bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficacy of Cover Crops for Pollinator Habitat Provision and Weed Suppression
Authors: Bryan Casey J , Sipes Sedonia D , Arduser Mike , Kassim Leila , Gibson David J , Scott Drew A , Gage Karla L
Published: January 2021

Pollinator declines have been documented globally, but little information is available about native bee ecology in Midwestern U.S. agriculture. This project seeks to optimize pollinator support and weed suppression in a 3-yr crop rotation with a fallow growing season. During fallow, one of five cover crop treatments (T1: crimson, red, and ladino clover and Bob oats [Fabales: Fabaceae - Trifolium incarnatum L., Trifolium pratense L., Trifolium repens L., and Cyperales: Poaceae - Avena sativa]; T2: crimson clover and oats; T3: red clover and oats; T4: ladino clover and oats; T5: no cover crop; T6/control: winter wheat [Cyperales: Poaceae - Triticum aestivum] L.) was seeded in one-half of 25 agricultural fields, whereas wheat was left unharvested in the other half as a comparison. Treatments that provide season-long floral resources support the greatest bee diversity and abundance (T1), and treatments with red clover support declining (Hymenoptera: Apidae) Bombus species (T1 and T3). Late-season floral resources may be important, yet limited (T1 and T4), and some species of agricultural weeds provide floral resources. Floral diversity may be less important than flower abundance or timing for pollinator diversity (T1–T4). Weed diversity was greatest in the no cover crop treatment (T5), least in winter wheat (T6), and intermediate in cover crop treatments (T1–T4) with no differences in weeds of economic concern. Wheat suppresses weeds but does not provide floral resources for pollinators. These results may also be applicable to marginal lands taken out of cultivation or field margin pollinator plantings in a typical corn–soybean rotation. Floral resource availability across the landscape is critical to maintain pollinator diversity.
Impact of left atrial strain mechanics on exercise intolerance and need for septal reduction therapy in hypertrophic cardiomyopathy
Authors: Saijo Yoshihito , Van Iterson Erik , Vega Brizneda Maria , Desai Milind Y , Lever Harry M , Smedira Nicholas G , Wierup Per , Thamilarasan Maran , Popović Zoran B , Grimm Richard A , Griffin Brian P , Xu Bo
Published: January 2021

Aims

We sought to assess the relationship between left atrial (LA) strain mechanics and exercise intolerance, and to evaluate the prognostic impact of LA strain mechanics on clinical deterioration necessitating septal reduction therapy in hypertrophic cardiomyopathy (HCM).

Methods and results

Consecutive HCM patients who underwent exercise stress echocardiography and cardiopulmonary exercise testing on the same day between October 2015 and April 2019 were enrolled prospectively. LA strain mechanics were analysed using speckle tracking echocardiography. LA stiffness was calculated as the ratio of E/e′ ratio to LA reservoir strain. The study cohort was divided into four groups based on the quartile of percent-predicted peak VO2, and exercise intolerance was defined as the lowest quartile (≤51%). Of 532 patients studied (mean age: 51 ± 15 years, 42% female), 138 patients demonstrated exercise intolerance. As exercise capacity worsened, LA strain mechanics worsened along a continuum (P < 0.001). LA contractile strain with a cut-off of −13.9% was optimal at identifying exercise intolerance. On multivariable analysis, worse LA contractile strain was an independent predictor for exercise intolerance (P = 0.002). Of patients with left ventricular outflow tract obstruction, patients with LA stiffness worse than the median value (≥0.41) were significantly more likely to require septal reduction therapy than those with better LA stiffness (P = 0.026).

Conclusion

Worse LA contractile strain was an independent predictor for exercise intolerance in HCM. Patients with worse LA stiffness had a higher probability of clinical deterioration necessitating septal reduction therapy.
Endoscopic pancreatic duct stenting for pain palliation in selected pancreatic cancer patients: a systematic review and meta-analysis
Authors: Siddappa Pradeep K , Hawa Fadi , Prokop Larry J , Murad M Hassan , Abu Dayyeh Barham K , Chandrasekhara Vinay , Topazian Mark D , Bazerbachi Fateh
Published: January 2021

Background

Abdominal pain is a debilitating symptom affecting ∼80% of pancreatic cancer (PC) patients. Pancreatic duct (PD) decompression has been reported to alleviate this pain, although this practice has not been widely adopted. We aimed to evaluate the role, efficacy, and safety of endoscopic PD decompression for palliation of PC post-prandial obstructive-type pain.

Methods

A systematic review until 7 October 2020 was performed. Two independent reviewers selected studies, extracted data, and assessed the methodological quality.

Results

We identified 12 publications with a total of 192 patients with PC presenting with abdominal pain, in whom PD decompression was attempted, and was successful in 167 patients (mean age 62.5 years, 58.7% males). The use of plastic stents was reported in 159 patients (95.2%). All included studies reported partial or complete improvement in pain levels after PD stenting, with an improvement rate of 93% (95% confidence interval, 79%–100%). The mean duration of pain improvement was 94 ± 16 days. Endoscopic retrograde cholangiopancreatography (ERCP)-related adverse events (AEs) were post-sphincterotomy bleeding (1.8%), post-ERCP pancreatitis (0.6%), and hemosuccus pancreaticus (0.6%). AEs were not reported in two patients who underwent endoscopic ultrasound-guided PD decompression. In the 167 patients with technical success, the stent-migration and stent-occlusion rates were 3.6% and 3.0%, respectively. No AE-related mortality was reported. The methodological quality assessment showed the majority of the studies having low or unclear quality.

Conclusion

In this exploratory analysis, endoscopic PD drainage may be an effective and safe option in selected patients for the management of obstructive-type PC pain. However, a randomized–controlled trial is needed to delineate the role of this invasive practice.
Pervasive Mitonuclear Coadaptation Underlies Fast Development in Interpopulation Hybrids of a Marine Crustacean
Authors: Han Kin-Lan , Barreto Felipe S
Published: January 2021

Cellular energy production requires coordinated interactions between genetic components from the nuclear and mitochondrial genomes. This coordination results in coadaptation of interacting elements within populations. Interbreeding between divergent gene pools can disrupt coadapted loci and result in hybrid fitness breakdown. While specific incompatible loci have been detected in multiple eukaryotic taxa, the extent of the nuclear genome that is influenced by mitonuclear coadaptation is not clear in any species. Here, we used F2 hybrids between two divergent populations of the copepod Tigriopus californicus to examine mitonuclear coadaptation across the nuclear genome. Using developmental rate as a measure of fitness, we found that fast-developing copepods had higher ATP synthesis capacity than slow developers, suggesting variation in developmental rates is at least partly associated with mitochondrial dysfunction. Using Pool-seq, we detected strong biases for maternal alleles across 7 (of 12) chromosomes in both reciprocal crosses in high-fitness hybrids, whereas low-fitness hybrids showed shifts toward the paternal population. Comparison with previous results on a different hybrid cross revealed largely different patterns of strong mitonuclear coadaptation associated with developmental rate. Our findings suggest that functional coadaptation between interacting nuclear and mitochondrial components is reflected in strong polygenic effects on this life-history phenotype, and reveal that molecular coadaptation follows independent evolutionary trajectories among isolated populations.
A Draft Genome Assembly ofCulex pipiens pallens(Diptera: Culicidae) Using PacBio Sequencing
Authors: Peng Cheng , Qian Zhang , Xinyu Zhang , Qianqian Le , Maoqing Gong , Zhong Zhang , Ruiling Zhang
Published: January 2021

The Northern house mosquito, Culex pipiens pallens, serves as important temperate vectors of several diseases, particularly the epidemic encephalitis and lymphatic filariasis. Reference genome of the Cx. pipiens pallens is helpful to understand its genomic basis underlying the complexity of mosquito biology. Using 142 Gb (∼250×) of the PacBio long reads, we assembled a draft genome of 567.56 Mb. The assembly includes 1,714 contigs with a N50 length of 0.84 Mb and a Benchmarking Universal Single-Copy Orthologs (BUSCO) completeness of 95.6% (n = 1,367). We masked 60.63% (344.11 Mb) of the genome as repetitive elements and identified 2,032 noncoding RNAs. A total of 18,122 protein-coding genes captured a 94.1% of BUSCO gene set. Gene family evolution and function enrichment analyses revealed that significantly expanded gene families mainly involved in immunity, gustatory and olfactory chemosensation, and DNA replication/repair.
ON SOME MODELS OF FERTILITY SELECTION
Authors: Feldman Marcus W , Christiansen Freddy B , Liberman Uri
Published: January 2021

Additive, multiplicative and symmetric models of fertility controlled by one diallelic gene are studied. For the completely symmetric fertility system a complete equilibrium and local stability analysis is possible. Contrary to previous conjectures, asymmetric equilibria can be stable. Conditions are derived under which a multiplicative model can be regarded as equivalent to a symmetric fertility system.
VIABILITY INTERACTIONS, IN VIVO ACTIVITY AND THE G6PD POLYMORPHISM IN DROSOPHILA MELANOGASTER
Authors: Eanes Walter F
Published: January 2021

Several biochemical studies have suggested that in Drosophila melanogaster the two common allozymes of G6PD differ in their in vitro activities and thermal stabilities. Yet, it remains to be shown that these characterizations reflect actual in vivo differences and are not artifacts of the biochemical approach. In this study it is shown that in vivo activity differences must exist between these two variants. This conclusion arises from the observation that the viability of flies bearing a low activity allele of 6PGD is strongly dependent on the genotype at the G6PD (Zw) locus, whereas no measurable difference in viability can be detected between Zw genotypes in a normal activity 6PGD background. These viability interactions are in the direction predicted by the reported in vitro activities of the allozymes and the proposed deleterious effects of 6-phosphogluconate accumulation.—In addition, a genetic scheme is used that uncouples and quantifies the effects of viability modifiers in the region of the Zw locus, while homogenizing 98% of the X chromosome. The viability of different Zw genotypes is measured by examining whole chromosome viabilities relative to the FM6 balancer chromosome. The advantages of this particular scheme are discussed.
THE ROLE OF PYRIMIDINE DIMERS AS PREMUTAGENIC LESIONS: A STUDY OF TARGETED VS. UNTARGETED MUTAGENESIS IN THE lacI GENE OF ESCHERICHIA COLI
Authors: Kunz Bernard A , Glickman Barry W
Published: January 2021

We have employed conjugal transfer of an F′ lac episome to examine targeted and untargeted mutagenesis in the lacI gene of Escherichia coli and to determine the relative importance of pyrimidine dimers as premutational UV lesions compared to (6-4) photoproducts that also may have a mutational role. This conjugal system allowed us to assess the premutagenic role of UV lesions independently from any role as inducers of SOS functions. F′ DNA was transferred to an SOS-induced recipient strain from: unirradiated donor cells, UV-treated donor cells or donor cells that were irradiated and then exposed to photoreactivating light. The results indicate that SOS-related, untargeted events may account for as much as one-third of the nonsense mutations (i.e., base substitutions) recovered after undamaged F′ DNA is transferred to UV-irradiated recipients. When the donor strain also is irradiated, in excess of 90% of the mutations detected following conjugation appear to be targeted. Photoreactivation of the UV-treated donor cells, prior to F′ transfer to the SOS-induced recipient strain, demonstrated that in this experimental system virtually all recovered UV-induced mutations are targeted by photoreactivable lesions. We presume that these lesions are pyrimidine dimers because (6-4) photoproducts are not photoreactivable.
SEX CHROMOSOME MEIOTIC DRIVE IN DROSOPHILA MELANOGASTER MALES
Authors: McKee Bruce
Published: January 2021

In Drosophila melanogaster males, deficiency for X heterochromatin causes high X-Y nondisjunction and skewed sex chromosome segregation ratios (meiotic drive). Y and XY classes are recovered poorly because of sperm dysfunction. In this study it was found that X heterochromatic deficiencies disrupt recovery not only of the Y chromosome but also of the X and autosomes, that both heterochromatic and euchromatic regions of chromosomes are affected and that the "sensitivity" of a chromosome to meiotic drive is a function of its length. Two models to explain these results are considered. One is a competitive model that proposes that all chromosomes must compete for a scarce chromosome-binding material in Xh  - males. The failure to observe competitive interactions among chromosome recovery probabilities rules out this model. The second is a pairing model which holds that normal spermiogenesis requires X-Y pairing at special heterochromatic pairing sites. Unsaturated pairing sites become gametic lethals. This model fails to account for autosomal sensitivity to meiotic drive. It is also contradicted by evidence that saturation of Y-pairing sites fails to suppress meiotic drive in Xh  - males and that extra X-pairing sites in an otherwise normal male do not induce drive. It is argued that meiotic drive results from separation of X euchromatin from X heterochromatin.
MORPHOGENETICALLY SPECIFIC MUTABILITY IN DROSOPHILA ANANASSAE
Authors: Hinton Claude W
Published: January 2021

A stock exhibiting hypermutability with respect to visible mutants (Om) affecting optic morphology was subjected to genetic analysis. The production of Om mutants, independently recovered with a frequency of two per 104, is restricted to females and depends primarily on homozygosity of their X chromosomes; in heterozygotes, Ommutability is stimulated by the presence of either one of two extrachromosomally replicating elements previously identified in other stocks having cryptic mutability systems. The semidominant and nonpleiotropic Om mutants are not associated with gross rearrangements and they map to at least 15 loci. Most of the loci defined by mapping are represented by two or more Ommutants which, despite considerable interlocus mimicry, sometimes display locus-specific phenotypes. Om mutants are moderately unstable, and they are subject to dominant suppressors that arise spontaneously at either of two X-linked loci. An interpretation of these observations invokes an X-linked transposable element (tom) that specifically inserts into control sequences shared by a set of structural genes involved in eye morphogenesis.
PLOIDY BARRIER TO ENDOSPERM DEVELOPMENT IN MAIZE
Authors: Lin Bor-Yaw
Published: January 2021

Maize kernels inheriting the indeterminate gametophyte mutant (ig) on the female side had endosperms that ranged in ploidy level from diploid (2x) to nonaploid (9x). In crosses with diploid males, only kernels of the triploid endosperm class developed normally. Kernels of the tetraploid endosperm class were half-sized but with well-developed embryos that regularly germinated. Kernels of endosperm composition other than triploid or tetraploid were abortive.—Endosperm ploidy level resulting from mating ig/igx tetraploid Ig similarly was variable. Most endosperms started to degenerate soon after pollination and remained in an arrested state. Hexaploid endosperm was exceptional; it developed normally during the sequence of stages studied and accounted for plump kernels on mature ears. Since such kernels have diploid maternal tissues (pericarp) but triploid embryos, the present finding favors the view that endosperm failure or success in such circumstances is governed by conditions within the endosperm itself.—Whereas tetraploid endosperm consisting of three maternal genomes and one paternal genome is slightly reduced in size but supports viable seed development, that endosperm having two maternal and two paternal chromosome sets was highly defective and conditioned abortion. Thus, development of maize endosperm evidently is affected by the parental source of its sets of chromosomes.
COPY NUMBER CONTROL OF Tn5 TRANSPOSITION
Authors: Johnson Reid C , Reznikoff William S
Published: January 2021

Transposition of Tn5 in Escherichia coli strains containing one or multiple copies of the transposable element was investigated. It was found that the overall frequency of transposition within a cell remained constant regardless of the number of copies of Tn5 present in that cell. Experiments measuring the transposition frequency of differentially marked Tn5s confirmed that the frequency of transposition of an individual Tn5 decreased proportionally with the total number of copies of the element present in a cell. The IS50R-encoded function, protein 2, which has previously been shown to be an inhibitor of transposition, is sufficient to mediate this inhibitory effect. The concentration of protein 2 in a cell appears to modulate the transposition of individual Tn5 elements in such a way that the overall transposition of Tn5 in a cell remains constant.
FREQUENT IMPRECISE EXCISION AMONG REVERSIONS OF A P ELEMENT-CAUSED LETHAL MUTATION IN DROSOPHILA
Authors: Voelker Robert A , Greenleaf Arno L , Gyurkovics Henrik , Wisely G Bruce , Huang Shu-Mei , Searles Lillie L
Published: January 2021

RpII215D  50 (= D50) is a lethal mutation caused by the insertion of a 1.3-kb P element 5′ to sequences encoding the largest (215 kilodaltons) subunit of Drosophila RNA polymerase II. In dysgenic males D50 reverted to nonlethality at frequencies ranging from 2.6 to 6.5%. These reversions resulted from loss of P element sequences. Genetic tests of function and restriction enzyme analysis of revertant DNAs revealed that 35% or more of the reversion events were imprecise excisions. Two meiotic mutations that perturb excision repair and postreplication repair (mei-9a and mei-41D  5, respectively) had no influence on reversion frequency but may have increased the proportion of imprecise excisions. We suggest that these excisions are by-products of, rather than intermediates in, the transposition process.
FACTORS INFLUENCING DISPROPORTIONATE REPLICATION OF THE RIBOSOMAL RNA CISTRONS IN DROSOPHILA MELANOGASTER
Authors: Dutton F Lee , Krider Hallie M
Published: January 2021

This report describes studies of the compensatory response employing D. melanogaster stocks that bear cloned-X chromosomes derived from laboratory populations of strains Oregon R and Canton S. We find that modification of the autosomal background in either the female or the (see PDF) male parent influences the expression of the compensatory response by X chromosomes derived from the Canton S population, whereas Oregon R isolates are unresponsive to these effects. We have also studied compensatory replication in X/O larvae produced from cloned-X derivatives of both Canton S and Oregon R. Canton S larval compensation exceeds that of the adult, whereas in Oregon R the converse is true. We have concluded that both X chromosomal and autosomal factors affect the expression and magnitude of the compensatory response.
RIBOSOMAL RNA CISTRONS OF X CHROMOSOMES CLONALLY DERIVED FROM D. MELANOGASTER LABORATORY POPULATIONS: REDUNDANCY, ORGANIZATION AND STABILITY
Authors: Dutton F Lee , Krider Hallie M
Published: January 2021

To determine whether heterogeneity exists in the organization or redundancy of the rRNA cistrons of inbred populations of Drosophila melanogaster, we have derived a number of sublines from the strains Oregon R and Canton S. These two strains were chosen because our previous studies have demonstrated a difference in the competence of these strains to exhibit a "compensatory response" of the rDNA. In each subline, the X chromosomes are descended from a single maternal X, that is, each line is homozygous for a particular nucleolus organizer (NO). These derivative lines have been characterized in terms of rDNA content and organization, using quantitative liquid hybridizations and Southern blot analyses, respectively. Our studies reveal that both of the highly inbred parent populations contained a heterogeneous array of X chromosomal rDNA contents. Once isogenized, the rDNA redundancy of a given X chromosomal NO can be shown to remain stable for at least 20 generations in culture. We detect no restriction pattern heterogeneity among X chromosomes isolated from a given strain, despite relatively large differences in their rDNA contents. This leads us to suggest that there is no significant clustering of intervening sequence-bearing (ivs  +) genes within the rDNA loci of chromosomes from the populations examined. Furthermore, we conclude that apparent alterations in rDNA redundancy known as the compensatory response are not related to the heterogeneity of rDNA content within a population.
THERMAL RESCUE OF UV-IRRADIATED BACTERIOPHAGE T4 AND BIPHASIC MODE OF ACTION OF THE WXY SYSTEM
Authors: Conkling Mark A , Drake John W
Published: January 2021

When ultraviolet-irradiated bacteriophage T4 is assayed at plating temperatures ranging from 20° to 40°, its survival increases at the higher temperatures. This "thermal rescue" requires an intact WXY system but not the denV pyrimidine dimer excision system. Mutation rates decrease with increasing temperature, indicating that some lesions processed in a mutagenic manner at lower temperatures are accurately repaired or circumvented at high temperatures. When both the cold sensitivity of UV survival in the wild type and the temperature sensitivity of newly isolated ts mutants of uvsX and uvsY were used, expression of the WXY system was monitored in temperature shift UV survival experiments and was found to be biphasic: the uvsX and uvsY functions increase UV survival in two increments, one at an early and another at a late stage of infection. The uvsW function, however, increases UV survival only early in infection.
MUTATIONS AFFECTING FUNCTIONS OF THE DROSOPHILA GENE GLUED
Authors: Garen Alan , Miller Barbara R , Paco-Larson M Luisa
Published: January 2021

Glued mutations in Drosophila comprise an essential complementation group with complex developmental effects. The original Glued mutation (Gl) has dominant nonlethal effects in heterozygous flies, principally on the morphogenesis of the visual system. Gl also has a recessive lethal effect early in development. Mutations that reverse the dominant visual effects of Gl (GlR mutations) were induced by γ-radiation or by insertions of the transposable P element. The GlR(G) mutations induced by γ-radiation do not reverse the lethal effect of Gl; these appear to be null mutations, some of which (and possibly all) delete segments of the Glued region. The GlR(P) mutations induced by insertion of the P element also reverse concomitantly a recessive lethal effect of Gl, suggesting that both the recessive and dominant effects are controlled by the same gene. The reversal of a lethal effect of Gl by the P element is remarkable, since it indicates that an essential gene function can be restored by insertion of unrelated DNA. Another class of lethal Glued mutations was induced in the normal Gl  + strain by ethyl methanesulfonate (EMS). The EMS mutations belong to the same essential complementation group as Gl, but do not have the strong dominant effects of Gl on the visual system.—The GlR(P) mutations provide a molecular marker for the Glued gene, which was used to map the gene to the 70C2 band of chromosome 3L by in situ hybridization of a P element probe to polytene chromosomes from the GlR(P) strains and also to isolate clones of Glued genomic DNA for molecular studies of the normal gene and the various Glued mutations.
CROSSES BETWEEN INSERTION AND POINT MUTATIONS IN Λ GENE cI: STIMULATION OF NEIGHBORING RECOMBINATION BY HETEROLOGY
Authors: Lieb M , Tsai M M , Deonier Richard C
Published: January 2021

Intragenic recombination between λcl point mutations and insertions was studied in four-factor crosses. In crosses between two point mutations, there is a linear relationship between recombination frequency and distance. However, in crosses between an insertion and point mutations, there is additional recombination in the regions 200 base pairs to the right and to the left of the insertion. The recombinational stimulation occurred with IS insertions and also with insertions consisting of HindIII fragments of SV40 and with a deletion that removes part of cI. This indicated that the stimulation was a result of heterology per se rather than of information encoded by the insertions. Either Rec or Red functions are sufficient for enhanced recombination near a heterology. The stimulation is attributed to more frequent resolution of recombinational intermediates in the neighborhood of a heterology. "Stalling" of migrating branches or invading strands at a heterology may increase the probability of local DNA cleavage.
GENETIC ANALYSIS OF CHROMOMERE 3D4 IN DROSOPHILA MELANOGASTER . II. REGULATORY SITES FOR THE DUNCE GENE
Authors: Salz Helen K , Kiger John A
Published: January 2021

Chromomere 3D4 of the X chromosome of D. melanogaster contains two genes, dunce (dnc) and sperm amotile (sam). Mutations in dnc cause defects in memory formation and female fertility and reduce or eliminate the activity of a cAMP-specific phosphodiesterase designated form II. A fine structure map of this region has been constructed showing the locations of two sam mutations, five dnc mutations and a newly identified locus designated control of fertility (cf) that acts in cis to regulate the female sterility phenotype of dnc. The two sam mutations are separated by 0.02 ± 0.01 cM, the rightmost being located 0.08 ± 0.02 cM to the left of the null mutation dncm  11. A cluster of null and form II-defective dnc mutations is located 0.04 ± 0.01 cM to the right of dncm  11. The cf locus is 0.06 ± 0.02 cM to the right of this cluster. The location of the dnc and cf sites identify a region of approximately 0.10 cM that is required for proper expression of dnc  +. The dncck mutation, associated with a reciprocal translocation between 3L and the X, exhibits reduced form II activity and female sterility. This translocation breakpoint has been mapped to the left of the dnc  + gene and is near the breakpoint of Df(1)N  64j15 which also reduces expression of dnc  +. The effect of these independent chromosomal breaks on the dnc  + gene suggests the existence of a site to the left of dnc  + that is also required for proper expression of the gene.
GENETIC ANALYSIS OF ISOZYME LOCI IN TETRAPLOID POTATOES (SOLANUM TUBEROSUM L.)
Authors: Martinez-Zapater J M , Oliver Jose L
Published: January 2021

The genetic control of eight isozyme loci revealed by starch gel electrophoresis was studied through the analysis of three progenies derived from four tetraploid cultivars of Solanum tuberosum (groups Andigena and Tuberosum). Duplicate gene expression was found in seven (Got-A, Got-B, Pgd-C, Pgi-B, Pgm-A, Pgm-B and Pox-C) isozyme loci. In another isozyme gene (Adh-A), the parental genotypes were not adequate to distinguish between a monogenic or a digenic model of genetic control. Tetrasomic inheritance was demonstrated in four (Got-A, Got-B, Pgd-C and Pgi-B) isozyme loci. In the remaining duplicate genes, the parental genotypes precluded discrimination between disomic or tetrasomic models. Tetrasomic segregations of the chromosomal type were generally found; however, the isozyme phenotypes shown by three descendants from selfing cv. Katahdin indicate the occurrence of chromatid segregations, although aneuploidy cannot be ruled out. Either autoploidy or amphidiploidy with lack of chromosome differentiation between the two diploid ancestors can account for the existence of tetrasomic inheritance in the common potato.
DETECTION OF NONRANDOM ASSOCIATION OF ALLELES FROM THE DISTRIBUTION OF THE NUMBER OF HETEROZYGOUS LOCI IN A SAMPLE
Authors: Chakraborty Ranajit
Published: January 2021

The distribution of the number of heterozygous loci in two randomly chosen gametes or in a random diploid zygote provides information regarding the nonrandom association of alleles among different genetic loci. Two alternative statistics may be employed for detection of nonrandom association of genes of different loci when observations are made on these distributions: observed variance of the number of heterozygous loci (s  2  k) and a goodness-of-fit criterion (X  2) to contrast the observed distribution with that expected under the hypothesis of random association of genes. It is shown, by simulation, that s  2  k is statistically more efficient than X  2 to detect a given extent of nonrandom association. Asymptotic normality of s  2  k is justified, and X  2 is shown to follow a chi-square (X2) distribution with partial loss of degrees of freedom arising because of estimation of parameters from the marginal gene frequency data. Whenever direct evaluations of linkage disequilibrium values are possible, tests based on maximum likelihood estimators of linkage disequilibria require a smaller sample size (number of zygotes or gametes) to detect a given level of nonrandom association in comparison with that required if such tests are conducted on the basis of s  2  k. Summarization of multilocus genotype (or haplotype) data, into the different number of heterozygous loci classes, thus, amounts to appreciable loss of information.
SPONTANEOUS UNSTABLE UNC-22 IV MUTATIONS IN C. ELEGANS VAR. BERGERAC
Authors: Moerman D G , Waterston R H
Published: January 2021

This paper describes a mutator system in the nematode Caenorhabditis elegans var. Bergerac for the gene unc-22. Of nine C. elegans and two C. briggsae strains tested only the Bergerac BO strain yielded mutant animals at a high frequency and the unc-22 IV gene is a preferred mutational target. The forward spontaneous mutation frequency at the unc-22 locus in Bergerac BO is about 1 × 10-4, and most of these spontaneous unc-22 mutations revert at frequencies between 2 × 10-3 and 2 × 10-4. Both the forward mutation frequency and the reversion frequency are sensitive to genetic background. Spontaneous unc-22 mutations derived in a Bergerac background and placed in a primarily Bristol background revert at frequencies of <10-6. When reintroduced into a Bergerac/Bristol hybrid background the mutations once again become unstable.

The mutator activity could not be localized to a discrete site in the Bergerac genome. Nor did mutator activity require the Bergerac unc-22 gene as a target since the Bristol unc-22 homolog placed in a Bergerac background also showed high mutation frequency. Intragenic mapping of two spontaneous unc-22 alleles, st136 and st137, place both mutations in the central region of the known unc-22 map. However, these mutations probably recombine with one another, suggesting that the unstable mutations can occur in more than one site in unc-22. Examination of the phenotypic effect of these mutations on muscle structure indicates that they are less severe in their effect than a known amber allele. We suggest that this mutator system is polygenic and dispersed over the nematode genome and could represent activity of the transposable element Tc1.
VALINE-RESISTANCE, A POTENTIAL MARKER IN PLANT CELL GENETICS. II. OPTIMIZATION OF UV MUTAGENESIS AND SELECTION OF VALINE-RESISTANT COLONIES DERIVED FROM TOBACCO MESOPHYLL PROTOPLASTS
Authors: Grandbastien M A , Bourgin J P , Caboche M
Published: January 2021

The induction and selection of valine-resistant mutants from haploid tobacco (Nicotiana tabacum L.) mesophyll protoplast-derived cells have been studied. Using cells from an original mutant plant obtained previously, we performed reconstruction experiments in order to determine the best conditions for the recovery of resistant cells among a population of sensitive cells. Optimal selective conditions were shown to depend on various factors including cell density, time of addition of valine and seasonal variations affecting the mother plants.—Using cell densities of approximately 104 cells/ml, we defined efficient selective conditions: more than 25% of the putative mutant clones selected from UV-mutagenized protoplasts were reproducibly confirmed to be valine resistant. Further characterization of some regenerated mutant plants indicated that valine-resistance was associated with an uptake deficiency, as in the case of the original mutant plant of the Valr-2 line used for reconstruction experiments. Spontaneous mutation rates for valine-resistance were below accurately detectable levels, i.e., less than 10-6 per cell per generation. Induced mutation frequency varied nonlinearily with UV dose from 10-5 to 5 × 10-4 resistant clones per surviving colony. Two independent loci (vr2 and vr3) were previously shown to be involved in valine-resistance due to amino acid uptake deficiency. Haploid tobacco plants were produced through anther culture from an F1 double-heterozygous plant obtained from a cross between the original mutant plant and a wild-type plant. Study of the level of resistance to valine of protoplast-derived cells allowed the classification of these haploid plants in four types: sensitive, resistant and two intermediary resistant types believed to result from the presence of a mutant allele at only one of the two loci involved. The frequencies of UV-induced mutations in cells derived from haploid plants of one of the intermediary types were compared to those observed in wild-type cells. The results are considered in light of the amphidiploid structure of the tobacco genome.
MUTATIONS LEADING TO EXPRESSION OF THE CRYPTIC HMR
a LOCUS IN THE YEAST SACCHAROMYCES CEREVISIAE
Authors: Kassir Yona , Simchen Giora
Published: January 2021

Mutations leading to expression of the silent HMR  a information in Saccharomyces cerevisiae result in sporulation proficiency in mat  a  1/MATα diploids. An example of such a mutation is sir5-2, a recessive mutation in the gene SIR5. As expected, haploids carrying the sir5-2 mutation are nonmaters due to the simultaneous expression of HMR  a and HMLα, resulting in the nonmating phenotype of an a/α diploid. However, sir5-2/sir5-2 mat  a  1/MATα diploids mate as α yet are capable of sporulation. The sir5-2 mutation is unlinked to sir1-1, yet the two mutations do not complement each other: mat  a  1/MATα sir5-2/SIR5 SIR1/sir1-1 diploids are capable of sporulation. In this case, recessive mutations in two unlinked genes form a mutant phenotype, in spite of the presence of the normal wild-type alleles.—The PAS1-1 mutation, Provider of a Sporulation function, is a dominant mutation tightly linked to HMR  a. PAS1-1 does not affect the mating ability of a strain, yet it allows diploids lacking a functional MAT  a locus to sporulate. It is proposed that PAS1-1 leads to partial expression of the otherwise cryptic a1 information at HMR  a.
MULTILOCUS POPULATION GENETICS WITH WEAK EPISTASIS. I. EQUILIBRIUM PROPERTIES OF TWO-LOCUS TWO-ALLELE MODELS
Authors: Hastings Alan
Published: January 2021

Using perturbation techniques, I determine the equilibrium of two-locus two-allele models with overdominance and weak epistasis. To lowest order, the allele frequencies, the mean fitness and the covariance between heterokaryotic and homokaryotic flies arising in the Sturtevant experimental design are independent of the recombination rate, r. The disequilibrium varies as one divided by the recombination rate, in contrast to neutral models. Although the disequilibrium generated by weak epistasis is small, too small to be experimentally detected, it can be large enough to have biological importance.
ANIMAL MODEL STUDIES OF ALLELISM: CHARACTERIZATION OF ARYLSULFATASE B MUTATIONS IN HOMOALLELIC AND HETEROALLELIC (GENETIC COMPOUND) HOMOZYGOTES WITH FELINE MUCOPOLYSACCHARIDOSIS VI
Authors: McGovern Margaret M , Mandell Nadine , Haskins Mark , Desnick Robert J
Published: January 2021

The identification of a second structural gene mutation at the feline arylsulfatase B locus (MPS VIb) provided the opportunity to investigate the expression of allelism by characterization of the residual enzymatic activity in feline mucopolysaccharidosis VI, an animal analogue of human Maroteaux-Lamy syndrome. Matings were designed to produce affected homozygotes who were homoallelic for the MPS VIa and MPS VIb mutations or heteroallelic genetic compounds (MPS VIa/VIb). The physicokinetic and immunological properties of the partially purified residual hepatic arylsulfatase B isozymes from the affected homoallelic and heteroallelic cats were compared to those of the normal feline enzyme. The residual hepatic arylsulfatase B activities from the inbred MPS VIa and MPS VIb homozygotes were distinguished by differences in physicokinetic and immunological properties. The newly identified mutant isozyme b had abnormal kinetic properties toward artificial and natural substrates, normal cryo- and thermostabilities, a normal molecular weight and an altered electrophoretic mobility. Polyacrylamide gel electrophoresis demonstrated that the mutant b subunits formed dimers with normal subunits in obligate heterozygotes (MPS VI  +/b). In contrast, mutant isozyme a subunits from obligate MPS VIa  /+ heterozygotes did not dimerize with the normal subunit, and the mutant and normal isozymes could be separated by anion exchange chromatography and polyacrylamide gel electrophoresis. Characterization of the partially purified residual hepatic arylsulfatase B activity from the heteroallelic homozygotes revealed the presence of both mutant isozymes a and b. The demonstration of two allelic mutations in the feline arylsulfatase B gene documented the occurrence of genetic heterogeneity in feline mucopolysaccharidosis VI and permitted characterization of the enzymatic defect in homoallelic and heteroallelic (genetic compound) homozygotes, providing a model for the study of allelism in human genetic disorders.
THE GENETIC STRUCTURE OF NATURAL POPULATIONS OF DROSOPHILA MELANOGASTER. XIX. GENOTYPE-ENVIRONMENT INTERACTION IN VIABILITY
Authors: Tachida Hidenori , Mukai Terumi
Published: January 2021

To investigate whether or not an excess of additive genetic variance for viability detected in southern natural populations of Drosophila melanogaster was created by diversifying selection, genotype-environment interaction was tested as follows. (1) Two karyotype chromosomes were used: 61 second chromosomes with the standard karyotype and 63 second chromosomes carrying In(2L)t. Their homozygote viabilities were larger than 50% of the average viability of random heterozygotes. (2) The effects of two factors (culture media and yeasts) were examined at three levels (the culture media: tomato, corn and banana; and the yeasts: sake, brewer's and baker's). The results of 16 three by three factorial experiments by the Cy method in the same karyotype groups for relative viabilities of homozygotes and heterozygotes elucidated the following findings: (1) there was no significant difference between the two karyotype groups, (2) the variance components of genotype-environment interaction were highly significant, (3) the variance component of heterozygotes was significantly smaller than that of homozygotes. From the experimental findings and previous results, diversifying selection in natural populations acting on viability polygenes to increase the additive genetic variance was suggested. The relation of the present result to protein polymorphism is also discussed.
DNA SEQUENCES OF FRAMESHIFT AND OTHER MUTATIONS INDUCED BY ICR-170 IN YEAST
Authors: Ernst Joachim F , Hampsey D Michael , Sherman Fred
Published: January 2021

ICR-170-induced mutations in the CYC1 gene of the yeast Saccharomyces cerevisiae were investigated by genetic and DNA sequence analyses. Genetic analysis of 33 cyc1 mutations induced by ICR-170 and sequence analysis of eight representatives demonstrated that over one-third were frameshift mutations that occurred at one site corresponding to amino acid positions 29-30, whereas the remaining mutations were distributed more-or-less randomly, and a few of these were not frameshift mutations. The sequence results indicate that ICR-170 primarily induces G·C additions at sites containing monotonous runs of three G·C base pairs. However, some (see PDF) sites within the CYC1 gene were not mutated by ICR-170. Thus, ICR-170 is a relatively specific mutagen that preferentially acts on certain sites with monotonous runs of G·C base pairs.
NATURAL SELECTION VS. RANDOM DRIFT: EVIDENCE FROM TEMPORAL VARIATION IN ALLELE FREQUENCIES IN NATURE
Authors: Mueller Laurence D , Barr Lorraine G , Ayala Francisco J
Published: January 2021

We have obtained monthly samples of two species, Drosophila pseudoobscura and Drosophila persimilis, in a natural population from Napa County, California. In each species, about 300 genes have been assayed by electrophoresis for each of seven enzyme loci in each monthly sample from March 1972 to June 1975. Using statistical methods developed for the purpose, we have examined whether the allele frequencies at different loci vary in a correlated fashion. The methods used do not detect natural selection when it is deterministic (e.g., overdominance or directional selection), but only when alleles at different loci vary simultaneously in response to the same environmental variations. Moreover, only relatively large fitness differences (of the order of 15%) are detectable. We have found strong evidence of correlated allele frequency variation in 13-20% of the cases examined. We interpret this as evidence that natural selection plays a major role in the evolution of protein polymorphisms in nature.
CELLULAR GENES IN THE MOUSE REGULATE IN TRANS THE EXPRESSION OF ENDOGENOUS MOUSE MAMMARY TUMOR VIRUSES
Authors: Traina-Dorge Vicki L , Carr Jean K , Bailey-Wilson Joan E , Elston Robert C , Taylor Benjamin A , Cohen J Craig
Published: January 2021

The transcriptional activities of the eleven mouse mammary tumor virus (MMTV) proviruses endogenous to two sets of recombinant inbred (RI) mouse strains, BXD and BXH, were characterized. Comparison of the levels of virus-specific RNA quantitated in each strain showed no direct relationship between the presence of a particular endogenous provirus or with increasing numbers of proviruses. Association of specific genetic markers with the level of MMTV-specific RNA was examined by using multiple regression analysis. Several cellular loci as well as proviral loci were identified that were significantly associated with viral expression. Importantly, these cellular loci associated with MMTV expression segregated independently of viral sequences.
DELETERIOUS MUTATIONS AS AN EVOLUTIONARY FACTOR. II. FACULTATIVE APOMIXIS AND SELFING
Authors: Kondrashov Alexey S
Published: January 2021

A population with u deleterious mutations per genome per generation is considered in which only those individuals that carry less than a critical number k of mutations are viable. Besides a large number of loci subject to mutation and selection, the genome contains one or two special loci responsible for the mode of reproduction. Amphimixis vs. selfing are considered separately. In the first case, the genome degradation rate v (=u/√k) is found to play the decisive role, as in the case of recombination. When v > 1.25, obligate amphimixis is established. If v decreases below this value, the alleles with first low and then larger penetrance are fixed, until alleles conferring obligate asexual reproduction become advantageous. The proportion of resources allocated to produce seeds also increases with decrease of v. These results are unlikely to depend on the genetic basis of the mode of reproduction. The result of competition between outcrossing and selfing depends on both u and k, as well as on whether the mutations are recessive. The alleles for selfing with low penetrance are selected against if the mutations are at all recessive. The fitness of alleles with high penetrance depends primarily on u, decreasing when u increases. There may exist conditions when only the alleles providing intermediate selfing rates can be fixed in a population. In other cases a population may exist with either obligate outcrossing or selfing at a high rate. Thus, truncation selection against deleterious mutations may be a factor supporting obligate or facultative sex despite the twofold advantage of apomixis or selfing.
MOLECULAR GENETICS OF THE ROSY-ACE REGION OF DROSOPHILA MELANOGASTER
Authors: Gausz Janos , Hall Lucinda M C , Spierer Anne , Spierer Pierre
Published: January 2021

Three hundred and fifteen kilobases of DNA from the rosy-Ace region on chromosome 3R of D. melanogaster have previously been cloned and extensively characterized. We describe the isolation of nine new deficiency mutants that break within the 315-kb interval. The position of these breakpoints on the DNA map was determined by in situ and Southern hybridization. Further, we more precisely mapped the breakpoints of several deletions previously analyzed. The results permit us to delimit sequences essential to the known complementation groups in the region within approximately 20 kb in most cases. However, one gene, B16-1, is shown to contain essential sequences that span about 50 kb. Also, we demonstrate by overlapping deficiencies that a 45-kb DNA segment from the region, which includes one known complementation group, allows limited survival when deleted.
THE EVOLUTION OF SELF-REGULATED TRANSPOSITION OF TRANSPOSABLE ELEMENTS
Authors: Charlesworth B , Langley C H
Published: January 2021

This paper examines the conditions under which self-regulated rates of transposition can evolve in populations of transposable elements infecting sexually reproducing hosts. Models of the evolution of both cis-acting regulation (transposition immunity) and trans-acting regulation (transposition repression) are analyzed. The potential selective advantage to regulation is assumed to be derived from the deleterious effects of mutations associated with the insertion of newly replicated elements. It is shown that both types of regulation can easily evolve in hosts with low rates of genetic recombination per generation, such as bacteria or bacterial plasmids. Conditions are much more restrictive in organisms with relatively free recombination. In haploids, the main selective force promoting regulation is the induction of lethal or sterile mutations by transposition; in diploids, a sufficiently high frequency of dominant lethal or sterile mutations associated with transpositions is required. Data from Drosophila and maize suggest that this requirement can sometimes be met. Coupling of regulatory effects across different families of elements would also aid the evolution of regulation. The selective advantages of restricting transposition to the germ line and of excising elements from somatic cells are discussed.
POLYMORPHISMS FOR PURELY CYTOPLASMICALLY INHERITED TRAITS IN BISEXUAL PLANTS
Authors: Gregorius Hans-Rolf
Published: January 2021

It is shown that cytoplasm polymorphisms transmitted only by the ovules can be maintained without gene-cytoplasmic interactions. The necessary prerequisites are asymmetry of the plasmotypes in production of ovules and pollen (sexual asymmetry), incomplete and frequency-dependent fertilization efficiency and differential selfing rates. These factors can generate the negative frequency dependence of cytoplasmic fitnesses required for a stable polymorphism. The model considered allows also for facultative fixation of either of two plasmotypes and, thus, may produce all of the dynamical characteristics known for nuclear selection with two alleles at one locus.

Strong sexual asymmetry, which probably occurs frequently in bisexual plants, may facilitate stable cytoplasmic polymorphisms. However, these polymorphisms may also endanger survival of the whole population in the absence of nuclear interactions. Gene-cytoplasmic interactions avoid this risk and, at the same time, utilize the advantages of sexual asymmetry in maintaining genetic polymorphisms.