bluuebunny/crossref_metadata_2025 huggingface dataset:
STUDIES ON THE MUTATION ABNORMAL OOCYTE AND ITS INTERACTION WITH THE RIBOSOMAL DNA OF DROSOPHILA MELANOGASTER
Authors: Krider Hallie M , Levine Bryan I
Published: April 2021

Sandler (1970) suggested that mutation, abnormal oocyte (abo:2–38), may influence the function of the ribosomal RNA cistrons. We have examined the abo mutation and its interaction with the ribosomal DNA of Drosophila melanogaster. We observed that the expression of the abo phenotype is unstable under the appropriate conditions, a behavior which paralleled changes in the phenotypic expression of bobbed mutations during the magnification of the ribosomal DNA. The change in the expression of the abo phenotype is correlated with an increase in the redundancy of the ribosomal cistrons, further suggesting a functional interaction of the abo and bobbed regions.
A SINGLE-GENE-DEPENDENT ABNORMALITY OF ADORAL MEMBRANELLES IN TETRAHYMENA PYRIFORMIS, SPECIES 1
Authors: Kaczanowski Andrezj
Published: April 2021

Strain D of species (syngen) 1, Tetrahymena pyriformis, differs from other inbred strains in its manifestation of certain abnormal patterns of adoral membranelles. Instead of the usual three membranelles some cells have a greater number, most frequently 4 or 5, but occasionally up to 7. The extra membranelles, or even all membranelles of any given set, are shorter than M-1 and M-2 of the normal pattern. In other cases, the only alteration observed is a change in the relative lengths of the three membranelles. The frequency of abnormal cells varies from about 5% to 15% during exponential growth to over 50% after prolonged stationary culture. The genetic basis for the abnormality is shown to be due to a single recessive gene which segregates normally in various crosses and which manifests vegetative assortment as do most allelic variants in species 1.
GENETIC ANALYSIS OF THE PROXIMAL REGION OF CHROMOSOME 2 OF DROSOPHILA MELANOGASTER. I. DETACHMENT PRODUCTS OF COMPOUND AUTOSOMES
Authors: Hilliker A J , Holm D G
Published: April 2021

To examine the genetic composition of proximal heterochromain in chromosome 2, the detachment of compound second autosomes, for generating proximal deficiencies, appeared a promising method. Compound seconds were detached by gamma radiation. A fraction of the detachment products were recessive lethals owing to proximal deficiencies. Analysis by inter se complementation, pseudo-dominance tests with proximal mutations and allelism tests with known deficiencies provided evidence for at least two loci between the centromere and the light locus in 2L and one locus in 2R between the rolled locus and the centromere. The data further demonstrate that rolled, and probably light, are located within the proximal heterochromatin. Thus, functional genetic loci are found in heterochromatin, albeit at low density.
GENETIC CHANGE AND RATES OF CLADOGENESIS
Authors: Avise John C , Ayala Francisco J
Published: April 2021

Models are introduced which predict ratios of mean levels of genetic divergence in species-rich versus species-poor phylads under two competing assumptions: (1) genetic differentiation is a function of time, unrelated to the number of cladogenetic events and (2) genetic differentiation is proportional to the number of speciation events in the group. The models are simple, general, and biologically real, but not precise. They lead to qualitatively distinct predictions about levels of genetic divergence depending upon the relationship between rates of speciation and amount of genetic change. When genetic distance between species is a function of time, mean genetic distances in speciose and depauperate phylads of equal evolutionary age are very similar. On the contrary, when genetic distance is a function of the number of speciations in the history of a phylad, the ratio of mean genetic distances separating species in speciose versus depauperate phylads is greater than one, and increases rapidly as the frequency of speciations in one group relative to the other increases. The models may be tested with data from natural populations to assess (1) possible correlations between rates of anagenesis and cladogenesis and (2) the amount of genetic differentiation accompanying the speciation process.

The data collected in electrophoretic surveys and other kinds of studies can be used to test the predictions of the models. For this purpose genetic distances need to be measured in speciose and depauperate phylads of equal evolutionary age. The limited information presently available agrees better with the model predicting that genetic change is primarily a function of time, and is not correlated with rates of speciation. Further testing of the models is, however, required before firm conclusions can be drawn.
DELETIONS INDUCED BY HEAT TREATMENT OF E. COLI K12 LYSOGENIC FOR Λ PROPHAGES
Authors: Marchelli C , Ghelardini P , Nasi S
Published: April 2021

We have investigated the production of prophage deletions in heat-induced λ lysogens of E. coli K12. Our results are indicative of a direct action of the heat-induced prophage in producing deletions. The temperature of 40° used for the experiments may be critical to prove this effect. The phage function involved in deletion formation is not known.
REGULATION OF MATING AND MEIOSIS IN YEAST BY THE MATING-TYPE REGION
Authors: Kassir Yona , Simchen Giora
Published: April 2021

A supposed sporulation-deficient mutation of Saccharomyces cerevisiae is found to affect mating in haploids and in diploids, and to be inseparable from the mating-type locus by recombination. The mutation is regarded as a defective a allele and is designated a*. This is confirmed by its dominance relations in diploids, triploids, and tetraploids. Tetrad analysis of tetraploids and of their sporulating diploid progeny suggests the existence of an additional locus, RME, which regulates sporulation in yeast strains that can mate. Thus the recessive homozygous constitution rme/rme enables the diploids a*/α, a/a*, and α/α to go through meiosis. Haploids carrying rme show apparent premeiotic DNA replication in sporulation conditions. This new regulatory locus is linked to the centromere of the mating-type chromosome, and its two alleles, rme and RME, are found among standard laboratory strains.
MUTATIONS MASKING THE LAMBDA CIN-1 MUTATION
Authors: McDermit Matthew , Pierce Mark , Staley Darrell , Shimaji Michael , Shaw Richard , Wulff Daniel L
Published: April 2021

A lambda cnc mutation masks the phenotype of the lambda cin-1 mutation. Eleven cnc mutations have been found. All appear to be identical and all map at a site just to the right of the cin-1 site. It is probable that cin-1 and cnc affect adjacent, or almost adjacent nucleotide pairs. Neither the cin-1 nor the cnc mutation involves large additions or deletions of genetic material.
THE EFFECTS OF HITCHHIKING ON A GENE FOR RECOMBINATION
Authors: Strobeck C , Smith J Maynard , Charlesworth B
Published: April 2021

This paper proposes that alleles increasing recombination rates may be selected for as a result of the perturbing effects of the spread of selectively favored alleles on neighboring loci maintained polymorphic by selection. The recombination genes are favored since their presence increases the production of selectively advantageous types of gametes with which they tend to remain associated. Numerical examples are presented, and some consequences of this model discussed. One such consequence is the widespread existence of polymorphism for genes affecting recombination values.
GAMMA-RAY MUTAGENESIS IN BACTERIOPHAGE T4
Authors: Conkling Mark A , Grunau John A , Drake John W
Published: April 2021

137Cs-gamma irradiation of bacteriophage T4 induces large deletions plus a variety of types of point mutations. All mutations arise with single-hit kinetics, and all by a misrepair process. The estimated point mutation rate is 1.5 × 10-9 per locus per rad.
MATERNAL AND RECIPROCAL EFFECTS ON SEEDLING CHARACTERS IN ARABIDOPSIS THALIANA (L.) HEYNH
Authors: Corey L A , Matzinger D F , Cockerham C Clark
Published: April 2021

Five early growth characters were examined in six races of Arabidopsis thaliana (L.) Heynh, their reciprocal F1 hybrids (1974) and F1 by tester hybrids, using a seventh race as a paternal tester. Three of the five characters were also examined at two nutrient levels in reciprocal F1 hybrids (1972) of all seven races. Analyses of F1 and F1 by tester hybrids revealed significant maternal effects in all characters examined in F1 hybrids (1972) and in root length and plant weight of F1 (1974) and F1 by tester hybrids. Significant reciprocal effects were found for plant weight in F1 by tester hybrids and for seed weight, percentage of germination and root length in F1 (1974) and F1 by tester hybrids. The presence of significant maternal and/or reciprocal components in both F1 (1974) and F1 by tester diallels suggests that differences in maternal cytoplasm rather than maternal genotype per se were responsible for much of the variation resulting from these non-direct genetic effects.
THE RELEASE OF A COMPOUND-CHROMOSOME STOCK IN A VINEYARD CELLAR POPULATION OF DROSOPHILA MELANOGASTER
Authors: McKenzie J A
Published: April 2021

The prospect of autocidal insect control was investigated in a cellar population of D. melanogaster using a compound-chromosome stock. The released stock was synthesized by irradiating virgin female progeny derived from the cellar and crossing to a second-chromsome compound laboratory stock. Incorporation of an appropriate genetic background into the compound stock was tested in laboratory studies. Larval development to adult emergence and adult survival studies indicated the compound release stock to be relatively similar to the wild population, while behavioral tests detected no mating isolation between wild or compound genotypes. An unstable equilibrium point of compound frequency 0.7 was observed in population cage experiments with the two genotypes.

Adults were released into the cellar at a 50:1 ratio in favor of the compound. Five hundred newly hatched compound-chromosome larvae were also released. Adult, larval and pupal samples were regularly made. The compound stock successfully bred in the cellar maintaining an adult frequency of at least 90% for 108 days after the release. The rapid decline in compound frequency after this period is thought to be due to the migration of inseminated wild-type females from wine storage areas adjacent to the cellar.

The results indicate that a compound stock may limit the rate of population expansion in an area and may be a useful mechanism of autocidal control. It cannot be overemphasized that the probability of a successful release will be related to the level of understanding of the adaptive strategy of the population into which the release is made.
GENETIC AND MORPHOLOGICAL STUDY OF AGGREGATION IN THE CELLULAR SLIME MOLD POLYSPHONDYLIUM VIOLACEUM
Authors: Warren A Jane , Warren Wayne D , Cox Edward C
Published: April 2021

A system for genetic analysis in the cellular slime mold P. violaceum has been developed. Two growth-temperature-sensitive mutants were isolated in a haploid strain and used to select rare diploid heterozygotes arising by spontaneous fusion of the haploid cells. A recessive mutations to cycloheximide resistance in one strain enables selection of segregants, which often appear to be aneuploid.—Aggregation-defective (ag-) mutants having a wide range of phenotypes were isolated in both temperature-sensitive strains after nitrosoguanidine treatment, and complementation tests were performed between pairs of these mutants. Of 380 diploids isolated, 32 showed defective aggregation and were considered to contain 2 noncomplementing ag-mutations. Among noncomplementing mutants interallelic complementation is common. Noncomplementing mutants fall into 4 complementation groups, and those within each complementation group are phenotypically similar. Statistical analysis of the results suggests that the number of complementation units involved in aggregation is about 50.
DETERMINATION OF THE CHROMOSOMAL LOCATION OF A GLUTAMATE OXALOACETATE TRANSAMINASE STRUCTURAL GENE USING TRITICUM-AGROPYRON TRANSLOCATIONS
Authors: Hart Gary E , McMillin David E , Sears E R
Published: April 2021

The glutamate oxaloacetate transaminase (GOT) zymogram phenotypes of a series of 15 translocation lines, a chromosome addition line and a chromosome substitution line were determined. In each of the translocation lines a segment of the long arm of Triticum aestivum chromosome 3D has been replaced by a portion of an Agropyron elongatum homoeologue. Evidence was obtained that the products of the T. aestivum GOT-3 triplicate structural gene set randomly dimerize with the product of the homoeologous A. elongatumgene. Each translocation chromosome was found to carry either Got-D3or Got-Ag3. By correlating the zymogram phenotype expressed by each translocation line with the observed frequency of meiotic pairing of each 3D/3Ag translocation chromosome with telocentric-3DL, it was shown that Got-D3 is located in the proximal portion of 3DL, slightly more than 4.3 crossover units from the centromere. The results of this genetic study confirm and extend earlier conclusions derived from cytogenetic studies as to the physical nature of the various 3D/3Ag chromosomes.
HETEROMORPHISM FOR HETEROKARYON INCOMPATIBILITY GENES IN NATURAL POPULATIONS OF NEUROSPORA CRASSA
Authors: Mylyk Orest M
Published: April 2021

Five Neurospora crassa isolates from each of three sites in Louisiana were compared for genotype at five heterokaryon incompatibility (het) loci. The comparisons were made using duplications (partial diploids), based on the fact that duplications heterozygous for het loci have strikingly abnormal phenotypes which greatly facilitate the study of such genes. Duplications were synthesized in crosses between the wild strains (normal chromosome sequence) and testers of defined het genotype and having duplication-producing chromosome rearrangements. Crosses segregating for phenotypes characteristic of duplications heterozygous for het loci indicated allelic differences between testers and wild strains for specific het genes. Whenever a wild strain differed from a tester for a specific het locus, but another wild strain did not, the two wild strains could be inferred to differ from each other.—No two isolates from any site were heterokaryon compatible (of identical het genotype), despite the fact that all isolates from each of two sites occurred within several meters of each other. Heteromorphism was found for all five genes studied at one site, four genes at another site, and three at another. Intra- and interpopulation differences between strains were approximately the same.—Confirmation is also provided that two het genes originally detected in duplications are in fact heterokaryon incompatibility loci.
CHLOROPLAST GENETICS OF CHLAMYDOMONAS. I. ALLELIC SEGREGATION RATIOS
Authors: Sager Ruth , Ramanis Zenta
Published: April 2021

This paper presents allelic segregation data from a series of 16 crosses segregated for nuclear and chloroplast genes. By means of pedigree analysis, segregants of chloroplast markers occurring in the zygote have been distinguished from those occurring in zoospore clones. The genes ac1, ac2, and tm1 showed little if any deviation from 1:1 either in zygotic segregation or in zoospore clones. The genes sm2, ery, and spc showed a significant excess of the allele from the mt  + parent in zygotes. However, in zoospores, mt  + excess was seen only when that allele was the mutant (resistant) form but not when it was wild type (sensitive).

These results show that the extent of preferential segregation differs in zygotes and in zoospores, and that preferential segregation is influenced by map location and by allele specificity. A comparison of progeny from zygotes mated after 0, 15˝, 30˝, and 50˝ UV irradiation of the mt  + gametes demonstrated the lack of an effect of UV upon allelic segregation ratios. In total, these results exclude the multi-copy model of chloroplast genome segregation suggested by Gillham, Boynton and Lee (1974) and support the diploid model we have previously proposed (Sager and Ramanis 1968, 1970; Sager 1972).
FOOD CONSUMPTION, FEED EFFICIENCY, METABOLIC RATE AND UTILIZATION OF GLUCOSE IN LINES OF TRIBOLIUM CASTANEUM SELECTED FOR 21-DAY PUPA WEIGHT
Authors: Medrano Juan F , Gall G A E
Published: April 2021

Food consumption, feed efficiency, metabolic rate and glucose utilization were studied throughout development in one control (1C) and three selected lines (3, 9, 10) of Tribolium castaneum that had been subjected to long term selection for 21-day pupae weight. Growth rate, body composition, cellular growth and the activity of four dehydrogenase enzymes in the same lines have been reported (Medrano and Gall 1976).—Larva of selected lines consumed 1.2 times as much food as the control and gained an average of 2.9 times as much weight. The rapid growth of the selected lines was associated with a gross feed efficiency 20 to 30% above that for the control line. There was also a small but consistent improvement in the conversion of digested food. Average digestibility was higher for selected lines.—There was little apparent differentiation between the control and selected lines in metabolic rate/individual, but the rate measured on a per-unit weight basis was two- to three-fold greater for the control during the active growth stages. Respiratory quotients (R.Q.) of 1.0, indicative of carbohydrate oxidation, were observed through larval growth in all lines. Pupae at 21 days showed R.Q. values greater than 1.0, which were interpreted as resulting from a phenomenon in insects in which CO2 is released by pupae, in large bursts at irregular intervals. The rate constant of glucose oxidation, measured as the rate of C14 labelled CO2 respired during 2- to 6-hour incubation periods, was two- to three-fold higher in the control. In addition, the control line larvae expired 5% to 17% more of the ingested C14 as CO2. It was apparent that control line individuals maintained a much more active turnover of metabolites but without an effective retention of carbon as body substances. The results are discussed in support of the hypothesis that selection for large body size resulted in improved control mechanisms that influence the biological efficiency of growth in Tribolium.
A MIXED MODEL OF MUTATION FOR ELECTROPHORETIC IDENTITY OF PROTEINS WITHIN AND BETWEEN POPULATIONS
Authors: Li Wen-Hsiung
Published: April 2021

A model which is a mixture of the model of infinite alleles and the Ohta-Kimura model of stepwise mutation has been proposed for the study of eletcrophoretic variants in natural populations. Mutations which alter the mobility of a protein are divided into two classes: stepwise mutations and nonstepwise mutations. It is assumed that stepwise mutations follow the Ohta-Kimura model while nonstepwise mutations follow the infinite allele model. It is then shown that even if the proportion of nonstepwise mutations is only 5%, with the other 95% stepwise mutations, the effective number of alleles given by the present model is considerably larger than that given by the Ohta-Kimura model of stepwise mutation. The result has also been applied to study Nei's genetic distance.
THE EVOLUTION OF ONE- AND TWO-LOCUS SYSTEMS
Authors: Nagylaki Thomas
Published: April 2021

Assuming age-independent fertilities and mortalities and random mating, continuous-time models for a monoecious population are investigated for weak selection. A single locus with multiple alleles and two alleles at each of two loci are considered. A slow-selection analysis of diallelic and multiallelic two-locus models with discrete nonoverlapping generations is also presented. The selective differences may be functions of genotypic frequencies, but their rate of change due to their explicit dependence on time (if any) must be at most of the second order in s, (i.e., O(s  2)), where s is the intensity of natural selection. Then, after several generations have elapsed, in the continuous time models the time-derivative of the deviations from Hardy-Weinberg proportions is of O(s  2), and in the two-locus models the rate of change of the linkage disequilibrium is of O(s  2). It follows that, if the rate of change of the genotypic fitnesses is smaller than second order in s (i.e., o(s  2)), then to O(s  2) the rate of change of the mean fitness of the population is equal to the genic variance. For a fixed value of s, however, no matter how small, the genic variance may occasionally be smaller in absolute value than the (possibly negative) lower order terms in the change in fitness, and hence the mean fitness may decrease. This happens if the allelic frequencies are changing extremely slowly, and hence occurs often very close to equilibrium. Some new expressions are derived for the change in mean fitness. It is shown that, with an error of O(s), the genotypic frequencies evolve as if the population were in Hardy-Weinberg proportions and linkage equilibrium. Thus, at least for the deterministic behavior of one and two loci, deviations from random combination appear to have very little evolutionary significance.
RP4 PROMOTION OF TRANSFER OF A LARGE AGROBACTERIUM PLASMID WHICH CONFERS VIRULENCE
Authors: Chilton Mary-Dell , Farrand Stephen K , Levin Richard , Nester Eugene W
Published: April 2021

Introduction of RP4 plasmid into Agrobacterium tumefacienspromotes the transfer on solid medium of large virulence-associated plasmids from virulent donor strains to a plasmidless avirulent recipient. Exconjugants were selected for the ability to utilize octopine or nopaline as the sole source of arginine, traits which are coded for by virulence-associated plasmids in the strains employed here. All exconjugants retained the arginine auxotrophy of the recipient strain, and were resistant to ampicillin and kanamycin, drugs to which RP4 confers resistance. Five exconjugant clones from one cross were shown by alkaline sucrose gradient analysis to contain both RP4 plasmid and the large virulence-associated plasmid of the donor strain. All five exconjugants exhibited virulence on carrot, sunflower and kalanchoe plants. These results indicate that virulence and the ability to degrade octopine are plasmid-borne traits in A. tumefaciens strains 15955 and A6, and extend the evidence that large plasmids in A. tumefaciens are vectors of virulence genes.
CHROMOSOME POLYMORPHISM OF TEOSINTE
Authors: Ting Y C
Published: April 2021

Florida teosinte from Honduras and Guanajuato teosinte have most of their knobs internally located and a common inversion in the short arm of chromosome 8. Teosintes from northern Guatemala, Huixta and Monajil, have all their knobs terminally located and do not have any inversions. Therefore, Florida teosinte from Honduras appears to be phylogenetically closer to Guanajuato teosinte than it is to Guatemalan teosintes.——The presence of B chromosomes and an In 8 in Guanajuato teosinte and Florida teosinte from Honduras may constitute evidence of introgression between maize and teosinte.
CLINES WITH VARIABLE MIGRATION
Authors: Nagylaki Thomas
Published: April 2021

The consequences of a discontinuity in the migration rate and of a geographical barrier in the habitat are studied in a diffusion model of migration and selection. The treatment is restricted to a single diallelic locus in a monoecious population in the absence of mutation and random drift. It is supposed further that migration is independent of genotype, the population density remains constant and uniform, and Hardy-Weinberg proportions obtain locally. It is shown that a discontinuity in the migration rate leads to a jump in the slope of the gene frequency, but not in the gene frequency itself, while a localized geographical barrier has precisely the opposite effect. These features of the gene frequency behavior are quantitatively related to the migration rate. The influence of the above inhomogeneities in migration on the maintenance of an allele in an environmental pocket is examined. The extent to which the critical condition for polymorphism is made less stringent by decreased migration outside the pocket and by a geographical barrier between the pocket and the rest of the habitat is evaluated.
PARTITIONING AVERAGE AND HETEROTIC COMPONENTS OF DIRECT AND MATERNAL GENETIC EFFECTS ON GROWTH IN MICE USING CROSSFOSTERING TECHNIQUES
Authors: Nagai J , Bakker H , Eisen E J
Published: April 2021

Crossfostering was performed using lines selected for increased 6-week body weight (H6) and increased 3-to 6-week postweaning gain (M16) and their reciprocal F1 crosses as nurse dams in the selected crossfostering group, and base population controls (C2, ICR) and their reciprocal F1 crosses in the control group. The offspring suckled were H6, M16 and F2 crosses in the selected group, and C2, ICR and their F2 crosses in the control group. Measurements taken on the individual offspring were body weights at birth (WB) and at 12, 21, 31, 42, and 63 days (W12, W21, W31, W42 and W63, respectively) and weight gains between adjacent ages (GB-12, G12–21, G21–31, G31–42 and G42–63, respectively). Least squares constants fitted to populations of genetic and nurse dams were used to calculate specific linear contrasts. Correlated responses to selection in average direct genetic effects were significant and positive for all traits examined in both H6 and M16, while the correlated responses in average maternal genetic effects were negative in M16 and negligible in H6. Selection response was primarily due to average direct genetic effects while the contribution of average maternal genetic effects was of secondary importance. The response in average direct genetic effects was smaller in M16 than in H6 through weaning (WB, W12 and W21), but was larger in M16 for postweaning weights (W31, W42 and W63). The correlated responses in average maternal genetic effects were consistently smaller in M16 than in H6. Direct heterosis was significant for all traits except for G12–21 and G42–63 in the control group, whereas maternal heterosis was significant for weight gains at early ages and for body weights. Direct heterosis tended to be larger than maternal heterosis in both selected and control crosses. Percent direct heterosis for body weight was larger in the selected crosses relative to the control crosses through 31 days of age, but the trend was reversed by 63 days. Percent maternal heterosis was consistently larger in the selected crosses.
GENETIC VARIATION IN A HETEROGENEOUS ENVIRONMENT. II. TEMPORAL HETEROGENEITY AND DIRECTIONAL SELECTION
Authors: Hedrick Philip W
Published: April 2021

The maintenance of genetic variation is investigated in a finite population where selection at an autosomal locus with two alleles varies temporally between two environments and the heterozygote has an intermediate fitness value. When there is additive gene action and equal selection in both environments, the autocorrelation between subsequent environments must be negative for more maintenance of genetic variation than for neutrality. The maximum maintenance occurs when there is equal selection in the two environments and the autocorrelation approaches -1.0 (for a stochastic model), or when there is short repeating cycle such as one related to seasons. Also comparison of the effects of stochastic variation in selection in finite and infinite populations is made by using Monte Carlo simulation. One situation was found where temporal environmental variation maintains genetic variation very effectively even in a small population and that is when there is evolution of dominance, i.e., the heterozygote is closer in fitness to the favored homozygote than the other homozygote. An important conclusion is that in a finite population genetic tracing of environmental change, particularly when there is a positive autocorrelation between environments or a long environmental cycle, leads to an increased loss of genetic variation making such a response undesirable in the long term, a result different from that in infinite populations.
THEORETICAL MODIFICATIONS OF RECIPROCAL RECURRENT SELECTION
Authors: Moreno-Gonzalez J , Grossman M
Published: April 2021

Reciprocal recurrent selection (RRS), which assumes overdominant loci to be important, alters two genetically different populations to improve their crossbred mean. Individual plants from two populations (A and B) are selfed and also crossed with plants from the reciprocal female tester population (B and A, respectively). Selection is based on the mean of crossbred families, and the selected individuals are randomly mated within A and B to form new populations.—We propose two alternatives to RRS. The first (RRS-I) uses, as the tester of population A, a population (LB) that is derived from population B by family selection for low yield. The second (RRS-II) is similar to RRS-I, but also uses, as the tester of B, a population (LA) that is derived from population A by family selection for low yield.—The expected crossbred means of RRS, RRS-I, and RRS-II were compared, assuming equal σP, at several cycles of selection for incomplete and complete dominance, and for several cases of overdominance (depending on the gene frequencies in A and B, and on the equilibrium gene frequency).—The choice of selection method depends on the importance of the effects of overdominant loci compared to loci exhibiting incomplete or complete dominance. If overdominance is unimportant, RRS-II is the best selection method, followed by RRS-I and RRS. If overdominance is important, both RRS and RRS-I are superior to RRS-II; RRS is preferred to RRS-I if the effects of overdominant loci are sufficiently important. If the genetic model is a mixture of levels of dominance at different loci, a combination of selection systems is suggested.
THE GENETIC ANALYSIS OF A UNIQUELY DOSE-SENSITIVE CHROMOSOMAL REGION OF DROSOPHILA MELANOGASTER
Authors: Denell R E
Published: April 2021

In their extensive analysis of the effects of segmental aneuploidy on development to the adult stage, Lindsley and Sandler et al. (1972) identified salivary chromosome region 83D-E as apparently uniquely dose-sensitive. Neither the hypoploid nor hyperploid classes appeared to survive to the adult stage, although segmental hyperploidy of all other regions of the genome is compatible with normal or quasi-normal development. In the present investigation, this genetic behavior is shown to be a concomitant of region 83D-E itself, and independent of the particular Y-autosome translocations utilized to generate aneuploid classes. Newly induced chromosomal duplications including 83D-E are recovered by their ability to complement the corresponding deficiency; these aberrations indicate that the phenomenon depends on genetic dosage per se and is independent of linkage relationships. Further tests involving the generation of large numbers of aneuploid zygotes support the conclusion that these individuals very rarely and possibly never survive to the adult stage. Finally, crosses yielding hypertriploid females and intersexes indicate that these aneuploids often survive and, in the former case, are fertile. No viable hypotriploid female or intersex was recovered.
SELECTION FOR MALE RECOMBINATION IN DROSOPHILA MELANOGASTER
Authors: Kidwell Margaret G , Kidwell J F
Published: April 2021

Two-way selection for male recombination over seven intervals of the third chromosome in Drosophila melanogaster was practiced for nine generations followed by relaxed selection for five generations. Significant responses in both directions were observed but these mainly occurred in early generations in the low line and in later generations in the high line. Divergence of male recombination frequencies between the two selection lines was not restricted to any specific region but occurred in every measured interval of the chromosome. However, right-arm intervals showed a more pronounced response than either left-arm intervals or the centromeric region. Correlated responses in sterility and distortion of transmission ratios occurred as a result of selection for male recombination. Cluster distributions of male recombinants suggested a mixture of meiotic and late gonial events but relative map distances more closely resembled those of the salivary chromosome than standard meiotic or mitotic distances. Patterns of male recombination over time in both second and third chromosomes strongly suggested a major effect associated with the presence of third chromosomes from the Harwich strain. Evidence was also found for modifiers with relatively small effects located in other regions of the genome. The overall results are interpreted in terms of a two-component model of hybrid dysgenesis.
TESTING THE HETEROGENEITY OF F VALUES: A SUGGESTION AND A CORRECTION
Authors: Tsakas S , Krimbas C B
Published: April 2021

The use of a pair of populations removes the problems posed by a structured phylogeny (pointed out by A. Robertson) and permits the application of the original test of Lewontin and Krakauer . In the case of 2n populations studied a suggestion is made to use only n pairs in such a way that no population appears in more than one pair. Data on Dacus analyzed this way show that at least two out of six genes studied are or have been selected.
RECOMBINATION AND RESPONSE TO SELECTION IN DROSOPHILA MELANOGASTER
Authors: Thompson Vinton
Published: April 2021

Most biologists believe that recombination speeds response to selection for traits determined by polygenic loci. To test this hypothesis, sixteen Drosophila melanogaster populations were selected for positive phototaxis for twenty-one generations. In some populations, balancer chromosomes were used to suppress autosomal recombination, and in others the autosomes were free to recombine. Suppression of recombination had no effect on mean rate of response to selection, though it may have increased variability in the rate of response among replicate lines. Suppressed recombination lines did not shift selection response to the freely recombining × chromosomes, despite fairly large increases in × chromosome recombination. The results suggest that in populations of moderate size, sex does not accelerate short term response to selection.
REGIONS OF STABLE EQUILIBRIA FOR MODELS OF DIFFERENTIAL SELECTION IN THE TWO SEXES UNDER RANDOM MATING
Authors: Kidwell J F , Clegg M T , Stewart F M , Prout T
Published: April 2021

The equilibrium structure of models of differential selection in the sexes is investigated. It is shown that opposing additive selection leads to stable polymorphic equilibria for only a restricted set of selection intensities, and that for weak selection the selection intensities must be of approximately the same magnitude in the sexes. General models of opposing directional selection, with arbitrary dominance, are investigated by considering simultaneously the stability properties of the trivial equilibria and the curve along which multiple roots appear. Numerical calculations lead us to infer that the average degree of dominance determines the equilibrium characteristics of models of opposing selection. It appears that if the favored alleles are, on the average, recessive, there may be multiple polymorphic equilibria, whereas only a single polymorphic equilibrium can occur when the favored alleles are, on the average, dominant. The principle that the average degree of dominance controls equilibrium behavior is then extended to models allowing directional selection in one sex with overdominance in the other sex, by showing that polymorphism is maintained if and only if the average fitness in heterozygotes exceeds one.
DEVELOPMENTAL GENETICS OF THE DROSOPHILA EGG I. IDENTIFICATION OF 59 SEX-LINKED CISTRONS WITH MATERNAL EFFECTS ON EMBRYONIC DEVELOPMENT
Authors: Mohler J Dawson
Published: April 2021

Sex-linked mutations to recessive female sterility were induced, sorted for egg-laying, mapped within broad regions and grouped by complementation tests into cistrons. The mutations have also been partially characterized for their temperature sensitivity and pleiotropic effects. Altogether 59 cistrons have been identified, including five allelic with previously known loci: cin, fs(1)N, mk, sn, and r.

All of the genes make maternal contributions to developing embryos. In some instances mutant defects are recognized in the egg envelopes; in the remainder the defects are presumably in the egg cytoplasm. For mutations in twenty-two genes, including cin, mk, and r alleles, the lethality of the maternal effect is reversed and the embryo is "rescued" by the action of a wild-type, paternal allele. The mutant strains are potentially important for the study of developing egg envelopes and for furthering the analysis of causation in embryogenesis and its origins in oogenesis.
GENETIC EFFECTS OF ACUTE SPERMATOGONIAL X-IRRADIATION OF THE LABORATORY RAT
Authors: Chambers J R , Chapman A B
Published: April 2021

The genetic effects of one generation of spermatogonial X-irradiation in rats, by a single dose of 600r in one experiment and by a fractionated dose of 450r in another, were measured in three generations of their descendants. Estimates of dominant lethal mutation rates—(2 to 3) × 10 -4/gamete/r—from litter size differences between irradiated and nonirradiated stock were consistent with previous estimates from rats and mice. Similar consistency was found for estimates of sex-linked recessive mutation rates—(1 to 2) × 10-4 chromosome/r—from male proportions within strains; however, when measured in crossbreds the proportion of males was higher in the irradiated than in the nonirradiated lines. This inconsistency in results is in keeping with the contradictory results reported for recessive sex-linked lethal mutation rates in mice. The effects used to estimate recessive lethal mutation rates which were unusually high—(2 to 14) × 10-4/gamete/r—were not significant. Other factors that could have contributed to the observed effects are postulated.
CONTROLLING ELEMENTS IN A TRIBAL MAIZE FROM COLOMBIA: Fcu, A TWO-UNIT SYSTEM
Authors: Gonella Jaime A , Peterson Peter A
Published: April 2021

The genetic basis for a striking aleurone color variegation of a maize population from Colombia is described. The variegation is the result of the interaction of a particular r allele, designated r-cu, and a specific factor, Fcu (Factor Cuna), that collectively compose a controlling element system. In the absence of Fcu, a variable dilute (nonvariegated) pigmentation is expressed in the aleurone. The degree of variegation is determined by differences in the dosage of the Fcu element; differences in variegation between kernels with one r-cu vs. two r-cu's cannot be detected. Because of the specificity of the interaction, Fcu is different from the three other well-known controlling elements, Dt, Ac and En(=Spm), and therefore represents a fourth controlling element system in maize. In addition to Fcu, the Cuna tribal maize contains two other controlling elements, Dt and a very weak En. The prevalence of controlling elements in natural maize populations is discussed.
MULTIVARIATE ANALYSIS OF GAMETIC DISEQUILIBRIUM IN THE YANOMAMA
Authors: Smouse Peter E , Neel James V
Published: April 2021

The gametic disequilibria between all possible pairs of loci were examined for a set of eight codominant loci in each of fifty Yanomama villages, using a multivariate correlation analysis which reduces the results to a single measure of departure from multiple-locus-gametic equilibrium. Thirty-two of the fifty villages departed significantly from multiple-locus gametic equilibrium. The largest contributions to the departure from multiple-locus equilibrium were due to the disequilibria between MN and Ss and between Rh(Cc) and Rh(Ee), indicating the effects of tight linkage. After removing the effects of these obvious sources of disequilibrium, sixteen of the fifty villages still remained significantly out of equilibrium. The disequilibrium between any particular pair of loci was highly erratic from village to village, and (with the exception of the MN-Ss and Cc-Ee disequilibria) averaged out very close to zero overall, suggesting a lack of systematic forces (epistatic selection). The departure from equilibrium in any one village is in excess of that expected from random sampling alone, and is attributed primarily to the fission-fusion mode of village formation operative in the Yanomama and the fact that a single village consists of a few extended lineages. Village allele frequencies are highly correlated across loci, and most of the non-independence is accounted for by large correlations in the average allelic frequencies of different loci for related villages. It is suggested that these correlations also are due to territorial expansion and population growth. For the tribe as a whole, all but the tightly linked markers of the MNSs and Rh complexes are approximately uncorrelated, and large departures from multiple-locus Hardy-Weinberg expectation are primarily due to substantial Wahlund variance within the tribe. There is no need to postulate a role for selection in these disequilibria.
THE EFFECTS OF OVERDOMINANCE ON LINKAGE IN A MULTILOCUS SYSTEM
Authors: Yamazaki Tsuneyuki
Published: April 2021

Computer simulations were performed with overdominant multiple alleles among tightly linked multiple loci under a multiplicative fitness model. The quantity X  2/N(n - 1) was introduced as a new measure of linkage disequilibrium which, unlike previously available measures, can be applied to multiple allele models, where N is the sample size, and n is the number of alleles at the locus possessing fewest alleles. Simulations showed that (1) With multiple (three or four) alleles, the approach to stable disequilibrium is slower and the amount of disequilibrium established is weaker than in a two allele system. (2) The number of complementary chromosomes is a function of number of alleles and of population size. (3) As population size increases, the rate of the approach to stable disequilibrium is slower. (4) There is an optimum selection coefficient which minimizes the transient fixation probability of alleles when linkage is present. (5) The absence of linkage disequilibrium is in most cases not a practical method of testing the hypothesis of balancing selection of genetic polymorphisms because it depends strongly on population size in determining linkage disequilibria.
ISOLATION AND CHARACTERIZATION OF MMS-SENSITIVE MUTANTS OF SACCHAROMYCES CEREVISIAE
Authors: Prakash Louise , Prakash Satya
Published: April 2021

We have isolated mutants sensitive to methyl methanesulfonate (MMS) in Saccharomyces cerevisiae. Alleles of rad1, rad4, rad6, rad52, rad55 and rad57 were found among these mms mutants. Twenty-nine of the mms mutants which complement the existing radiation-sensitive (rad and rev) mutants belong to 22 new complementation groups. Mutants from five complementation groups are sensitive only to MMS. Mutants of 11 complementation groups are sensitive to UV or X rays in addition to MMS, mutants of six complementation groups are sensitive to all three agents. The cross-sensitivities of these mms mutants to UV and X rays are discussed in terms of their possible involvement in DNA repair. Sporulation is reduced or absent in homozygous diploids of mms mutants from nine complementation groups.
ON THE COMPONENTS OF SEGREGATION DISTORTION IN DROSOPHILA MELANOGASTER
Authors: Ganetzky Barry
Published: April 2021

The segregation distorter (SD) complex is a naturally occurring meiotic drive system with the property that males heterozygous for an SD-bearing chromosome 2 and an SD  +-bearing homolog transmit the SD-bearing chromosome almost exclusively. This distorted segregation is the consequence of an induced dysfunction of those sperm that receive the SD  + homolog. From previous studies, two loci have been implicated in this phenomenon: the Sd locus which is required to produce distortion, and the Responder (Rsp) locus that is the site at which Sd acts. There are two allelic alternatives of Rsp—sensitive (Rspsens) and insensitive (Rspins); a chromosome carrying Rspins is not distorted by SD. In the present study, the function and location of each of these elements was examined by a genetic and cytological characterization of X-ray-induced mutations at each locus. The results indicate the following: (1) the Rsp locus is located in the proximal heterochromatin of 2R; (2) a deletion for the Rsp locus renders a chromosome insensitive to distortion; (3) the Sd locus is located to the left of pr(2-54.5), in the region from 37D2-D7 to 38A6-B2 of the salivary chromosome map; (4) an SD chromosome deleted for Sd loses its ability to distort; (5) there is another important component of the SD system, E(SD), in or near the proximal heterochromatin of 2L, that behaves as a strong enhancer of distortion. The results of these studies allow a reinterpretation of results from earlier analyses of the SD system and serve to limit the possible mechanisms to account for segregation distortion.
LOCALIZATION OF STRUCTURAL AND REGULATORY GENES FOR PHOSPHODIESTERASE IN WHEAT (TRITICUM AESTIVUM)
Authors: Wolf G , Rimpau J , Lelley T
Published: April 2021

Genes (Pde-A3; Pde-B3; Pde-D3) for phosphodiesterase (PDE; E.C. 3.1.4.1.) isoenzymes in hexaploid wheat were located on the three homoeologous chromosomes of group 3 by testing the electrophoretic banding pattern of monosomic, nullisomic and nullisomic/tetrasomic compensation lines of "Chinese Spring" variety. In plants nullisomic for chromosome 5B, the 3D structural gene is not expressed and this lack of expression can be overcome by four doses of either homoeologous chromosome 5A or 5D. Our data conclusively indicate that there are genes on group 5 chromosomes which positively control the expression of the 3D structural gene. In addition, the expression of the "regulatory genes" is dosage dependent. Thus, our study reveals a complex interaction of the three genomes of wheat for regulation of PDE gene expression.
Introduction to Company Law
Authors: Davies Paul
Published: April 2021

Introduction to Company Law provides a conceptual introduction and a clear framework with which to navigate the intricacies of company law. The book analyses the mechanisms through which the law provides an organisational structure for the conduct of business. Given that structure, the book discusses how the law seeks to reduce the costs of using it, whether these are costs for managers, shareholders as a class, non-controlling shareholders, creditors, or employees, identifying the trade-offs involved. This discussion takes in both the Companies Act 2006 and various types of ‘soft law’, notably the Corporate Governance and Stewardship Codes. This third edition contains two new chapters: one on liability and enforcement and the other on the social function of corporate law. Both are issues that have come to prominence in the aftermath of the financial crisis of 2007–09.