bluuebunny/crossref_metadata_2025 huggingface dataset:
PRESENCE OF A BASE LINE LEVEL OF SISTER CHROMATID EXCHANGES IN SOMATIC CELLS OF DROSOPHILA MELANOGASTER IN VIVO AND IN VITRO
Authors: Tsuji Hideo
Published: April 2021

Sister chromatid exchanges (SCEs) under in vivo and in vitro conditions were examined in ganglion cells of third-instar larvae of Drosophila melanogaster (Oregon-R). In the in vivo experiment, third-instar larvae were fed on synthetic media containing 5-bromo-2′-deoxyuridine (BrdUrd). After two cell cycles, ganglia were dissected and treated with colchicine. In the in vitro experiment, the ganglia were also incubated in media containing BrdUrd for two cell cycles, and treated with colchicine. SCEs were scored in metaphase stained with Hoechst 33258 plus Giemsa. The frequencies of SCEs stayed constant in the range of 25-150 vg/ml and 0.25-2.5 vg/ml of BrdUrd in vivo and in vitro, respectively. SCEs gradually increased at higher concentrations, strongly suggesting that at least a fraction of the detected SCEs are spontaneous. The constant levels of SCE frequency were estimated, on the average, at 0.103 per cell per two cell cycles for females and 0.101 for males in vivo and at 0.096 for females and 0.091 for males in vitro. No difference was found in the SCE frequency between sexes at any of the BrdUrd concentrations. The analysis for the distribution of SCEs within chromosomes revealed an extraordinarily high proportion of the SCEs at the junctions between euchromatin and heterochromatin; the remaining SCEs were preferentially localized in the euchromatic regions of the chromosomes and in the heterochromatic Y chromosome. These results were largely inconsistent with those of Gatti et al. (1979).
A NEW MAPPING METHOD EMPLOYING A MEIOTIC REC- MUTANT OF YEAST
Authors: Klapholz Sue , Esposito Rochelle Easton
Published: April 2021

A rapid new mapping method has been developed for localizing a dominant or recessive mutation to a particular chromosome of yeast. The procedure utilizes the ability of strains homozygous for the spo11-1 mutation to undergo chromosome segregation without appreciable recombination during sporulation. The level of sporulation in spo11-1/spo11-1 diploids is reduced and asci are often immature or abnormal in appearance; spore viability is less than 1%. The first step of the mapping procedure is the construction of a haploid spo11-1 strain carrying a recessive drug-resistance marker and the unmapped mutation(s). This strain is crossed to a set of three spo11-1 mapping tester strains containing, among them, a recessive marker on each chromosome. The resulting spo11-1/spo11-1 diploids are sporulated and plated on drug-containing medium. Viable meiotic products that express the drug-resistance marker due to chromosome haploidization are selectively recovered. These meiotic products are haploid for most, but generally not all, chromosomes. The level of disomy for individual chromosomes averages 19%. Each of the recessive chromosomal markers is expressed in approximately a third of the drug-resistant segregants. Ninety-eight percent of these segregants show no evidence of intergenic recombination. Thus, two markers located on the same chromosome, but on different homologs, are virtually never expressed in the same drug-resistant clone. The utility of this mapping procedure is demonstrated by confirming the chromosomal location of seven known markers, as well as by the assignment of a previously unmapped mutation, spo12-1, to chromosome VIII. In addition, the analysis of the products of spo11-1 meiosis indicates that several markers previously assigned to either chromosome XIV or chromosome XVII are actually on the same chromosome.
ANALYSIS OF THE ALBINO-LOCUS REGION OF THE MOUSE: IV. CHARACTERIZATION OF 34 DEFICIENCIES
Authors: Russell Liane B , Montgomery Clyde S , Raymer G D
Published: April 2021

Thirty-four independent nonviable c-locus mutations (types cal, albino lethal and cas, albino subvital), derived from radiation experiments, were tested for involvement of nearby markers tp, Mod-2, sh-1, and Hbb: 10, 22, and 2 involved, respectively, none of these markers, Mod-2 alone, and Mod-2 plus sh-1. When classified on this basis, as well as according to developmental stage at which homozygotes die, and by limited complementation results, the 34 independent mutations fell into 12 groups. From results of a full-scale complementation grid of all 435 possible crosses among 30 of the mutations, we were able to postulate an alignment of eight functional units by which the 12 groups fit a linear pattern. Abnormal phenotypes utilized in the complementation study were deaths at various stages of prenatal or postnatal development, body weight, and reduction or absence of various enzymes. Some of these phenotypes can be separated by complementation (e.g., there is no evidence that mitochondrial malic enzyme influences survival at any age); others cannot thus be separated (e.g., glucose-6-phosphatase deficiency and neonatal death).—We conclude that all of the nonviable albino mutations are deficiencies overlapping at c, and ranging in size from <2cM to 6-11 cM. The characterization of this array of deficiencies should provide useful tools for gene-dosage studies, recombinant-DNA fine-structure analyses, etc. Since many of the combinations of lethals produce viable albino animals that resemble the standard c/c type, we conclude (a) that the c locus contains no sites essential for survival, and (b) that viable nonalbino c-locus mutations (cxv) are the result of mutations within the c cistron. Viable albinos (cav, the majority of radiation-induced c-locus mutations) may be intracistronic mutations or very small deficiencies.
INDIRECT SUPPRESSION INVOLVING BEHAVIORAL MUTANTS WITH ALTERED NERVE EXCITABILITY IN DROSOPHILA MELANOGASTER
Authors: Ganetzky Barry , Wu Chun-Fang
Published: April 2021

Two classes of X-linked behavioral mutants of Drosophila melanogaster, leg-shaking mutants and bang-sensitive mutants, are suppressed by napts (no action potential, temperature-sensitive), an autosomal temperature-sensitive paralytic mutation. So far, napts is found to suppress thirteen mutations at seven loci, two of which produce leg shaking and five bang-sensitivity. Suppression is recessive, occurs at temperatures permissive for napts, and is indirect and function-specific rather than allele-specific. At restrictive temperatures, napts is known to completely block all nerve activity. Several of the mutants suppressed by napts are shown by neurophysiological experiments to have increased nerve excitability. The physiological defect of these mutants as well as their behavioral defect is suppressed by napts. Thus, suppression occurs within individual neurons at the level of excitable membranes and apparently depends on the reduction in membrane excitability caused by napts even under permissive conditions. We suggest that all mutants suppressed by napts may have related defects leading to enhanced nerve excitability. Genetic interactions of this type help reveal functional relationships between different behavioral mutants and suggest ways of isolating new mutants with altered excitable membranes.
THE MATHEMATICS OF MOSAIC ANALYSIS I: THE RELATIONSHIP BETWEEN STURTS AND DISTANCE
Authors: Wyman Robert J , Thomas John B
Published: April 2021

In mosaic fate mapping the fraction of mosaics in which two structures are of different genotype is calculated. This frequency of separation has been called a "distance" and the units of this distance are called "sturts". The fundamental assumption of fate mapping is that the frequency of separation increases continuously with the actual distance between the anlage for these structures on the blastoderm. This paper shows that the frequency of separation does not increase beyond a certain value.—For the current theory to work as proposed, each mosaic animal must be half mutant and half normal. This is rarely the case in collections of mosaics. It has been thought that if some flies are less than half mutant and others more than half, these two types would introduce compensating errors in mapping distance. We show that this is not true and describe the nature of the errors introduced. It is probable that these errors are the main reason that mapping distances reported from different sets of mosaics have not been reproducible. This paper presents methods for the proper handling of data from mosaics with different amounts of mutant tissue.—We prove here that for mosaics with an arbitrary fraction of mutant tissue (m), the largest frequency of separation that can occur is 2m. We prove that sturts underestimate actual distance on the blastoderm by a factor of r/m, where r is the radius of the mutant patch, and that sturts give no information on distances greater than 2r. This, and not double crossing over, is the reason for the nonadditivity of sturts and the shrinking of large distances in sturt measures. Sturtoids overestimate distances by a factor of 1/(2r) and also give no information on distances over 2r. This paper gives formulae for correctly estimating distance when using a collection of mosaics with varying amounts of mutant tissue. We also describe the nature of the errors introduced by convoluted or elongate mosaic boundaries and by multiple mosaic patches.
SITE-SPECIFIC INSTABILITY IN DROSOPHILA MELANOGASTER: EVIDENCE FOR TRANSPOSITION OF DESTABILIZING ELEMENT
Authors: Laverty Todd R , Lim J K
Published: April 2021

In this study, we show that at least one lethal mutation at the 3F-4A region of the X chromosome can generate an array of chromosome rearrangements, all with one chromosome break in the 3F-4A region. The mutation at 3F-4A (secondary mutation) was detected in an X chromosome carrying a reverse mutation of an unstable lethal mutation, which was mapped in the 6F1-2 doublet (primary mutation). The primary lethal mutation at 6F1-2 had occurred in an unstable chromosome (Uc) described previously (Lim 1979). Prior to reversion, the 6F1-2 mutation had generated an array of chromosome rearrangements, all having one break in the 6F1-2 doublet (Lim 1979, 1980). In the X chromosomes carrying the 3F-4A secondary lethal mutation the 6F1-2 doublet was normal and stable, as was the 3F-4A region in the X chromosome carrying the primary lethal mutation. The disappearance of the instability having a set of genetic properties at one region (6F1-2) accompanied by its appearance elsewhere in the chromosome (3F-4A) implies that a transposition of the destabilizing element took place. The mutant at 3F-4A and other secondary mutants exhibited all but one (reinversion of an inversion to the normal sequence) of the eight properties of the primary lethal mutations. These observations support the view that a transposable destabilizing element is responsible for the hypermutability observed in the unstable chromosome and its derivaties.
Sex-related differences in crossing over in Caenorhabditis elegans.
Authors: Zetka M C , Rose A M
Published: April 2021

In the nematode Caenorhabditis elegans, hermaphrodite recombination has been characterized and is the basis of the genetic map used in this organism. In this study we have examined male recombination on linkage group I and have found it to be approximately one-third less than that observed in the hermaphrodite. This decrease was interval-dependent and nonuniform. We observed less recombination in the male in 5 out of 6 intervals examined, and no observable difference in one interval on the right end of LG I. Hermaphrodite recombination frequencies are the result of recombination in two germlines; oocyte and hermaphrodite spermatocytes. We have measured recombination in the oocyte and have found it to be approximately twofold lower than that calculated for hermaphrodite spermatocytes and not significantly different from the male spermatocyte frequency. Thus, recombination frequencies appear to be a function of gonad physiology rather than the sex of the germline. Evidence from experiments examining the effect of karyotype on recombination in males sexually transformed by the her-1 mutation into XO hermaphrodites (normally XX), suggests the sexual phenotype rather than genotype determines the recombination frequency characteristic of a particular sex. Hermaphrodite recombination is known to be affected by temperature, maternal age, and the rec-1 mutation. We have examined the effect of these parameters on recombination in the male and have found male recombination frequency increased with elevated temperatures and in the presence of Rec-1, and decreased with paternal age.
Nucleotide sequence and gene organization of the starfish Asterina pectinifera mitochondrial genome.
Authors: Asakawa S , Himeno H , Miura K , Watanabe K
Published: April 2021

The 16,260-bp mitochondrial DNA (mtDNA) from the starfish Asterina pectinifera has been sequenced. The genes for 13 proteins, two rRNAs and 22 tRNAs are organized in an extremely economical fashion, similar to those of other animal mtDNAs, with some of the genes overlapping each other. The gene organization is the same as that for another echinoderm, sea urchin, except for the inversion of a 4.6-kb segment that contains genes for two proteins, 13 tRNAs and the 16S rRNA. Judging from the organization of the protein coding genes, mammalian mtDNAs resemble the sea urchin mtDNA more than that of the starfish. The region around the 3' end of the 12S rRNA gene of the starfish shows a high similarity with those for vertebrates. This region encodes a possible stem and loop structure; similar potential structures occur in this region of vertebrate mtDNAs and also in nonmitochondrial small subunit rRNA. A similar stem and loop structure is also found at the 3' end of the 16S rRNA genes in A. pectinifera, in another starfish Pisaster ochraceus, in vertebrates and in Drosophila, but not in sea urchins. The full sequence data confirm the presumption that AGA/AGG, AUA and AAA codons, respectively, code for serine, isoleucine, and asparagine in the starfish mitochondria, and that AGA/AGG codons are read by tRNA(GCUSer), which possesses a truncated dihydrouridine arm, that was previously suggested from a partial mtDNA sequence. The structural characteristics of tRNAs and possible mechanisms for the change in the mitochondrial genetic code are also discussed.
Sodium orthovanadate-resistant mutants of Saccharomyces cerevisiae show defects in Golgi-mediated protein glycosylation, sporulation and detergent resistance.
Authors: Kanik-Ennulat C , Montalvo E , Neff N
Published: April 2021

Orthovanadate is a small toxic molecule that competes with the biologically important oxyanion orthophosphate. Orthovanadate resistance arises spontaneously in Saccharomyces cerevisiae haploid cells by mutation in a number of genes. Mutations selected at 3 nM sodium orthovanadate have different degrees of vanadate resistance, hygromycin sensitivity, detergent sensitivity and sporulation defects. Recessive vanadate-resistant mutants belong to at least six genetic loci. Most mutants are defective in outer chain glycosylation of secreted invertase (van1, van2, van4, van5, van6, VAN7-116 and others), a phenotype found in some MNN or VRG mutants. The phenotypes of these vanadate-resistant mutants are consistent with an alteration in the permeability or specificity of the Golgi apparatus. The previously published VAN1 gene product has a 200 amino acid domain with 40% identity with the MNN9 gene product and 70% identity with the ANP1 gene product. Cells containing the van1-18, mnn9 (vrg6) or anp1 mutations have some phenotypic similarities. The VAN2 gene was isolated and its coding region is identified and reported. It is an essential gene on chromosome XV and its translated amino acid sequence predicts a unique 337 amino acid protein with multiple transmembrane domains.
Alterations in ribosomal protein RPS28 can diversely affect translational accuracy in Saccharomyces cerevisiae.
Authors: Anthony R A , Liebman S W
Published: April 2021

Three small-subunit ribosomal proteins shown to influence translational accuracy in Saccharomyces cerevisiae are conserved in structure and function with their procaryotic counterparts. One of these, encoded by RPS28A and RPS28B (RPS28), is comparable to bacterial S12. The others, encoded by sup44 (RPS4) or, sup46 and YS11A (RPS13), are homologues of procaryotic S5 and S4, respectively. In Escherichia coli, certain alterations in S12 cause hyperaccurate translation or antibiotic resistance that can be counteracted by other changes in S5 or S4 that reduce translational accuracy. Using site-directed and random mutagenesis, we show that different changes in RPS28 can have diametrical influences on translational accuracy or antibiotic sensitivity in yeast. Certain substitutions in the amino-terminal portion of the protein, which is diverged from the procaryotic homologues, cause varying levels of nonsense suppression or antibiotic sensitivity. Other alterations, found in the more conserved carboxyl-terminal portion, counteract SUP44- or SUP46-associated antibiotic sensitivity, mimicking E. coli results. Although mutations in these different parts of RPS28 have opposite affects on translational accuracy or antibiotic sensitivity, additive phenotypes can be observed when opposing mutations are combined in the same protein.
Colonization of the Americas by Drosophila subobscura: lethal-gene allelism and association with chromosomal arrangements.
Authors: Mestres F , Serra L , Ayala F J
Published: April 2021

Drosophila subobscura is a Palearctic species that has recently colonized the Americas. It was first found in 1978 in Puerto Montt, Chile, and in 1982 in Port Townsend, WA. The colonization and rapid expansion of the species in western South and North America provides distinctive opportunities for investigating the process of evolution in action. The inversion polymorphism in the O chromosome from populations of central California and northern Washington, separated by 1300 km, corresponds to a previously observed latitudinal cline, also observed in Europe. Recessive lethal genes are not randomly distributed among the chromosomal arrangements. The incidence of lethal allelism is high, yielding unrealistically low estimates of the effective size of these populations (on the order of 1000 individuals). The high incidence of lethal allelism is likely to be a consequence of the low number of the American colonizers (on the order of 10-100 individuals), but the persistence of the allelism over several years suggests that some lethal-carrying chromosomes may be heterotic owing to shared associations between lethal and other genes.
A screen for modifiers of Deformed function in Drosophila.
Authors: Harding K W , Gellon G , McGinnis N , McGinnis W
Published: April 2021

Proteins produced by the homeotic genes of the Hox family assign different identifies to cells on the anterior/posterior axis. Relatively little is known about the signalling pathways that modulate their activities or the factors with which they interact to assign specific segmental identifies. To identify genes that might encode such functions, we performed a screen for second site mutations that reduce the viability of animals carrying hypomorphic mutant alleles of the Drosophila homeotic locus, Deformed. Genes mapping to six complementation groups on the third chromosome were isolated as modifiers of Deformed function. Products of two of these genes, sallimus and moira, have been previously proposed as homeotic activators since they suppress the dominant adult phenotype of Polycomb mutants. Mutations in hedgehog, which encodes secreted signalling proteins, were also isolated as Deformed loss-of-function enhancers. Hedgehog mutant alleles also suppress the Polycomb phenotype. Mutations were also isolated in a few genes that interact with Deformed but not with Polycomb, indicating that the screen identified genes that are not general homeotic activators. Two of these genes, cap 'n' collar and defaced, have defects in embryonic head development that are similar to defects seen in loss of function Deformed mutants.
Complete sequence and gene organization of the mitochondrial genome of the land snail Albinaria coerulea.
Authors: Hatzoglou E , Rodakis G C , Lecanidou R
Published: April 2021

The complete sequence (14,130 bp) of the mitochondrial DNA (mtDNA) of the land snail Albinaria coerulea was determined. It contains 13 protein, two rRNA and 22 tRNA genes. Twenty-four of these genes are encoded by one and 13 genes by the other strand. The gene arrangement shares almost no similarities with that of two other molluscs for which the complete gene content and arrangement are known, the bivalve Mytilus edulis and the chiton Katharina tunicata; the protein and rRNA gene order is similar to that of another terrestrial gastropod, Cepaea nemoralis. Unusual features include the following: (1) the absence of lengthy noncoding regions (there are only 141 intergenic nucleotides interspersed at different gene borders, the longest intergenic sequence being 42 nucleotides) (2) the presence of several overlapping genes (mostly tRNAs), (3) the presence of tRNA-like structures and other stem and loop structures within genes. An RNA editing system acting on tRNAs must necessarily be invoked for posttranscriptional extension of the overlapping tRNAs. Due to these features, and also because of the small size of its genes (e.g., it contains the smallest rRNA genes among the known coelomates), it is one of the most compact mitochondrial genomes known to date.
GENETIC MODULATION OF RNA METABOLISM IN DROSOPHILA. I. INCREASED RATE OF RIBOSOMAL RNA SYNTHESIS
Authors: Clark Stephen H , Strausbaugh Linda D , Kiefer Barry I
Published: April 2021

It has been suggested that a particular Y chromosome which is rDNA-deficient (YbbSuVar-5) may be associated with an increased utilization of rDNA template in adult testes (Shermoen and Kiefer 1975). To extend the observations on this chromosome, experiments were designed to determine if the chromosome has an effect on rRNA synthesis in bobbed adults and on classic bobbed phenotypes (shortened and thinner scutellar bristles and delayed development). Specific activity measurements were made on rRNA extracted from adult males of the genotypes car bb/Ybb- and car bb/YbbSuVar-5, which are rDNA-deficient to the same extent, and from Samarkand+ isogenic (Sam+ iso), which is a wild-type stock. The resulting data demonstrated that the presence of the YbbSuVar-5 chromosome increases the rate of ribosomal RNA synthesis in adult flies. In addition, it was found that the presence of this particular Y chromosome restores wild-type bristle phenotype and development time. Appropriate genetic crosses indicate that the observed effects (increased rRNA synthesis, restoration of wild-type phenotype) are a function of this particular Y chromosome, and are not due to autosomal factors. The results of these experiments suggest that the rate of rRNA accumulation is under genetic control.
INDUCTION OF THIOGUANINE- AND OUABAIN-RESISTANT MUTANTS AND SINGLE-STRAND BREAKS IN THE DNA OF CHINESE HAMSTER OVARY CELLS BY 3H-THYMIDINE
Authors: Cleaver James E
Published: April 2021

Cultured Chinese hamster cells were labeled with 6-3H-thymidine or 5-methyl-3H-thymidine and allowed to accumulate damage from 3H decays for various periods of time while frozen. The frequencies of cells resistant to 6-thioguanine or ouabain and the amount of DNA damage (i.e., number of single-strand breaks) were determined and compared with the mutation frequencies resulting from X and ultraviolet light irradiation. Whereas 3H decays and X rays made only 6-thioguanine-resistant mutants, ultraviolet light made both 6-thioguanine- and ouabain-resistant mutants. 3H decays originating at the 6 position were two to three times as effective as decays at the 5-methyl position in making drug-resistant mutants, but decays at both sites were equally effective in making single-strand breaks. Mutants and strand breaks produced by beta irradiation of the nucleus probably are the same irrespective of the site of the decay in thymine; these results indicate that the local transmutation effects of 3H decay produce more mutations when they occur at the 6 position than at the 5-methyl position.
ALLELIC VARIANTS AT THE XANTHINE DEHYDROGENASE LOCUS AFFECTING ENZYME ACTIVITY IN DROSOPHILA PSEUDOOBSCURA
Authors: Prakash Satya
Published: April 2021

Quantitative studies of enzyme activity on gels show about four-fold differences in enzyme activity of different xanthine dehydrogenase (XDH) alleles. At least three different activity classes could be distinguished among the 23 strains isogenic for the XDH locus. No association of high activity with the high frequency electromorph was observed; instead, the low frequency electromorphs had 0.5 to 2 times the activity of the high frequency electromorph. The frequency of low activity, high activity and intermediate activity XDH alleles among these 23 lines is 0.13, 0.09, and 0.78, respectively.
STABILIZING SELECTION FOR PUPA WEIGHT IN TRIBOLIUM CASTANEUM
Authors: Kaufman Pamela K , Enfield Franklin D , Comstock Ralph E
Published: April 2021

Ninety-five generations of stabilizing selection for pupa weight in Tribolium castaneum resulted in a significant decrease in phenotypic variance, moderate reductions in additive genetic variance, but only slight changes in heritability for the trait. Sterility was significantly lower and the average number of live progeny per fertile mating was significantly higher in populations where stabilizing selection was practiced as compared with random selected populations. The results indicate that more genetic variability is being maintained than would be expected unless a fraction of the genes have a heterozygote advantage on the fitness scale. The reduction in phenotypic variance indicated that the populations with stablizing selection became somewhat more buffered against environmental sources of variation over the course of the experiment.
SPONTANEOUS AND ETHYL METHANESULFONATE-INDUCED MUTATIONS CONTROLLING VIABILITY IN DROSOPHILA MELANOGASTER. I. RECESSIVE LETHAL MUTATIONS
Authors: Ohnishi Ohmi
Published: April 2021

The efficiency of the adult feeding method for EMS treatment in Drosophila melanogaster was studied by measuring the frequency of induced recessive lethals on the second chromosome. The treatment was most effective when mature spermatozoa or spermatids were treated and was much less effective on earlier stages. The number of mutations induced was proportional to the concentration except at the highest doses. The recessive lethal rate was estimated to be about 0.012 per second chromosome per 10-4m. In addition, about 0.004-0.005 recessive lethals per 10-4 m were found in a later generation in chromosomes that had not shown the lethal effect in the previous generation. When the experiments are done in a consistent manner and gametes treated as mature sperm or spermatids are sampled, the results are highly reproducible. However, modifications of the procedure, such as starvation before EMS treatment, can considerably alter the effectiveness of the mutagen.
ESTIMATION OF FITNESS COMPONENTS IN DROSOPHILA MELANOGASTER. I. HETEROZYGOTE VIABILITY INDICES
Authors: Katz Alan J , Cardellino Ricardo A
Published: April 2021

We examine the assumption of "dominance" with regard to viability of the Cy and Pm marker chromosomes in D. melanogaster. This assumption is often invoked for the extraction of wild-type second chromosomes from natural populations and for the calculation of relative viability indices. Significant genotypic variances for viability are found among both C y / f i and P m / f i heterozygotes in California and Japanese populations. The magnitude of the Pm/+i genotypic variance is substantially less than that of the Cy/+j heterozygotes (less than one half). Significant reciprocal effects are also found to influence Cy/+j, Pm/+i and + J f j viabilities. We conclude that viability indices of heterozygotes based on the Curly method are biased. We suggest that viability indices in the future be expressed relative to the viability of the Cy/Pm genotype (Curly-Plum method) or possibly that of the Pm/+i genotype (Plum method).
THE PRODUCTION OF CHROMOSOME ABERRATIONS IN VARIOUS MAMMALIAN CELLS BY TRIETHYLENEMELAMINE
Authors: Luippold H E , Gooch P C , Brewen J G
Published: April 2021

The cytogenetic effects of triethylenemelamine (TEM) were studied using five different mammalian tissues. Treatments of 0.1 and 0.2 mg/kg TEM on differentiating mouse spermatogonia and bone marrow cells showed no significant differences in the frequency of chromosomal aberrations produced in these two tissues. At higher doses, however, the sensitivities of the two tissues appear to be different. The frequency of aberrations varies with time after treatment, with the greatest amount occurring at the later fixation times. Results of an experiment on primary spermatocytes indicated a correlation between the frequency of chromosome aberrations and DNA replication. Human peripheral leukocytes were utilized in an attempt to clarify the cellstage specificity of TEM-induced chromosome aberrations. Cultures were treated with TEM prior to PHA stimulation (G0), as well as various time intervals after stimulation (late G,1 S, and G2). The most sensitive stages of the cell cycle to aberration induction were later G1 and S, with chromatid aberrations the predominant type. A very low yield of chromosome damage was observed with the G0 and G1 treated stages. The experiments described tend to support the view that TEM is most effective at inducing aberrations when an intervening round of DNA replication has occurred.
A CHROMOSOMAL TRANSLOCATION CAUSING OVERPRODUCTION OF ISO-2-CYTOCHROME c IN YEAST
Authors: Sherman Fred , Helms Cynthia
Published: April 2021

The CYC7-1 mutation in the yeast Saccharomyces cerevisiae causes the production of approximately 30 times the normal amount of iso-2-cytochrome c. Genetic analysis established that the CYC7-1 mutation is a reciprocal translocation involving the left arm of chromosome V and the right arm of chromosome XVI. The chromosome V arm was broken adjacent to the gene CYC7, which determines the primary structure of iso-2-cytochrome c, and this fragment containing the CYC7 gene was joined to the segment of chromosome XVI. It appears as though the elevation of iso-2-cytochrome c is caused by an abnormal controlling region adjacent to the structural region of the CYC7 gene.
A FINE-STRUCTURE GYNANDROMORPH FATE MAP OF THE DROSOPHILA HEAD
Authors: Baker William K
Published: April 2021

A gynandromorph fate map of the head of D. melanogaster was produced using 28 landmarks derived from one imaginal disc. An examination of the meaning of fine-structure mapping discloses that the sturt value observed between one pair of landmarks within a disc may approximate the relative physical distance of their progenitor cells at blastoderm, but for another pair of landmarks (assuming no directed cell movements), the sturt value may simply reflect their close geographic location at the time the cells are specified for their particular differentiation, a time much later in development when most cell division within the disc has come to an end. The formation of early developmental compartments has little effect on fate-map distances. Our analysis of the data suggests there are approximately ten cells present at the blastoderm stage that are head progenitors. Each blastoderm cell is likely to be the progenitor of a particular array of landmarks, but there is overlap between arrays from different blastoderm cells.
CLINES WITH ASYMMETRIC MIGRATION
Authors: Nagylaki Thomas
Published: April 2021

The consequences of asymmetric dispersion on the maintenance of an allele in a one-dimensional environmental pocket are examined. The diffusion model of migration and selection is restricted to a single diallelic locus in a monoecious population in the absence of mutation and random drift. It is further supposed that migration is homogeneous and independent of genotype, the population density is constant and uniform, and Hardy-Weinberg proportions obtain locally. If dispersion is preferentially out of an environmental pocket at the end of a very long habitat, the condition for maintaining the allele favored in the pocket becomes less stringent than for symmetric migration; dispersion preferentially into the pocket increases the severity of the condition for polymorphism. If an allele is harmful in large regions on both sides of an environmental pocket, the probability for polymorphism is decreased by asymmetric migration. The criterion for the existence of a cline is independent of the sense of the asymmetry; the cline itself is not. These phenomena are studied both analytically and numerically.—It is shown for symmetric migration and variable population density that the more densely populated parts of the habitat are more influential in determining gene frequency than the others. Thus, the higher the population density in an environmental pocket, the more easily an allele beneficial in the pocket will be maintained in the population.
GENETIC INSTABILITY IN AUXOTROPHS OF SALMONELLA TYPHIMURIUM REQUIRING CYSTEINE OR METHIONINE AND RESISTANT TO INHIBITION BY 1,2,4-TRIAZOLE
Authors: Kingsman A J , Smith D A , Hulanicka M D
Published: April 2021

Triazole-resistant (Trzr) derivatives of six cysteine- or methionine-requiring (Cym-) mutants of Salmonella typhimurium were isolated. Some of the derivatives of each mutant (CTS) were prototrophic, i.e., Cym- was suppressed. In every case suppression was initially unstable, Cym- auxotrophs being segregated at high frequency, although Trzr was stable. After several subcultures on selective medium, CTS strains were classified as either persistently unstable or stabilized. The unstable strains segregated Cym- auxotrophs at frequencies of 50-70%, whereas the stabilized strains segregated at frequencies of less than 1%. All suppressed strains had a stable Trzr marker co-transducible with cysA. However, there was a correlation between the class of CTS strain and Cym- phenotype. The stabilized strains were Cym+, whereas the unstable strains were Cym-. Acriflavin and ethidium bromide increased segregation in the unstable strains, suggesting the involvement of a plasmid. The stabilized strains were refractory to the curing agents. There was no detectable change in the quantity or quality of the S. typhimurium cryptic plasmid. The Trzr phenotype of the CTS strains suggested that Trzr mutations were of the stable TrzA type. It is suggested that correction of the Cym- lesions in CTS strains results from an insertion within the cysCDHIJ gene cluster of a DNA species originating in the cysALKptsHI region of the S. typhimurium chromosome.
THE NATURE OF GENETIC INSTABILITY IN AUXOTROPHS OF SALMONELLA TYPHIMURIUM REQUIRING CYSTEINE OR METHIONINE AND RESISTANT TO INHIBITION BY 1,2,4-TRIAZOLE
Authors: Kingsman A J , Smith D A
Published: April 2021

We tested the hypothesis that unstable suppression of auxotrophy in triazole-resistant derivatives of Cym- mutants of Salmonella typhimurium is due to reversible insertion at the Cym- site of genetic material originating in the cysALKptsHI region. We have shown that the unstable phenotype was co-transducible with markers in the cysCDHIJ region. The suppression of the Cym phenotype was recA dependent and frequencies of segregation were affected by UV irradiation. Restored enzyme activity in suppressed strains was determined by wild-type enzyme, suggesting that the unstable regions are located in cys gene regulatory regions. These results support the hypothesis. In contradiction, we found no evidence for a deletion in the cysALKptsHI region.
INDUCED RESISTANCE TO 6-METHYLPURINE AND CYCLOHEXIMIDE IN TETRAHYMENA. I. GERM LINE MUTANTS OF T. THERMOPHILA
Authors: Byrne Bruce C , Brussard Trudy B , Bruns Peter J
Published: April 2021

Two new mutant lines of Tetrahymena thermophila (T. pyriformis, syngen 1), each conferring resistance to a different agent, are described. Resistance to cycloheximide and 6-methylpurine are each determined by dominant genes, ChxA2 and Mpr; the traits show phenotypic assortment. The method used to select these mutations, the critical importance of backcrossing to wild type following mutagenesis, and the utility of these marker genes in further mutagenic selection schemes and studies of the sexual cycle of Tetrahymena are noted.
INTRAGENIC SUPPRESSION AT THE b2 LOCUS IN ASCOBOLUS IMMERSUS. I. IDENTIFICATION OF THREE DISTINCT GROUPS OF SUPPRESSION
Authors: Leblon G , Paquette N
Published: April 2021

A reversion study of EMS- or ICR170-induced ascospore color mutants in Ascobolus immersus is reported. Twenty-three new intragenic suppressors were isolated within the b2 locus. These are localized within three distinct groups on a genetic fine-structure map containing 21 identifiable sites. The pattern of reversion is discussed according to the known specificity of EMS and ICR170 in Ascobolus immersus.
NOVEL INTERALLELIC COMPLEMENTATION AT THE his1 LOCUS OF YEAST
Authors: Lax Carol , Fogel Seymour
Published: April 2021

In yeast, 17 histidine-requiring mutants derived from and interallelically complementary to his1—7 were analyzed. The genetic basis of the complementation response was elucidated by mitotic and meiotic gene conversion. Each allele probably carries an unaltered 7-site mutation and a unique second-site alteration. The second-site alterations appear to be clustered within the proximal and distal segments of the his1 structural gene. Models of intraallelic complementation are reviewed in light of the unique complementational response between a single-site mutant and a double mutant including the identical altered base sequence.
THE ISLAND MODEL WITH STOCHASTIC MIGRATION
Authors: Nagylaki Thomas
Published: April 2021

The island model with stochastically variable migration rate and immigrant gene frequency is investigated. It is supposed that the migration rate and the immigrant gene frequency are independent of each other in each generation, and each of them is independently and identically distributed in every generation. The treatment is confined to a single diallelic locus without mutation. If the diploid population is infinite, selection is absent and the immigrant gene frequency is fixed, then the gene frequency on the island converges to the immigrant frequency, and the logarithm of the absolute value of its deviation from it is asymptotically normally distributed. Assuming only neutrality, the evolution of the exact mean and variance of the gene frequency are derived for an island with finite population. Selection is included in the diffusion approximation: if all evolutionary forces have comparable roles, the gene frequency will be normally distributed at all times. All results in the paper are completely explicit.
LOCALIZED MUTAGENESIS FOR THE ISOLATION OF TEMPERATURE-SENSITIVE MUTANTS OF ESCHERICHIA COLI AFFECTED IN PROTEIN SYNTHESIS
Authors: Champney W Scott
Published: April 2021

Two variations of the method of localized mutagenesis were used to introduce mutations into the 72 min region of the Escherichia coli chromosome. Twenty temperature-sensitive mutants, with linkage to markers in this region, have been examined. Each strain showed an inhibition of growth in liquid medium at 44°, and 19 of the mutants lost viability upon prolonged incubation at this temperature. A reduction in the rate of in vivo RNA and protein synthesis was observed for each mutant at 44°, relative to a control strain. Eleven of the mutants were altered in growth sensitivity or resistance to one or more of three ribosomal antibiotics. The incomplete assembly of ribosomal subunits was detected in nine strains grown at 44°. The characteristics of these mutants suggest that many of them are altered in genes for translational or transcriptional components, consistent with the clustering of these genes at this chromosomal locus.
INTERALLELIC COMPLEMENTATION AT THE sh LOCUS IN MAIZE AT THE ENZYME LEVEL
Authors: Chourey Prem S , Nelson Oliver E
Published: April 2021

EMS-induced sh mutants and their heterozygotes were examined for the enzyme, sucrose synthetase, which has previously been shown to be coded by the Sh locus. Complementing heterozygotes have a wild-type phenotype, but show no hybrid protein band after starch gel electrophoresis. The existence of a heteromeric complex, however, is inferred from the two-fold elevation in sucrose cleavage activity in the complementing heterozygotes as compared to the mutant homozygotes. The observations on complementation described here are unique, as the elevation in the activity of this reversible enzyme is noticed only in one direction (viz, sucrose cleavage) of the reaction and not the other (sucrose synthesis).
FINE-STRUCTURE MAPPING OF THE ACETAMIDASE STRUCTURAL GENE AND ITS CONTROLLING REGION IN ASPERGILLUS NIDULANS
Authors: Hynes M J
Published: April 2021

A large number of amdS mutants altered in acetamide utilization have been used to construct a fine-structure map of the amdS locus. The mutagen diepoxyoctane generated most of the deletion strains used for mapping. A minimum of 14 sites within the amdS gene were found. Biochemical analysis of amds mutants defined the extent of the probable coding region. A new mutant, amd-205, which did not produce detectable inactive gene product, was found to be inseparable by recombination from the "up-promoter" mutation amdl8 and was located outside of the apparent amdS coding region. The cis dominant mutation, amdI9, was also located at this end of the gene. This work, therefore, provides evidence for the separation of a eukaryotic gene into controlling and structural regions.
A GENETICALLY DISTINCT FORM OF CYCLIC AMP PHOSPHODIESTERASE ASSOCIATED WITH CHROMOMERE 3D4 IN DROSOPHILA MELANOGASTER
Authors: Kiger John A , Golanty Eric
Published: April 2021

Two cyclic AMP phosphodiesterase enzymes (E.C.3.1.4.17) are present in homogenates of adult Drosophila melanogaster. The two enzymes differ from one another in heat stability, affinity for Mg++, Ca++ activation and molecular weight. They do not differ markedly in their affinities for cyclic AMP, and both exhibit anomalous Michaelis-Menten kinetics. The more heatlabile enzyme is controlled in a dosage-dependent manner by chromomere 3D4 of the X chromosome and is absent in flies that are deficient for chromomere 3D4. Chromomere 3D4 is also necessary for the maintenance of normal cAMP levels, for male fertility, and for normal female fertility and oogenesis. The structural gene(s) for the more heat-stable enzyme is located outside of chromomeres 3C12-3D4. Whether 3D4 contains a structural gene, or a regulatory gene necessary for the presence of the labile enzyme, remains to be determined.
THE GENETICS OF COPPER TOLERANCE IN THE YELLOW MONKEY FLOWER, MIMULUS GUTTATUS. I. CROSSES TO NONTOLERANTS
Authors: Macnair Mark R
Published: April 2021

The biometrical genetics of copper tolerance has been investigated in two Californian populations of Mimulus guttatus by crosses to a nontolerant British population. A simple biometrical model involving only additive and dominance effects is not sufficient. When the first order interactions are included, the model is shown to fit the data. Interactions between the dominance effects of different loci, and between dominance and additive effects, are the most important. These interactions can be explained either by a threshold model, or by postulating dominance modification.
AN EXTENSION OF A MODEL FOR THE EVOLUTION OF MULTIGENE FAMILIES BY UNEQUAL CROSSING OVER
Authors: Ohta Tomoko
Published: April 2021

Evolution of a multigene family is studied from the standpoint of population genetics. It is assumed that the multigene family is undergoing continuous interchromosomal unequal crossing over, mutation and random frequency drift. The equilibrium properties of the probability of gene identity (clonality) are investigated, using two measures: identity probability within and between chromosomes. The measures represent homogeneity of genes within a family in one chromosome and $milarity of gene families between two homologous chromosomes. The means, the variances and the covariance of these two measures of identity probability are obtained by using the diffusion equation method. It is shown that the means and the variances are generally smaller than those predicted in the previous model assuming intrachromosomal (sister chromatid) unequal crossing over (OHTA 1978a,b).
A MUTANT KILLER PLASMID WHOSE REPLICATION DEPENDS ON A CHROMOSOMAL "SUPERKILLER" MUTATION
Authors: Toh-E Akio , Wickner Reed B
Published: April 2021

Yeast strains carrying a 1.5 × 106 molecular weight linear double-stranded RNA in virus-like particles (M dsRKA, the killer plasmid or virus) secrete a toxin that is lethal to strains not carrying this plasmid. Recessive mutations in any of four chromosomal genes (called skil-ski4) result in increased production of toxin activity. We report here a mutation of the killer plasmid (called [KIL-sd] for ski-dependent) that makes the killer plasmid dependent for its replication on the presence of a chromosomal mutation in any ski gene. Thus, the [KIL-sd] plasmid is lost from SKI+ strains. When the wild-type killer plasmid, [KIL-k], is introduced into a ski2-2 [KIL-o] strain, the killer plasmid changes to a [KIL-sd] plasmid. This may represent a specific form of mutagenesis or selective replication in the ski2-2 strain of [KIL-sd] variants (mutants) in the normal [KIL-k] population. The ski2-1 and ski2-3 mutations do not convert [KIL-k] to [KIL-sd], but ski2-3 does allow maintenance of the [KIL-sd] plasmid. The [KIL-sd] plasmid thus lacks a plasmid site or product needed for replication in wild-type cells.
POST-TRANSLATIONAL MODIFICATION AS A POTENTIAL EXPLANATION OF HIGH LEVELS OF ENZYME POLYMORPHISM: XANTHINE DEHYDROGENASE AND ALDEHYDE OXIDASE IN DROSOPHILA MELANOGASTER
Authors: Finnerty Victoria , Johnson George
Published: April 2021

Xanthine dehydrogenase (XDH) and aldehyde oxidase (AO) in Drosophila melanogaster require for their activity the action of another unlinked locus, maroon-like (mal), While the XDH and A 0 loci are on chromosome 3, mal maps to the X chromosome. Although functional mal gene product is required for XDH and A 0 activity, it is possible to examine the effects of mutant mal alleles in those cases when pairs of mutants complement to produce a partial restoration of activity. To test whether mal mediates a post-translational modification of the XDH and A0 proteins, we constructed several mal heteroallelic complementing stocks of Drosophila in which the third chromosomes were co-isogenic. Since all lines were co-isogenic for the XDH and A0 structural genes, any variation in these enzymes seen when comparing these stocks must have been produced by post-translational modification by mal. We examined the XDH and A 0 proteins in these stocks by gel-sieving electrophoresis, a procedure that permits independent characterization of a protein's charge and shape, and is capable of discriminating many variants not detected in routine electrophoresis. In every mal heteroallelic combination, there is a significant alteration in protein shape, when compared to wild type. The magnitude of differences in shape of XDH and AO is correlated both with differences in their enzyme activities and with differences in their thermal stabilities. As the body of this variation appears heritable, any functional differences resulting from these variants are of real genetic and evolutionary interest. A similar post-translational modification of XDH and A0 by yet another locus, lxd, was subsequently documented in an analogous manner. The pattern of electrophoretic differences produced by mal and lxd modification is similar to that reported for electrophoretic "alleles" of XDH in natural populations. The implication is that heritable variation in electrophoretic mobility at these two enzyme loci, and potentially at other loci, is not necessarily allelic to the structural gene loci.