DNA. All four species have the same sequence, but the amount of this polypyrimidine/polypurine DNA varies greatly. Four other species in the hydei subgroup were found to contain a poly-pyrimidine/polypurine sequence, with an oligonucleotide composition different from that of D. melanogaster. This polypyrimidine DNA varies from as much as 10% of the total DNA in D. nigrohydei, to as little as 0.4% in D. neohydei. The long pyrimidine tracts in the hydei subgroup are often more than a thousand nucleotides in length, representing exceedingly homogeneous repetitious sequences. These results show a rapid but discontinuous pattern of evolution for polypyrimidine/polypurine DNA. These sequences are not species specific, yet closely related species have greatly different amounts of polypyrimidines. Drastic changes occur in the amounts of these satellite type DNA sequences, as if the sequence had no continuous selective advantage in evolution. The implications of these results with regard to the general function and evolution of satellite DNA are discussed.
POPULATION GENETIC CONSEQUENCES OF FEEDING HABITS IN SOME FOREST LEPIDOPTERA
Authors: Mitter Charles , Futuyma Douglas J 
Published: April 2021

ABSTRACT
By surveying variation at allozyme loci in several phytophagous lepidopteran species (Geometridae), we have tested two hypotheses about the relationship of genetic variation to environmental heterogeneity: (1) that allozyme polymorphisms may exist because of associations between genotypes and "niches" (different host plants, in this instance), and (2) that the overall genetic variation of a species is correlated with environmental heterogeneity (or breadth of the species' overall ecological niche) .—Genetic differentiation among samples of oligophagous or polyphagous species taken from different host species was observed in one of three species, at only one of seven polymorphic loci. The data thus provide no evidence for pronounced genetic sub-structuring, or "host race" formation in these sexually reproducing species, although host plant-genotype associations in a parthenogenetic moth give evidence of the potential for diversifying selection.—In a comparison of allozyme variation in polyphagous ("generalized") and oligophagous ("specialized") species, heterozygosity appeared to be higher in specialized species, at all polymorphic loci but one. I t is possible that this unexpected result arises from a functional relation between breadth of diet and genetic variation.
SWITCHING OF A MATING-TYPE a MUTANT ALLELE IN BUDDING YEAST SACCHAROMYCES CEREVISIAE
Authors: Klar Amar J S , Fogel Seymour , Radin David N 
Published: April 2021

ABSTRACT
Aimed at investigating the recovery of a specific mutant allele of the mating type locus (MAT) by switching a defective MAT allele, these experiments provide information bearing on several models proposed for MAT interconversion in bakers yeast, Saccharomyces cerevisiae. Hybrids between heterothallic (ho) cells carrying a mutant MAT a allele, designated mata-2, and MATα ho strains show a high capacity for mating with MAT a strains. The MATα/mata-2 diploids do not sporulate. However, zygotic clones obtained by mating MATa homothallic (HO) cells with mata-2 ho cells are unable to mate and can sporulate. Tetrad analysis of such clones revealed two diploid (MATa/MATa) :two haploid segregants. Therefore, MAT switches occw in MATα/mata-2 HO/ho cells to produce MATα/MAT a cells capable of sporulation. In heterothallic strains, the mata-2 allele can be switched to a functional MATα and subsequently to a functional MATa. Among 32 MATα to MATa switches tested, where the MATα was previously derived from the mata-2 mutant, only one mata-2 like isolate was observed. However, the recovered allele, unlike the parental allele, conplements the matα stel-5 mutant, suggesting that these alleles are not identical and that the recovered allele presumably arose as a mutation of the MATα locus. No mata-2 was recovered by HO-mediated switching of MATα (previously obtained from mata-2 by HO) in 217 switches analyzed. We conclude that in homothallic and heterothallic strains, the mata-2 allele can be readily switched to a functional MATα and subsequently to a functional MATa locus. Overall, the results are in accord with the cassette model (HICKS, STRATKERN and HERSKO-WITZ 1977b) proposed to explain MAT interconversions.
RAPID CHANGE OF CHROMOMERIC AND PAIRING PATTERNS OF POLYTENE CHROMOSOME TIPS IN D. MELANOGASTER: MIGRATION OF POLYTENE-NONPOLYTENE TRANSITION ZONE?
Authors: Roberts Paul A 
Published: April 2021

ABSTRACT
The high variability of chromomeric patterns in near-terminal regions of polytene chromosome a m has been explored in a number of races, strains and hybrids of Drosophila melanogasier. Traditional explanations for tip differences between strains (differential compaction of chromatin, somatic or germinal deletion) are examined and, in the light of the reported observations, rejected. The range of polytene tip variability and rates of change in wild races are greater than has been supposed: strains formerly considered to be terminally deleted appear to gain terminal bands; others, formerly considered normal, appear to have lost them. Strains with high cell-to-cell tip variability are also described. Cell-to-cell variations, as well as much of the observed rapid changes in tip appearance, are probably due to heritable differences in the location of an abrupt transition zone between polytene and nonpolytene chromatin. A quantitative relationship between the amount of certain sub-terminal bands present and the frequency of tip association of nonhomologous chromosomes is shown and its possible significance for chromosome pairing discussed.
EVIDENCE FOR GENE INACTIVATION IN THE VIRUS-INDUCED ABERRANT RATIO PHENOMENON IN MAIZE
Authors: Samson R G , Brakke M K , Compton W A 
Published: April 2021

ABSTRACT
Reciprocal crosses were made between pairs of plants showing the "aberrant ratio" (AR) effect at the a locus, and simultaneously between these plants and an aa tester. The results suggested that the AR effect in the particular line that was used could be explained by inactivation of a gene other than A, but also required for aleurone color. Segregation ratios in additional crosses largely fit expectations predicted on the basis of this hypothesis.
RHO AND RIBOSOME MUTATION INTERACTION: LETHALITY OF rho-15 IN rpsL or rpsE STRAINS, AND rho-15 METHIONINE AUXOTROPHY IN rps
+ STRAINS OF ESCHERICHIA COLI
Authors: Guterman S K , Howitt C L 
Published: April 2021

ABSTRACT
The phenotype of Escherichia coli K-12 carrying rho-15 in the genetic background DW319 ilv lacZ: :IS1 is described. Seventy-eight percent (70/90) of Ilv+ transductants acquired the following phenotype: temperature-sensitive growth on minimal salts medium, Ts+ growth on complex medium and suppression of the lac polar mutation. At 42° on minimal medium, the rho-15 transductants were cross-fed by a substance diffusing from Rho+ transductants or controls. The requirement for this substance was satisfied by methionine or cystathionine, but not by any other single amino acid or combination of amino acids, by spermidine, or by mono- or divalent cationic salts.—Transduction of rho-15 into four other Ilv- recipients revealed two phenotypic patterns. Recipients with rpsL or rpsE ribosomes yielded rho-15 transductants that were Ts on all media, or Ts on minimal medium whether or not methionine was present. The effect of the ribosome on expression of rho15 was confirmed by transduction of appropriate rps alleles into DW319, followed by co-transduction of rho-15 with Ilv+. The growth rate of double rho-15 rpsL or rho-15 rpsE strains was severely reduced at 42° in comparison with strains carrying any of these single mutations. Models for rho and ribosome interaction are presented.
STUDIES OF ESTERASE-6 IN DROSOPHILA MELANOGASTER. II. THE GENETICS AND FREQUENCY DISTRIBUTIONS OF NATURALLY OCCURRING VARIANTS STUDIED BY ELECTROPHORETIC AND HEAT STABILITY CRITERIA
Authors: Cochrane Bruce J , Richmond Rollin C 
Published: April 2021

ABSTRACT
Measurements of the electrophoretic mobility and thermostability of esterase-6 allozymes have been used to determine the amount of allelic variation at the esterase-6 locus in Drosophila melanogaster. We studied 39.8 homozygous lines obtained from four natural populations. Use of a spectro-photometric assay for esterase-6 activity has allowed precise quantitation of heat-stability variants. Using these methods, eight putative alleles were detected within the two most common electrophoretic classes. Analyses of F1 and F2 progeny show that the behavior of stability variants is consistent with the hypothesis that this variation is due to allelic variation at the Est-6 locus. Analyses of the gene-frequency distributions within and between populations show (1) that observed allele-frequency distributions do not deviate significantly from those expected for neutral variants, and (2) that there is little evidence for an increase in apparent divergence of the different populations at the genotypic o r phenotypic levels when the additional variation detected is considered. These findings suggest that gene-frequency analysis alone is unlikely to resolve the question of the selective significance of allozyme variation.
THE GENETIC AND CYTOGENETIC LOCALIZATION OF THE THREE STRUCTURAL GENES CODING FOR THE MAJOR PROTEIN OF DROSOPHILA LARVAL SERUM
Authors: Roberts David B , Evans-Roberts Susan 
Published: April 2021

ABSTRACT
The α, β and γ polypeptides that make up Drosophila Larval Serum Protein-I seem to be coded for by genes that have evolved by duplication of a common ancestral gene. We have found variants of all three polypeptides, and these are variants of the coding sequences. The α-chain variant mapped to 39.5 on the X chromosome and to the polytene interval 1IA7-11B9. The β-chain variant mapped to 1.9 on chromosome 2L and to 21D2-22A1. The γ-chain variant was mapped as 0.13 map units from the tip of chromosome 3L or to —1.41 with respect to ru, which has been defined as 0.0, and to 61A1 -61A6.
CIRCULARIZATION OF TRANSDUCED FRAGMENTS: A MECHANISM FOR ADDING SEGMENTS TO THE BACTERIAL CHROMOSOME
Authors: Schmid Molly , Roth John R 
Published: April 2021

ABSTRACT
Generalized transducing fragments that have redundant sequences in direct order can circularize during transduction events. The length of the required redundant sequences can be at least as short as IS10 (1.4 kb) (KLECRNER 1977).The circular transduced fragment is able to recombine with homologous sequences in the chromosome. Circularization and insertion of transduced fragments allow addition of segments to the bacterial chromosome rather than replacement of recipient segments as in a normal transductional cross. It also provides a method for translocation of bacterial genes to a variety of specific sites on the chromosome in either orientation. The significance of these events to bacterial eiolution is discussed.
NEW ANTIBIOTIC RESISTANCE LOCI IN THE RIBOSOMAL REGION OF YEAST MITOCHONDRIAL DNA
Authors: Knight Jeffrey A 
Published: April 2021

ABSTRACT
A large number of mitochondrial antibiotic-resistant mutants have been isolated following mutagenesis with manganese. These include several different phenotypic classes of mutants, as distinguished by cross-resistance patterns, that have been found to be allelic at capl or eryl; some have been found to be heteroalle1ic.—Seven chloramphenicol-resistant mutants have been identified that are nonallelic by recombination tests with the three loci (capl, spil and eryl) previously identified in the ribosomal region. Four of these are allelic with each other and define a new locus, cap3; two others are allelic and define another new locus, cap2; the seventh maps at yet a different locus, cap4. One new spiramycin-resistant mutant has been identified that defines still another new locus, spi2. A variety of genetic techniques have been used to map these loci within the ribosomal region of the mitochondrial genome.—Manganese has been shown to be effective in inducing the mutation from ω- to ωn in many mutants that experience a simultaneous mutation at the closely linked capl locus. The ωn mutation has also been described in the capl mutant, and this locus has been shown to be more closely linked to o than capl is to ω.
METHODS FOR ANALYSIS OF THE C CISTRON OF TEMPERATE PHAGE 16–3 OF RHIZOBIUM MELILOTI
Authors: Orosz LÁszló 
Published: April 2021

ABSTRACT
A series of clear mutants of the temperate phage 16-3 of Rhizobium meliloti were isolated that included various point and deletion mutants ofthe Ccistron, coding for the phage repressor. It was observed that recombinant genotypes, such as c+ and ti (temperature-sensitive allele), which form turbid plaques, can be detected quantitatively as lysogenic colonies and scored even at frequencies as low as 10-6. Point mutations, deletions and the autonomy of intracistronic second-site mutations were characterized by this method. Further analysis has shown that each possible pair from three ti mutants gave non-conditional clear recombinants. It was shown that these latter bear the two initial ti mutations, suggesting a cumulative effect of two conditional mutations on the structure of the repressor protein. The double mutants were utilized in fine-structure mapping of the Ccistron.
AN EXPERIMENTAL COMPARISON OF SELECTION ALTERNATIVES TO PLATEAUED RESPONSE
Authors: Brown Wm P , Bell A E 
Published: April 2021

ABSTRACT
Three alteriiative selection methods for extending selection limits or breaking respome plateaus were compared over ten generations in a replicated model experiment using two unrelated populations of Drosophila melunoguster that no longer responded to purebred selection for high egg number, a heterotic pclygenic trait. The three methods were: (1) reciprocal recurrent selection (RRS) with selection within each of the plateaued populations based solely on crossbred performance, (2)a modification of reciprocal recurrent selection (MRRS) with selection within each population based on both purebred and crossbred performance, and (3)purebred selection within a new synthetic population formed by crossing the two plateaued populations.—Conflicting estimates were obtained for heritability of purebred egg number in each of the plateaued populations. The realized heritability values and estimates from diallel analyses indicated an absence ofadditive genetic variation for both populations; however, estimates from conventional intraclass correlation methods were positive. The diallel analyses revealed significant amounts of nonadditive gene effects for purebred egg number in each population, while the significant gene effects for crossbred egg numbers were additive. Estimates of the genetic correlation between purebred and crossbred egg number were negative (—0.85 ± 0.68 and -0.32 ± 0.25) for the two base populations.—All three alternatives to continued purebred selection gave significant responses, with the average gain pergeneration from MRRS being significantly superior to the other two methods. Observed purebred and crossbred responses under RRS were in agreement with quantitative genetic theory. Such was not the case for MRRS, which suggested the possibility of major gene segregation.—Evidence supparting a negative genetic correlation between purebred and crossbred performance and the possibility of overdominance is presented and discussed.
REGION-SPECIFIC RECOMBINATION IN PHAGE T4. I. A SPECIAL GLUCOSYL-DEPENDENT RECOMBINATION SYSTEM
Authors: Levy Jack N , Goldberg Edward B 
Published: April 2021

ABSTRACT
In this communication, we describe a recombination mechanism in bacteriophage T4D that acts only on glucosylated phage, acts in some regions of the genome, but not others, and is heat sensitive, showing decreasing activity with increasing temperature.
REGION-SPECIFIC RECOMBINATION IN PHAGE T4. III. THE EFFECT OF HOST MUTATIONS ON GLUCOSYLATION-DEPENDENT RECOMBINATION IN BACTERIOPHAGE T4D
Authors: Levy Jack N , Goldberg Edward B 
Published: April 2021

ABSTRACT
Mutations in the Escherichia coli genes recK, recL and (probably) uvrE and polA increase special (glucosylation-dependent),but not general recombination in bactriophage T4D.
EVOLUTION OF THE ALPHA-ESTERASE DUPLICATION WITHIN THE MONTANA SUBPHYLAD OF THE VIRILIS SPECIES GROUP OF DROSOPHILA
Authors: Baker William K 
Published: April 2021

ABSTRACT
Previous studies on linkage disequilibrium involving four tightly linked genes that code for the alpha-esterases of Drosophila montana suggest that these loci arose from a primitive esterase gene by gene duplication, Iollowed by tandem duplication (ROBERTS and BAKER 1973). We have examined the esterase variants in the closely related species, Zacicola, fluvomontana and borealis. These studies reveal that borealis has only a single esterase locus, and flmomontana may have only two loci. Cytological studies, using aceto-orcein staining and Hoechst fluorescence of squashes of ganglion chromosomes, reveal acrocentric Y chromosomes for all six species of the montana phylad, with the exception of borealis, which has the primitive rod-shaped Y chromosome. These studies provide evidence ayainst the hypothesis (STONE, GUEST and WILSON 1960) that borealis and flavomontana are derived from montana, but support THROCKMORTON'S (1978) conclusion of the early divergence of the former two species. This phylogenetic relationship supports our contention that the difference in the number of esterase genes with active alleles between borealis and montana is based on an increase in the number of genes coding for the alpha-esterases, rather than the retention in borealis of three genes with null alleles.
AN n LOCUS MULTIALLELE MODEL FOR GENE SUBSTITUTION
Authors: Koehler Donald O , Whitten Barbara L , Gregg Thomas G 
Published: April 2021

ABSTRACT
We discuss the conceptual conflict between a slow series of gene substitutions as the mechanism of evolutionary change, and the apparent need for rapid and coordinated changes at many loci simultaneously in producing complex adaptations. To improve on the limitations of classical theory and accommodate the enormous amount of variability disclosed by electrophoretic studies, we develop a model that can deal with gene substitution at n loci, with numerous alleles at each locus. Fitness is treated somewhat differently from the usual way by allowing it to vary between zero and the number of offspring an individual of a particular species can produce. As maximum fitnesses, we chose five as typical of large mammals, 100 for insects like Drosophila, and 1000 for very prolific species. When our model is applied to the classical problem of determining the number of generations required to change the gene frequency from 0.0001 to 0.9999 (but for 100 loci rather than one), we find that it requires 22,899 generations when maximum fitness is five, 7,984 generations when maximum fitness is 100 and 5,333 generations when it is 1000. This is something Df an improvement over the 300,000 generations calculated by HALDANE (1957). By allowing the fitnesses in our model to be explicitly frequency dependent, these results are reduced considerably. In addition, allowing varying proportions of the population to inbreed reduces the number of generations required for the classical problem by as much as 50%. We also point out that, given the large amount of observed genetic variation, evolutionary change may not be so much a matter of classical gene substitution a5 it is of changing from one array of alleles to another. With our model, the array (0.5, 0.15, 0.2, 0.1, 0.05) can be changed to (0.03, 0.1, 0.2, 0.17, 0.5) at 1000 loci in 6,043, 2,108, or 1,408 generations, depending on whether the maximum fitness is five, 100, or 1000. Finally, we note that it is possible to substitute one array for another while continuously favoring heterozygotes.