bluuebunny/crossref_metadata_2025_split huggingface dataset:
CHLOROPLAST AND MITOCHONDRIAL DNA VARIATION IN HORDEUM VULGARE AND HORDEUM SPONTANEUM
Authors: Holwerda Barry C , Jana Sakti , Crosby William L 
Published: January 2021

ABSTRACT
A survey of restriction fragment polymorphism in Hordeum vulgare and Hordeum spontaneum was made using 17 and 16 hexanucleotide restriction endonucleases on chloroplast (cp) and mitochondrial (mt) DNA, respectively. The plant accessions originated from various places throughout the Fertile Cresent and Mediterranean. The types of changes in cpDNA consisted of nucleotide substitutions and insertions and deletions on the order of 100 base pairs. In contrast, mtDNA has most likely undergone larger insertions and deletions of up to 20 kilobase pairs in addition to rearrangements. Grouping of mtDNA fragment data showed that in some cases geographical affinities existed between the two species, whereas in others there were no clear affinities. Nucleotide diversity estimates derived from the restriction fragment data were used in a number of comparisons of variability. Comparisons of overall mtDNA variability (nucleotide diversity = 9.68 × 10-4) with cpDNA variability (nucleotide diversity = 6.38 × 10-4) indicated that the former are somewhat more variable. Furthermore, there was no indication that the wild H. spontaneum (cpDNA diversity = 5.57 × 10-4; mtDNA diversity = 6.04 × 10-4) was more variable than the land races of H. vulgare (cpDNA diversity = 5.88 × 10-4; mtDNA diversity = 9.79 × 10-4). In fact, on the basis of mtDNA diversity, H. vulgarewas the more variable species. Comparison of organelle nucleotide diversity estimates with an estimate of nuclear nucleotide diversity derived from existing isozyme data provided evidence that both organelle genomes are evolving at a slower rate than the nuclear genome.
X-Linked Gene Expression in the Virginia Opossum: Differences Between the Paternally Derived Gpd and Pgk-A Loci
Authors: Samollow Paul B , Ford Allen L , VandeBerg John L 
Published: January 2021

ABSTRACT
Expression of X-linked glucose-6-phosphate dehydrogenase (G6PD) and phosphoglycerate kinase-A (PGK-A) in the Virginia opossum (Didelphis virginiana) was studied electrophoretically in animals from natural populations and those produced through controlled laboratory crosses. Blood from most of the wild animals exhibited a common single-banded phenotype for both enzymes. Rare variant animals, regardless of sex, exhibited single-banded phenotypes different in mobility from the common mobility class of the respective enzyme. The laboratory crosses confirmed the allelic basis for the common and rare phenotypes. Transmission of PGK-A phenotypes followed the pattern of determinate (nonrandom) inactivation of the paternally derived Pgk-A allele, and transmission of G6PD also was consistent with this pattern. A survey of tissue-specific expression of G6PD phenotypes of heterozygous females revealed, in almost all tissues, three-banded patterns skewed in favor of the allele that was expressed in blood cells. Three-banded patterns were never observed in males or in putatively homozygous females. These patterns suggest simultaneous, but unequal, expression of the maternally and paternally derived Gpd alleles within individual cells (i.e., partial paternal allele expression). The absence of such partial expression was noted in a parallel survey of females heterozygous at the Pgk-A locus. Thus, it appears that Gpd and Pgk-A are X-linked in D. virginiana and subject to preferential paternal allele inactivation, but that dosage compensation may not be complete for all paternally derived X-linked genes. The data establish the similarity between the American and Australian marsupial patterns of X-linked gene regulation and, thus, support the hypothesis that this form of dosage compensation was present in the early marsupial lineage that gave rise to these modern marsupial divisions. In addition, the data provide the first documentation of the differential expression of two X-linked genes in a single marsupial species. Because of its combination of X-linked variation, high fecundity, and short generation time, D. virginiana is a unique model for pursuing questions about marsupial gene regulation that have been difficult to approach through studies of Australian species.
Amplified RNase H Activity in Escherichia coli B/r Increases Sensitivity to Ultraviolet Radiation
Authors: Bockrath Richard , Wolff Lee , Farr Abigail , Crouch Robert J 
Published: January 2021

ABSTRACT
Strains of E. coli B/r transformed with the plasmid pSK760 were found to be sensitized to inactivation by ultraviolet radiation (UV) and to have elevated levels of RNase H activity. Strains transformed with the carrier vector pBR322 or the plasmid pSK762C derived from pSK760 but with an inactivated rnh gene were not sensitized. UV-inactivation data for strains having known defects in DNA repair and transformed with pSK760 suggested an interference by RNase H of postreplication repair: uvrA cells were strongly sensitized, wild-type and uvrA recF cells were moderately sensitized and recA cells were not sensitized; and minimal medium recovery was no longer apparent in sensitized uvrA cells. Biochemical studies showed that post-UV DNA synthesis was sensitized and that the smaller amounts of DNA synthesized after irradiation, while of normal reduced size as indicated by sedimentation position in alkaline sucrose gradients, did not shift to a larger size (more rapidly sedimenting) upon additional incubation. We suggest an excess level of RNase H interferes with reinitiation of DNA synthesis on damaged templates to disturb the normal pattern of daughter strand gaps and thereby to inhibit postreplication repair.
Local DNA Sequence Control of Deletion Formation in Escherichia coli Plasmid pBR322
Authors: DasGupta Ujjala , Weston-Hafer Kathleen , Berg Douglas E 
Published: January 2021

ABSTRACT
The specificity of deletion formation was studied using tests involving reversion of palindromic insertion mutations. Insertions of a Tn5-related transposon at 13 sites in the ampicillin-resistance (amp) gene of plasmid pBR322 were shortened to a nested set of perfect palindromes, 22, 32 and 90 bp long. We monitored frequencies of reversion to Ampr, which is the result of deletion of the palindrome plus one copy of the flanking 9 bp direct repeats (which had been formed by transposition). Revertant frequencies were found to depend on the location and the sequence of the palindromic insert. Changing a 45-kb interrupted palindrome to a 22-bp perfect palindrome stimulated deletion formation by factors of from fourfold to 545-fold among the 13 sites, while elongation of the perfect palindrome from 22 to 90 bp stimulated deletion formation by factors of from eight- to 18,000-fold. We conclude that deletion formation is strongly affected by subtle features of DNA sequence or conformation, both inside and outside the deleted segment, and that these effects may reflect specific interactions of DNA processing proteins with template DNAs.
The Genetical Response to Natural Selection by Varied Environments. IV. Gametic Disequilibrium in Spatially Varied Environments
Authors: Birley A J , Haley C S 
Published: January 2021

ABSTRACT
Gametic disequilibria between allozyme loci were related to spatial variation of the environment in caged populations of Drosophila melanogaster . Two experiments, one with flies collected at "Chateau Tahbilk," South Australia, and the other with flies from "Groningen," The Netherlands, were sampled at generations 16 and 32. Spatial variation of the environment was stimulated using three food media. Eight polymorphic allozyme loci were used to estimate gametic disequilibria from digenic combinations of allotypes. All populations were duplicated within an environment and maintained at about 2500 adults. Standardized gametic disequilibria were compared by a weighted least squares analysis of the z-transformed statistical correlation of allele frequencies. Gametic disequilibria were strongly dependent upon food niche and food-niche interactions. The effects also varied with sampling time and were similar in duplicate populations. Gametic disequilibria were most often detected in the "Groningen"-derived populations and their strength was not strongly associated with recombination fraction. Many of the disequilibria concerned unlinked loci. The strength of selection was probably considerable and populations were evolving genetic architectures which reflected niche selection by the different foods without marked genetic isolation between foods; gene frequencies did not vary between niches within a population cage.
Regulatory and Structural Genes for Lysozymes of Mice
Authors: Hammer Michael F , Wilson Allan C 
Published: January 2021

ABSTRACT
The molecular and genetic basis of large differences in the concentration of P lysozyme in the small intestine has been investigated by crossing inbred strains of two species of house mouse (genus Mus). The concentration of P in domesticus is about 130-fold higher than in castaneus . An autosomal genetic element determining the concentration of P has been identified and named the P lysozyme regulator, Lzp-r . The level of P in interspecific hybrids (domesticus x castaneus) as well as in certain classes of backcross progeny is intermediate relative to parental levels, which shows that the two alleles of Lzp-r are inherited additively. There are two forms of P lysozyme in the intestine of the interspecific hybrid-one having the heat stability of domesticus P, the other being more stable and presumably the product of the castaneus P locus. These two forms occur in equal amounts, and it appears that Lzp-r acts in trans. The linkage of Lzp-r to three structural genes (Lzp-s, Lzm-s1, and Lzm-s2), one specifying P lysozyme and two specifying M lysozymes, was shown by electrophoretic analysis of backcrosses involving domesticus and castaneus and also domesticus and spretus . The role of regulatory mutations in evolution is discussed in light of these results.
The Consequences of Fluctuating Selection for Isozyme Polymorphisms in Daphnia
Authors: Lynch Michael 
Published: January 2021

ABSTRACT
Temporal sequences of allele frequencies in natural populations of Daphnia are analyzed to obtain the mean and variance of the selection coefficient for both asexual and sexual phases. In general, the alleles at enzyme loci appear to be quasi-neutral. Although significant variation exists for the estimated selection coefficients, the means are in all cases close to zero. Estimates of the variance of selection intensity are applied to existing models to demonstrate the implications of fluctuating selection for the spatial and temporal distribution of gene frequencies in Daphnia. The empirical and analytical results are shown to provide a possible solution to some previously puzzling aspects of Daphnia population genetic surveys. Neither genetic drift nor diversifying selection are necessary conditions for the local diversification of gene frequencies.
Molecular-Marker-Facilitated Investigations of Quantitative-Trait Loci in Maize. I. Numbers, Genomic Distribution and Types of Gene Action
Authors: Edwards M D , Stuber C W , Wendel J F 
Published: January 2021

ABSTRACT
Individual genetic factors which underlie variation in quantitative traits of maize were investigated in each of two F2 populations by examining the mean trait expressions of genotypic classes at each of 17–20 segregating marker loci. It was demonstrated that the trait expression of marker locus classes could be interpreted in terms of genetic behavior at linked quantitative trait loci (QTLs). For each of 82 traits evaluated, QTLs were detected and located to genomic sites. The numbers of detected factors varied according to trait, with the average trait significantly influenced by almost two-thirds of the marked genomic sites. Most of the detected associations between marker loci and quantitative traits were highly significant, and could have been detected with fewer than the 1800–1900 plants evaluated in each population. The cumulative, simple effects of marker-linked regions of the genome explained between 8 and 40% of the phenotypic variation for a subset of 25 traits evaluated. Single marker loci accounted for between 0.3% and 16% of the phenotypic variation of traits. Individual plant heterozygosity, as measured by marker loci, was significantly associated with variation in many traits. The apparent types of gene action at the QTLs varied both among traits and between loci for given traits, although overdominance appeared frequently, especially for yield-related traits. The prevalence of apparent overdominance may reflect the effects of multiple QTLs within individual marker-linked regions, a situation which would tend to result in overestimation of dominance. Digenic epistasis did not appear to be important in determining the expression of the quantitative traits evaluated. Examination of the effects of marked regions on the expression of pairs of traits suggests that genomic regions vary in the direction and magnitudes of their effects on trait correlations, perhaps providing a means of selecting to dissociate some correlated traits. Marker-facilitated investigations appear to provide a powerful means of examining aspects of the genetic control of quantitative traits. Modifications of the methods employed herein will allow examination of the stability of individual gene effects in varying genetic backgrounds and environments.
Premeiotic and Meiotic Instability Generates Numerous b2 Mutation Derivatives in Ascobolus
Authors: Nicolas A , Hamza H , Mekki-Berrada A , Kalogeropoulos A , Rossignol J L 
Published: January 2021

ABSTRACT
We have studied the genetic characteristics of an unstable mutation located in the central region of the b2 gene of the fungus Ascobolus. In crosses to wild type, this spontaneous white ascospore mutation (G0) gives rise to a stable white spored derivative (G1) at a frequency of 5 × 10-3. G1 is a frameshift mutation and differs from G0 by its gene conversion pattern. In self crosses, G0 gives asci with colored spore derivatives at a frequency of 1 × 10-3. We isolated and analyzed genetically 97 independent colored derivatives ("G2" series). All but one are pseudorevertants. By the criteria of phenotype and gene conversion pattern with wild type and with G1, the pseudorevertants represent at least 13 distinct classes. Two of them are large silent deletion mutations. In crosses with wild type, some G2 derivatives, represented by G21, continue to exhibit instability, G21 yields white spored b2 mutant derivatives at a frequency of 2.6 × 10-3. In turn, some of these "G3" mutants are themselves unstable. All the derivatives lie at the same site within the b2 locus as the parental mutation G0 . Different mutations in the G series manifest their instability at different times in the Ascobolus life cycle. Derivatives of G0 arise premeiotically (leading to two derivative meiotic products among the four), while those of G21 arise during meiosis (leading to only one derivative out of four products). The characteristics of the G instability system are similar to those of unstable mutations in other eukaryotes which are due to insertion of mobile elements.
Altered Turnover of Hypoxanthine Phosphoribosyltransferase in Erythroid Cells of Mice Expressing Hprt a and Hprt b Alleles
Authors: Johnson Gerald G , Chapman Verne M 
Published: January 2021

ABSTRACT
We have previously shown that mice expressing Hprt a allele(s) have erythrocyte hypoxanthine phosphoribosyltransferase (HPRT) levels that are approximately 25-fold (Mus musculus castaneus) and 70-fold (Mus spretus) higher than in mice that express the Hprt b allele (Mus musculus domesticus; C57BI/6J; C3H/HeHa), and that these differences in erythrocyte HPRT levels are due to differences in the turnover rates of the HPRT A and B proteins as reticulocytes mature to erythrocytes. We show here that: (1) the taxonomic subgroups of the genus Mus are essentially monomorphic for the occurrence of either the Hprt a or the Hprt b allele, with Hprt a being common in the aboriginal species (M. spretus, Mus hortulanus and Mus abbotti) and in several commensal species (Mus musculus musculus, M. m. castaneus, Mus musculus molossinus), while Hprt b is common in feral M. m. domesticus populations as well as in all inbred strains of mice tested; (2) in all these diverse Mus subgroups there is a strict association of Hprt a with high and Hprt b with low levels of erythrocyte HPRT; and, (3) the association between the occurrence of the Hprt a allele and elevated erythrocyte HPRT levels is retained following repeated backcrosses of wild-derived Hprt a allele(s) into the genetic background of inbred strains of mice with the Hprt b allele. Collectively, these observations indicate that the elevated and low levels of erythrocyte HPRT are specified by differences in the Hprt a and b structural genes. Since evidence indicates that Hprt a and b encode HPRT proteins which differ in primary structure, we infer that the structure of HPRT is an important factor in determining its sensitivity to turnover in mouse erythroid cells. Hprt a and b may provide a useful system of "normal" allelic gene products for identifying factors that participate in protein turnover during mouse reticulocyte maturation.
Mosaic Analysis of Two Genes That Affect Nervous System Structure in Caenorhabditis elegans
Authors: Herman Robert K 
Published: January 2021

ABSTRACT
The mutation mec-4(e1611), identified by M. Chalfie, leads to the degeneration and death of the six neurons, called the microtubule cells, that mediate the response of wild-type animals to light touch. The fates of two of these cells, PLML and PLMR, which are responsible for response to light touch in the tail of the animal, have been monitored in animals mosaic for the mec-4(e1611) mutation. The results are consistent with the view that the mutation behaves cell autonomously in its killing effect; in particular, none of the neurons that make either chemical synapses or gap junctions to PLML or PLMR is responsible for the deaths of PLML or PLMR. The results of gene dosage and dominance tests suggest that the mec-4(+) gene product, which is required for wild-type microtubule cell function, is altered by the e1611 mutation into a novel product that kills the microtubule cells. Mutation in the gene unc-3 leads to the derangement of the processes of the motor neurons of the ventral cord. Mosaic analysis strongly suggests that unc-3(+) expression is required only in the motor neurons themselves for normal neuronal development. In particular, the hypodermis surrounding the ventral cord is not the primary focus of unc-3 action (body muscle was excluded in earlier work). Finally, the mosaic analysis supports an earlier suggestion that a sensory defect caused by a daf-6 mutation is localized to a non-neuronal cell called the sheath cell.
Evolution of Steroid-Inducible RP2 mRNA Expression in the Mouse Kidney
Authors: Tseng-Crank Julie , Berger Franklin G 
Published: January 2021

ABSTRACT
We have examined the structure and expression of mRNAs encoded by the androgen-inducible RP2 gene in the kidneys of nine mouse species within the genus Mus. There is considerable interspecies variation in the lengths of the major RP2 transcripts; some of this variation is due to the presence or absence of a B1 repetitive element in the 3′-untranslated region of the gene. In addition, the extent of RP2 mRNA induction by testosterone differs among the species. Two species show 10-20-fold induction, while others display a reduced response or none at all. Analysis of an interspecific hybrid indicates that the inducibility phenotype is inherited in an additive fashion. A correlation between RP2 inducibility and the time of formation of lineages within the Mus genus suggests that induction evolved in a stepwise fashion, with the acquisition of a modest hormonal response being followed by the appearance of a greater response. The interspecies variations in RP2 mRNA structure and regulation provide a useful model for the identification and study of genetic elements that elicit evolutionary alterations in steroid-modulated gene expression.
Monotonic Change of the Mean Phenotype in Two-Locus Models
Authors: Hastings Alan 
Published: January 2021

ABSTRACT
It is shown that the mean phenotype monotonically approaches the optimum in a class of symmetric, two-locus, two-allele models with stabilizing selection. In this model, mean fitness does not change monotonically. Thus, Fisher's fundamental theorem does not hold, even though another quantity of evolutionary interest, the mean phenotype, can be shown to change monotonically. Using this quantity, it is proven that global stability results for this model.
Polarity effects in the hisG gene of salmonella require a site within the coding sequence.
Authors: Ciampi M S , Roth J R 
Published: January 2021

Abstract
A single site in the middle of the coding sequence of the hisG gene of Salmonella is required for most of the polar effect of mutations in this gene. Nonsense and insertion mutations mapping upstream of this point in the hisG gene all have strong polar effects on expression of downstream genes in the operon; mutations mapping promotor distal to this site have little or no polar effect. Two previously known hisG mutations, mapping in the region of the polarity site, abolish the polarity effect of insertion mutations mapping upstream of this region. New polarity site mutations have been selected which have lost the polar effect of upstream nonsense mutations. All mutations abolishing the function of the site are small deletions; three are identical, 28-bp deletions which have arisen independently. A fourth mutation is a deletion of 16 base pairs internal to the larger deletion. Several point mutations within this 16-bp region have no effect on the function of the polarity site. We believe that a small number of polarity sites of this type are responsible for polarity in all genes. The site in the hisG gene is more easily detected than most because it appears to be the only such site in the hisG gene and because it maps in the center of the coding sequence.
Detection of new MHC mutations in mice by skin grafting, tumor transplantation and monoclonal antibodies: a comparison.
Authors: Egorov I K , Egorov O S 
Published: January 2021

Abstract
Two mechanisms of major histocompatibility complex (MHC) mutations have been described in mice; gene conversion and homologous but unequal recombination. However, our knowledge of mutations in MHC is incomplete because studies have been limited almost exclusively to two haplotypes, H-2b and H-2d, while hundreds of haplotypes exist in nature; it has been biased by the use of only one procedure of screening for mutation, skin grafting. We used three procedures to screen for MHC mutations: (1) conventional techniques of skin grafting, (2) syngeneic tumor transplantation and (3) typing with monoclonal anti-MHC antibodies (mAbs) and complement. The faster technique of tumor transplantation detected mutants similar to those discovered by skin grafting technique. Screening with mAbs allowed us to detect both mutants that are capable of rejecting standard skin grafts and those that are silent in skin grafting tests, and which therefore resulted in a higher apparent mutation frequency. Two mutants of the H-2a haplotype were found that carry concomitant class I and class II antigenic alterations. Both MHC mutants silent in skin grafting tests and mutants carrying concomitant class I and class II alterations have never been studied before and are expected to reveal new mechanisms of generating MHC mutations. 1-Ethyl-1-nitrosourea (ENU) failed to induce de novo MHC mutations in male mice in our skin grafting series.