bluuebunny/crossref_metadata_2025 huggingface dataset:
RESOLVING THE ENIGMA OF MULTIPLE MUTANT SECTORS IN STAMEN HAIRS OF TRADESCANTIA
Authors: Mericle L W , Mericle R P
Published: January 2021

Mutant sectors in stamen hairs of Clone 02 Tradescantia are designated as "multiple sectors" when two or more occupy the same hair, separated by nonmutant cells. Statistical analyses show that most multiple sectors do not arise as chance associations of independent events: when the frequency of stamens with two or more sectors is lowest, the probability that the sectors will be located in the same, rather than in different, hairs is highest. Ontogenetically, the ratio of sector pairs in different hairs to pairs in the same hair is highest in that period of response to acute irradiation prior to the appearance of entirehair sectors; thereafter, the ratio subsides, approaching that of spontaneous mutation and indicating that the initiating event takes place early in hair development. Most mononemic chromosome models will not account for the production of multiple mutant and non-mutant sectors, dispersed along a linear structure such as a stamen hair, following a single mutational event. Consideration is given to two models (one mononemic, and the other dinemic) which will readily provide the possibilities for either the immediate segregation of mutant and non-mutant cells, or for the perpetuation in daughter nuclei of a "heterozygous" chromosome capable of segregation at some later mitosis. The dinemic model is preferred because it affords operation of the mutation mechanism (including breakage and deletion) at either the DNA molecule or subunit level.
SELECTIVE SOMATIC ELIMINATION OF NICOTIANA GLUTINOSA CHROMOSOMES IN THE F1 HYBRIDS OF N. SUAVEOLENS AND N. GLUTINOSA
Authors: Gupta S B , Gupta Pratibha
Published: January 2021

The F, hybrids of Nicotiana suaveolen (subgenus Petunioides, 2n = 32) and N. glutinosa (subgenus Tabacum, 2n = 24), were examined during their development, from seedlings to mature plants. It was observed that in the hybrids, there was a progressive change of dominant N. glutinosa morphological characteristics towards those of N. suaveolens, in leaf shape, stem, flower color and branching pattern. A study of mitotic chromosomes in the root-tips and in very young anthers of the mature plants indicated a significantly high average frequency of aberrant mitotic anaphases (bridges and fragments, 12% and 11 % respectively). As a consequence of this phenomenon, variability in the number and size of chromosomes was observed in the PMC's and in mitotic metaphases (29-24 chromosomes). In order to establish whether the N. glufinosa chromosomes were preferentially last, a karyological study of the parents and their F, hybrids was carried out and it was established that the F, hybrids were losing N. glutinosa chromosomes preferentially. A mechanism was suggested for the loss of these chromosomes by means of a chromatid type of breakage-fusion-bridge cycle (b-f-b cycle) and initiation of the b-f-b cycle in the hybrid due to an interaction of the regulatory mechanism of DNA replication in the haploid genomes of the parental species. However, loss of these chromosomes owing to interaction of certain genes from the two parental species cannot be ruled out.
MEIOTIC BEHAVIOR OF ASYMMETRIC DYADS IN THE MALE DROSOPHILA
Authors: Zimmering S , Bendbow E B
Published: January 2021

Crossing over in the interstitial region of the heterozygous V4 translocation in Drosophila melanogaster generates asymmetric dyads each consisting of a shorter and a longer chromatid It was shown previously that in the female the shorter is recovered preferentially (ZIMMERING 1955); the present work suggests that the same occurs in the male as weI1. The mechanism in the female is envisioned as involving the non-random inclusion of the shorter chromatid into the functional egg (NOVITSK 1951); in the male, the two formal possibilities appear to be (1) that some proportion of sperm carrying the longer chromatid derived from an asymmetric dyad undergoes dysfunction, or (2) the longer chromatid is preferentially included into regularly-produced nonfunctional sperm, the nonfunctionality set up at the second division and distinguishing second division daughter cells.
INHERITANCE OF ALPHA-GLYCEROPHOSPHATE DEHYDROGENASE IN THE PINK SALMON, ONCORHYNCHUS GORBUSCHA (WALBAUM)
Authors: Aspinwall Nevin
Published: January 2021

Genetic crosses of alpha-glycerophosphate dehydrogenase (alpha-GPDH) phenotypes in the pink salmon, Oncorhynchus gorbuscha (Walbaum), reveal that this enzyme is encoded by a single locus with two codominant alleles (Slow and Fast). The significance of single gene control of alpha-GPDH is discussed in relation to the purported tetraploid nature of the salmonids.
EVIDENCE FOR LINKAGE DISEQUILIBRIUM MAINTAINED BY SELECTION IN TWO NATURAL POPULATIONS OF DROSOPHILA SUBOBSCURA
Authors: Zouros E , Krimbas C B
Published: January 2021

One island and one mainland population of Drosophila subobscura were found polymorphic at the XDH (xanthine dehydrogenase) and the A0 (aldehyde oxidase) loci. It was observed that one allele at the XDH locus, which has a low frequency in both populations, is nonrandomly associated with the alleles at the A0 locus. Two lines of evidence support the thesis that this linkage disequilibrium is due to epistasis rather than random drift: (I)D or r, measures of the disequilibrium, have the same sign and magnitude in both populations. (2) The linkage disequilibrium is not due to inversions. Inversions segregating on the chromosome carrying XDH and A0 have been separated into two classes, between which exchange of alleles at the two loci is suppressed. Linkage disequilibrium for XDH and A0 was observed within each class. In the absence of any exchange of alleles, these disequilibria must have arisen and been maintained independently. The suggestion is made that the epistatic disequilibrium results from the close structural and physiological relationship which exists between the tn-o enzymes.
THE ANALYSIS OF QUANTITATIVE TRAITS FOR SIMPLE GENETIC MODELS FROM PARENTAL, F1 AND BACKCROSS DATA
Authors: Elston R C , Stewart John
Published: January 2021

The following models are considered for the genetic determination of quantitative traits: segregation at one locus, at two linked loci, at any number of equal and additive unlinked loci, and at one major locus and an indefinite number of equal and additive loci. In each case an appropriate likelihood is given for data on parental, F1 and backcross individuals, assuming that the environmental variation is normally distributed. Methods of testing and comparing the various models are presented, and methods are suggested for the simultaneous analysis of two or more traits.
TEMPERATURE-SENSITIVE MUTANTS FOR THE REPLICATION OF PLASMIDS IN ESCHERICHIA COLI II. PROPERTIES OF HOST AND PLASMID MUTATIONS
Authors: Kingsbury David T , Sieckmann Donna G , Helinski Donald R
Published: January 2021

Host mutations in Escherichia coli K12 selected for the temperature-sensitive replication of the bacterial plasmid colicinogenic factor E1 (ColE1) exhibit a pleiotropic effect with respect to the effect of the mutation on other extrachromosomal elements. The mutations also vary with respect to the time of incubation of the cells at 43°C required for complete cessation of COlE1, DNA synthesis. While the synthesis of the bacterial chromosome appears unaffected, supercoiled ColE1 DNA replication stops immediately in some mutants and gradually decreases during several generations of cell growth before stopping in others. Mutations isolated in the ColE1 plasmid resulted in only a gradual cessation of ColE1 DNA synthesis over several generations of cell growth at 43°C. Conjugal transfer of the ColE1 and COlV factors occurs normally in the host mutants when the transfer is carried out at the permissive temperature; however, the presence of a group I mutation in the donor cell prohibited conjugal transfer of either plasmid DNA at 43°C to a normal recipient cell. Similarly, the presence of this mutation in the recipient prevented the establishment of COlE1 or COlV in the mutant recipient cell upon conjugation with a normal donor at 43°C. Various host COlE1, replication mutants carrying either ColE1 or ColE2 were also defective in the mitomycin Cinduced production of colicin E1 or colicin E2 at 43°C. The majority of the host mutations examined exhibited a temperature sensitivity to growth in deoxycholate in addition to the inhibition of plasmid DNA replication, suggesting a membrane alteration in these mutants when grown at the restrictive temperature.
THE TIMING OF TEMPERATURE SENSITIVITY OF LEAKY FERTILITY FACTOR MUTATIONS IN MALE DROSOPHILA MELANOGASTER
Authors: Frankel Anne W Koopmans
Published: January 2021

Some of the mutations of the male fertility factors on the Y chromosome give rise to a small proportion of fertile males, each of which produces only a small number of progeny. Many of these mutations are temperature-sensitive, producing a larger proportion of fertile males at 25°C than at 19°C. One of these mutants was carefully analyzed and it was found that only sperm which mature in the first five days of adult life can effect fertilization, regardless of the temperature regimen. A unique temperature-sensitive period was localized to the mid-pupal stage by single twenty-four-hour 25°C treatments applied at various times in the life cycle to flies otherwise grown at 19°C. The temperature sensitivity associated with this pupal sensitive period is adequate to account for all of the difference in fertility between flies. grown continuously at the two temperatures. The timing of the temperature-sensitive process in combination with a cytological study of spermiogenesis indicates that temperature sensitivity occurs after the first meiotic metaphase during a spermatid stage. Thus it affects some post-transcriptional event in the expression of the phenotype of the fertility factor.
EFFECTS OF POPULATION SIZE AND SELECTION INTENSITY ON CORRELATED RESPONSES TO SELECTION FOR POSTWEANING GAIN IN MICE
Authors: Eisen E J , Hanrahan J P , Legates J E
Published: January 2021

Correlated responses to selection for postweaning gain in mice were studied to determine the influence of population size and selection intensity. Correlated traits measured were three-, six- and eight-week body weights, litter size, twelve-day litter weight, proportion infertile matings and two indexes of reproductive performance. In general, the results agreed with observations made on direct response: correlated responses in the body weight traits and litter size increased as (1) selection intensity increased and (2) effective population size increased. Correlated responses in the body weight traits and litter size were positive in the large population size lines (16 pairs), as expected from the positive genetic correlation between these traits and postweaning gain. However, several negative correlated responses were observed at small population sizes (one and two pairs). Within each level of selection intensity, traits generally associated with fitness tended to decline most in the very small populations (one and two pairs) and in the large populations (16 pairs) for apparently different reasons. The fitness decline at the small effective population sizes was attributable to inbreeding depression. In contrast, it was postulated that the fitness decline at the large effective population size was due to selection moving the population mean for body weight and a trait positively correlated genetically with body weight (i.e., percent body fat) away from an optimum
TEMPERATURE-SENSITIVE MUTANTS FOR THE REPLICATION OF PLASMIDS IN ESCHERICHIA COLI I. ISOLATION AND SPECIFICITY OF HOST AND PLASMID MUTATIONS
Authors: Kingsbury David T , Helinski Donald R
Published: January 2021

Temperature-sensitive mutants of Escherichia coli defective in the replication of the plasmid colicinogenic factor E1 (ColE1) were isolated following mutagenesis of E. coli K12 strain carrying the ColE1 factor. Following the mutagenic treatment an enrichment procedure utilizing the replacement of thymine with bromouracil in the ColE1 DNA duplicated at the restrictive temperature was used. The mutants isolated following this enrichment step were the result of a mutation event either in the host chromosome or in the ColE1 plasmid. The host mutants fell into three phenotypic classes based on the effect each mutation had on the maintenance of a variety of other extrachromosomal DNA elements. Phenotypic class I mutations affected all E. coli plasmids, both the I and F sex factor types as well as the ColE1 factor. Phenotypic class II mutations affected the maintenance of the ColE1 and the F sex factor type plasmids and not the I type, while phenotypic class III mutations affected only ColE1 replication. None of these mutations was found to have a significant effect on the replication of the E. coli chromosome. The plasmid-linked mutations fell into two phenotypic classes on the basis of the ability of the Flac episome to complement the mutation in the ColE1 plasmid.
SELECTION FOR MIGRATION MODIFICATION
Authors: Balkau Beverley J , Feldman Marcus W
Published: January 2021

Simple models for the genetic control of the tendency to migrate are considered. It is shown that migration from a more favorable regime to a less favorable regime is selected against. The ramifications for general modifier theory are discussed.
MUTATIONAL ANALYSIS OF MATING TYPE INHERITANCE IN SYNGEN 4 OF PARAMECIUM AURELIA
Authors: Byrne Bruce C
Published: January 2021

Six genic mutations restricting clones to mating type VII (O) were isolated in syngen 4, Paramecium aurelia. The only three extensively tested were neither allelic nor closely linked. A second type of mutation, allelic to one of the O restricted mutants, was also found. Clones homozygous for this mutant gene were selfers, producing both O and E (VIII) mating types, but only when they were progeny of mating type E parental clones. While all seven mutant genes behaved as recessives in monohybrid crosses, clones heterozygous at two different loci often demonstrated an unanticipated phenotype: selfing. The significance of the findings is discussed in relation to mating type determination and the evolution of mating type systems.
REGULATORY SEROTYPE MUTATIONS IN TETRAHYMENA PYRIFORMIS, SYNGEN 1
Authors: Doerder F P
Published: January 2021

A method utilizing allelic exclusion has been developed to isolate mutants of Tetrahymena pyriformis, syngen 1, in which the normal pattern of expression of mutally exclusive surface antigens is altered. Cells homozygous for the recessive mutant allele R-1r do not express the L, H and T serotypes when grown under conditions appropriate for their expression. Rather, a new immobilization antigen, r, is expressed. Cells homozygous for the recessive mutant allele R-3r also express the r antigen instead of H serotypes, but are normal in their expression of T antigens. Genetic analyses show that R-1 and R-3 are not closely linked, that R-1 is linked to T by 9.3 units, and that R-3 may be loosely linked to the mt locus. Different linkage values were obtained, however, when different inbred laboratory strains were used, suggesting the possible existence of crossover modifying genes. The rates of assortment of R-1R/R-1r and R-3R/R-3r heterozygotes into pure sublines expressing either H or r serotypes are close to the values observed for the differentiation of heterozygotes at other loci. The data confirm the previous observation that genetic coupling relationships are not maintained in macronuclear phenotypes and are consistent with the hypothesis that the macronucleus contains 45 assorting subunits. The assortment of the double heterozygote R-1R/R-1r, R-3R/R-3r at Rf=0.0112 suggests that the units of assortment are not individual genetic loci or chromosome fragments, but that the units may be complete genomes.
TRANSPOSITION OF THE ARSENATE RESISTANCE LOCUS OF BACILLUS SUBTILIS STRAINS 23 AND 168
Authors: Adams Alice
Published: January 2021

Wild-type Bacillus subtilis strains 23 and 168 are resistant to high concentrations of sodium arsenate. The genetic configurations of the arsenate resistance loci of these two related strains of B. subtilis have been characterized. The transformable 168 strain has a single resistance locus which maps between phe and aroD in the terminal third of the genome. In contrast, strain 23 is shown to have its single arsenate resistance locus between purB and thr in the first third of the bacterial chromosome. Moreover, in strain 23 the chromosomal segment equivalent to the phe-linked asa region of 168 strains is missing. DNA isolated from 23 strains is able to transform 168 arsenate-sensitive strains to resistance and the heterologous 23 DNA is found to preferentially establish a new purB linked asa locus in such transformed cells. Thus, the majority of phenotypically arsenate-resistant cells recovered after exposure of competent 168 sensitive mutants to 23 DNA are "heterozygous" and still retain their phe-linked mutated asa locus. The tolerance of several of these heterologously transformed hybrid strains to arsenate suggests that the 168 and 23 asa gene products are similar, and a transposition model for the evolution of arsenate resistance in B. subtilis is proposed.
SEGREGATION OF INDUCED FRAMESHIFT MUTATIONS AND THE SEQUENCE OF GENE REPLICATION IN ESCHERICHIA COLI K12
Authors: Hoess Ronald H , Herman Robert K
Published: January 2021

We have constructed a strain of E. coli K12 carrying six mutations induced by the acridine half-mustard ICR-191. The mutations are widely spaced on the E. coli linkage map and are all easily reverted by ICR-191. Mapping of ten independent revertants for each of five markers indicated that the reversions induced by ICR-191 occurred near the original mutations. Exponentially and nonsynchronously growing cultures of this strain were exposed to ICR-191 for 0.85 generation, quickly washed free of mutagen, and resuspended in the original medium minus mutagen. Total viable cell number maintained its exponential increase both during and immediately after exposure to mutagen, whereas the number of revertants of any particular type remained constant for a characteristic period after removal of mutagen before finally assuming an exponential increase. Theoretically, the length of such a segregation lag should depend on the position of the particular reverted gene in the sequence of gene replication: the earlier a gene is replicated in the chromosome replication cycle, the longer its segregation lag should be. Our results are consistent with this prediction and fit a unidirectional, clockwise replication scheme with an origin between 55 and 74 min on the E. coli linkage map. The results also fit a very asymmetric bidirectional replication scheme.
THE INDUCTION OF MITOTIC GENE CONVERSION BY X-IRRADIATION OF HAPLOID SACCHAROMYCES CEREVISIAE
Authors: Campbell D A
Published: January 2021

Mitotic recombination in Saccharomyces cerevisiae was examined by means of experiments in which one of the haploid parents was X-irradiated prior to zygote formation. By this method radiation-induced lesions are restricted to only one of the two non-sister chromatids that may be expected to undergo mitotic exchange in the diploid. The principal results of this work are: (1) X-irradiated haploid cells that are incapable of further vegetative growth (colony formation) are efficiently rescued into viable diploids by mating with unirradiated haploid cells. (2) X-rays delivered to only one of the two haploid parents are recombinogenic in the resultant diploid. The frequency of detected recombinational events increases as a probable linear function of the X-ray dose. (3) A majority of the induced recombinational events are nonreciprocal in nature (mitotic gene conversion). These results complement those obtained from X-irradiation of the vegetative diploid itself, where the induced genetic exchanges are principally reciprocal.
GENETIC CONTROL OF THE CELL DIVISION CYCLE IN YEAST: V. GENETIC ANALYSIS OF cdc MUTANTS
Authors: Hartwell Leland H , Mortimer Robert K , Culotti Joseph , Culotti Marilyn
Published: January 2021

One hundred and forty-eight temperature-sensitive cell division cycle (cdc) mutants of Saccharomyces cerevisiae have been isolated and characterized. Complementation studies ordered these recessive mutations into 32 groups and tetrad analysis revealed that each of these groups defines a single nuclear gene. Fourteen of these genes have been located on the yeast genetic map. Functionally related cistrons are not tightly clustered.

Mutations in different cistrons frequently produce different cellular and nuclear morphologies in the mutant cells following incubation at the restrictive temperature, but all the mutations in the same cistron produce essentially the same morphology. The products of these genes appear, therefore, each to function individually in a discrete step of the cell cycle and they define collectively a large number of different steps.

The mutants were examined by time-lapse photomicroscopy to determine the number of cell cycles completed at the restrictive temperature before arrest. For most mutants, cells early in the cell cycle at the time of the temperature shift (before the execution point) arrest in the first cell cycle while those later in the cycle (after the execution point) arrest in the second cell cycle. Execution points for allelic mutations that exhibit first or second cycle arrest are rather similar and appear to be cistron-specific. Other mutants traverse several cycles before arrest, and its suggested that the latter type of response may reveal gene products that are temperature-sensitive for synthesis, whereas the former may be temperature-sensitive for function.

The gene products that are defined by the cdc cistrons are essential for the completion of the cell cycle in haploids of a and α mating type and in a/α diploid cells. The same genes, therefore, control the cell cycle in each of these stages of the life cycle.
ALLELIC COMPLEMENTATION IN THE FIRST GENE FOR HISTIDINE BIOSYNTHESIS IN SACCHAROMYCES CEREVISIAE. I. CHARACTERISTICS OF MUTANTS AND GENETIC MAPPING OF ALLELES
Authors: Korch Christopher T , Snow Richard
Published: January 2021

A number of his1 mutants were tested for suppressibility, for reversion by EMS, ICR-170, and nitrous acid, for their allelic complementation response, and for their temperature sensitivity and osmotic remediability. None of 52 mutants tested was suppressible by a known ochre suppressor. This is a very surprising result compared with other studies of suppressibility in yeast and suggests that another function essential to the cell is associated with the his1 gene product, the polarity effect of a nonsense mutation destroying the activity of the his1 enzyme and this second function.

Sixty-four his1 alleles were ordered by allelic mapping methods utilizing gamma rays, X-rays, and MMS. The three maps agree well in placement of alleles and have been oriented on chromosome V of yeast with respect to the centromere. The 18 noncomplementing alleles are localized in the distal half of the gene, whereas the complementing alleles are distributed more or less evenly. Mutations which revert to feedback resistance map in the proximal end. Also at this end are mutations having a very high X-ray or MMS induced homoallelic reversion rate. This suggests that a number of missense mutations can occur in this region which result in innocuous amino acid substitutions in the enzyme. One X-ray map unit is estimated to correspond to about 131 base pairs or 43 amino acids, in agreement with results for the cytochrome-c protein obtained by Parker and Sherman (1969).
ALLELIC COMPLEMENTATION IN THE FIRST GENE FOR HISTIDINE BIOSYNTHESIS IN SACCHAROMYCES CEREVISIAE. II. COMPLEMENTATION MAPPING OF MUTANTS AND A SUBUNIT MODEL OF THE ENZYME
Authors: Korch Christopher T
Published: January 2021

Sixty-two alleles of the histidine-1 (his1) gene were tested for complementation. The 44 complementing mutants fell into 31 complementation groups which were used to construct a complex complementation map with 18 complementation units. Cluster analysis of the complementation map by either visual inspection or the computer method of Gillie and Peto (1969) shows two very definite clusters. The molecular weight estimate of the his1 enzyme, phosphoribosyl adenosine triphosphate: pyrophosphate phosphoribosyltransferase, is 1.8 . 105 by sucrose density gradient analysis and 2.4 . 105 by Sephadex gel chromatography. Correlating the length of the his1 gene to the molecular weight of the enzyme indicates that this enzyme is composed of 6 subunits, as is the analogous enzyme in Salmonella typhimurium. A model of the subunit and tertiary and quaternary structure of the enzyme has been developed from consideration of the genetic and complementation data, the distribution of the various mutant types within the gene, and the biochemical properties of the enzyme encoded by the his1 gene.
DOSAGE COMPENSATION IN DROSOPHILA MELANOGASTER TRIPLOIDS. II. GLUCOSE-6-PHOSPHATE DEHYDROGENASE ACTIVITY
Authors: Maroni Gustavo , Plaut Walter
Published: January 2021

The level of activity of the enzyme glucose-6-phosphate dehydrogenase was determinel in flies having seven different chromosomic constitutions. All those having an integral number of chromosomes [XAA, XXAA, XAAA, XXAAA, and XXXAAA (X=X chromosome, A=set of autosomes)] were found to have similar units of enzyme activity/mg live weight, while diploid females with a duplication and triploid females with a deficiency showed dosage effect. The amount of enzyme activity per cell, on the other hand, is also independent of the number of X's present but appears roughly proportional to the number of sets of autosomes.—It is proposed that dosage-compensated sex-linked genes are controlled by a positively acting regulatory factor(s) of autosomal origin. With this hypothesis it is possible to explain dosage compensation as a consequence of general regulatory mechanisms without invoking a special device which applies only to the X chromosomes.
DIVERGENT SELECTION UNDER TWO NUTRITIONAL ENVIRONMENTS FOR PACKED ERYTHROCYTE VOLUME IN JAPANESE QUAIL
Authors: Stino F K R , Washburn K W
Published: January 2021

Two-way selection for two-week packed erythrocyte volume (PCV) was practiced for four generations under two nutritional environments in the Japanese quail (Coturnix coturnix japonica). One environment was an iron, copper-"adequate" diet and the other was iron, copper-deficient "stress" diet. Response to selection was greater in both directions under the adequate environment than under the stress environment. After four generations of selection there were 29% and 18% differences between the high and low lines under the adequate and the stress environments, respectively. An asymmetry of response was observed toward the low line under the adequate environment and toward the high line under the stress environment. The realized heritability estimates for the high and low Fe-Cu-adequate lines were.26 and.35, respectively, while those for the high and low Fe-Cu-deficient lines were.16 and.06, respectively.
THYMINELESS MUTAGENESIS IN BACTERIOPHAGE T4
Authors: Smith M Diane , Green Ronald R , Ripley Lynn S , Drake John W
Published: January 2021

Thymine deprivation can be achieved in bacteriophage T4 either by the use of the thymidylate synthetase inhibitor FUdR, or by an appropriate combination of genetic blocks; both methods produce marked mutagenesis. Extensive tests of the specificity of thymineless mutagenesis reveal that only A:T base pairs are affected, and that transitions and possibly transversions are produced. This system therefore constitutes the fist example of an A: T-specific mutagen. Thymineless mutagenesis in bacteriophage T4 exhibits a marked dependence upon the functional state of the DNA polymerase gene, but is largely independent of the px-γ misrepair system.
ON THE ORIGIN OF MITOCHONDRIAL MUTANTS: EVIDENCE FOR INTRACELLULAR SELECTION OF MITOCHONDRIA IN THE ORIGIN OF ANTIBIOTIC-RESISTANT CELLS IN YEAST
Authors: Birky C W
Published: January 2021

In wild-type Sacchromyces cerevisiae, erythromycin and certain other antibacterial antibiotics inhibit the formation of respiratory enzymes in mitochondria by inhibiting translation on mitochondrial ribosomes. This paper is concerned with the origin of mutant cells, resistant to erythromycin by virtue of having a homogeneous population of mutant mitochondrial DNA molecules. Such mutant cells are obtained by plating wild-type (sensitive) cells on a nonfermentable substrate plus the antibiotic. Colonies of mutant cells appear first about four days after the time of appearance of established mutant cells; new colonies continue to appear, often at a constant rate, for many days. Application of the NEWCOMBrEes preading experiment demonstrates that most or all of the mutant cells which form the resistant colonies on selective medium arise only after exposure of the population to erythromycin. It is suggested that this result is most probably due to intracellular selection for mitochondrial genomes. Resistant mitochondria arising from spontaneous mutatLon are postulated to be at a selective disadvantage in the absence of erythromycin; reproducing more slowly than wild-type sensitive mitochondria, they cannot easily accumulate in sufficient numbers in a cell to render it resistant as a whole. In the presence of erythromycin, resistant mitochondria can continue to reproduce while sensitive mitochondria cannot, until there is a sufficient number to make the cell resistant, i.e. to permit normal cell growth. The same phenomenon is seen with respect to chloramphenicol resistance. Intracellular selection is considered more likely than direct induction of mutation by the antibiotic, since mutant cells do not accumulate in the presence of erythromycin if the mitochondrial genome is rendered nonessential by growth on glucose or nontranslatable by chloramphenicol. Intracellular selection provides a mechanism for direct adaptation at the cell level, compatible with currently acceptable ideas of spontaneous miitation and selection at the organelle level.
INDUCTION OF MITOTIC CROSSING OVER IN SACCHAROMYCES CEREVISIAE BY BREAKDOWN PRODUCTS OF DIMETHYLNITROSAMINE, DIETHYLNITROSAMINE, 1-NAPHTHYLAMINE AND 2-NAPHTHYLAMINE FORMED BY AN IN VITRO HYDROXYLATION SYSTEM
Authors: Mayer V W
Published: January 2021

Dimethylnitrosamine and diethylnitrosamine, two potent carcinogens, are nonmutagenic when tested directly in microorganisms. Likewise 1-naphthylamine and 2-naphthylamine are also nonmutagenic but the N-hydroxy derivatives are mutagenic in microorganisms. Apparently these compounds require metabolism to breakdown products which are then the proximately active agents, and microorganisms lack the enzymes necessary to effect this conversion. These compounds are mutagenic in Saccharomyces after conversion to breakdown products in an in vitro hydroxylation medium. The induction of mitotic crossing over in Saccharomyces cerevisiae by breakdown products of dimethylnitrosamine, diethylnitrosamine, 1-naphthylamine and 2-naphthylamine formed in the Udenfriend hydroxylation medium is reported in this communication. Mitotic crossing over was detected as red sectored colonies resulting from induced homozygosity of the ade2 marker. Dimethylamine and diethylamine, which lack the nitroso group of the nitrosamines, did not induce mitotic crossing over under any of the test conditions. To further confirm that the induced sectored colonies were the result of mitotic crossing over they were tested for the presence of reciprocal products. The expected reciprocal products were found in over 67% of the isolates tested. The significance and practicality of using mitotic recombination as an indicator of genetic damage potential of chemicals is discussed.
GENETIC CONTROL OF INSECT POPULATIONS: I. CAGE STUDIES OF CHROMOSOME REPLACEMENT BY COMPOUND AUTOSOMES IN DROSOPHILA MELANOGASTER
Authors: Fitz-Earle M , Holm D G , Suzuki D T
Published: January 2021

A genetic method for insect control was evaluated using the test organism, Drosophila melanogaster. The technique involved the displacement under a system of continuous reproduction, of standard strains by those carrying compound autosomes. The eradication of the replacements could subsequently be achieved through the use of temperature-sensitive lethal mutations.—While certain compound autosome strains failed to displace standards in population cages, even at the initial release ratio of 25:1, others were highly successful. Indeed, for some strains when the ratio of compounds to standards was as low as 9:1, the population rapidly went to fixation in favor of the compound line.—Hatchability was found to be an insufficient index of fitness to estimate the initial ratios of compounds to standards that would guarantee fixation of the former. Differences in other fitness components, such as development time, were detected that could seriously modify displacement, especially with continuous overlapping generations. The importance of examining the fitness of various compound lines and selecting the most competitive in cages, prior to field tests, cannot be overemphasized.
HYPERPRODUCTION OF DIHYDROFOLATE REDUCTASE IN DIPLOCOCCUS PNEUMONIAE AFTER MUTATION IN THE STRUCTURAL GENE. EVIDENCE FOR AN EFFECT AT THE LEVEL OF TRANSCRIPTION
Authors: Sirotnak F M , McCuen R W
Published: January 2021

Dihydrofolate reductase is markedly hyperproduced in strains of Diplococcus pneumoniae which bear any one of a unique group of sense to sense mutations (amer) in the corresponding structural gene. Increased enzyme levels mediated by the amer mutations are apparently the result of increased rates of de novo synthesis. The basis for these effects could be transcriptional, translational or could involve an increase in messenger RNA stability. Data revealing no difference in stability of the related mRNA in a variety of mutants and the wild-type strain appear to eliminate the last possibility. Other data support the idea of an effect on transcription. This includes the extreme sensitivity of amer mutation expression following genetic transformation, to inhibition by actinomycin D and rifampacin, and the presence in one extremely high level mutant (amer-3 with 120 times the wild-type enzyme content) of increased amounts of mRNA. The data are most compatible with the idea of a regulatory function for the dihydrofolate reductase protein in this organism.
RECOGNITION OF STREPTOCOCCAL DNA BY A MUTANT PNEUMOCOCCUS UNABLE TO DISCRIMINATE AMONG MARKERS IN PNEUMOCOCCAL DNA
Authors: Tiraby Gerard , Ravin Arnold W
Published: January 2021

A mutant strain of pneumococcus which fails to discriminate against low-efficiency markers during transformation by homospecific pneumococcal donor DNA retains the wild-type capacity to discriminate against heterospecific (streptococcal) donor DNA. We conclude that discrimination against heterospecific DNA must differ from that against low-efficiency markers by the kind or number of elements being recognized.
TWO DIFFERENT h
- MATING TYPES IN SCHIZOSACCHAROMYCES POMBE
Authors: Gutz Herbert , Doe Frank J
Published: January 2021

In the strains of Schizosaccharomyces pombe introduced by Leupold (1950, 1958) into genetic research, heterothallic and homothallic mating types are known. The mating types are determined by two closely linked genes. We show that two distinct heterothallic - mating types exist: a stable one (h-S) and an unstable one (h-U), which can mutate to heterothallism + and homothallism. A proposal for incorporation of the new mating type h-U into Leupold's two-gene scheme is discussed.
COMPLEMENTATION ANALYSIS OF METABOLITE-RESISTANT MUTATIONS WITH FORCED HETEROKARYONS OF NEUROSPORA CRASSA
Authors: Thwaites W M , Knauert F K , Carney S S
Published: January 2021

The double mutant strain pyr-3  arg-12s is a prototroph because a common precursor of arginine and pyrimidine is supplied by the arginine pathway. Growth of this strain is inhibited by exogenous citrulline or arginine. Citrulline-resistant mutants of this strain were selected, and they resulted from modifier mutations at other loci. Forced heterokaryons were used to study complementation among these modifiers. Since the complementation test requires the scoring of non-growth as the positive result, there was concern that variations in nuclear ratios could give erroneous results. This possibility does not seem significant, since groups of mutants established by complementation correspond with groups established by physiological, enzymatic, and recombinational measurements.—The technique has revealed that the most frequently mutated loci are arg-1 and what is probably un-3. Arg-1 mutations affect the conversion of citrulline to argininosuccinate, while un-3 mutations reduce the citrulline uptake rate. Since most of these mutations are of the intracistronic complementing type, a complementation map was constructed for most of the affected loci. The high proportion of complementors in each map can be explained by assuming that partially functioning gene products are more likely to complement with each other than are those which are nonfunctional.
COMPARISONS OF RELATIVE ACTIVITIES OF MAIZE Adh
1 ALLELES IN HETEROZYGOTES—ANALYSES AT THE PROTEIN (CRM) LEVEL
Authors: Schwartz Drew
Published: January 2021

The method of high-resolution electrophoresis was employed to compare the relative amounts of enzyme produced by the Adh1F and Adh1S alleles in heterozygotes at different stages of development. The results are in complete agreement with those obtained from enzymatic analyses and support the competition hypothesis for the regulation of the alcohol dehydrogenase gene.
THE MECHANISM OF A BROODING EFFECT ASSOCIATED WITH SEGREGATION DISTORTION IN DROSOPHILA MELANOGASTER
Authors: Hartl D L
Published: January 2021

The recovery of the SD chromosome from a heterozygous SD male increases with brood. This is independent of the age of the female, occurs during the time the sperm are stored in the females, disappears when the segregation distortion is suppressed, and is temperature-sensitive-temperature shocks above or below 25°C applied to the mature sperm both tend to accelerate the increase in the recovery of SD. All this suggests the existence of a class of sperm affected by SD in which the sperm are able to fertilize eggs for a short time following ejaculation but become dysfunctional thereafter.
GENE DUPLICATION WITHIN THE FAMILY SALMONIDAE: DISOMIC INHERITANCE OF TWO LOCI REPORTED TO BE TETRASOMIC IN RAINBOW TROUT
Authors: Allendorf Frederick W , Utter Fred M
Published: January 2021

We describe our studies of the genetics of allelic variation for NADP-dependent isocitrate dehydrogenase (IDH) in rainbow trout (Salmo gairdneri). Five populations of rainbow trout were studied to determine the phenotypic distribution of IDH; 453 progeny from a number of controlled matings were examined to determine the nature of inheritance of these alleles. The variation was found to be the result of four alleles producing protein subunits of differing electrophoretic mobilities. Progeny from crosses clearly demonstrated the presence of two disomic loci controlling the variation, rather than one tetrasomic locus as had been previously reported. These findings support our contention that the hypothesis of a tetraploid event in salmonid evolution should not be uncritically accepted.
ANALYSES OF GENE FREQUENCIES OF MATES
Authors: Cockerham C Clark
Published: January 2021

A genic analysis of variance of data on mate pairs for a codominant gene is developed. This analysis provides estimators of the correlation, F, of genes within individuals, of the correlation, Θ, of genes between mates, and of various variances-all relative to the correlation or variation among genes of nonmates. The data are manipulated into marginal distributions to produce another method of obtaining the same estimators. Several examples are given of how assumptions about the model and parameters modify the estimators and which were utilized in constructing X2 tests of hypotheses concerning F and Θ.—A recessive gene is also considered. Only the frequency of recessive genotypes and the correlation of recessive mates are estimable in this case unless one makes very demanding assumptions about the model.—Numerical examples of the analysis of variance and estimators are given for both a codominant and recessive gene.
RATES OF ELECTRON TRANSFER AND OF NON-CYCLIC PHOTOPHOSPHORYLATION FOR CHLOROPLASTS ISOLATED FROM MAIZE POPULATIONS SELECTED FOR DIFFERENCES IN JUVENILE PRODUCTIVITY AND IN LEAF WIDTHS
Authors: Hanson W D , Grier R E
Published: January 2021

In vitro studies with chloroplasts isolated from maize populations differing in juvenile productivity by the sixth leaf stage of growth demonstrated differences in rates of ferricyanide reduction and of non-cyclic photophosphorylation. Similar results were obtained for two independent sets of replicate selections for high and for low productivity. Chloroplasts from low productive selections had about 115 percent of the reduction rate and 129 percent of the phosphorylation rate found for the high productive selections. Differences in ferricyanide reduction held for a fourfold range of experimentally induced rates. The contrasting rates of electron flow did not result from differential extraction environments following cell disruption nor from the failure to protect chloroplasts during extraction. Light-dependent phosphate uptake gave evidence, though inconclusive, of being so modified. No evidence was found for reciprocal effects between low-high and high-low hybrids. No difference in activities was found between chloroplasts isolated from two populations selected for narrow and for wide leaf widths. These two selections differed markedly in leaf areas. While in vitro measures of chloroplast efficiency reflected differences which were under genetic control, the results did not follow those expected from photosynthetic studies. The differences in rates appeared to reflect modification of processes other than those in the photosynthetic pathway.
SOMATIC CROSSING OVER IN GLYCINE MAX (L.) MERRILL: MUTAGENICITY OF SODIUM AZIDE AND LACK OF SYNERGISTIC EFFECT WITH CAFFEINE AND MITOMYCIN C
Authors: Vig B K
Published: January 2021

Glycine max (soybean) is one angiosperm which lends itself to the study of somatic crossing over. This is made possible because some varieties have gene combinations Y11Y11, Y11y11 and y11y11 in the segregating populations from Y11y11 plants. The gene in question is responsible for chlorophyll synthesis. The Y11Y11 plants have dark green leaves, Y11y11 are light green and y11y11 plants are golden yellow. The heterozygous plants have dark green, yellow and dark green-yellow (double) spots on the leaves of the untreated control material, whereas the two homozygotes are almost always devoid of somatic sectoring. Application of caffeine, or mitomycin C, to the seeds increased the frequency of double, dark green and yellow spots on the Y11y11 background. Possibly, some dark green or yellow spots originate by failure of one of the two components of what might start as a double spot due to somatic crossing over. The application of NaN3 increases the frequency of dark green or yellow spots, almost exclusively. The two spots increase in equal frequency. The y11y11 plants so treated do not have any light green sectors, but dark green, Y11Y11, plants do develop a few light green or very dark green spots. The data indicate that NaN3 is capable of inducing nondisjunction, but does not cause mutations (at this locus), chromosome fragmentations (segmental losses) or somatic crossing over to an appreciable degree. It has previously been shown that caffeine-induced chromosome rejoining in Vicia faba can be inhibited by treating the roots with NaN3. In the present experiments NaN3 did not affect the processes of somatic crossing over as induced by caffeine or mitomycin C. The effect was additive. This system offers advantages for studying chemical mutagens in that somatic crossing over, point mutations, segmental losses through chromosome breakage and nondisjunction can all be studied in a single treatment to the seeds.
ISOLATION OF P22 SPECIALIZED TRANSDUCING PHAGE FOLLOWING F'-EPISOME FUSION
Authors: Kaye Robert , Barravecchio John , Roth John
Published: January 2021

A P22 specialized transducing phage has been constructed which carries the structural gene for aspartate transcarbamylase (ATCase). This gene (pyrB) was first brought close to the P22 attachment site by fusing an F' pyrB  + episome to an F' prolac episome which carries a P22 prophage attachment site. A prophage was added to these fused F' episomes and the lysogen was UV-induced. The specialized transducing phage was isolated from the resulting lysate. The phage also carries argI, the structure gene for ornithine transcarbamylase.
GENETIC CONTROL OF CHROMOSOMAL AND PLASMID RECOMBINATION IN STAPHYLOCOCCUS AUREUS
Authors: Wyman L , Goering R V , Novick R P
Published: January 2021

Recombination-deficient mutants of Staphylococcus aureus have been isolated and found to have properties similar to those of recombination-deficient Escherichia coli. In addition, one Rec- mutant was found to be defective in the restriction and modification of DNA. There is a marked reduction (∼ 104-fold) in recombination between penicillinase plasmids in the Rec- mutants suggesting that these elements do not encode an efficient recombination system. There is, however, a demonstrable residuum of interplasmid recombination; evidence is lacking on whether this residuum is a plasmid or host function. In the absence of the generalized host recombination system it has been possible to demonstrate that interplasmid recombination occurs during vegetative bacteriophage growth and is presumably mediated by a phage-determined recombination system.
ARE MITOTIC FUNCTIONS REQUIRED IN MEIOSIS?
Authors: Simchen G
Published: January 2021

Sporulation of diploid yeasts (Saccharomyces cerevisiae), homozygous or heterozygous for temperature-sensitive mitotic cell-cycle mutations, was examined at the restrictive and permissive temperatures. Twenty genes, represented by 32 heterozygotes and 60 homozygotes, were divided into three groups, showing (i) normal sporulation, (ii) no sporulation at the restrictive temperature but normal sporulation at the permissive temperature, (iii) no sporulation at both temperatures. Group (i) as well as several other strains were tested for their meiotic behavior with regard to intragenic recombination and haploidization. The conclusion reached was that all the mitotic nuclear-division and DNA-synthesis functions were required in meiosis. The only cell-division mutations not to affect meiosis were in three cytokinesis loci and in one budemergence locus.
HAIRPIN-TAIL: A CASE OF POST-REDUCTIONAL GENE ACTION IN THE MOUSE EGG?
Authors: Johnson D R
Published: January 2021

Hairpin-tail (Thp) is a new allele of brachyury on chromosome 17 (linkage group IX) of the mouse. The morphological effects in the heterozygote are on the notochord and the tail. The homozygous abnormal is unknown. Thp is unique in that the phenotype of the heterozygote seems to depend on the source of the Thp gene. If it is inherited via the egg the phenotype is extreme and death follows in utero. Embryos derived from a Thp sperm and a+egg are less abnormal and viable. This is not a simple maternal effect, as Thp×Thp matings produce two distinct types of heterozygous embryos.