bluuebunny/crossref_metadata_2025 huggingface dataset:
INTERNUCLEAR GENETIC TRANSFER IN DIKARYONS OF SCHIZOPHYLLUM COMMUNE. II. DIRECT RECOVERY AND ANALYSIS OF RECOMBINANT NUCLEI
Authors: Leonard Thomas J , Gaber Richard F , Dick Stanley
Published: April 2021

The recessive gene, mound (mnd), allows the appearance of globose masses of compacted hyphae. Dikaryons of Schizophyllum commune that are heteroallelic for mnd [(mosaic dikaryons: (mnd+ mnd  +)] have been successfully dedikaryotized in cholate-containing medium in order to recover the component nuclear types directly. The relative proportion of the two recovered monokaryotic types shows in all cases a marked deviation from 1:1. Hyphae from nonmound mycelial regions yield monokaryotic types identical to those originally used to form the dikaryons. In hyphae from mound-forming regions, however, homoallelism of the mnd allele has been demonstrated; the nuclear type that formerly contained the mnd  + allele acquired a mnd allele.—The process of internuclear transfer or recombination is unaccompanied by the simultaneous alteration of any additional genetic markers carried by the recipient nucleus. The newly acquired mnd allele segregates in Mendelian fashion in subsequent outcrosses and appears to be chromosomally located. A novel process of somatic recombination, with several features distinct from classical parasexual mitotic recombination, appears to be in operation.
STUDIES OF LINKAGE IN POPULATIONS. IX. THE EFFECT OF ALTITUDE ON X-CHROMOSOMAL ARRANGEMENT COMBINATIONS IN DROSOPHILA ROBUSTA
Authors: Levitan Max
Published: April 2021

Data are presented concerning the gene arrangements in both arms of the X-chromosome of Drosophila robusta in eight altitudinal transects. The major change appears to be the increase of gene arrangement XL-1 (and decrease in XL, sometimes also XL-2) with increasing altitude. In each transect only one combination of XL-1 with a right arm arrangement seems primarily responsible for the increases with altitudinal change, and only one combination of XL for the decreases. In four of the transects the increasing combination appears to be XL-1.XR, XL-1.XR-2 in the other four. A substantial decrease with elevation in XL-2.XR-2 occurs only in the four areas where XL-1.XR exhibits the major increase. These results indicate that interactions between arrangements play a significant role in the adaptation of this species to altitude. The interactions appear related to the X-chromosomal linkage equilibriums in these regions. The data also suggest that the species employs its inversions in different methods of adaptation in the Appalachian Mountains from those it uses in other parts of the range.
MAINTENANCE OF GENETIC VARIABILITY UNDER THE JOINT EFFECT OF MUTATION, SELECTION AND RANDOM DRIFT
Authors: Li Wen-Hsiung
Published: April 2021

Formulae are developed for the distribution of allele frequencies (the frequency spectrum), the mean number of alleles in a sample, and the mean and variance of heterozygosity under mutation pressure and under either genic or recessive selection. Numerical computations are carried out by using these formulae and Watterson's (1977) formula for the distribution of allele frequencies under overdominant selection. The following properties are observed: (1) The effect of selection on the distribution of allele frequencies is slight when 4Ns ≤ 4, but becomes strong when 4Ns becomes larger than 10, where N denotes the effective size and s the selective difference between alleles. Genic selection and recessive selection tend to force the distribution to be U-shaped, whereas overdominant selection has the opposite tendency. (2) The mean total number of alleles in a sample is much more strongly affected by selection than the mean number of rare alleles in a sample. (3) Even slight heterozygote advantage, as small as 10-5, increases considerably the mean heterozygosity of a population, as compared to the case of neutral mutations. On the other hand, even slight genic or recessive selection causes a great reduction in heterozygosity when population size is large. (4) As a test statistic, the variance of heterozygosity can be used to detect the presence of selection, though it is not efficient when the selection intensity is very weak, say when 4Ns is around 4 or less. A model, which is somewhat similar to Ohta's (1976) model of slightly deleterious mutations, has been proposed to explain the following general patterns of genic variation: (i) There seems to be an upper limit for the observed average heterozygosities. (ii) The distribution of allele frequencies is U-shaped for every species surveyed. (iii) Most of the species surveyed tend to have an excess of rare alleles as compared with that expected under the neutral mutation hypothesis.
ORGANIZATION OF THE ROSY LOCUS IN DROSOPHILA MELANOGASTER: FURTHER EVIDENCE IN SUPPORT OF A CIS-ACTING CONTROL ELEMENT ADJACENT TO THE XANTHINE DEHYDROGENASE STRUCTURAL ELEMENT
Authors: McCarron M , O'Donnell J , Chovnick A , Bhullar B S , Hewitt J , Candido E P M
Published: April 2021

The present report summarizes our recent progress in the genetic dissection of an elementary genetic unit in a higher organism, the rosy locus (ry: 3-52.0) in Drosophila melanogaster. Pursuing the hypothesis that the rosy locus includes a noncoding control region, as well as a structural element coding for the xanthine dehydrogenase (XDH) peptide, experiments are described that characterize and map a rosy locus variant associated with much lower than normal levels of XDH activity. Experiments are described that fail to relate this phenotype to alteration in the structure of the XDH peptide, but clearly associate this character with variation in number of molecules of XDH per fly. Large-scale fine-structure recombination experiments locate the genetic basis for this variation in the number of molecules of XDH per fly to a site immediately to the left of the XDH structural element within a region previously designated as the XDH control element. Moreover, experiments clearly separate this "underproducer" variant site from a previously described "overproducer" site within the control region. Examination of enzyme activity in electrophoretic gels of appropriate heterozygous genotypes demonstrates the cis-acting nature of this variation in the number of molecules of XDH. A revision of the map of the rosy locus, structural and control elements is presented in light of the additional mapping data now available.
HETEROCHROMATIC EFFECTS ON THE BEHAVIOR OF REVERSED ACROCENTRIC COMPOUND-X CHROMOSOMES IN DROSOPHILA MELANOGASTER
Authors: Sandler L , O'Tousa Joseph
Published: April 2021

Previous studies of reversed acrocentric compound-X chromosomes suggested peculiar influences of heterochromatin on both the synthesis and meiotic behavior of such compounds. It seemed, with respect to synthesis, that the long arm of the Y chromosome on an X.YL chromosome was necessary in order for the heterochromatic exchange giving rise to reversed acrocentrics to occur, even though YL itself did not participate in the compound-generating event. With respect to behavior, the resulting compounds appeared, presumably as a consequence of their singular generation, to contain an interstitial heterochromatic region that caused the distribution of exchanges between the elements of the compound to be abnormal (many zero and two-exchange tetrads with few, if any, single-exchange tetrads). Removing the interstitial heterochromatin (or, curiously, appending YL as a second arm of the compound) eliminated the recombinational anomalies and resulted in typical tetrad distributions.—We provide evidence that these peculiarities, while presumably real, were likely the consequence of a special X.YL chromosome that was used to synthesize the reversed acrocentrics examined in the early studies and are not general properties of either reversed acrocentric compounds or of interstitial heterochromatin. However, we show that specific heterochromatic regions do, in fact, profoundly influence the behavior of (apparently all) reversed acrocentric compound-X chromosomes. In particular, we demonstrate that specific portions of the Y chromosome and of the basal X-chromosome heterochromatin, when present as homologs for reversed acrocentric compounds, markedly and coordinately increase bath the frequency of exchange between the elements of the compound and the fertility (egg production) of compound-bearing females. It is, we suppose, some aspect of this heterochromatic effect, produced by the% special X.YL chromosome, that caused the earlier-analyzed compounds to exhibit the observed anomalies.
SELECTION ON RECOMBINATION IN CLINES
Authors: Charlesworth D , Charlesworth B
Published: April 2021

Computer runs have been done to examine SLATKIN'S (1975) model for selection on recombination rates in linear sets of populations with environmental changes affecting two loci. In order to determine whether the suggested selection pressures on recombination do, in fact, exist, we follow the changes in frequency at a third locus that is polymorphic for alleles affecting the recombination rate between the two selected loci. With haploid or diploid selection models, there can be selection for increased recombination if the parameter values are chosen suitably, but changes in parameter values often lead to changes in the direction of selection, so that decreased recombination is favored, The selection for increased recombination is usually weak, while that for decreased recombination is frequently much stronger. Weaker selection on the selected loci often leads to increasing selection for decreased recombination.
GENETICS OF CATALASE IN DROSOPHILA MELANOGASTER: RATES OF SYNTHESIS AND DEGRADATION OF THE ENZYME IN FLIES ANEUPLOID AND EUPLOID FOR THE STRUCTURAL GENE
Authors: Lubinsky Sharon , Bewley Glenn C
Published: April 2021

A screen for allelic variants of the enzyme catalase indicated that the Cat+ locus is essentially monomorphic in D. melanogaster. Segmental aneuploidy was used to screen the genome for a dosage-sensitive region for catalase activity. One region, 75D-78A on the polytene chromosome map of 3L, exhibited a hyperploid/euploid ratio of enzyme activity of 1.5. Further dissection localized the region to 75D-76A. We suggest that this region contains the structural locus for catalase in D. melmogaster.

Simple methods have been developed using the specific inhibitor, 3-amino-1,2,4-triazole, for the direct analysis of rates of synthesis and degradation of the Cat+ gene product. Based on kinetic studies of catalase synthesis in flies aneuploid and euploid for region 75D-76B, we suggest that these techniques can be readily applied to an examination of mutants that control the expression of the structural gene for catalase in Drosophila.
QUANTITATIVE GENETIC ANALYSIS OF TEMPERATURE REGULATION IN MUS MUSCULUS. I. PARTITIONING OF VARIANCE
Authors: Lacy Robert C , Lynch Carol Becker
Published: April 2021

Heritabilities (from parent-offspring regression) and intraclass correlations of full sibs for a variety of traits were estimated from 225 litters of a heterogeneous stock (HS/Ibg) of laboratory mice. Initial variance partitioning suggested different adaptive functions for physiological, morphological and behavioral adjustments with respect to their thermoregulatory significance. Metabolic heat-production mechanisms appear to have reached their genetic limits, with little additive genetic variance remaining. This study provided no genetic evidence that body size has a close directional association with fitness in cold eiivironments, since heritability estimates for weight gain and adult weight were similar and high, whether or not the animals were exposed to cold. Behavioral heat conservation mechanisms also displayed considerable amounts of genetic variability. However, due tc strong evidence from numerous other studies that behavior serves an important adaptive role for temperature regulation in small mammals, we suggest that fluctuating selection pressures may have acted to maintain heritable variation in these traits.
CENTRAL EQUILIBRIA IN MULTILOCUS SYSTEMS. I. GENERALIZED NONEPISTATIC SELECTION REGIMES
Authors: Karlin Samuel , Liberman Uri
Published: April 2021

The generalized nonepistatic selection regime encompasses combinations of multiplicative and neutral viability effects distributed across a set of loci. These subsume, in particular, mixtures of the classical modes of multiplicative and additive fitness evaluations for multilocus traits. Exact analytic conditions for existence and stability of a multilocus Hardy-Weinberg (H-W) polymorphic equilibrium cmfiguration are ascertained. It is established that the central H-W polymorphism is stable only if the component loci are "overdominant" and sufficient recombination is in force. The H-W central equilibrium is never stable for tight linkage whenever some multiplicative selection effects are contributed by at least two of the loci involved. In the case of additive selection expression and individual overdominant loci, the H-W polymorphism is stable independently of the level of recombination. In the context of "natural" recombination schemes, "more recombination" enhances the stability 3f the H-W polymorphic equilibrium.
THE INTERCELLULAR DISTRIBUTION OF MUTATIONS INDUCED IN OOCYTES OF DROSOPHILA MELANOGASTER BY CHEMICAL AND PHYSICAL MUTAGENS
Authors: Traut H
Published: April 2021

When females of Drosophila melanogaster are treated with chemical or physical mutagens, not only in one but also in both of the two homologous X chromosomes of a given oocyte, a recessive sex-linked lethal mutation may be induced. A method is described that discriminates between such "single" and "double mutations." A theory is developed to show how a comparison between the expected and the observed frequency of double mutations yields an indication of the intercellular distribution (random or nonrandom) of recessive lethal mutations induced by mutagenic agents in oocytes and, consequently, of the distribution (homogeneous or nonhomogeneous) of those agents.—Three agents were tested: FUdR (12.5, 50.0 and 81.0,μg/ml), mitomycin C (130.0 μg/ml) and X rays (2000 R, 150 kV). After FUdR feeding, no increase in the mutation frequency usually observed in D. melanogaster without mutagenic treatment was obtained (u=0.13%, namely three single mutations among 2332 chromosomes tested). After mitomycin C feeding, 104. single and three double mutations were obtained. All of the 50 mutations observed after X irradiation were single mutations. The results obtained in the mitomycin C and radiation experiments favor the assumption of a random intercellular distribution of recessive lethal mutations induced by these two agents in oocytes of D. melanogaster. Reasons are discussed why for other types of mutagenic agents nonrandom distributions may be observed with our technique.
REPRODUCTIVE ISOLATION WITH LITTLE GENETIC DIVERGENCE IN SYMPATRIC POPULATIONS OF BROWN TROUT (SALMO TRUTTA)
Authors: Ryman Nils , Allendorf Fred W , Ståhl Gunnar
Published: April 2021

Two reproductively isolated demes of brown trout coexist in a small Swedish mountain lake, Lake Bunnersjoarna. We electrophoretically examined 102 specimens from that lake for 27 enzymes encoded by 54 loci. The two demes are fixed for different alleles at a lactate dehydrogenase locus (LDH-1); statistically significant allele frequency differences at five other loci further support the complete lack of gene flow between these demes. There are significant differences in growth rates between fish in the two demes, but no further morphological differentiation has been detected.——In light of these findings, the genetic distance between these populations is surprisingly small (NEI'S I=0.975). These demes represent one of the least genetically divergent, reproductively isolated sympatric pair of vertebrate populations that have been identified. The results are discussed from both an evolutionary and ecological perspective.
THE USE OF RESTRICTION ENDONUCLEASES TO MEASURE MITOCHONDRIAL DNA SEQUENCE RELATEDNESS IN NATURAL POPULATIONS. I. POPULATION STRUCTURE AND EVOLUTION IN THE GENUS PEROMYSCUS
Authors: Avise John C , Lansman Robert A , Shade Rosemary O
Published: April 2021

In this study we introduce to natural population analysis a molecular technique that involves the use of restriction endonucleases to compare mitochondrial DNA (mtDNA) sequences. We have examined the fragment patterns produced by six restriction endonucleases acting upon mtDNA isolated from 23 samples of three species of the rodent Peromyscus. Our observations confirm the following conclusions derived from previous experiments with laboratory animals: (1) mtDNA within an individual appears homogeneous; (2) at least the majority of mtDNA present in an individual is inherited from the female parent. Our experiments demonstrate for the first time that there is detectable heterogeneity in mtDNA sequences within and among natural geographic populations of a species and that this heterogeneity can readily be used to estimate relatedness between individuals and populations. Individuals collected within a single locale show less than 0.5% sequence divergence, while those collected from conspecific populations separated by 50 to 500 miles differ by approximately 1.5%. The mtDNAs of the closely related sibling species P. polionotus and P. mniculutus differ from each other by 13 to 17%; nonsibling species differ by more than 20%. Qualitative and quantitative approaches to analysis of digestion patterns are suggested. The results indicate that restriction analysis of mtDNA may become the most sensitive and powerful technique yet available for reconstructing evolutionary relationships among conspecific organisms.
NUMERICAL ANALYSIS OF WEAK RANDOM DRIFT IN A CLINE
Authors: Luskin Mitchell , Nagylaki Thomas
Published: April 2021

The equilibrium state of a diffusion model for weak random genetic drift in a cline is analyzed numerically. The monoecious organism occupies an unbounded linear habitat with constant, uniform population density. Migration is homogeneous, symmetric, and independent of genotype. A single diallelic locus with a step environment is investigated in the absence of dominance and mutation. The ratio of the variance of either gene frequency to the product of the expected gene frequencies decreases monotonically to a non-zero constant. The correlation between the gene frequencies at two points decreases monotonically to zero as the separation is increased with the average position fixed; the decrease is asymptotically exponential. The correlation decreases monotonically to a positive constant depending 011 the separation as the average position increasingly deviates from the center of the cline with the separation fixed. The correlation also decreases monotonically to zero if one of the points is fixed and the other is moved outward in the habitat, the ultimate decrease again being exponential. All the results are parameter free. Some asymptotic formulae are derived analytically.
THE INTERGRADATION, GENETIC INTERCHANGEABILITY AND INTERPRETATION OF GENE CONVERSION SPECTRUM TYPES
Authors: Lamb Bernard C , Ghikas Aglaia
Published: April 2021

In the Pasadena strains of Ascobolus immersus, the gene conversion propperties of 29 induced (nine UV, nine NG, and 11 ICR-170) and nine spontaneous white-ascospore mutations have been studied. Each mutant was cyossed to three types of derived wild-type strains; single mutants often gave very different conversion results in the three types of crosses, with any or all of the following changes in: percentage with post-meiotic segregation among aberrant-ratio asci; percentage with conversion to wild type among aberrant-ratio asci; and in total conversion frequency. — These results are compared with those of LEBLON (1972 a, b) from Ascobolus immersus and Yu-SUN, WICRRAMARATNE and WHITEHOUSE (1977) from Sordaria breuicollis. It is shown that conversion spectrum types are not necessarily distinct, but can completely intergrade, on the criteria of both post-meiotic segregation frequency and direction of correction. Genetic differences between strains in the present work resulted in much interchangeability of spectrum types for the same mutation in different crosses; e.g., from type C in one cross to type B/D type in another cross, although the mutation is presumably of the same molecular type (addition or deletion frame shift, or base substitution) in each cross. These changes of conversion properties for a given mutation in different crosses mean that previous interpretations of spectrum types in terms of specific conversion properties for various molecular types of mutation are inapplicable, or inadequate on their own, to explain the present data. Other factors, such as heterozygous cryptic mutations or conversion control genes, are probably involved. Because of asymmetric hybrid DNA formation, correction properties may differ from observed conversion properties.
DUPLICATIONS IN CAENORHABDITIS ELEGANS
Authors: Herman Robert K , Madl James E , Kari Claire K
Published: April 2021

Thirteen chromosomal duplications, all unlinked to their linkage group of origin, have been identified following X-irradiation. Ten are X-chromosome duplications, of which six are half-translocations on three autosomomal linkage groups and four are free fragments. Five of the half-translocations are homozygous fertile and two are recognizable cytologically as chromosome satellites, both of which show some mitotic instability. The free-X duplications show varying tendencies for loss. Three appear not to overlap in extent previously identified free-X duplications. The fourth carries genes from linkage group V, as well as X. Three duplications of a portion of linkage group II were identified and found to be free and quite stable in hyperploids. Some of the free duplications tend to disjoin from the X chromosome in males. New X-chromosome map data are presented.
CONTROL OF MALE REPRODUCTIVE BEHAVIOR BY THE CENTRAL NERVOUS SYSTEM OF DROSOPHILA: DISSECTION OF A COURTSHIP PATHWAY BY GENETIC MOSAICS
Authors: Hall Jeffrey C
Published: April 2021

In gynandromorphs of Drosophila, a detailed examination was made of the association between male courtship behavior and the chromosomal genotype of various parts of the central nervous system. Mosaic flies that behave as males repeatedly show a shorter murtship than normal males. If there is to be male behavior, the posterior dorsal brain must be haplo-X on at least one side for occurrence of the early courtship events. tapping, following of females and wing extension. Licking (proboscis extension) has nearly the same focus but is submissive; that is, male tissue must be present in both left and right dorsal brain. The next courtship step, attempted copulation, has a focus (especially for actual genital contact) located in the thoracic ganglia, though apparently not in a discrete region. Attempted copulation, which can occur even in mosaics with a gravid abdomen, may be correlated with the presence of sex combs. The role of courtship foci are interpreted in terms of known sensory inputs to and functions of the major insect ganglia.
INDEPENDENT PRODUCTION OF CO2 SENSITIVITY BY NUCLEAR GENE DLY AND A TRANSMISSIBLE AGENT FROM DELAYED-RECOVERY DROSOPHILA MELANOGASTER
Authors: Clark M A , McCrady W B , Fielding C L
Published: April 2021

Flies of stocks designated delayed-recovery by MCCRADY and SULERUD (1964) remain temporarily paralyzed after exposure to carbon dioxide. This condition is similar to CO2 sensitivity, which occurs in flies infected with the maternally transmitted sigma virus, but is due, at least in part, to the third chromosome mutant gene DlY. Because earlier work indicated that extracts of delayed-recovery flies could occasionally transmit CO2, sensitivity when injected into resistant recipients, we have tested the possibility that some delayed-recovery stocks contain a sigma-like transmissible virus, in addition to the Dly gene. We found that TDR-orange, a stock derived from the original delayed-recovery line, and temperature-cured populations of the same stock, both contain some agent that is transmissible by injection. TDR-BC3f, a stock derived by backcrossing through the male line to eliminate maternally transmitted factors, does not appear to contain such an infectious agent, but remains sensitive to CO2. These observations lead us to the conclusion that the originally described delayed-recovery stocks harbor an infectious extrachromosomal agent, in addition to possessing the Dly gene, and each is capable of producing a sensitivity to carbon dioxide.
ON THE NUMBER OF STABLE EQUILIBRIA AND THE SIMULTANEOUS STABILITY OF FIXATION AND POLYMORPHISM IN TWO-LOCUS MODELS
Authors: Feldman Marcus W , Libermann Url
Published: April 2021

It is shown that in simple symmetric two-locus, two-allele constant fitness models the bound of four simultaneously stable equilibria previously accepted for general two-locus, two-allele models is exceeded. Situations with five and six stable equilibria are exhibited. These involve four chromosomal fixations and either one or two polymorphic stable equilibria.
AN UNSTABLE ALLELE OF THE am LOCUS OF NEUROSPORA CRASSA
Authors: Kinsey John A , Fincham J R S
Published: April 2021

The mutant strain am126 was isolated, using the direct selection procedure, after nitrous acid mutagenesis. It produced neither measurable NADP-dependent glutamate dehydrogenase (GDH) nor immunologically cross-reacting material. That the am,126 strain produced some form of GDH product was shown by the fact that it complemented several other am mutant strains. The GDH formed by complementation between am126 and each of two other am mutants was relatively thermolabile, but could not be distinguished from wild-type GDH by electrophoresis in polyacrylamide gels. This, together with the relatively high yield of the complementation enzymes, suggests that the am126 product is a polypeptide chain not grossly abnormal in structure. The spontaneous revertant frequency was between 0.3 and 3 protatrophic revertants per 105 live cells. This frequency was at least 40 times greater than that for am19, which had the second highest spontaneous revertant frequency among the mutants tested. Neither meiosis nor mutagenesis increased the revertant frequency, nor did incubation at elevated temperatures lower it. Sixty-eight revertant strains were examined for thermostability of their GHD. All appeared to be identical to wild type. Seven of the revertant strains were also tested for instability with regard to Iorward mutation to am auxtrophy. None was found to be unstable. Models for the genetic instability of the am126 mutation are discussed.
SPORE KILLER, A CHROMOSOMAL FACTOR IN NEUROSPORA THAT KILLS MEIOTIC PRODUCTS NOT CONTAINING IT
Authors: Turner Barbara C , Perkins David D
Published: April 2021

Three chromosomal factors called Spore killer (Sk) have been found in wild populations of Neurospora sitophila and N . intermedia. Sk resembles other examples of meiotic drive such as Segregation Distorter in Drosophila, Pollen killer in wheat, and Gamete eliminator in tomato. In crosses heterozygous for Sk, each ascus contains four viable black ascospores and four inviable, undersize, clear ascospores, with second-division segregations infrequent. The survivors contain the killer allele Skk, while unlinked markers segregate normally. Reciprocal crosses are identical. When crosses are homozygous for an allele of Sk, all eight ascospores are viable and black in most asci. (Many homozygms crosses have a background level of randomly occurring inviable spores; however, the pattern of 4 viable : 4 small clear ascospores is not found in any of the asci of Sk-homozygous crosses.)—killer (Sk-1K) and sensitive (Sk-1S) alleles occur in about equal numbers among a worldwide sample of N. sitophila strains, following no geographic pattern. No killer allele has been found in N . crassa. Sk-2K and Sk-3k, found in N . intermedia, are rare. Most N. intermedia strains are Sk-2S and Sk-3S, but some are wholly o r partially resistant to one or both of the killer alleles, while not themselves acting as killers. Sk-2K and Sk-2R are both specific in conferring resistance to Sk-2K, but not to Sk-3K. Likewise Sk-3K and Sk-3R are resistant specifically to Sk-3K, but not to Sk-2K. Resistance segregates as an allele of SkK.——Sk-2 and Sk-3 have been mapped near the centromere of linkage group I11 after introgression into N . crassa, where crossing over is normally 11 % between the proximal I11 markers acr-2 and leu-1. But crossing over is absent in this region when either of the killer alleles is heterozygous (Sk-2K x Sk-2S, Sk-3K x Sk-3S and Sk-2K X Sk-2R have been examined).
GENETIC CONTROL OF PHOSPHORUS ASSIMILATION IN NEUROSPORA CRASSA: DOSE-DEPENDENT DOMINANCE AND RECESSIVENESS IN CONSTITUTIVE MUTANTS
Authors: Metzenberg Robert L , Chia William
Published: April 2021

Mutants called nuc-1C, constitutive for alkaline phosphatase synthesis, were isolated and mapped very close to nuc-1 mutants in which this enzyme is not expressed. nuc-1 is epistatic to nuc-1C. nuc-1C acts only if it is cis to normal nuc-1 function. The preparation of partial diploids heterozygous for various nuc-1 alleles is described; nuc-1C is dominant to nuc-1+, which in turn is dominant to nuc-1. In heterocaryons with nuc-1+, nuc-1C is dominant when it is present in high proportion, but essentially recessive if it is present in low proportions. In heterocaryons with nuc-1, nuc-1C is again dominant when present in high proportions, but in low proportions it "complements" to give essentially normal repressibility. A model of regulation consistent with these findings is presented.
ABSENCE OF DETECTABLE MITOCHONDRIAL RECOMBINATION IN PARAMECIUM
Authors: Adoutte André , Knowles Jonathan K , Sainsard-Chanet Annie
Published: April 2021

An extensive search for recombination between mitochondrial markers was carried out in Paramecium tetraurelia. Thirty-two combinations, altogether involving 24 different markers, were studied. The markers belonged to the three main categories of mitochondrial mutations presently available in this organism. (a) Spontaneous or UV-induced antibiotic resistance mutations, most probably affecting mitochondrial ribosomes, (b) nitrowguanidine-induced antibiotic resistance markers displaying thermosensitivity or slow growth, enabling easy selection of possible wild-type recombinants, and (c) mitochondrial partial suppressors of a nuclear gene, probably corresponding to molecular alterations distinct from the preceding two categories. In addition, different genetic configurations were analyzed (i e., mutant x mutant, double-mutant x wild-type, etc.).——None of the combinations yielded any evidence for the occurrence of recombined genomes despite the fact that: (1) all of them were studied on a large scale involving the screening of at least several thousand mitochondrial genomes (often several millions), (2) in many of them the detection level was sufficiently high to enable the isolation of spontaneous mutants in control cells, and (3) in several of them, reconstitution experiments carried out in parallel show that the conditions were fully adequate to detect recombinant genotypes. The results are in marked contrast with those obtained on the few other organisms in which mitochondrial recombination has been studied, particularly Saccharomyces cerevisiae, in which mitochondrial recombination is intense.——The most likely basis for the various manifestations of mitochondrial genetic autonomy in Paramecium, described in this as well as in previous publications, is that the chondriome of this organism is made up of thousands of structurally discrete, noninteracting units.
VEGETATIVE INCOMPATIBILITY AND THE MATING-TYPE LOCUS IN THE CELLULAR SLIME MOLD DICTYOSTELIUM DISCOIDEUM
Authors: Robson Gillian E , Williams Keith L
Published: April 2021

The genetic basis of vegetative incompatibility in the cellular slime mold, Dictyostelium discoideum, is elucidated. Vegetatively compatible haploid strains form parasexual diploids at a frequency of between 10-6 and 10-5, whereas "escaped" diploids are formed between vegetatively incompatible strains at a frequency of ~10-8. There is probably only a single vegetative incompatibility site, which appears to be located at, or closely linked to, the mating-type locus. The nature of the vegetative incompatibility is deduced from parasexual diploid formation between wild isolates and tester strains of each mating type, examination of the frequency of formation of "escaped" diploids formed between vegetatively incompatible strains, and examination of the mating type and vegetative incompatibility of haploid segregants obtained from "escaped" diploids.
X-LINKAGE OF A HUMAN GENETIC LOCUS THAT CORRECTS THE DNA SYNTHESIS LESION IN tsC1AGOH MOUSE CELLS
Authors: Giles Richard E , Ruddle Frank H
Published: April 2021

GM 126 human diploid fibroblasts were fused with a heat-sensitive mouse cell mutant defective in DNA synthesis, and primary hybrids were selected at permissive and nonpermissive temperatures in HAT medium. Primary hybrids, primary hybrid clones back-selected in 8-azaguanine at the permissive temperature, and subclones of heat-resistant primary hybrids isolated under nonselective conditions or after 8-azaguanine treatment were tested for heat sensitivity, the expression of 26 human enzymes assigned to 19 different human chromosomes, and the presence of human chromosomes. Only the human X chromosome and X-linked marker enzymes exhibited a clear pattern of concordant segregation with the heat-resistant phenotype. On the basis of these observations, we have defined the human genetic locus that corrects the heat-sensitive lesion in tsC1AGOH as hrC1AGOH and have assigned this locus to the X chromosome. This observation provides the first instance where two selectable markers (heat resistance and 8-azaguanine sensitivity) are found on a single human chromosome and suggests that these markers may prove to be a valuable push-pull selective system of use in determining the linear arrangement of genes on human chromosomes by somatic cell genetics.
GENIC HETEROGENEITY WITHIN ELECTROPHORETIC "ALLELES" AND THE PATTERN OF VARIATION AMONG LOCI IN DROSOPHILA PSEUDOOBSCURA
Authors: Singh Rama S
Published: April 2021

An investigation, similar to our previously reported xanthine dehydrogenase study, was undertaken to examine the extent of hidden genic variation at nine loci (five larval proteins, three esterases and one aldehyde oxidase) by sequential application of various electrophoretic criteria employing pH, gel concentration and buffer variation. Polymorphic loci appear to fall into two distinct groups: weakly polymorphic, including larval protein 6, 7, 8, 10 and 13 and esterase-1 and -6; and highly polymorphic, including esterase-5, Xdh and possibly Ao. Monomorphic loci may belong to a third group different from all polymorphic lori. Bogota, a geographical isolate that is reproductively isolated from the mainland population, was found to be genetically distinct at four of the ten loci examined in detail so far, including Xdh, whereas previously it was found to be genetically distinct at none. These results are discussed in the light of balancing selection, neutral and mutation-selection hypotheses of genic variation in natural populations.
THE GENETIC COVARIANCE BETWEEN CHARACTERS MAINTAINED BY PLEIOTROPIC MUTATIONS
Authors: Lande Russell
Published: April 2021

A statistical genetic model of a multivariate phenotype i s derived to investigate the covariation of pleiotropic mutations with additive effects under the combined action of phenotypic selection, linkage and the mating system. Equilibrium formulas for large, randomly mating populations demonstrate that, when selection on polygenic variation is much smaller than twice the harmonic mean recombination rate between loci with interacting fitnesses, linkage disequilibrium is negligible and pleiotropy is the main cause of genetic correlations between characters. Under these conditions, approximate expressions of or the dynamics of the genetic covariances due to pleiotropic mutations are obtained. Patterns of genetic covariance between characters and their evolution are discussed with reference to data on polygenic mutation, chromosomal organization and morphological integration.
DIRECTIONALITY AND NONRECIPROCALITY OF CHI-STIMULATED RECOMBINATION IN PHAGE Λ
Authors: Stahl Franklin W , Stahl Mary M , Malone Robert E , Crasemann Jean M
Published: April 2021

Chi's are genetic elements that stimulate generalized recombination in their locale in phage λ. All Chi's, wherever located on λ's chromosome, act asymmetrically in crosses blocked in DNA replication: (1) They stimulate exchange primarily to their left on the conventional λ map, and (2) the stimulated exchange is frequently nonreciprocal, the recombinant carrying the Chi element being produced less often than the complementary product.
A COMPARISON OF TWO-POINT, THREE-POINT AND DELETION MAPPING IN THE C CISTRON OF RHIZOBIOPHAGE 16–3, WITH AN EXPLANATION FOR THE RECOMBINATION PATTERN
Authors: Orosz LÁszlÓ , RostÁs Katalin , Hotchkiss Rollin D
Published: April 2021

A general tendency for additivity prevailed in recombination frequencies for two-point fine-structure mapping of 14 mutants in the C cistron of Rhizobium meliloti phage 16-3, with little evidence of any marker effect. Intracistronic three-point mapping indicated that double crossovers are rare. Deletion mapping indicated that the two- and three-point mapping data gave the correct order of the mutations. A high frequency (5 to 8%) of c/c+ heterozygotic phage progenies was observed in standard crosses. This pattern implies formation of a relatively long region of heterozygosity. Together with the results of the three-point tests, it suggests certain properties of the branch migration and resolution steps envisioned in current mechanisms of recombination.
A CIS-ACTING MUTATION WITHIN THE MAT
a LOCUS OF SACCHAROMYCES CEREVISIAE THAT PREVENTS EFFICIENT HOMOTHALLIC MATING-TYPE SWITCHING
Authors: Mascioli Deborah Wygal , Haber James E
Published: April 2021

Homothallic strains of Saccharomyces cerevisiae are able to switch from one mating-type to the other as frequently as every cell division. We have identified a cis-dominant mutation of the MATa locus, designated MATa-inc, that can be converted to MATα at only about 5% of the normal efficiency. In homothallic MATa-inc/mata* diploids, the MATa-inc locus switched to MATα in only one of 30 cases, while the mata* locus switched to MATα in all 30 cases. The MATa-inc mutation can be "healed" by a series of switches, first to MATα and then to a normal allele of MATa. These data are consistent with the "cassette" model of HICKS, STRATHERN and HERSKOWITZ (1977), in which mating conversions involve the transposition of wild-type copies of a or α information from silent genes elsewhere in the genome. The MATa-inc mutation appears to alter a DNA sequence necessary for the replacement of MATa by MATα. The MATa-inc mutation has no other effect on MATa functions. In heterothallic backgrounds, the mutation has no effect on the sensitivity to α-factor, synthesis of a-factor, expression of barrier phenotype or ability to mate or sporulate.—The MATa-inc allele does, however, exhibit one pleiotropic effect. About 1% of homothallic MATa-inc cells become completely unable to switch mating type because ofmutations at HMa, the locus proposed to carry the silent copy of α information.—In addition, we have isolated a less efficient allele of the HO gene.
REGION-SPECIFIC RECOMBINATION IN PHAGE T4. II. STRUCTURE OF THE RECOMBINANTS
Authors: Levy Jack N , Goldberg Edward B
Published: April 2021

In this paper, we present results of crosses designed to elucidate the structure of recombinants in the tail-fiber region of bacteriophage T4, in which a glucosylation-dependent recombination mechanism is operative, and the cause of this "special" recombination in glucosylated crosses is discussed. We present evidence that, when phage are nonglucosylated, recombination in the tail-fiber region proceeds via long heteroduplex overlaps. Mismatched bases within such regions (in nonglucosylated phage) are repaired efficiently (as contrasted to those of glucosylated phage), bnt asymmetrically; that is, there may not be an equal probability of resolving the mismatch to mutant or wild type.
GENETIC ANALYSIS OF THE DUMPY COMPLEX LOCUS IN DROSOPHILA MELANOGASTER: COMPLEMENTATION, FINE STRUCTURE AND FUNCTION
Authors: Grace Dale
Published: April 2021

An extensive genetic analysis of the dumpy locus is presented. This study includes complementation, fine structure mapping and allelic interaction. A number of complementing recessive lethals of the dp complex have been genetically mapped. Two alleles of the ol(v) type that complement l alleles map to the left portion of the locus. A number of olv alleles that complement both l and lv lethals map within the right portion of the locus.—Fine-structure analysis demonstrated that both olv and o alleles are distributed among various subloci. Evidence for spacer regions between subloci is presented.—An extensive discussion of the data considers whether the locus is unicistronic or multicistronic. The conclusion reached is that the locus is not a single functional cistron. The possibility of a single cistron encoding a multifunctional polypeptide is discussed.—The hypothesis is proposed that the left portion of the map and the l mutations function as regulatory sequences and that the right portion of the map encodes structural sequences.
GENETIC MAPPING OF A GROUP OF TEMPERATURE-SENSITIVE dna INITIATION MUTANTS IN BACILLUS SUBTILIS
Authors: Imada Sumi , Carroll Lynn E , Sueoka Noboru
Published: April 2021

Recombination frequencies among temperature-sensitive dna mutants from various laboratories were analyzed, and eleven dna mutants were found to be closely linked. They are classified as group B dna mutants, since these are closely linked with dnaB19, originally isolated and approximately mapped near leuA8 by KARAMATA and GROSS (1970). However, the dnaB19 mutation itself has relatively high recombination frequencies with the other mutations, thus, we propose to subdivide the dnaB group into two subgroups—dnaBI, including ten mutants (dna-I, dna-3, dna-5, dna-17, dna-27, dna-51, dna-60, dna-62, dna-103 and dna-134) and dnaBII, including dnaB19. The map order of dnaB and markers in the vicinity was determined to be argA-citH-citC- phoP-phoR-polA-dnaBI-dnaBII-cilF-leuA-pheA.
MITOTIC RECOMBINATION IN YEAST: ISOLATION AND CHARACTERIZATION OF MUTANTS WITH ENHANCED SPONTANEOUS MITOTIC GENE CONVERSION RATES
Authors: Maloney Daniel H , Fogel Seymour
Published: April 2021

Semi-dominant mutants displaying greatly elevated (up to 200-fold above control) levels of spontaneous mitotic recombination have been isolated in a disomic haploid strain of yeast heteroallelic at the arg4 locus. They are designated by the symbol MIC. The mutants variously exhibit associated sensitivity to UV and ionizing radiation and to methyl methanesulfonate, enhanced UV-induced mitotic recombination, and enhanced spontaneous forward mutation rates. Possible enzyme defects and involvement in repair and editing of DNA are discussed. The mutants are expected to simplify the analysis of recombination pathways in yeast.
DUPLICATED GENES PRODUCING TRANSPOSABLE CONTROLLING ELEMENTS FOR THE MATING-TYPE DIFFERENTIATION IN SACCHAROMYCES CEREVISIAE
Authors: Oshima Takehiro , Takano Isamu
Published: April 2021

Mutation of the two homothallic genes, HMLα/HMLa and HMRa/HMRα, in homothallic strains of Saccharomyces cereuisiae was studied. Of 11 mutants of the HMLa gene, eight were due to a phenotypic mutation from HMLα to HMLa, i.e., a mutation causing a change in function of the original HML allele to that of the other HML allele (functional mutation), and three were due to a defective mutation at the HMLα gene, i.e., a mutation causing a non-functional allele (nonfunctional mutation). All 14 mutants of the HMRa gene, on the other hand, were due to a phenotypic mutation from HMRa to HMRα i.e., a functional mutation. Phenotypic reverse mutations, i.e., HMLa to HMLα and HMRα to HMRa, were also observed in the cultivation of EMS (ethyl methanesulfonate) treated spores having the HO HMRα HMLa genotype. Mutation from heterothallic cells to homothallism was observed in a nonfunctional mutant of the HMLα gene, by mutagenesis with EMS, but not in the functional mutants of the HMLα and HMRa genes or in the authentic strains having the α HO HMRα HMLα (α Hp) and a HO HMRa HMLa (a Hq) genotypes. These observations suggest that the functional mutation is not caused by the direct mutation from a homothallic allele to the opposite, but by replacement of a transposable genic element produced from a homothallic locus with a region of a different homothallic locus. These observations also support the controlling-element model and the cassette model, which have been proposed to explain the mating-type differentiation by the homothallic genes.
DEPENDENCE ON MATING TYPE FOR THE OVERPRODUCTION OF ISO-2-CYTOCHROME c IN THE YEAST MUTANT CYC7–H2
Authors: Rothstein Rodney J , Sherman Fred
Published: April 2021

The CYC7-H2 mutation causes an approximately 20-fold overproduction of iso-2-cytochromo c in a and α haploid strains of the yeast Saccharomyces cerevisiae due to an alteration in the nontranslated regulatory region that is presumably contiguous with the structural region. In this investigation, we demonstrated that heterozygosity at the mating type locus, a /α or a/a/α/α, prevents expression of the overproduction, while homozygosity, a/a and α/α and hemizygosity, a/O and α/O, allow full expression of the CYC7-H2 mutation, equivalent to the expression observed in a and α haploid strains. There is no decrease in the overproduction of iso-2-cytochrome c in a/α diploid strains containing either of the other two similar mutations, CYC7-H1 and CYC7-H3. It appears as if active expression of one or another of the mating-type alleles is required for the overproduction of iso-2-cytochrome c in CYC7-H2 mutants.
GENETIC ANALYSIS OF MATING TYPE DIFFERENTIATION IN PARAMECIUM TETRAURELIA. II. ROLE OF THE MICRONUCLEI IN MATING-TYPE DETERMINATION
Authors: Brygoo Y , Sonneborn T M , Keller A M , Dippell R V , Schneller M V
Published: April 2021

The two complementary mating types, 0 and E, of Paramecium tetrauretia are normally inherited cytoplasmically. This property has generally been interpreted to indicate the presence of cytoplasmic factors that determine macronuclear differentiation towards 0 or E . In these macronuclear-cytoplasmic interactions, the micronuclei were held to be unbiased and the determination to be established in the course of macronuclear development. In order to ascertain whether the micronuclei were actually neutral, amicronucleate clones were needed and a method to produce them was developed. In crosses between amicronucleate clones and normal micronucleate clones, we have observed regular deviations from cytoplasmic inheritance: the commonest deviation is that most 0 amicronucleate cells become E when they receive a micronucleus from an E partner. The data can be interpreted by assuming that the micronuclei are predetermined and that the apparent "cytoplasmic" inheritance of the two mating types is due, in E cells, to E-determining factors present in the cytoplasm and in the nucleus; and, in 0 cells, to 0-determining factors present only or mainly in the nucleus.