bluuebunny/crossref_metadata_2025 huggingface dataset:
FITNESS EFFECTS OF EMS-INDUCED MUTATIONS ON THE X CHROMOSOME OF DROSOPHILA MELANOGASTER. I. VIABILITY EFFECTS AND HETEROZYGOUS FITNESS EFFECTS
Authors: Mitchell Joyce A
Published: April 2021

Drosophila melanogaster X chromosomes were mutagenized by feeding males sucrose solutions containing ethyl methanesulfonate (EMS); the concentrations of EMS in the food were 2.5 mm, 5.0 mm, and 10.0 mm. Chromosomes were exposed to the mutagen up to three times by treating males in succeeding generations. After treatment, the effective exposures were 2.5, 5.0, 7.5, 10.0, 15.0, and 30.0 mm EMS. X chromosomes treated in this manner were tested for effects on fitness in both hemizygous and heterozygous conditions, and for effects on viability in hemizygous and homozygous conditions. In addition, untreated X chromosomes were available for study. The viability and heterozygous fitness effects are presented in this paper, and the hemizygous fitness effects are discussed in the accompanying one (Mitchell and Simmons 1977). Hemizygous and homozygous viability effects were measured by segregation tests in vial cultures. For hemizygous males, viability was reduced 0.5 percent per mm EMS treatment; for homozygous females, it was reduced 0.7 percent per mm treatment. The decline in viability appeared to be a linear function of EMS dose. The viabilities of males and females were strongly correlated. Heterozygous fitness effects were measured by monitoring changes in the frequencies of treated and untreated X chromosomes in discrete generation populations which, through the use of an X-Y translocation, maintained them only in heterozygous condition. Flies that were heterozygous for a treated chromosome were found to be 0.4 percent less fit per m m EMS than flies heterozygous for an untreated one.
GLYCOLYSIS MUTANTS IN SACCHAROMYCES CEREVISIAE
Authors: Clifton Drago , Weinstock Shelley B , Fraenkel Dan G
Published: April 2021

Mutants have been isolated in S. cereuisiae with the phenotype of growth on pyruvate but not on glucose, or growth on rich medium with pyruvate but inhibition by glucose. Screening of mutagenized cultures was either without an enrichment step, or after enrichment using the antibiotic netropsin (YOUNG et al. 1976) or inositol starvation (HENRY, DONAHUEand CULBERTSON 1975). One class of mutants lacked pyruvate kinase (p y k), another class had all the enzymes of glycolysis, and one mutant lacked phosphoglucose isomerase (pgi, MAITRA 1971). Partial reversion of pyruvate kinase mutants on rich medium containing glucose gave double mutants now'also lacking hexokinase (hzk), phosphofructokinase (pfk), or several enzymes of glycolysis (gcr) . In diploids the mutations were recessive. pyk, pgi, pfk, and gcr segregated 2:2 from their wild-type alleles. PYK hxk, PYK pfk, and PYK gcr segregants grew on glucose.
VARIANCE COMPONENT ANALYSIS OF ALLOZYME FREQUENCY DATA FROM EASTERN POPULATIONS OF DROSOPHILA MELANOGASTER
Authors: Smith Diana B , Langley Charles H , Johnson Frank M
Published: April 2021

Gene frequency variation at eight polymorphic allozyme loci in Drosophila meianogaster populations in North Carolina and the east coast of the United States were analyzed utilizing the variance component estimation procedures suggested by COCKERHAM (1969, 1973). These variance components were used to estimate correlations of genes within small geographic regions. The average (over loci) correlation between genes in the same individual within subpopulations was estimated to be 0.033. That between genes in the same subpopulation in different individuals was estimated to be very small, although significantly different from zero. The macrogeographic variation measured by the correlation of genes sampled from the same local region was large for some loci and smaller for others. This variation was also analyzed by correlation with latitude and longitude. Several previously recognized clines were identified as were several new clines.—These results were interpreted as indicating either some degree of nonrandom mating and locel breeding unit isolation or a low frequency of null alleles. The geographic and temporal variation has no simple interpretation.
ISOLATION AND CHARACTERIZATION OF PERITHECIAL DEVELOPMENT MUTANTS IN NEUROSPORA
Authors: Johnson Thomas E
Published: April 2021

The isolation and characterization of mutants that block perithecial development in Neurospora crassa are described. Several classes of mutants have been isolated after UV mutagenesis, and those that block perithecial development when used as the female (protoperithecial) component of a cross have been further characterized. These mutants fall into 29 complementation groups. Twelve of the 33 mutants block development at the protoperithecial stage; no other clustering of block points is observed. Many of the mutants show an altered vegetative growth rate as well; in several mutants this lower growth rate cosegregates with the female sterile phenotype. Only one mutant also blocks development of the perithecium when used as the conidial parent. None of the mutants are temperature sensitive; two can be suppressed by growth on a complete crossing medium. There is no indication that the mutants are at or in the mating-type locus, nor are any of the mutants mating-type specific. Genetic mosaics have been formed using mixtures of mutant and marked wild-type nuclei; no mutants are cell autonomous by this criterion. The significance of these results in terms of "developmental" mutants isolated in other organisms and in relation to models of eukaryotic development is discussed.
CROSSOVER SUPPRESSORS AND BALANCED RECESSIVE LETHALS IN CAENORHABDITIS ELEGANS
Authors: Herman Robert K
Published: April 2021

Two dominant suppressors of crossing over have been identified following X-ray treatment of the small nematode C. elegans. They suppress crossing over in linkage group II (LGII) about 100-fold and 50-fold and are both tightly linked to LGII markers. One, called C1, segregates independently of all other linkage groups and is homozygous fertile. The other is a translocation involving LGII and X. The translocation also suppresses rrossing over along the right half of X and is homozygous lethal. CI has been used as a balancer of LGII recessive lethal and sterile mutations induced by EMS. The frequencies of occurrence of lethals and steriles were approximately equal. Fourteen mutations were assigned to complementation groups and mapped. They tended to map in the same region where LGII visibles are clustered.
SELECTION OF SALMONELLA TYPHIMURIUM MUTANTS WITH ALTERED SERINE TRANSHYDROXYMETHYLASE REGULATION
Authors: Stauffer George V , Brenchley Jean E
Published: April 2021

In Salmonella typhimurium the glyA gene product, serine transhydroxymethylase (E.C. 2.1.2.1; L-serine:tetrahydrofolate-5,10-hydroxymethyltransferase) is responsible for the interconversion of serine and glycine. This reaction also provides the cell with one-carbon units from the 5,10-methylenetetrahydrofolate formed during glycine synthesis. Despite the importance of this enzyme, however, no mutants in which its regulation has been specificially altered have been isolated. To isolate such mutants, we have devised a selection procedure using a strain (glyA951) in which the serine transhydroxymethylase activity is reduced. When this enzyme is completely repressed, the mutant requires glycine for growth. Revertants which retain the glyA951 lesion, but no longer require glycine, have been isolated and the serine transhydroxymethylase regulation examined. One revertant has a 7-fold elevated serine transhydroxymethylase level, which can be repressed the normal amount (about 5-fold) when the cells are grown in supplemented media. Another revertant has only a 2-fold higher serine transhydroxymethylase level; however, the amount of repression is reduced. The new lesions in both mutants cotransduce with the glyA gene and are distinct from other mutations that alter the regulation of both serine transhydroxymethylase and the methionine biosynthetic enzymes.
MUTATIONS OF THE a MATING-TYPE GENE IN NEUROSPORA CRASSA
Authors: Griffiths A J F , DeLange A M
Published: April 2021

In Neurospora, the mating-type locus controls both mating (A + a is fertile) and heterokaryosis (A + a is incompatible). The two alleles appear stable: no novel fertility reactions have ever been reported, and attempts to separate fertility and heterokaryon incompatibility functions by recombination have been unsuccessful. In the present approach the locus was studied through a mutational analysis of heterokaryon incompatibility function. A selection system was used that detects vigorous (A + a) heterokaryotic colonies against a background of inhibited growth. Twenty-five mutants of an a strain were produced following mutagenic treatment with UV and NG: 15 were viable as homokaryons and 10 were not. All but one were infertile, but most showed an abortive mating reaction involving the production of barren, well-developed perithecia with A and (surprisingly) a testers. None of the mutants complement each other to restore fertility. Seven mutants have been mapped to the mating-type locus region of chromosome 1. Restoration of fertility was used to detect revertants, and these were found in five out of the eight mutants tested. (A dose response was observed). In four cases incompatibility was fully restored and in one case it was not.—The results suggest two positive actions of the locus when in heterozygous (A/a) combination (the stimulation of some stage of ascus production and the inhibition of vegetative heterokaryosis), and one positive action in homozygous combination (the production of a perithecial inhibitor).
GENETIC AND PHYSIOLOGICAL CHARACTERISTICS OF A SLOW-GROWING CIRCADIAN CLOCK MUTANT OF NEUROSPORA CRASSA
Authors: Feldman Jerry F , Atkinson Cheryl A
Published: April 2021

A circadian clock mutant of Neurospora crassa with a period length of about 25.8 hours (4 hr longer than wild type) has been isolated after mutagenesis of the band strain. This mutant, called frq-5, segregates as a single nuclear gene, maps near the centromere on linkage group III, and is unlinked to four previously described clock mutants clustered on linkage group VII R (Feldman and Hoyle 1973, 1976). frq-5 differs from the other clock mutants in at least two other respects: (1) it is recessive in heterokaryons, and (2) it grows at about 60% the rate of the parent band strain on both minimal and complete media. Double mutants between frq-5 and each of the other clock mutants show additivity of period length-two long period mutants produce a double mutant whose period length is longer than either of the two single mutants, while a long and a short period double mutant has an intermediate period length. Although slow growth and long periodicity of frq-5 have segregated together among more than 300 progeny, slow growth per se is not responsible for the long period, since all the double mutants have the slow growth characteristic of frq-5, but have period lengths both shorter and longer than wild type.
GENETIC ANALYSIS OF THE GENE FOR N-ACETYLGLUCOSAMINIDASE IN DICTYOSTELIUM DISCOIDEUM
Authors: Loomis William F
Published: April 2021

Three independent mutations affecting N-acetylglucosaminidase in Dictyostelium discoideum were mapped by the parasexual system and found to lie on linkage group IV. These mutations as well as two others were found to be recessive and noncomplementing in heterozygous diploids. Thus they all appear to affect the nagA locus. Since two of the mutations give rise to thermolabile enzyme, this defines the structural gene for N-acetylglucosaminidase.

The enzyme is a homodimer of a 68,000 dalton subunit and thus would be expected to be determined by a single locus. The expression of this gene is regulated by the stages of development; however, it should be mentioned that none of the mutations fell in a separate locus that might determine a specific positive regulatory protein.
CHARACTERIZATION OF TEMPERATURE-SENSITIVE, FERTILIZATION-DEFECTIVE MUTANTS OF THE NEMATODE CAENORHABDITIS ELEGANS
Authors: Ward Samuel , Miwa Johji
Published: April 2021

The isolation and characterization of three Caenorhabditis elegans temperature-sensitive mutants that are defective at fertilization are described. All three are alleles of the gene fer-1. At the restrictive temperature of 25°, mutant hermaphrodites make sperm and oocytes in normal numbers. No oocytes are fertilized, although they pass through the spermatheca and uterus normally. The oocytes can be fertilized by sperm transferred by wild-type males, indicating that the mutant defect is in the sperm. The temperature-sensitive period for the mutants coincides with spermatogenesis. Sperm made by mutants at 25° cannot be distinguished from wild-type sperm by light microscopy. The sperm do contact oocytes in mutant hermaphrodites, but do not fertilize. Mutant sperm appear to be nonmotile. Mutant males are also sterile when grown at 25°. They transfer normal numbers of sperm to hermaphrodites at mating, but these sperm fail to migrate to the spermatheca and are infertile. The phenotype of these mutants is consistent with a primary defect in sperm motility, but the cause of this defect is not known.
SELECTION DIFFERENTIALS AND SELECTION COEFFICIENTS
Authors: Milkman Roger
Published: April 2021

Proof is offered that s ≃ ig for all forms of selection where fitness is a nondecreasing function of a normally distributed phenotype (called fitness potential); s is selection coefficient, i is standard selection differential, and g is standard differential effect of a locus genotype.

Evidence is presented that the cost of selection does not limit genic polymorphism; that truncation selection is not necessary for high cost-efficiency; and that opposing directions of selection in a heterogeneous environment do not reduce cost-efficiency critically.
THE HOMOZYGOSITY TEST OF NEUTRALITY
Authors: Watterson G A
Published: April 2021

An earlier paper showed that the homozygosity (of a population or sample) was a good statistic for testing departures from selective neutrality in the direction of heterozygote advantage or disadvantage. It is here shown that homozygosity is also influenced by the presence of deleterious alleles and by other departures from neutrality, but at a lower order of magnitude of effect if the selection coefficients are of the same small order of magnitude. Tables are provided for the significance points and moments of the homozygosity, under the null hypothesis of neutrality.
THE RELATION OF EXCHANGE TO NONDISJUNCTION IN HETEROLOGOUS CHROMOSOME PAIRS IN THE DROSOPHILA FEMALE
Authors: Novitski E
Published: April 2021

An analysis of the relationships in Drosophila melanogaster between one set of homologues (third chromosome) undergoing crossing over and a second, independent set (X chromosome) undergoing nondisjunction shows that the nondisjunctional set almost invariably segregates from one of the members of the crossover set and not the other. The results seem contradictory to the expectations based on the "distributive pairing hypothesis" according to which nondisjunctional (i.e., noncrossover) elements form a "distributive pool" whose members behave independently of those which have been involved in exchange.
TESTING HYPOTHESES ABOUT LINKAGE DISEQUILIBRIUM WITH MULTIPLE ALLELES
Authors: Weir B S , Cockerham C Clark
Published: April 2021

For loci with multiple alleles, hypotheses about linkage disequilibrium may be tested on the complete set of gametic data, or on various collapsed sets of data. Collapsing data into a few alleles at each locus can change the power of the tests, as implied in a recent paper by Zouros, Golding and Mackay (1977). We show that the nature of such changes can be found from properties of the noncentral chi-square distribution, and that the magnitude and direction of these changes depend on the levels of linkage disequilibria, allelic frequencies and degrees of freedom.
NUCLEAR MUTATION INCREASES STREPTOMYCIN AND SPECTINOMYCIN SENSITIVITY IN CHLAMYDOMONAS
Authors: Lee Robert W , Sapp Jan A
Published: April 2021

A spontaneously arising nuclear mutation, ss-1, has been identified in Chlamydomonas reinhardtii that decreases both streptomycin and spectinomycin resistance levels about 10-fold after its introduction into all wild-type, streptomycin-resistant and spectinomycin-resistant strains examined. The mutations for resistance map to nuclear and uniparentally inherited (chloroplast) loci. In contrast, no modification of erythromycin resistance was detected after introducing ss-1 into wild-type strains or into strains carrying nuclear or uniparentally inherited erythromycin-resistance mutations. We suggest that ss-1 affects the small subunit of the chloroplast ribosome because others have shown that streptomycin and spectinomycin resistance in C. reinhardtii are associated with this subunit, whereas erythromycin resistance is associated with the large subunit. ss-1 shows no linkage with the nuclear locus for streptomycin resistance.
THE EFFECT OF INTRAGENIC RECOMBINATION ON THE NUMBER OF ALLELES IN A FINITE POPULATION
Authors: Strobeck Curtis , Morgan Kenneth
Published: April 2021

A two-site infinite allele model is constructed to study the effect of intragenic recombination on the number of neutral alleles and the distribution of their frequencies in a finite population. The results of theory and Monte Carlo simulation of the two-site model demonstrate that intragenic recombination significantly increases the mean and variance of the number of alleles when the rates of mutation and recombination are as large as the reciprocal of the population size. Data from natural populations indicate that this may be a significant process in generating variation and determining its distribution.
GENETIC ANALYSIS OF TWO ALLELIC TEMPERATURE-SENSITIVE MUTANTS OF DROSOPHILA MELANOGASTER BOTH OF WHICH ARE ZYGOTIC AND MATERNAL-EFFECT LETHALS
Authors: Shearn Allen , Hersperger Grafton , Hersperger Evelyn
Published: April 2021

After fertilization, the development of a zygote depends upon both gene products synthesized by its maternal parent and gene products synthesized by the zygote itself. To analyze genetically the relative contributions of these two sources of gene products, several laboratories have been isolating two classes of mutants of Drosophila melanogaster: maternal-effect lethals and zygotic lethals. This report concerns the analysis of two temperature-sensitive mutants, OX736hs and PC025hs, which were isolated as alleles of a small-disc mutant, l(3)1902. These alleles are not only zygotic lethals, but also maternal-effect lethals. They have temperature-sensitive periods during larval life and during oogenesis. Mutant larvae exposed continuously to restrictive temperature have small discs. One- or two-day exposures to the restrictive temperature administered during the third larval instar lead to a homeotic transformation of the midlegs and hindlegs to the pattern characteristic of the forelegs. Mutant females exposed to the restrictive temperature during oogenesis produce eggs that can develop until gastrulation, but do not hatch. —The existence of these mutants, and one that was recently described by another group, implies that there may be a class of genes, heretofore unrecognized, whose products are synthesized during oogenesis, are essential for embryogenesis and are also synthesized during larval stages within imaginal disc cells.
GENETIC VARIATION IN A HETEROGENEOUS ENVIRONMENT. V. SPATIAL HETEROGENEITY IN FINITE POPULATIONS
Authors: Hedrick Philip W
Published: April 2021

The spatial model of Levene (1953) was examined in a finite population and compared to a temporal model. The spatial model was much more effective in retaining genetic variation in a finite population. Furthermore, the haploid spatial model was more effective in retaining genetic variation than the analogous diploid absolute dominance model. This is the opposite from that found for the temporal model, where the diploid model was more effective than the haploid. Here is an example where diploidy (sexual reproduction) may be disadvantageous. A model that permitted both spatial and temporal variation to act in concert gave retention of genetic variation in situations where either spatial or temporal variation, separately, did not. The relationship between the amount of heterozygosity and the retardation factor was discussed. An example of how spatial or temporal variation affects the proportion of populations fixed after a certain number of generations was given. It seems that these models have biological analogues, several examples of which are mentioned.
ESTIMATION OF AVERAGE HETEROZYGOSITY AND GENETIC DISTANCE FROM A SMALL NUMBER OF INDIVIDUALS
Authors: Nei Masatoshi
Published: April 2021

The magnitudes of the systematic biases involved in sample heterozygosity and sample genetic distances are evaluated, and formulae for obtaining unbiased estimates of average heterozygosity and genetic distance are developed. It is also shown that the number of individuals to be used for estimating average heterozygosity can be very small if a large number of loci are studied and the average heterozygosity is low. The number of individuals to be used for estimating genetic distance can also be very small if the genetic distance is large and the average heterozygosity of the two species compared is low.
TETRAPLOID STRAINS OF SACCHAROMYCES CEREVISIAE THAT ARE TRISOMIC FOR CHROMOSOME III
Authors: Riley Michael I , Manney T R
Published: April 2021

Meiotic segregation of several genes has been studied in tetraploid strains that are trisomic for chromosome III. The segregation data were compared to a computer simulation that assumes trivalent pairing of homologues involved in exchanges, followed by nonpreferential segregation. Trivalent pairing was characterized by higher frequencies of exchange as compared to bivalent pairing, and by the presence of spores resulting from at least double crossovers involving all three homologues. Trivalent segregation was characterized by a unique recombinant class. The strong interference normally exhibited in diploid meiotic recombination was not evident from the frequency of double crossovers in these strains.
ALLELE-SPECIFIC MODIFICATION OF THE EXPRESSION OF THE Adh2 GENE IN MAIZE BY ETHYLENE
Authors: Schwartz Drew
Published: April 2021

The effect of ethylene on the induction of alcohol dehydrogenase-2 in seedling roots of maize is reported. Allele-specific differences are observed in the response to the hormone. Hormonal treatment acts to eliminate the difference in gene expression that is characteristic of the alleles in untreated roots.
PROPERTIES OF THE TRANSLOCATABLE TETRACYCLINE-RESISTANCE ELEMENT Tn10 IN ESCHERICHIA COLI AND BACTERIOPHAGE LAMBDA
Authors: Kleckner Nancy , Barker David F , Ross Donald G , Botstein David
Published: April 2021

A number of independent insertions into bacteriophage λ of the translocatable tetracycline-resistance element Tn10 have been isolated and characterized.—The physical positions and relative orientations of several such insertions were determined. Two independent insertions appear to lie in the same orientation at or very near the same site in the cI gene, and two more lie in opposite orientations at or near the same position in or near the rex gene.—Insertions in or near genes cI, rex, and cIII have been characterized genetically for their effects on expression of nearby genes. Tn10 appears to exert a polar effect on expression of distal genes when it is inserted within an operon, even when expression of that operon is under the influence of λ N-function. In addition, Tn10 insertions in rex appear to influence in some way expression of an "upstream" gene, cI.—Lambda derivatives carrying Tn10 give rise to spontaneously occurring, tetracycline-sensitive deletions at high frequencies. It is likely that formation of these deletions is promoted in some way by the Tn10 element.—Lambda::Tn10 phages carrying a Tn10 element that has undergone several successive cycles of translocation since its first isolation and characterization have been analyzed. The results confirm that Tn10 often retains its physical and functional integrity during many cycles of translocation.—Lambda derivatives carrying Tn10 have been used to generate insertions of Tn10 in the chromosome of Escherichia coli. This process is independent of recA function, and seems to be quite analogous to the translocation of Tn10 in Salmonella typhimurium as studied previously.
REVERSION AT THE HIS1 LOCUS OF YEAST
Authors: Fogel Seymour , Lax Carol , Hurst Donald D
Published: April 2021

The his1 gene (chromosome V) of Saccharomyces cerevisiae specifies phosphoribosyl transferase (E.C.2.4.2.17), the first enzyme of histidine biosynthesis. This hexameric enzyme has both catalytic and regulatory functions.—The spontaneous reversion rates of seven his1 mutations were studied. The reversion rates of the alleles at the proximal end of the locus (relative to the centromere) were about 50-fold higher than distal alleles.—Spontaneous reversion to prototrophy was studied in diploids homoallelic for each of the seven his1 mutations. Based on tetrad analysis, the prototrophy revertants could be assigned to three classes: (1) revertant tetrads that carried a prototrophic allele indistinguishable from wild type; (2) revertant tetrads that carried a prototrophic allele characterized by histidine excretion and feedback resistance; and (3) revertant tetrads that did not contain a prototrophic spore, but rather a newly derived allele that complemented the original allele intragenically. Four of the seven his1 mutations produced the excretor revertant class, and two mutations produced the complementer revertant class. The significance of these findings to our understanding of gene organization and the catalytic and regulatory functions of gene products are discussed.
REGIONAL CONTROL OF NONDISJUNCTION OF THE B CHROMOSOME IN MAIZE
Authors: Lin Bor-Yaw
Published: April 2021

Control of nondisjunction in the maize B chromosome was studied using a set of B-10 translocations. The study focused on the possible effect of the proximal region of the B long arm. The experimental procedure utilized a combination of a 10B chromosome from one translocation with a B10 from another translocation. The breakpoints of the two translocations were so located that combination of the two elements created a deletion in the proximal region of the B chromosome, but no deletion in chromosome 10. Two different types of deletions were established; one involved a portion of the euchromatic region and the other the entire heterochromatic portion comprising the distal half of the B long arm, except for the small euchromatic tip. Deletion of the heterochromatic portion did not exert any effect on nondisjunction. Deletions of different portions of the euchromatic region produce different responses. Some deletions resulted in typical B nondisjunctional activity; others resulted in the disappearance of this activity. It is concluded that a region within the euchromatic portion of the chromosome is critical for the nondisjunction of B chromosomes. Among 22 translocations with breakpoints in the euchromatic regions, three were proximal to the critical region, 16 were distal and the position of three others was not determined.
ISOLATION, GENETIC MAPPING AND SOME CHARACTERIZATION OF A MUTATION IN ESCHERICHIA COLI THAT AFFECTS THE PROCESSING OF RIBONUCLEIC ACID
Authors: Apirion David
Published: April 2021

Temperature-sensitive mutants were isolated from an rnc (RNase III-) strain of Escherichia coli, and their rRNA metabolism was analyzed on 3% polyacrylamide gels. One of these mutants was unable to produce 23S and 5S rRNAs at the nonpermissive temperature. When an rnc  + allele was introduced to this strain, it remained temperature sensitive. At the nonpermissive temperature, this strain could then produce 23S rRNA but was unable to make normal levels of 5S rRNA. In matings and transduction experiments, the defect in rRNA metabolism and temperature sensitivity behaved as a syndrome caused by a single point mutation, which was mapped at min 23.5 on the E. coli chromosome. This mutation probably affects an enzyme, ribonuclease E (RNase E), which introduces a cut in the nascent rRNA transcript between the 23S and the 5S rRNA cistrons. The mutation rne is recessive with respect to temperature sensitivity and the pattern of rRNA. Revertants able to grow at 43° and with normal metabolism of rRNA were isolated; genetic analysis showed that they do not contain the original rne mutation, suggesting that they were true revertants. By combining the rne mutation with an rnc mutation, double rnc rne strains were synthesized, which behaved very similarly to the original rnc strain from which the rne mutation was isolated. Such strains have RNA metabolism that is similar to that of rnc strains at permissive temperatures, but at the nonpermissive temperature they fail to synthesize p23, m23 and 5S rRNAs. Thus, the experiments reported here, together with previous studies, suggest the existence of a new processing ribonuclease activity in Escherichia coli, which is called ribonuclease E.
AN ALTERED STATE OF A SPECIFIC EN REGULATORY ELEMENT INDUCED IN A MAIZE TILLER
Authors: Fowler Robert G , Peterson Peter A
Published: April 2021

A search for mitotic recombination was carried out using mutant subclones of cultured Chinese hamster ovary cells. Recombination events were sought between the linked loci specifying the enzymes hypoxanthine phosphoribosyl transferase and glucose-6-phosphate dehydrogenase. It was shown by fluctuation analysis that markers at these two loci co-segregate from doubly heterozygous pseudotetraploid hybrid cells more than 90% of the time. The minority class of segregants, which had lost one marker without losing the other, were genetically analyzed to distinguish between the possibilities of mitotic recombination and deletion of chromosomal material. Nine clones in which a linkage disruption had occured were studied, using further cell hybridization and segregation. In three cases, a recessive lethal loss of genetic information was indicated, suggesting the deletion mechanism. In six cases, it was demonstrated that no new linkage relationships had been established concomitant with linkage disruption. Thus, in all nine clones, the evidence indicated that mitotic recombination was not involved in the events that disrupted linkage between these two loci. If mitotic recombination takes place at all in this system, the rate must be less than about 10-6 per cell per generation.
CHROMOSOMAL POLYMORPHISM AND FEMALE RECEPTIVITY IN A NATURAL POPULATION OF DROSOPHILA PERSIMILIS
Authors: Yu Hui Fang , Spiess Eliot B
Published: April 2021

In a natural population of Drosophila persimilis (McDonald Ranch, Napa Valley, California), KL and MD chromosomal arrangement frequencies undergo a seasonal cycle, with MD common in spring and KL common in summer. Samples collected from spring and summer provided isofemale strains established as homozygous KL and MD pairs (kinlines) with each pair derived from a single heterokaryotype wild progenitor. Haploid doses of chromosomes 2 and 4 were controlled by marker-cross derivations of kinlines. Percentage onset of female receptivity was measured from cultures at 25° and at 15°, using ten kinlines from spring and nine from summer collections, with fast-mating hybrid males as standard testers. Mating tests consisted of 20 tester males x 20 females of specific age, karyotype, and kinline observed for 30 min. At 25° females became receptive at 48 hr after eclosion: parental line (KLi/KLi and MDi/MDi) females were approximately equal at 55 to 60% receptive, while among hybrids, MDi/MDj homokaryotype females were significantly less receptive (68%) than all other outbred combinations (73 to 77%). At 15°, females became receptive at four days of age, with increases on the fifth and sixth days: both parental line and outbred MD/MD females were significantly more receptive (28% at four days and 62% at six days) than all heterokaryotype females (20 to 26% at four days and 55 to 59% at six days), which in turn were more receptive than KL/KL parental and outbred females (10% at four days and 40% at six days). Heterosis was expressed at 25°, but not at 15°. Thus, dominance for female receptivity was temperature dependent. Females polymorphic for these third chromosomal karyotypes possess differential temperature sensitivity for onset of receptivity and are likely to contribute in a significant way to the observed seasonal frequency cycle in the natural population from which they have been derived.
SIMULTANEOUS STABILITY OF D=0 AND D≠0 FOR MULTIPLICATIVE VIABILITIES AT TWO LOCI
Authors: Karlin Samuel , Feldman Marcus W
Published: April 2021

The two-locus, two-allele multiplicative viability model is investigated. It is shown that the well-known region of recombination values for which D = 0 is locally stable does not preclude the local stability of an equilibrium with D ≠ 0. This is shown numerically and is true for every case investigated in which both loci are overdominant and the viabilities not symmetric.
ANALYSIS OF THE ALBINO-LOCUS REGION OF THE MOUSE. I. ORIGIN AND VIABILITY
Authors: Russell Liane B , Russell W L , Kelly E M
Published: April 2021

Numerous specific-locus experiments designed to test the mutagenic effect of external radiation have yielded, in over 3,600,000 animals observed, altogether 119 presumed mutations involving the c locus. Of these, 55 were viable and albino (cav)13, w ere viable and of various intermediate pigment types (cxv), four were subvital (cas and cxs)), seven were neonatally lethal albinos (cal), 28 prenatally lethal albinos (cal); 12 died untested. All of the prenatally lethal and at least one of the neonatally lethal c-locus mutations (caz classes) are probably deficiencies that we have analyzed extensively in other experiments. Since absence of the locus mimics albino in phenotype, the intermediates (cxv and cxs groups) probably resulted from intragenic changes. The class of viable albino mutants (cav) might include, in addition to intragenic changes, some extremely small deficiencies.—The effects on viability of c-locus lethals (cal's) in heterozygous condition are not drastic enough to be perceived in stocks of mixed genetic background except in the case of the two longest known deficiencies and a few others.—Analysis 3f the relation between radiation treatment and type of c-locus mutants obtained shows that the relative frequency of viable mutations, for each germ-cell type, is greater for low-LET than for neutron irradiation; however, the difference for any individual cell type is not significant. The majority (66.7%) of mutations derived from X-or γ-ray irradiated spermatogonia are viable, and the proportion of "intermediates" among these viables is similar to that among presumed spontaneous c-locus mutations. No significant dose-rate effect on the proportion of lethals could be demonstrated within the set of mutants induced by low-LET irradiation of spermatogonia. Although sets from other germ-cell stages are too small for statistical tests, the results for oocytes are similar, as far as they go. Furthermore, most of the c-locus mutations induced in spermatogonia, even by highdose-rate X-ray or γ irradiation, are of a type most likely to result from single-track events (62% cxv, cxs, and cav; plus 16% presumed deficiencies not involving the closest marker). These results support the view that most of the reduction in mutation frequency at low dose rates is not due to a change in relative proportion of two-track and one-track ionizing events.
ANALYSIS OF THE ALBINO-LOCUS REGION OF THE MOUSE. II. MOSAIC MUTANTS
Authors: Russell Liane B
Published: April 2021

Among 119 mutations involving the c locus that were recovered in the course of mouse specific-locus experiments with external radiations, 16 were found in mosaic, or fractional, mutants. The number of additional c-locus fractionals that could have occurred in these experiments and, for a variety of reasons, might not have been clearly identified, probably does not exceed the present number.——There was no evidence for radiation induction of the fractionals, and even those cccurring in the irradiated groups may thus be assumed to be of spontaneous origin. Since only two mutations in the control groups were found in whole-body mutants, it appears that the bulk of spontaneous c-locus mu tations are fractionah——None of the mutations recovered in fractional mutants was homozygous lethal; 25% were viable intermediate alleles, and the remainder were albino-like mutants, all viable except for one subvital and one not tested.——Genetic tests of the fractionals indicated no major selection against the new mutations, either gametically or in the progeny.——For the group of fractionals as a whole, about one-half of the germinal tissue carried the mutation, indicating that the fractionals came from an overall blastomere population that was one-half mutant. Such a population could result from mutation in one strand of the gamete DNA, in a daughter chromosome derived from pronuclear DNA synthesis of the zygote, or in one of the first two blastomeres prior to replication. Since the mouse embryo does not stem from all of the cleavage products of the zygote, the frequency of fractionals observed underestimates the frequency of mutational events that result in two types of blastomeres.
THE CAN1 LOCUS OF SACCHAROMYCES CEREVISIAE: FINE-STRUCTURE ANALYSIS AND FORWARD MUTATION RATES
Authors: Whelan William L , Gocke Elmar , Manney Thomas R
Published: April 2021

A system of strains and growth media was developed to allow efficient detection of forward mutation, reversion, complementation, and suppression at the canavanine-resistance (CAN1) locus of Saccharomyces cerevisiae. Genetic finestructure analysis revealed that the map length is at least 40, and possibly as much as 60 X-ray map units; this is the longest gene map yet reported in S. cerevisiae. Allelic complementation was not observed, despite testing of a large number of allele pairs, and alleles suppressible by the ochre suppressor SUP11 were absent from a sample of 48 spontaneous mutants and occurred infrequently (7%) among a sample of ultraviolet-induced mutants. Infrequent mutant types included canavanine-resistant mutants capable of arginine uptake and alleles thought to represent deletions or inversions. In contrast to previous raports in the literature, the spontaneous forward mutation rate at CAN1 did not increase during meiosis.
EXPRESSION OF RADIATION-INDUCED MUTATIONS AT THE ARGININE PERMEASE (CAN1) LOCUS IN SACCHAROMYCES CEREVISIAE
Authors: Gocke Elmar , Manney Thomas R
Published: April 2021

In the yeast Saccharomyces cerevisiae, the expression of resistance to the L-arginine analog, L-canavanine, after mutagenesis, is strongly dependent on the metabolic state of the cell. The frequency of mutations recovered after exposure to ultraviolet light or X rays was measured under a variety of culture conditions. The results indicate that the frequency of mutants recovered is determined by the following three factors: (1) The potential mutants still possess enough permease activity to take up some of the cell poison, and some are therefore killed before they can express the mutant genotype. The sensitivity is strongly influenced by the endogenous free arginine, which is in turn influenced by the growth medium. (2) The rapid decay of the permease molecules and the inability of the potential mutants to resynthesize this protein results in a rapidly increasing chance of expression when selection is delayed. (3) During the time when the permease activity is decaying, repair of the mutagen-induced damage appears to occur.
EVIDENCE OF THE INSENSITIVITY OF THE α-inc ALLELE TO THE FUNCTION OF THE HOMOTHALLIC GENES IN SACCHAROMYCES YEASTS
Authors: Takano Isamu , Arima Kenji
Published: April 2021

The possible function of the α-inc allele (an α mating-type allele that is insensitive to the function of the homothallic gene system) was investigated by means of protoplast fusion. The fusion of protoplasts prepared from haploid strains of α-inc  HO HMα HMa and α ho hmα HMa gave rise mainly to nonmating clones (58 of 64 isolates) and a few clones (six of 64 isolates) showing a mating type. Thirty of the 56 nonmating clones showed the diploid cell size and 28 clones had a larger cell size. Tetrad analysis of the nonmating clones with diploid cell size indicated that they were a/α-inc diploid; the normal α allele in α/α-inc cells was preferentially switched to an a allele. This observation further indicated that the HO/ho HMα/hmα HMa/HMa genotype is effective for the conversion of the α to a and that the inconvertibility of the a-inc allele is due to the insensitivity of the mating-type allele to the functional combination of the homothallic genes. It was suspected that fusion products larger than diploid cells might have been caused by multiple fusion of protoplasts.
NON-MENDELIAN FEMALE STERILITY IN DROSOPHILA MELANOGASTER: CHARACTERIZATION OF THE NONINDUCER CHROMOSOMES OF INDUCER STRAINS
Authors: Picard Georges , Pelisson Alain
Published: April 2021

In relation to non-Mendelian female sterility, Drosophila melanogaster strains can be divided into two main classes, inducer and reactive. The genetic element responsible for the inducer condition (I factor) is chromosomal and may be linked to any inducer-strain chromosome. Each chromosome carrying the I factor (i  + chromosome) can, when introduced by the paternal gamete into a reactive oocyte, give rise to females (denoted SF) showing more-or-less reduced fertility. As long as i  + chromosomes are transmitted through heterozygous males with reactive originating chromosomes (r chromosomes), I factor follows Mendelian segregation patterns. In contrast, in heterozygous i+/r females, a varying proportion of r chromosomes may irreversibly acquire I factor, independently of classical genetic recombination, by a process called chromosomal contamination. The contaminated reactive chromosomes behave as i  + chromosomes.—In the present paper, evidence is given that the Luminy inducer strain displays a polymorphism for two kinds of second chromosomes. Some of them are i  +, while others, denoted io, are unable t3 induce any SF sterility when introduced by paternal gametes into reactive oocytes. They are also unable to induce contamination of r chromosomes, but, like r chromosomes, they may be contaminated by i+ chromosomes in SF or RSF females. The study of the segregation of i  + and io second chromosomes in the progeny of heterozygous Luminy males and females leads to the conclusion that on chromosome 2 of the Luminy stock the I factor is at a single locus. —XI second and third io chromosomes have been found in several inducer strains. Since these chromosomes can be maintained with i  + chromosomes in inducer strains in spite of their ability to be contaminated in RSF females, it can be concluded that chromosomal contamination does not take place in females of inducer strains. This implies that contamination occurs only in cells having cytoplasm in a reactive state.
SELECTION ON RECOMBINATION IN A MULTI-LOCUS SYSTEM
Authors: Charlesworth D , Charlesworth B
Published: April 2021

The model of WILLS and MILLER (1976) for selection on recombination rates in finite populations was studied by means of a computer model involving 80 selected loci and a linked or unlinked modifier gene affecting the map length occupied by the selected loci. The selected loci were subject to heterozygote advantage, and multiplicative fitness interactions between loci were assumed. In all cases studied, selection for reduction in recombination outweighed any selection for increased recombination that may have been present.
A MATHEMATICALLY TRACTABLE FAMILY OF GENETIC MAPPING FUNCTIONS WITH DIFFERENT AMOUNTS OF INTERFERENCE
Authors: Felsenstein Joseph
Published: April 2021

By extension of the argument of KOSAMBI (1944), a family of mapping functions can be derived, which has a parameter regulating the intensity of interference. Different values of this parameter yield the HALDANE (1919) and KOSAMBI mapping functions as special cases. The parameter is the coincidence coefficient for nearby small intervals. The family includes mapping functions for negative interference. A simple rule for combining recombination fractions in adjacent intervals is also obtained.
CENTRAL EQUILIBRIA IN MULTILOCUS SYSTEMS. II. BISEXUAL GENERALIZED NONEPISTATIC SELECTION MODELS
Authors: Karlin Samuel , Liberman Uri
Published: April 2021

This paper is a continuation of the paper "Central Equilibria in Multilocus Systems I," concentrating on existence and stability properties accruing to central H-W type equilibria in multilocus bisexual systems acted on by generalized nonepistatic selection forces coupled to recombination events. The stability conditions are discussed and interpreted in three perspectives, and the influence of sexual differences in linkage relationships together with sex-dependent selection is appraised. In this case we deduce that the stability conditions of the H-W polymorphism in the bisexual model coincide exactly with the conditions for the corresponding monoecious model, provided that the recombination distribution imposed is that of the arithmetic mean of the male and female recombination distributions. A second concern has the same recombination distribution for both sexes, but contrasting selection regimes between sexes. It is then established that, with respect to discerning the relevance of the H-W equilibrium, there is an equivalent monoecious selection regime which is an appropriate "weighted combination" of the male and female selection forms. Finally, in the case where the selection and recombination structures are both sex dependent, a hierarchy of comparisons is elaborated, seeking to unravel the nature of selection-recombination interaction for monoecious versus diocecious systems.
HISTIDINE MUTANTS REQUIRING ADENINE: SELECTION OF MUTANTS WITH REDUCED hisG EXPRESSION IN SALMONELLA TYPHIMURIUM
Authors: Johnston H Mark , Roth John R
Published: April 2021

A method is described for the selection of Salmonella typhimurium mutants with reduced levels of hisG enzyme activity. This method is based on the fact that the hisG enzyme catalyzes the consumption of ATP in the first step of histidine biosynthesis. Normally, this reaction is closely regulated, both by feedback inhibition and by repression of the operon. However, conditions can be set up that result in the uncontrolled use of adenine in histidine biosynthesis. Cells grown under these conditions become phenotypic adenine auxotrophs. Some revertant clones that no longer require adenine contain mutations in hisG, hisE, or the his-control region. The hisG mutations are of all types (non-sense, frameshift, missense, deletion and leaky types), and they map throughout the hisG gene.
THE GENETICS OF A SMALL AUTOSOMAL REGION OF DROSOPHILA MELANOGASTER CONTAINING THE STRUCTURAL GENE FOR ALCOHOL DEHYDROGENASE. II. LETHAL MUTATIONS IN THE REGION
Authors: Woodruff R C , Ashburner M
Published: April 2021

Forty-seven lethal mutations and alleles of nine visible loci (including alcohol dehydrogenase) have been mapped by both deficiency mapping and, in most cases, by recombination mapping to a small region (34D-35C) of chromosome arm 2L of Drosophila melanogaster. The lethals fall into approximately 21 complementation groups, and we estimate that the total number of lethal plus visible complementation groups within the 34-band deficiency, Df(2L)64j, is approximately 34, a remarkable numerical coincidence. The possible genetic significance of this coincidence is discussed. Lethals mapping close to the structural gene for alcohol dehydrogenase, both distally and proximally, have been identified and will be used for the construction of selective crosses for the study of exchange within this locus. Despite many abnormal cytological features (e.g., ectopic pairing, weak points) region 35 of chromosome arm 2L does not display any unusual genetic features; indeed, in terms of the aniount of recombination per band and the average map distance between adjacent loci, this region is similar to that between zeste and white on the X chromosome.