bluuebunny/crossref_metadata_2025 huggingface dataset:
Behavior and cytogenetics of fruitless in Drosophila melanogaster: different courtship defects caused by separate, closely linked lesions.
Authors: Gailey D A , Hall J C
Published: April 2021

The fruitless (fru) courtship mutant was dissected into three defects of male reproductive behavior, which were separable as to their genetic etiologies by application of existing and newly induced chromosomal aberrations. fru itself is a small inversion [In(3R) 90C; 91B] on genetic and cytological criteria. Uncovering the fru distal breakpoint with deletions usually led to males with two of the fru courtship abnormalities: no copulation attempts with females (hence, behavioral sterility) and vigorous courtship among males, including the formation of "courtship chains." However, certain genetic changes involving region 91B resulted in males who formed courtship chains but who mated with females. Uncovering the fru proximal breakpoint led to males that passively elicit inappropriately high levels of courtship. This elicitation property was separable genetically from the sterility and chain formation phenotypes and provisionally mapped to the interval 89F-90F, which includes the fru proximal breakpoint. Behavioral sterility and chaining were also observed in males expressing certain abnormal genotypes, independent of the fru inversion. These included combinations of deficiencies, each with a breakpoint in 91B, and a transposon inserted in 91B.
Inbreeding depression due to overdominance in partially self-fertilizing plant populations.
Authors: Ziehe M , Roberds J H
Published: April 2021

The effect of the rate of partial self-fertilization and viability selection on the magnitude of inbreeding depression was investigated for the overdominance genetic model. The influence of these factors was determined for populations with equilibrium genotypic frequencies. Inbreeding depression was measured as the normalized disadvantage in mean viability of selfed progeny as compared to outcrossed progeny. When caused by symmetric homozygous disadvantage at a single locus it is shown always to be less than one-third. Moreover, for fixed rates of self-fertilization, its maximum value is found at intermediate levels of homozygous disadvantage. As the rate of self-fertilization increases, inbreeding depression increases and the homozygote viability that results in maximum depression tends toward one-half the heterozygote viability. Symmetric selection against homozygotes at multiple loci can lead to substantially higher values than selection at a single-locus. As the number of independent loci involved increases, inbreeding depression can reach high levels even though the selfing rate is low. Viability distributions for progenies produced from both random mating and self-fertilization were derived for the case of symmetric selection at independently assorting multiple loci. Distributions of viabilities in progenies resulting from mixtures of selfing and outcrossing were shown to be bimodal when inbreeding depression is high.
Extragenic suppressors of mar2(sir3) mutations in Saccharomyces cerevisiae.
Authors: Lin C I , Livi G P , Ivy J M , Klar A J
Published: April 2021

The silent mating-type genes (HML and HMR) of Saccharomyces cerevisiae are kept under negative transcriptional control by four trans-acting MAR (or SIR) loci. We have isolated extragenic suppressors of the mar2-1 mutation which, based on genetic complementation tests, define two additional loci involved in regulating the expression of HML and HMR. A strain with the genotype HMLa MAT alpha HMRa mar2-1 is sterile due to the simultaneous expression of a and alpha information. Two mutants exhibiting an alpha phenotype (which may result from the restoration of MAR/SIR repression) were isolated and genetically characterized. The mutations in these strains: (1) are recessive, (2) are capable of suppressing a mar2-deletion mutation, (3) are unlinked to MAT, (4) complement one another as well as the previously identified sum1-1 mutation, and (5) are not new alleles of the known MAR/SIR loci. We designate these new regulatory loci SUM2 and SUM3 (suppressor of mar). Unlike the sum1-1 mutation, suppression by sum2-1 and sum3-1 is mar2-locus specific. Both sum2-1 and sum3-1 affect the expression of a information at the HM loci. Transcript analysis shows a significant reduction in HMLa and HMRa gene transcription in mar2-1 sum2-1 and mar2-1 sum3-1 cells. Furthermore, we have found genetic evidence to suggest that mar2-1 sum2-1 cells exhibit only partial expression of silent alpha information. We conclude that the SUM2 and SUM3 gene products are required for expression of the HM loci and act downstream of the MAR2 (SIR3) gene function. Possible mechanisms for the action of the SUM gene products are discussed.
Genetic analysis of the Shaker gene complex of Drosophila melanogaster.
Authors: Ferrús A , Llamazares S , de la Pompa J L , Tanouye M A , Pongs O
Published: April 2021

The Shaker complex (ShC) spans over 350 kb in the 16F region of the X chromosome. It can be dissected by means of aneuploids into three main sections: the maternal effect (ME), the viable (V) and the haplolethal (HL) regions. The mutational analysis of ShC shows a high density of antimorphic mutations among 12 lethal complementation groups in addition to 14 viable alleles. The complex is the structural locus of a family of potassium channels as well as a number of functions relevant to the biology of the nervous system. The constituents of ShC seem to be linked by functional relationships in view of the similarity of the phenotypes, antimorphic nature of their mutations and the behavior in transheterozygotes. We discuss the relationship between the genetic organization of ShC and the functional coupling of potassium currents with the other functions encoded in the complex.
Molecular structure of frizzled, a Drosophila tissue polarity gene.
Authors: Adler P N , Vinson C , Park W J , Conover S , Klein L
Published: April 2021

The function of the frizzled (fz) locus is required to coordinate the cytoskeletons of pupal epidermal cells so that a parallel array of cuticular hairs and bristles is produced. We report here the molecular cloning and characterization of the fz locus. The locus is very large. Mutations that inactivate the gene are spread over 100 kb of genomic DNA. The major mRNA product of the gene is a 4-kb RNA that is encoded by 5 exons spread over more than 90 kb of genomic DNA. Conceptual translation of this mRNA indicates that it encodes an integral membrane protein that is likely to contain both extracellular and cytoplasmic domains.
Interval mapping of quantitative trait loci employing correlated trait complexes.
Authors: Korol A B , Ronin Y I , Kirzhner V M
Published: April 2021

An approach to increase the resolution power of interval mapping of quantitative trait (QT) loci is proposed, based on analysis of correlated trait complexes. For a given set of QTs, the broad sense heritability attributed to a QT locus (QTL) (say, A/a) is an increasing function of the number of traits. Thus, for some traits x and y, H(xy)2(A/a) > or = H(x)2(A/a). The last inequality holds even if y does not depend on A/a at all, but x and y are correlated within the groups AA, Aa and aa due to nongenetic factors and segregation of genes from other chromosomes. A simple relationship connects H2 (both in single trait and two-trait analysis) with the expected LOD value, ELOD = -1/2N log(1-H2). Thus, situations could exist that from the inequality H(xy)2(A/a) > or = H(x)2(A/a) a higher resolution is provided by the two-trait analysis as compared to the single-trait analysis, in spite of the increased number of parameters. Employing LOD-score procedure to simulated backcross data, we showed that the resolution power of the QTL mapping model can be elevated if correlation between QTs is taken into account. The method allows us to test numerous biologically important hypotheses concerning manifold effects of genomic segments on the defined trait complex (means, variances and correlations).
IDENTITY COEFFICIENTS IN FINITE POPULATIONS. I. EVOLUTION OF IDENTITY COEFFICIENTS IN A RANDOM MATING DIPLOID DIOECIOUS POPULATION
Authors: Chevalet C , Gillois M , Nassar R F
Published: April 2021

Properties of identity relation between genes are discussed, and a derivation of recurrent equations of identity coefficients in a random mating, diploid dioecious population is presented. Computations are run by repeated matrix multiplication. Results show that for effective population size (Ne) larger than 16 and no mutation, a given identity coefficient at any time t can be expressed approximately as a function of (1—f), (1—f)3 and (1—f)6, where f is the mean inbreeding coefficient at time t. Tables are presented, for small Ne values and extreme sex ratios, showing the pattern of change in the identity coefficients over time. The pattern of evolution of identity coefficients is also presented and discussed with respect to N eu, where u is the mutation rate. Applications of these results to the evolution of genetic variability within and between inbred lines are discussed.
INCREASED SPONTANEOUS MITOTIC SEGREGATION IN MMS-SENSITIVE MUTANTS OF SACCHAROMYCES CEREVISIAE
Authors: Prakash Satya , Prakash Louise
Published: April 2021

Methyl methanesulfonate (MMS)-sensitive mutants of Saccharomyces cerevisiae belonging to four different complementation groups, when homozygous, increase the rate of spontaneous mitotic segregation to canavanine resistance from heterozygous sensitive (canr/+) diploids by 13- to 170-fold. The mms8—1 mutant is MMS and X-ray sensitive and increases the rate of spontaneous mitotic segregation 170-fold. The mms9—1 and mms13—1 mutants are sensitive to X rays and UV, respectively, in addition to MMS, and increase the rate of spontaneous mitotic segregation by 13-fold and 85-fold, respectively. The mutant mms21—1 is sensitive to MMS, X rays and UV and increases the rate of spontaneous mitotic segregation 23-fold.
PROTOPLASMIC INCOMPATIBILITY AND CELL LYSIS IN PODOSPORA ANSERINA. I. GENETIC INVESTIGATIONS ON MUTATIONS OF A NOVEL MODIFIER GENE THAT SUPPRESSES CELL DESTRUCTION
Authors: Labarere Jacques , Bernet Jean
Published: April 2021

In Podospora anserina, protoplasmic incompatibility (a phenomenon that prevents heterokaryon formation because of the destruction of the fused cells) can be studied in homokaryotic strains that combine nonallelic incompatibility genes or carry mutations at the lys loci. In these strains cell destruction occurs early in development and is associated with an arrest of growth.—From the self-lysing strains lysA(1) and RV (R and V are nonallelic incompatibility genes) mutations have been selected that suppress the self-lysing trait, i.e., that prevent cell destruction and remove growth inhibition. Some of them were derived from a novel modifier locus, modC, located near the mating-type locus.—In C/D and C/E incompatibility systems, modC mutations, which per se have no obvious effect, were considered in addition to mutations in the previously identified modifier loci, modA and modB. The demonstration of a functional interdependence among the three mod genes suggested that modC is not the structural gene for the protease associated with cell lysis, but is involved, like modA and modB, in its control.—All three modC mutant strains investigated exhibit defects in the formation of protoperithecia, suggesting that the modC gene function is essential to the occurrence or development of the female organs. This is the third argument that supports the hypothesis (Boucherie, Bégueret and Bernet 1976) that protoplasmic incompatibility and female organ formation might be related phenomena.
AGE-CORRELATED CHANGES IN EXPRESSION OF MICRONUCLEAR DAMAGE AND REPAIR IN PARAMECIUM TETRAURELIA
Authors: Rodermel Steven R , Smith-Sonneborn Joan
Published: April 2021

In Paramecium, age is defined as the number of mitotic divisions which have elapsed since the previous cross-fertilization (conjugation) or self-fertilization (autogamy). As the mitotic interval between fertilizations increases, the percentage of nonviable progeny clones increases. In the current study, resolution of conflicting previous reports on the pattern of increase of death and reduced viability in progeny from aging parent cells is found. Some exautogamous clones exhibit a high mortality at young clonal ages, others show no mortality throughout their life span, but most (73%) show an abrupt increase in the percent death and reduced viability in progeny from cells 50-80 fissions old.

Ultraviolet-irradiation-induced micronuclear mutations, repairable by photoreactivation, increased with increased clonal age when monitored by percent death and reduced viability of exautogamous progeny of irradiated cells. Loss of dark repair is considered a contributor to the increased expression of micronuclear mutations with increased clonal age.
PHYLOGENETIC RELATIONSHIPS AMONG DROSOPHILA LONGICORNIS, DROSOPHILA PROPACHUCA AND DROSOPHILA PACHUCA, A TRIAD OF SIBLING SPECIES
Authors: Wasserman Marvin , Koepfer H Roberta
Published: April 2021

Drosophila longicornis, D. propachuca and D. pachuca comprise a triad of sibling species. They are morphologically indistinguishable, sympatric forms that, under laboratory conditions, are capable of exchanging genes through the production of fertile F1 females. However, we have no evidence for introgressive hybridization in nature. The chromosomal constitution of our strains indicates that the ancestral species had the Primitive E gene sequence, and therefore differed from the standard repleta sequence by being Xabc; 2abcg; 3abc. This Primitive E sequence is found in both D. propachuca and D. longicornis. Each of these two species has its own unique rearrangements. D. pachuca is a derived species, which evolved from propachuca. It is cytologically more advanced and has, as its most primitive gene arrangement, one of the more advanced arrangements found in propachuca.
INBREEDING IN POPULATIONS WITH OVERLAPPING GENERATIONS
Authors: Johnson D L
Published: April 2021

An inbreeding matrix is defined for populations with overlapping generations. In the short term it can be expressed in terms of a matrix specifying the passage of genes between the different age groups (and sexes) and a diagonal matrix whose elements depend on the number of individuals in each age group. Formulae for the inbreeding effective number are derived using matrix theory. A comparison is made between the inbreeding coefficients predicted by this theory and those obtained by assuming a uniform rate of inbreeding from the outset, and these in turn are compared with the exact inbreeding coefficients.
GENETICS OF EXTRACELLULAR PROTEASE PRODUCTION IN SACCHAROMYCOPSIS LIPOLYTICA
Authors: Ogrydziak David M , Mortimer Robert K
Published: April 2021

Mutants of Saccharomycopsis lipolytica with reduced ability to produce zones of clearing on skim-milk agar plates were isolated and their properties studied. For 18 mutants it was possible to score unambiguously segregants of crosses between these mutants and wild type for extracellular protease production. These mutants all produce reduced levels of extracellular protease in liquid culture. The mutations are recessive and are in nuclear genes. The 18 mutations define 10 or 11 complementation groups, no two of which are closely linked. Mutants in four of the complementation groups also produced reduced levels of extracellular RNAse, and the reduced levels of extracellular protease and RNAse production segregate together. Five of the mutants exhibited reduced mating frequency, and one mutant was osmotic remedial for extracellular protease production. These results demonstrate that many genes can affect extracellular protease production. Besides mutations in the structural gene and in regulatory genes, mutations are likely to be in genes involved in steps common to the production of several extracellular enzymes or in genes coding for cell wall or membrane components necessary for extracellular enzyme production.
CHROMOSOMAL ANALYSIS OF DDT-RESISTANCE IN A LONG-TERM SELECTED POPULATION OF DROSOPHILA MELANOGASTER
Authors: Dapkus D , Merrell D J
Published: April 2021

The genetic basis of DDT-resistance was studied in a population of Drosophila melanogaster. This population was unique in that it had been continually selected for DDT-resistance since 1952 and had achieved a very high level of resistance. The genetic basis of resistance was studied by means of a chromosomal analysis. Fifteen combinations of resistant and control chromosomes were tested using a time-based DDT test. The analysis of the data showed that resistance was multifactorial with each of the three major chromosomes involved. Dominant and recessive second and third chromosome effects were found to be much more important than those of the first chromosome, which had no detectable recessive effects. Second and third chromosome resistance genes showed incomplete dominance. The average dominance of the second chromosome was much less than that of the third chromosome. These large-scale differences between chromosomes' effects and average dominance may indicate that a small number of resistance genes are involved. Two significant interactions between chromosomes were found. Scaling difficulties make the interactions difficult to interpret without further data. It seems possible that positive interactions between resistance have been developed by the long-term directional selection in this population.
AN ANALYSIS OF MULTI-ALLELIC DATA
Authors: Watterson G A
Published: April 2021

Some multi-allelic data obtained by COYNE (1976) and by SINGH, LEWONTIN and FELTON (1976) are analyzed for their compatibility with the neutral alleles theory. It is found that strict neutrality appears not to be the case, but that if further alleles were to be distinguished in the samples, neutrality could become a possible explanation.
AN ANALYSIS OF MALE-RECOMBINATION ELEMENTS IN A NATURAL POPULATION OF DROSOPHILA MELANOGASTER IN SOUTH TEXAS
Authors: Matthews Kathleen A , Hiraizumi Yuichiro
Published: April 2021

Genomes from a group of Drosophila melanogmter collected from a natural population at San Benito, South Texas, in March of 1975 were analyzed for the presence of male-recombination elements. All three autosomes and both sex chromosomes were examined, with emphasis placed on the two major autosomes, the second and third chromosomes. In samples of 16 second and 16 third chromosomes, at least half, but not all, of each were found to carry male-recombination elements. It is suggested, although the data are not conclusive, that some of the fourth, X, and Y chromosomes might also be associated with male-recombination elements.—When a male-recombination element, or elements, was located in the second chromosome, relatively more male recombination was induced in the second than in the third chromosome. This situation was reversed when the element(s) was located in the third chromosome.—Distortion of transmission frequency, one of the characteristics of previously studied second chromosome lines associated with male recombination, was confirmed for these second chromosomes that carried male-recombination elements. Similar, but less pronounced, distortion was observed for the third chromosome lines that carried male-recombination elements.
ALCOHOL DEHYDROGENASE MUTANTS OF CHINESE HAMSTER SOMATIC CELLS RESISTANT TO ALLYL ALCOHOL
Authors: Thirion Jean-Paul , Talbot Brian
Published: April 2021

Alcohol dehydrogenase (alcohol: NAD oxidoreductase, E.C. 1.1.1.1.) mutants of Chinese hamster somatic cells were isolated as resistant to allyl alcohol (ALLR). The ALLR phenotypes of the mutant clones were reproducible with high fidelity and stable over long intervals of growth in the absence of the selecting drug. Several mutants, Adh-1, Adh-2, Adh-9 and Adh-13, resistant to allyl alcohol were characterized. They have between 15 and 40% of the alcohol dehydrogenase activity of the wild-type cell lines. Cell-cell hybridization experiments using Adh-1 and wild-type Chinese hamster cells indicate that resistance to allyl alcohol is recessive to the wild-type allele. This phenotype is therefore a useful marker to analyze gene segregation of somatic cell mutations and to study the expression of the genes involved in the metabolism of ethanol in mammalian cells.
GENETIC LENGTHS AND BREAK POINTS IN TWELVE CHROMOSOMES OF GOSSYPIUM HIRSUTUM INVOLVED IN TEN RECIPROCAL TRANSLOCATIONS
Authors: Menzel Margaret Y , Brown Meta S
Published: April 2021

Chromosome configurations were recorded in about 5500 pollen mother cells (PMC's) in 2n and 2n-1 (missing the intact A-genome chromosome) heterozygotes of ten reciprocal translocations involving six A-genome chromosomes (H1, H2, H3, H4, H6 and H7) and six D-genome chromosomes (H14, H15, H16, H19, H20 and H21) of Gossypium hirsutum. From these records, chiasma frequencies at each of six positions were determined for nine translocations and at two positions for one. These frequencies were used to calculate recombination frequencies in different chromosome regions, and from these distances the breakpoints in 15 chromosome arms were mapped relative to each other and to their respective centromeres, insofar as the data permitted. The karyotype so derived for twelve chromosomes is in reasonably good agreement with data from genetic mapping, telosome and monosome mapping, and the mitotic idiogram.
CHARACTERIZATION OF A MUTATION IN YEAST CAUSING NONRANDOM CHROMOSOME LOSS DURING MITOSIS
Authors: Liras Paloma , McCusker John , Mascioli Stephen , Haber James E
Published: April 2021

Diploid strains of the yeast Saccharomyces cerevisiae homozygous for a recessive chromosome loss mutation (chl) exhibit a high degree of mitotic instability. Cells become monosomic for chromosome III at a frequency of approximately one percent of all cell divisions. Chromosome loss at this high frequency is also found for chromosome I, and at lesser frequencies for chromosomes VIII and XVI. In contrast, little or no chromosome loss is found for six other linkage groups tested (II, V, VI, VII, XI and XVII). The chl mutation also induces a ten-fold increase in both intergenic and intragenic mitotic recombination on all ten linkage groups tested. The chl mutation does not cause an increase in spontaneous mutations, nor are mutant strains sensitive to UV or γ irradiation. The effects of chl during meiosis are observed primarily in reduced spore viability. A decrease in chromosome III linkage relationships is also found.
GENE DUPLICATION IN SACCHAROMYCES CEREVISIAE
Authors: Hansche P E , Beres V , Lange P
Published: April 2021

Five indepdendent duplications of the acid-phosphatase (aphtase) structural gene (acp1) were recovered from chemostat populations of S. cerevisiae that were subject to selection for in vivo hyper-aphtase activity. Two of the duplications arose spontaneously. Three of them were induced by UV. All five of the duplication events involved the transpositioning of the aphtase structural gene, acp1, and all known genes distal to acp1 on the right arm of chromosome II, to the terminus of an arm of other unknown chromosomes. One of the five duplicated regions of the right arm of chromosome II was found to be transmitted mitotically and meiotically with very high fidelity. The other four duplicated regions of the right arm of chromosome II were found to be unstable, being lost at a rate of about 2% per mitosis. However, selection for increased fidelity of mitotic transmission was effective in one of these strains. No tandem duplications of the aphtase structural gene were found.
NONESSENTIAL SEQUENCES, GENES, AND THE POLYTENE CHROMOSOME BANDS OF DROSOPHILA MELANOGASTER
Authors: Young Michael W , Judd B H
Published: April 2021

From earlier work, there appears to be an underlying one-to-one correspondence of polytene chromosome bands and complementation groups within a sizeable, continuous X-chromosome segment, 3A1-3C7 (Judd, Shen and Kaufman 1972; Lefevre and Green 1972). However, most of the data supporting this one-to-one relation of bands and genes were gathered from mutants that upset vital functional units, thus leading to lethality. Among this series of mutants, only four loci, zeste, white, roughest and verticals, have no known lethal alleles. If phenotypic changes less drastic than lethality result from the loss of other chromosomal segments, they probably would not have been recognized in the earlier studies.—We report here some chromosomal sequences localized in 3A, 3B, and 3C whose loss effects no lethal change in the development of the animal. A portion of the 3A3-3A4 region can be disrupted in a nonlethal fashion, yet this sequence does not seem to be a part of either the zeste locus or l(1)zw1, which are known to be located in these bands. Two more complementation groups have been discovered that have no lethal alleles and map to 3B4-3B6; a third falls within 3B1-2. The loss of a sequence in 3C2-3 is tolerated without any genetically observable effect. Between 3C7 and the boundary of 3D there is at least one more sequence that behaves in this manner.—The discovery of these units, which are not allelic to any of the loci previously known, makes it clear that division 3B contains more genes (i.e., complementation groups) than polytene chromosome bands, while portions of 3A and 3C seem to have no functional significance. Accordingly many polytene chromosome bands may be composites of several complementing functional units. This investigation also indicates that there are chromosomal segments that are seemingly dispensible and thus function in a manner that is difficult or impossible to define with available methods.
DNA DISTRIBUTION IN SPERMATID NUCLEI OF NORMAL AND SEGREGATION DISTORTER MALES OF DROSOPHILA MELANOGASTER
Authors: Hauschteck-Jungen E , Hartl D L
Published: April 2021

Using the DNA-specific dye BAO [2,5-bis-(4′-aminophenyl-(1′)]-1,3,4-oxadiazol), we have examined spermiogenesis in wild-type males of Drosophila melanogaster and in males carrying various combinations of the Sd and Rsp mutations involved in segregation distortion. Wild-type strains, even those newly collected from nature, are heterogeneous with respect to the incidence of spermiogenic abnormalities, principally in having a variable number of spermatid nuclei per cyst that fail to undergo complete elongation. Among segregation distorter males, Rsp/Rsp homozygotes have the greatest incidence of nuclear nonelongation or incomplete elongation, Rsp/Rsp  + heterozygotes are intermediate, while Rsp  +/Rsp  + homozygotes have the least amount of abnormality. Indeed, Sd Rsp  +/Sd  +  Rsp  + males have significantly fewer spermiogenic aberrations than do wild-type strains.
INDUCED RESISTANCE TO 6-METHYLPURINE AND CYCLOHEXIMIDE IN TETRAHYMENA. II. VARIATION WITHIN VEGETATIVE CULTURES OF MICRONUCLEATE T. THERMOPHILA AND AMICRONUCLEATE T. PYRIFORMIS
Authors: Byrne Bruce C
Published: April 2021

Resistance to 6-methylpurine and cycloheximide has been induced in both the micronucleate species Tetrahymena thermophila and the amicronucleate species T. pyriformis. Resistance follows only after mutagen treatment and vegetative growth. The frequencies with which resistant variants are induced and the independence of mutagenesis and selection are demonstrated. All evidence is consistent with the hypothesis that macronuclear subunits are assorting in both species during vegetative growth to produce new phenotypes among subclones.
BROMODEOXYURIDINE-INDUCED MUTATIONS IN SYNCHRONOUS CHINESE HAMSTER CELLS: TEMPORAL INDUCTION OF 6-THIOGUANINE AND OUABAIN RESISTANCE DURING DNA REPLICATION
Authors: Burki H John , Aebersold Paul M
Published: April 2021

Mutations were induced in synchronous Chinese hamster cells by bromodeoxyuridine (BUdR) incorporated into cells for one-hour periods in the cell cycle. There was a very pronounced temporal dependence during the first half of the DNA synthesis period for the induction of damage leading to 6-thioguanine (6TG) and ouabain resistance. No mutants above background were induced by exposure to BUdR in G1 and G2 cells, and very few mutants were induced in the latter part of the DNA synthesis period. The peak for the induction of 6TG resistance occurs at about two hr in the DNA synthesis period; one hour later there is a peak for the induction of ouabain resistance. Both peaks occur before the time of maximum incorporation of BUdR into DNA. These results suggest that the mutagenesis by BUdR is associated with at least two nuclear genes, which replicate at two hr and three hr in the DNA synthesis period.
USE OF GENETIC EFFECTS AND GENOTYPE BY ENVIRONMENTAL INTERACTIONS FOR THE CLASSIFICATION OF MEXICAN RACES OF MAIZE
Authors: Cervantes Tarcicio S , Goodman Major M , Casas Eduardo D , Rawlings John O
Published: April 2021

To examine the questions of whether the additive and dominance effects present for morphological characters in racial crosses are of sufficient consistency and magnitude to allow such genetic effects to be used for racial classification, we used a diallel experiment among the 25 well-defined Mexican races of maize, which include the ancestral stocks of most commercial and genetic maize types. With such an experiment, genetic effects and genotype by environmental interactions for one or more characters can be used to measure genetic and adaptational or environmental similarity. We used average parental effects (general combining abilities), specific effects, and genotype by environmental effects of 21 characters from the diallel (grown at three locations) to group the Mexican races of maize. The groupings based upon average genetic effects and upon genotype by environmental interactions are more satisfactory than groupings based upon specific effects. The standard errors for genetic distances based upon specific (largely dominance) effects seem to be too high for practical use. Principal components analyses of the same data suggest a similar conclusion.—The groupings based upon average genetic effects are in general agreement with previous studies, with the exception of Maíz Dulce, which is grouped with the Cónicos, rather than being isolated from the other Mexican races of maize.
SITE SPECIFICITY AND VARIABILITY IN THE MUTATOR AND ANTIMUTATOR EFFECTS OF PHAGE T4 GENE 43 MUTANTS
Authors: Ronen Amiram , Halevy Calomira , Kass Nava
Published: April 2021

Spontaneous, 2-aminopurine- and 5-bromouracil-induced mutations at six rII nonsense codons were studied in phage T4 strains possessing wild-type and mutant gene 43 alleles. The mutation pathways studied included interconversions and reversions of nonsense codons. The tsCB87 allele, which specifies an antimutator DNA polymerase, reduced base-analogue-induced mutation frequencies along all pathways. However, GC base pairs were less affected than AT base pairs. The frequency of spontaneous UAA→UAG conversions was also reduced by tsCB87, but that of spontaneous UAA→UGA conversions was often increased. Mutation in the presence of the mutator allele tsL56 was increased along all pathways, with no preference for either AT or GC base pairs. Mutation frequencies in the presence of the two mutant DNA polymerases were highly variable. A strong correlation was found between 2-aminopurine-induced mutation frequencies in ts  + and tsCB87 phage along the reversion and UAA→UAG (but not UAA→UGA) pathways.
NONDISJUNCTION MUTANTS OF THE NEMATODE CAENORHABDITIS ELEGANS
Authors: Hodgkin Jonathan , Horvitz H Robert , Brenner Sydney
Published: April 2021

The frequency of males (5AA; XO) among the self progeny of wild-type Caenorhabditis elegans hermaphrodites (5AA; XX) is about one in 500. Fifteen him (for "high incidence of males") mutations have been identified that increase this frequency by a factor of ten to 150, as a result of increased X-chromosome nondisjunction. The mutations define ten complementation groups, which have been mapped: nine are autosomal, and one sex linked. Most of the mutants are superficially wild type in anatomy and behavior; however, him-4 mutants display gonadal abnormalities, and unc-86 mutants, which have a Him phenotype, exhibit a variety of anatomical and behavioral abnormalities. All the mutants segregate fertile 3X hermaphrodite progeny as well as XO male progeny, Some produce large numbers of inviable zygotes. Mutants in all ten genes produce diplo-X and nullo-X exceptional ova, and in the four strains tested, diplo-X and nullo-X exceptional sperm are produced by 2X "transformed" males. It appears likely that most of the mutants have defects in both gamete lines of the hermaphrodite. XO males of him strains other than him-4 and unc-86 are similar to wild-type males in anatomy and behavior, and all produce equal or almost equal numbers of haplo-X and nullo-X sperm, and no diplo-X sperm. Male fertility is reduced to varying extents in all him mutants. In four of the strains, nondisjunction during oogenesis has been shown to occur at a reductional division, and in three of these strains, abnormalities in recombination have been demonstrated. One mutant also exhibits autosomal nondisjunction, but many of the others probably do not. Therefore, the X chromosome of C. elegans may differ from the autosomes in the mechanisms controlling its meiotic behavior.——3x hermaphrodites are shorter and less fertile than 2X hermaphrodites, and they produce many inviable zygotes among their self progeny: these are probably 4X zygotes. Haplo-X and diplo-X ova are produced in 2:l ratio by 3X hermaphrodites. him mutations are expressed in these animals, increasing the frequency of self-progeny males and 2X hermaphrodites.
GENETIC ANALYSIS OF THE ACHAETE-SCUTE SYSTEM OF DROSOPHILA MELANOGASTER
Authors: García-Bellido A
Published: April 2021

Several mutations in the achaete-scute region of Drosophila have been analyzed phenotypically and cytologically. One group of them corresponds to point mutations, another t o rearrangements with one breakpoint in this region. Trans heterozygotes of the different point mutations or of the different rearrangements show poor complementation or fail to complement; therefore, they could be interpreted as mutations affecting the same gene product. However, left-right inversion recombinants and duplication-deficiency combinations between rearrangements with different cytological breakpoints uncover a complex organization of the achaete-scute region. This region seems to contain several independent achaete and scute functions, as well as a lethal function, arranged as a tandem reverse repeat at both sides of a lethal locus. Since all of the mutants show the same phenotype qualitatively, though different quantitatively, we suggest that these functions are of a reiterative nature. The achaete-scute wild-type condition may well be dependent on a multimeric gene product made of several evolutionary related monomers.
POPULATION DYNAMICS OF SEX-DETERMINING ALLELES IN HONEY BEES AND SELF-INCOMPATIBILITY ALLELES IN PLANTS
Authors: Yokoyama Shozo , Nei Masatoshi
Published: April 2021

Mathematical theories of the population dynamics of sex-determining alleles in honey bees are developed. It is shown that in an infinitely large population the equilibrium frequency of a sex allele is l/n, where n is the number of alleles in the population, and the asymptotic rate of approach to this equilibrium is 2/(3n) per generation. Formulae for the distribution of allele frequencies and the effective and actual numbers of alleles that can be maintained in a finite population are derived by taking into account the population size and mutation rate. It is shown that the allele frequencies in a finite population may deviate considerably from l/n. Using these results, available data on the number of sex alleles in honey bee populations are discussed. It is also shown that the number of self-incompatibility alleles in plants can be studied in a much simpler way by the method used in this paper. A brief discussion about general overdominant selection is presented.
MAXIMUM LIKELIHOOD ESTIMATION OF LINKAGE AND INTERFERENCE FROM TETRAD DATA
Authors: Snow Richard
Published: April 2021

Maximum likelihood equations have been derived for estimation of map distance and interference from two-point and ranked tetrad data. The estimators have been applied to data from Saccharomyces cerevisiae and Schizosac-charomyces pombe. S. cerevisiae consistently shows quite strong interference over the mapped genome. In striking contrast, S. pombe consistently shows much weaker interference and many crosses exhibit negative interference. In neither species was there a conspicuous tendency for intervals spanning a centromere to show less interference than those that did not. Since the amount of recombination per microgram of DNA in the two species is similar, the difference in interference characteristics seems to be a reflection of some fundamental difference in the recombination process of the two species.
REALIGNMENT OF THE GENETIC MAP OF THE TERMINUS OF THE rIIB CISTRON OF BACTERIOPHAGE T4
Authors: Parma David H , Dill Marsha , Slocum Mary K
Published: April 2021

Duplication end-point mapping in the rIIB cistron indicates that the order of the B8-Bl0b segments is the inverse of that presented in BENZER'S (1961) genetic maps. This finding is supported by two- and three-factor crosses and the phenotypes of rII deletions extending into the D region.
ESCHERICHIA COLI K-12 AUXOTROPHS INDUCED BY INSERTION OF THE TRANSPOSABLE ELEMENT Tn5
Authors: Shaw Karen J , Berg Claire M
Published: April 2021

The siies of insertion of the transposable kanamycin-neomycin resistance determining element, Tn5, in the E. coli K-12 chromosome were assessed in a collection of over 300 auxotrophs. Although mutations in at least 45 different cistrons were obtained, the distribution of insertion sites was not completely random: proA or proB; cysG; and cysH, cysD or cysC mutants were found in excess.
THE GENETICS OF HEXOKINASE IN A MOSQUITO, CULEX PIPIENS
Authors: Cheng Min-Lee , Hacker Carl S
Published: April 2021

The genetics of hexokinase (HK) variants in a mosquito, Culex pipiens L., was studied using starch gel electrophoresis. Three isozymic forms of HK, all migrating anodally, were present in all three body regions, but in differing pmportions. No obvious difference in specificity for three hexose sugars was detected among the three isozymic bands. However, qualitative differences in staining intensity indicate the following order of substrate affinity: glucose > fructose > mannose. The inheritance of the HK variants is controlled by a pair of co-dominant alleles at a single genetic locus.
SUPPRESSION OF THE FORMATION OF POLYGENOTYPIC RECOMBINANT COLONIES BY A maf MUTATION IN MATING WITH HfrH
Authors: Ou Jonathan T , Kuo Li-Mei
Published: April 2021

W3011, a Cavalli-type Hfr (HfrC), was mated with F-KY9474, maf-1, which cannot maintain F or F-like plasmids, and with F-OU9474, Maf+, a spontaneous revertant of KY9474. The recombinant colonies obtained were 100% monogenotypic from KY9474 and 90% monogenotypic from OU9474. On the other hand, in matings with OU11, a Hayes-type Hfr (HfrH), and these two F-strains, recombinant colonies derived from KY9474 showed only 22% polygenotypic recombinant colonies; whereas, those derived from OU9474 showed a high production rate (57%) of polygenotypic recombinant colonies. Among the polygenotypic recombinant colonies derived from KY9474 maf-1, 50% contained three or more recombinant types. These were probably derived from a small fraction of Maf+ revertants in the KY9474 population, as suggested by the results of mating this strain with M80, an F′ strain that contains an amber mutation in traH. These results support the hypothesis that the donor DNA fragments derived from an HfrH can undergo a limited replication in the recipient to produce polygenotypic recombinant colonies, whereas those derived from HfrC cannot.
POLYPLOIDS AND SEX DETERMINATION IN CAENORHABDITIS ELEGANS
Authors: Madl James E , Herman Robert K
Published: April 2021

Tetraploid stocks of Caenorhabditis elegans var. Bristol carrying autosomal and X-linked markers have been produced. Tetraploid hermaphrodites fall into two categories: those that give about 1% male self-progeny and those that give 25 to 40% male self-progeny, The former are basically 4A;4X—four sets of autosomes and four sex chromosomes—and the latter are 4A;3X. Males are 4A;2X. (Diploid hermaphrodites are 2A;2X; males are 2A;IX.) Triploids wsre produced by crossing tetraploid hermaphrodites and diploid males. Triploids of composition 3A;3X are hermaphrodites; 3A;2X animals are fertile males. Different X-chromosome duplications were added to a 3A;2X chromosome constitution to increase the X-to-autosome ratio. Based on the resulting sexual phenotypes, we conclude that there exists on the C. elegans X chromosome at least three (and perhaps many mare) dose-sensitive sites that act cumulatively in determining sex.
FREQUENCY- AND DENSITY-DEPENDENT SELECTION ON A QUANTITATIVE CHARACTER
Authors: Slatkin Montgomery
Published: April 2021

The equilibrium distribution of a quantitative character subject to frequency- and density-dependent selection is found under different assumptions about the genetical basis of the character that lead to a normal distribution in a population. Three types of models are considered: (1) one-locus models, in which a single locus has an additive effect on the character, (2) continuous genotype models, in which one locus o r several loci contribute additively to a character, and there is an effectively infinite range of values of the genotypic contributions from each locus, and (3) correlation models, in which the mean and variance of the character can change only through selection at modifier loci. I t is shown that the second and third models lead to the same equilibrium values of the total population size and the mean and variance of the character. One-locus models lead to different equilibrium values because of constraints on the relationship between the mean and variance imposed by the assumptions of those models.—The main conclusion is that, at the equilibrium reached under frequency- and density-dependent selection, the distribution of a normally distributed quantitative character does not depend on the underlying genetic model as long as the model imposes no constraints on the mean and variance.
GENETIC CONTROL OF MALATE DEHYDROGENASE ISOZYMES IN MAIZE
Authors: Goodman M M , Stuber C W , Lee C N , Johnson F M
Published: April 2021

At least six nuclear loci are responsible for the genetic control of malate dehydrogznase (L-malate: NAD oxidoreductase; EC 1.1 .I .37; MDH) in coleoptiles of maize. Three independently segregating loci (Mdh1, Mdh2, Mdh3) govern the production of MDH isozymes resistant to inactivation by ascorbic acid and found largely or solely in the mitochondria. A rare recessive allele found at a fourth nuclear locus (mmm) causes increased electrophoretic mobility of the MDH isozymes governed by the Mdh1, Mdh2 and Mdh3 loci. -Two loci (Mdh4, Mdh5) govern MDH isozymes that are selectively in- activated by homogenization in an ascorbic acid solution and that appear to be nonmitochondrial (soluble). Mdh4 and Mdh5 segregate independently of each other and independently of Mdhl, Mdh2 and Mdh3. However, there is close linkage between the migration modifier and Mdh4.—Multiple alleles have been found for all of the Mdh loci except the migration modifier, and electrophoretically "null" or near "null" alleles (as expressed in standardized sections of maize coleoptile) have been found for all loci except Mdh4. Duplicate inheritance commonly occurs for Mdhl and Mdh2 and also for Mdh4 and Mdh5.—Inter- and intragenic heterodimers are formed between sub-units specified by the three loci governing the mitochondrial MDH isozymes. The same is true of the alleles and nonalleles at the two loci governing the soluble variants. No such heterodimers are formed by interactions between mitochondrial and soluble MDH isozymes.
CYTOKININ AUTONOMY IN TISSUE CULTURES OF PHASEOLUS: A GENOTYPE-SPECIFIC AND HERITABLE TRAIT
Authors: Mok Machteld C , Mok David W S , Armstrong Donald J , Rabakoarihanta Aimée , Kim Sang-Gu
Published: April 2021

Intra- and interspecific differences in cytokinin requirement were detected in callus cultures of Phaseolus vulgaris L. and P. lunatus L. Of the ten geno-types of P. uulgaris tested in the present study, one required cytokinin for callus growth, six exhibited some to moderate growth on cytokinin-free medium, and the remaining three grew uniformly in the absence of cytokinin. In contrast, six of the P. lunatus genotypes were strictly cytokinin-dependent, while four genotypes displayed irregular amount of callus growth on cytokinin-free medium. The genotype-specific behavior of Phaseolus callus tissues was independent of the tissue of origin and the time in culture. The inheritance of the cytokinin requirement of Phareolus tissue cultures was studied in hybrid tissues resulting from crosses between a strictly cytokinin-dependent genotype (P.I. 2aO960) and two independent genotypes (cv. G 50 and P.I. 286303) of P . vulgaris. Fresh weights of hybrid tissues on cytokinin-free medium were intermediate between and significantly different from the parental tissues. No differences were found between reciprocal hybrids. These results suggest that cytokinin autonomy in tissue cultures of P. uulgaris is a genetic trait under nuclear control. Both parental and intermediate phenotypes were recovered in the F, progeny. The frequency distribution of cytokinin-dependent progeny in F, and backcross populations indicates that the cytokinin requirement of P. vulgaris callus tissue may be regulated by one set of alleles.
GENETIC VARIANCE AND CORRELATION AFTER SELECTION FOR TWO TRAITS BY INDEX, INDEPENDENT CULLING LEVELS AND EXTREME SELECTION
Authors: Bennett G L , Swiger L A
Published: April 2021

Three two-trait selection methods were analyzed for their effects on genetic variance and correlation by multivariate methods, two-locus methods and computer simulation. The two-trait selection methods studied were independent culling levels (ICL), index (IND) and extreme (EXT) selection. The effects of the selection methods on genetic variance and correlation were partitioned into permanent effects due to changes in gene frequencies and temporary effects due to nonrandom association of alleles at different loci. Multivariate methods were used to predict temporary effects from a single generation of selection by each method and from several generations of index selection. Two-locus theory was used to determine the stability and rank of temporary effects on genetic correlation for all three methods. Predictions were compared to computer simulation results. When selection increased the means of both traits, EXT had the lowest (closest to,—l.O) genetic correlation and highest variances, while ICL tended to have the highest (closest to 1.0) genetic correlation. When selection increased the mean of one trait and decreased the mean cjf the other, EXT had the highest genetic variances and correlation, while ICL had the lowest genetic variances and correlation.
LINKAGE DISEQUILIBRIUM IN A FINITE POPULATION THAT IS PARTIALLY SELFING
Authors: Golding G B , Strobeck C
Published: April 2021

The linkage disequilibrium expected in a finite, partially selfing population is analyzed, assuming the infinite allele model. Formulas for the expected sum of squares of the linkage disequilibria and the squared standard linkage disequilibrium are derived from the equilibrium values of sixteen inbreeding coefficients required to describe the behavior of the system. These formulas are identical to those obtained with random mating if the effective population size Ne = (l—½S)N and the effective recombination value re = (l-S)r/(l-½S), where S is the proportion of selfing, are substituted for the population size and the recombination value, Therefore, the effect of partial selfing at equilibrium is to reduce the population size by a factor 1 — ½S and the recombination value by a factor (l-S)/(l—½S).