bluuebunny/crossref_metadata_2025 huggingface dataset:
STABLE AND UNSTABLE MUTATIONS IN ABERRANT RATIO STOCKS OF MAIZE
Authors: Mottinger John P , Dellaporta Stephen L , Keller Patrick B
Published: January 2021

Aberrant Ratio (AR) stocks of maize were tested for transposition activity. Lines exhibiting AR and homozygous for the dominant alleles at the Sh Bz and Wx loci in the short arm of chromosome 9 were crossed as males to a sh bz wx tester. Among a population of 346,201 kernels, eight mutations of sh and two of bz were recovered. Eight of the ten mutations survived and none was as vigorous as its normal sibs. At least five of the sh mutants appear to be unstable in F2 and subsequent generations. An unexpected observation was the high incidence of somatic loss of chromosome 9 markers (Sh Bz and Wx), indicating chromosome breakage or nondisjunction. Southern blot hybridization analysis of the sh alterations indicate that all but one mutant are associated with structural DNA rearrangements at the shrunken locus. Possible mechanisms by which these alterations arose are discussed.
DIFFERENT FREQUENCY IN THE RECOVERY OF CROSSOVER PRODUCTS FROM MALE AND FEMALE GAMETES OF PLANTS HYPOPLOID FOR B-A TRANSLOCATIONS IN MAIZE
Authors: Robertson D S
Published: January 2021

The percentage of crossovers is consistently higher in plants hypoploid for six B-A translocations when crossed as males than when crossed as females; in most instances, this excess of male crossing over exceeds that found in control crosses (involving normal chromosomes). Thus, there seems to be something about the hypoploid condition that is responsible for the higher percentage of male crossovers. Several explanations for this "hypoploid effect" are possible, but none has been demonstrated to be responsible for the phenomenon.
PRIMARY TRISOMICS OF RICE: ORIGIN, MORPHOLOGY, CYTOLOGY AND USE IN LINKAGE MAPPING
Authors: Khush G S , Singh R J , Sur S C , Librojo A L
Published: January 2021

Twelve primary trisomics of Oryza sativa L. were isolated from the progenies of spontaneous triploids and were transferred by backcrossing to the genetic background of IR36, a widely grown high yielding rice variety. Eleven trisomics can be identified morphologically from one another and from diploids. However, triplo 11 is difficult to distinguish from diploid sibs.—The extra chromosome of each trisomic was identified cytologically at pachytene stage of meiosis, and the chromosomes were numbered according to their length at this stage. The major distinguishing features of each pachytene chromosome were redescribed.—The female transmission rates varied from 15.5% for triplo 1, the longest chromosome, to 43.9% for triplo 12, the shortest chromosome. Seven of the 12 primary trisomics transmitted the extra chromosome through the male. The low level of chromosomal imbalance tolerated by rice and other evidence are interpreted to indicate that this species is a basic diploid.—Genetic segregation for 22 marker genes in the trisomic progenies was studied. Of a possible 264 combinations, involving 22 genes and 12 trisomics, 120 were examined. Marker genes for each of the 12 chromosomes were identified. The results helped establish associations between linkage groups and cytologically identifiable chromosomes of rice for the first time. Relationships between various systems of numbering chromosomes, trisomics, linkage groups and marker genes are described, and a revised linkage map of rice is presented.
A SUPPRESSOR OF snf1 MUTATIONS CAUSES CONSTITUTIVE HIGH-LEVEL INVERTASE SYNTHESIS IN YEAST
Authors: Carlson Marian , Osmond Barbara C , Neigeborn Lenore , Botstein David
Published: January 2021

The SNF1 gene product of Saccharomyces cerevisiae is required to derepress expression of many glucose-repressible genes, including the SUC2 structural gene for invertase. Strains carrying a recessive snf1 mutation are unable to ferment sucrose. We have isolated 30 partial phenotypic revertants of a snf1 mutant that were able to ferment sucrose. Genetic characterization of these revertants showed that the suppressor mutations were all recessive and defined eight complementation groups, designated ssn1 through ssn8 (suppressor of snf1). The revertants were assayed for secreted invertase activity, and although activity was detected in members of each complementation group, only the ssn6 strains contained wild-type levels. Synthesis of secreted invertase in ssn6 strains was found to be constitutive, that is, insensitive to glucose repression; moreover, the ssn6 mutations also conferred constitutivity in a wild-type (SNF1) genetic background and are, therefore, not merely suppressors of snf1. Pleiotropic defects were observed in ssn6 mutants. Genetic analysis suggested that the ssn6 mutations are allelic to the cyc8 mutation isolated by R. J. Rothstein and F. Sherman, which causes increased production of iso-2-cytochrome c. The data suggest a regulatory function for SSN6.
GENETIC EVIDENCE FOR PHYSICAL INTERACTIONS BETWEEN ENZYMES OF NUCLEOTIDE SYNTHESIS AND PROTEINS INVOLVED IN DNA REPLICATION IN BACTERIOPHAGE T4
Authors: Macdonald Paul M , Hall Dwight H
Published: January 2021

We have found that mutations in phage T4 genes 41 (five of five) and 61 (three of three) cause resistance to the folate analogue pyrimethamine that inhibits T4 dihydrofolate (FH2) reductase. These genes code for subunits of a T4 primase and are part of a putative T4 replication complex. In contrast to many previously isolated folate analogue-resistant (Far) T4 mutants, these T4 primase mutants do not overproduce FH2 reductase nor do they alter its primary structure. A new mutant with a single lesion in gene 41 was isolated which proved resistant to the folate analogue at 30° and was lethal at 42°. This mutant induced normal levels of FH2 reductase (encoded by the frd gene) and appeared to have normal expression of other T4 genes at 30°. Like other mutations in gene 41, tsP129 reduced phage-induced DNA synthesis to about 15% that of wild-type T4 as measured by thymidine incorporation under restrictive conditions. Double mutants carrying mutations in genes 41 and 61, 41 and frd or 61 and frd showed allele-specific suppression suggesting that the products of these genes interact. We suggest that abnormal interactions between components of the replication complex and a DNA precursor synthesizing complex cause folate analog resistance by allosterically altering the T4 FH2 reductase.
COINCIDENT GENE CONVERSION DURING MITOSIS IN SACCHAROMYCES
Authors: Golin John E , Esposito Michael S
Published: January 2021

During mitosis, gene conversion events at the TRP5 locus on chromosome VII are coupled with conversion events at LEU1, a locus 18 cM away, 1200 times more frequently than would be expected for two independent acts of recombination. Such coincident conversion events that occur over relatively long distances could be due to several mechanisms. We discuss these possibilities and describe an experiment that indicates that a portion of coincident events is due to extensive heteroduplexes. The phenomenon of coincident gene conversion is discussed in relation to our earlier evidence that spontaneous recombination between homologues occurs prereplicationally in mitosis.
RECOMBINATION BETWEEN COMPONENTS OF A MUTABLE GENE SYSTEM IN MAIZE
Authors: Kermicle Jerry L
Published: January 2021

An unstable component (I-R) of the R-stippled allele interacts with a linked modifier which enhances stippled's expression (M-st) to delete the intervening segment. The precision of deletion formation suggests a recombinational basis, specifically unequal crossing over between I-R and M-st. Four deletions were selected as losses of R function from plants homozygous for R-st and M-st. Also lost are stippled's near-colorless seed phenotype, its paramutagenicity and a closely linked gene, Inhibitor of striate. The deletion chromosomes, missing a 6-cM segment, are transmitted normally by ovules but in reduced frequency by pollen. Homozygous and heteroallelic combinations of the deletions confer defective seed lethality. The four did not differ detectably in transmissibility or breakpoint termini. The recurrence of deletions that have the same termini is explained by recombination between I-R and M-st. The homology between M-st and I-R, and their presence in the same chromosome arm, favors the view that M-st originated by I-R transposition.
MECHANISM OF IS1 TRANSPOSITION IN E. COLI: CHOICE BETWEEN SIMPLE INSERTION AND COINTEGRATION
Authors: Biel Susan W , Berg Douglas E
Published: January 2021

nsertion element IS 1 and IS 1-based transposon Tn 9 generate cointegrates (containing vector and target DNAs joined by duplicate copies of IS 1 or Tn 9) and simple insertions (containing IS 1 or Tn 9 detached from vector sequences). Based on studies of transposon Tn 5 we had proposed a conservative (non-replicative) model for simple insertion. Others had proposed that all transposition is replicative, occurring in a rolling circle structure, and that the way DNA strands are joined when replication terminates determines whether a simple insertion or a cointegrate is formed.—We selected for the transposition of amp and cam resistance markers from pBR322::Tn 9 plasmids to an F factor in recA  -  E. coli and identified products containing three and four copies of IS 1, corresponding to true cointegrates (from monomeric plasmids), and simple insertions (from dimeric plasmids). The simple insertions with four copies of IS 1 outnumbered those with three by a ratio of about 3:1, whereas true cointegrates containing three copies of IS 1 were more numerous than those with four.—A straightforward rolling circle model had predicted that the simple insertions containing three copies of IS 1 should be more frequent than those with four. Because we obtained the opposite result we propose that simple insertions only arise when the element fails to replicate or if replication starts but then terminates prematurely. The two classes of products, simple insertions and cointegrates, reflect alternative conservative and replicative fates, respectively, of an early intermediate in transposition.
HETEROCHROMATIC POSITION EFFECT AT THE ROSY LOCUS OF DROSOPHILA MELANOGASTER: CYTOLOGICAL, GENETIC AND BIOCHEMICAL CHARACTERIZATION
Authors: Rushlow C A , Chovnick A
Published: January 2021

This report describes cytological, genetic and biochemical studies designed to characterize two Υ-radiation induced, apparent "underproducer" variants of the rosy locus (ry:3-52.0), ryps  1149 and ryps  11136. The following observations provide a compelling basis for their diagnosis as heterochromatic position effect variants. (1) They are associated with rearrangements that place heterochromatin adjacent to the rosy region of chromosome 3 (87D). (2) The effect of these mutations on rosy locus expression is subject to modification by abnormal Y chromosome content. (3) The rearrangement alters only the expression of the rosy allele on the same chromosome (cis-acting). (4) The Y chromosome modification is only on the position-affected allele's expression. (5) The recessive lethality associated with the rearrangements relate to specific rosy region vital loci, and for ryps  11136, the lethality is not Y chromosome modified. (6) The peptide product of the position-affected allele is qualitatively normal by several criteria. (7) Heterozygous deletion of 87E2-F2 is a suppressor of the rosy position effect. (8) The rosy position effect on XDH production may be assayed in whole larvae and larval fat body tissue as well as in adults.
THE MOLECULAR BASIS OF GENETIC DIVERSITY AMONG CYTOPLASMS OF TRITICUM AND AEGILOPS. III. CHLOROPLAST GENOMES OF THE M AND MODIFIED M GENOME-CARRYING SPECIES
Authors: Terachi T , Ogihara Y , Tsunewaki K
Published: January 2021

The restriction fragment patterns of chloroplast DNAs of all M or modified M genome-carrying Aegilops species, and those of common wheat (Triticum aestivum), Ae. umbellulata and Ae. squarrosa as referants, have been analyzed using eight restriction endonucleases, BamHI, Eco RI, Hin dIII, Kpn I, Pst I, Sal I, Sma I and Xho I. Nine distinctly different chloroplast genomes are evident, and the mutual relatedness among them is estimated based on the number of different restriction fragments. The results lead to the following conclusions. (1) Chloroplast genomes of three Comopyrum species, Ae. comosa, Ae. heldreichii and Ae. uniaristata, are more closely related with each other and are greatly different from those of the Amblyopyrum species, Ae. mutica, and of Ae. umbellulata and Ae. squarrosa. (2) Ae. crassa's chloroplast genome lies at the center of chloroplast genome diversification, whereas those of common wheat, Ae. squarrosa and Ae. uniaristata are three extreme forms lying far from the center. (3) Chloroplast genomes of three 4x species, Ae. biuncialis, Ae. columnaris and Ae. triaristata, arose from Ae. umbellulata, and that of a fourth 4x species, Ae. ventricosa, arose from Ae. squarrosa. The chloroplast origins of two other 4x species, Ae. ovata and Ae. crassa, remain unsolved. (4) The chloroplast genomes of two Ae. mutica strains are identical, even though their cytoplasms exert quite different effects on male fertility, heading date and growth vigor of common wheat.
THE SELECTIVE VALUE OF ALLELES UNDERLYING POLYGENIC TRAITS
Authors: Lynch Michael
Published: January 2021

To define the genetic and ecological circumstances that are conductive to evolution via genetic drift at the allelic level, the selection coefficient for a constituent allele of arbitrary effect is derived for a polygenic character exposed to stabilizing selection. Under virtually all possible conditions, alleles within the class for which the absolute value of the average effect is <10-2 phenotypic standard deviations are neutral with respect to each other. In addition, when the mean phenotype is at the optimum and the genetic variance is in selection-drift-mutation equilibrium, a considerable amount of neutral evolution is expected in the class of alleles with intermediate effects on the phenotype. These results help clarify how molecular evolution via genetic drift may occur at a locus despite intense selection and provide a potential mechanistic explanation for the neutral theory of molecular evolution.
MERODIPLOIDY IN ESCHERICHIA COLI-SALMONELLA TYPHIMURIUM CROSSES: THE ROLE OF UNEQUAL RECOMBINATION BETWEEN RIBOSOMAL RNA GENES
Authors: Lehner Andreas F , Hill C W
Published: January 2021

Previous workers have shown that intergeneric crosses between Salmonella typhimurium and Escherichia coli produce a high proportion of merodiploid recombinants among the viable progeny. We have examined the unequal crossover event that was responsible for a number of intergeneric merodiploids. The merodiploids that we studied were all heterozygous for the metB–argH interval and were the products of intergeneric conjugal crosses. We found that when the S. typhimurium donor had its transfer origin closely linked to metB and argH, all recombinants examined were merodiploid, and they generally arose as F-prime factors. Many of these F-prime factors had been created by recombination between flanking rrn genes in the donor. When the S. typhimurium Hfr transfer origin was more distant from the selected markers, quite different results were obtained. (1) Depending on the donor, 19–47% of the recombinants that acquired the donor argH  + or metB  + genes were merodiploid for these loci, but none of the recombinants were F-prime. (2) A majority of the merodiploids had a novel (nonparental) rrn gene, indicating that unequal recombination between nonidentical rrn genes was a prevalent mechanism for establishing the merodiploidy. (3) Both tandem and nontandem duplications were found. (4) Some of the merodiploids duplicated E. coli genes in addition to acquiring S. typhimurium genes. (5) Some merodiploids contained the oriC region from each parent. Of a total of 118 intergeneric merodiploids characterized from all donors, 48 different genotypes were observed, and 38 of the 48 had one or more nonparental rrn operons.
ISOLATION AND GENETIC ANALYSIS OF MUTATIONS AT THE SerH IMMOBILIZATION ANTIGEN LOCUS OF TETRAHYMENA THERMOPHILA
Authors: Doerder F P , Berkowitz M S , Skalican-Crowe J
Published: January 2021

Multiple alleles at the SerH locus specify the major cell surface protein (immobilization antigen) of the ciliate Tetrahymena thermophila. Following mutagenesis of SerH1 homozygotes, two mutations, H1-1 and H1-2, were recovered in heterozygous form. Mutant homozygotes do not express H1 antigen, nor is H1 expressed in F1 progeny of crosses to wild-type strains homozygous for SerH2 or SerH3. H1-1 and H1-2 segregate without recombination from these wild-type alleles in expected F2 and testcross Mendelian ratios. H1-1 and H1-2 do, however, complement each other to express H1 antigen. Experiments suggest this complementation is due neither to recombination during macronuclear development nor to interallelic complementation of defective SerH1 gene products. These results suggest that SerH1 is intact in one mutant, and possibly both, although no such allele has been segregated in testcross progeny (N = 205). The hypothesis is presented that complementation between H1-1 and H1-2 is due to interaction between allele-specific regulators closely linked to the SerH1 gene.
ISOLATION AND CHARACTERIZATION OF MUTATIONS IN THE β-TUBULIN GENE OF SACCHAROMYCES CEREVISIAE
Authors: Thomas James H , Neff Norma F , Botstein David
Published: January 2021

Of 173 mutants of Saccharomyces cerevisiae resistant to the antimitotic drug benomyl (BenR), six also conferred cold-sensitivity for growth and three others conferred temperature-sensitivity for growth in the absence of benomyl. All of the benR mutations tested, including the nine conditional-lethal mutations, were shown to be in the same gene. This gene, TUB2, has previously been molecularly cloned and identified as the yeast structural gene encoding β-tubulin. Four of the conditional-lethal alleles of TUB2 were mapped to particular restriction fragments within the gene. One of these mutations was cloned and sequenced, revealing a single amino acid change, from arginine to histidine at amino acid position 241, which is responsible for both the BenR and the cold-sensitive lethal phenotypes. The terminal arrest morphology of conditional-lethal alleles of TUB2 at their restrictive temperature showed a characteristic cell-division-cycle defect, suggesting a requirement for tubulin function primarily in mitosis during the vegetative growth cycle. The TUB2 gene was genetically mapped to the distal left arm of chromosome VI, very near the actin gene, ACT1; no CDC (cell-division-cycle) loci have been mapped previously to this location. TUB2 is thus the first cell-division-cycle gene known to encode a cytoskeletal protein that has been identified in S. cerevisiae.
RECESSIVE MUTATIONS FROM NATURAL POPULATIONS OF NEUROSPORA CRASSA THAT ARE EXPRESSED IN THE SEXUAL DIPLOPHASE
Authors: Leslie John F , Raju Namboori B
Published: January 2021

Wild-collected isolates of Neurospora crassa Shear and Dodge were systematically examined for recessive mutations affecting the sexual phase of the life cycle, which is essentially diploid. Seventy-four of 99 wild-collected isolates from 26 populations in the United States, India and Pakistan carried one or more recessive mutations that reduced fertility significantly when homozygous; mutations affecting spore morphology were also detected. Limited complementation tests indicate that most of the 106 recovered mutations are unique.—The recessive diplophase (= sexual phase) mutations were uncovered by crossing each wild-collected isolate to a marked two-chromosome double-reciprocal translocation strain as "balancer." Surviving progeny receive approximately 60% of their genome from the wild parent, but receive the mating-type allele from the "balancer" parent. These progeny were backcrossed to the wild parent and were also crossed with a standard laboratory strain (fl). Reduced fertility in the backcross vs. normal fertility in the cross with the laboratory standard signals the presence of a recessive mutation in the wild-collected isolate.—Most of the mutants (95 of 106) fall into two major classes: those producing barren perithecia with no or few viable ascospores (51) and those with spore maturation defects (44). Most of the recessive barrens result either from an early block in meiosis or ascus development (25) or from a late disturbance in postmeiotic ascus behavior (18).—These recessive mutations are formally equivalent to recessive lethals in higher eukaryotes and may be important in determining the breeding structure of natural Neurospora populations.
MEIOTIC NONDISJUNCTION AND ANEUPLOIDS IN INTERSYNGENIC HYBRIDS OF PARAMECIUM CAUDATUM
Authors: Tsukii Yuuji , Hiwatashi Koichi
Published: January 2021

Artificially induced intersyngenic crosses in Paramecium caudatum can produce viable and fertile hybrids. When F1 hybrids of double E mating type (Mt  1/Mt  3 or Mt  12/Mt  3) were crossed with mating type O (mt/mt), aberrant segregants of double E and single O type were produced. This segregation was not explained by ordinary equal or unequal crossing over. Breeding analyses of these segregants by using linkage between Mt and cnrA (a behavioral mutant) revealed that they were produced by meiotic nondisjunction of bivalent chromosomes carrying Mt genes, and thus the double E and single O segregants were aneuploids: trisomics (Mt  1/Mt  3/mt or Mt  12/Mt  3/mt) and monosomics (mt), respectively. An aberrant segregant was also obtained for another locus, tnd 2, independent of both Mt and cnrA, suggesting the occurrence of meiotic nondisjunction throughout hybrid genomes. These aneuploids will be useful for genetic study in this species. The occurrence of meiotic nondisjunction in the intersyngenic hybrids also suggests that syngens of P. caudatum have been reproductively isolated for long enough to develop chromosomal incompatibility in their meiotic process.
MOST OF THE HOMOEOLOGOUS PAIRING AT METAPHASE I IN WHEAT-RYE HYBRIDS IS NOT CHIASMATIC
Authors: Orellana Juan
Published: January 2021

The use of telomeric C-bands in wheat-rye hybrids has made it possible to distinguish three types of wheat-wheat (1BL) and wheat-rye associations (a, end-to-end extremely distal; b, end-to-ed distal; and c, interstitial) between homoeologous chromosomes at different metaphase I stages (early, middle and late) and also to estimate the actual recombination frequencies for such associations at anaphase I. There was a decrease of the a and b association frequencies during the different metaphase I stages, whereas the c type remained without variation in all stages. A good fit between the frequencies of c associations at metaphase I and the number of recombinant chromosomes at anaphase I, assuming a maximum of one chiasma per bond, was found; however, there was no correspondence between metaphase I and anaphase I data when all associations (a + b + c) were considered. In addition, rye-rye homologous pairing was observed at metaphase I, but no evidence for rye-rye recombination was found at anaphase I. The results indicate that most of end-to-end (a and b) homoeologous and nonhomologous associations are actually nonchiasmatic and are a remnant of prophase pairing.
GENETICS OF PARTHENOGENESIS IN DROSOPHILA MELANOGASTER. I. THE MODES OF DIPLOIDIZATION IN THE GYNOGENESIS INDUCED BY A MALE-STERILE MUTANT, ms(3)K81
Authors: Fuyama Yoshiaki
Published: January 2021

Sperm that are produced by males homozygous for ms(3)K81, a male sterile mutant of Drosophila melanogaster, are defective in syngamy but are capable of activating eggs to develop gynogenetically. The activated eggs usually produce haploid embryos, but a small fraction (10-4-10-5) of them give rise to diploid impaternate adults. To know the cytological mechanisms by which these impaternates restore diploidy, the genotypes of impaternate progeny obtained from females doubly heterozygous for visible markers were examined. The results show that, as generally found among parthenogenetic Drosophila, diploidy is restored after completing meiosis either by pronuclear fusion or by gamete duplication (doubling of a haploid cleavage nucleus). The fusion of two nonsister nuclei following meiosis II (central fusion) was indicated to be a predominant mode of diploidization in this species. Two meiotic mutants, mei-9 and mei-S332, which are known to greatly increase meiotic nondisjunction, did not cause an increased incidence of impaternates. This seems to exclude the possibility that some impaternates might have been derived from diploid egg nuclei produced through nondisjunction.
EVIDENCE FOR REGULATORY VARIANTS OF THE DOPA DECARBOXYLASE AND ALPHA-METHYLDOPA HYPERSENSITIVE LOCI IN DROSOPHILA
Authors: Marsh J Lawrence , Wright T R F
Published: January 2021

We have analyzed two variants of Drosophila melanogaster(RS and RE) which lead to the dual phenotype of elevated DDC activity and increased resistance to dietary alpha-methyldopa relative to Oregon-R controls. Both phenotypes show tight genetic linkage to the dopa decarboxylase, Ddc, and l(2)amd genes (i.e., < 0.05 cM distant). We find that low (Oregon-R), medium (RS) and high (RE and Canton-S) levels of DDC activity seen at both pupariation and eclosion in these strains are completely accounted for by differences in accumulation of DDC protein as measured by immunoprecipitation. Genetic reconstruction experiments in which Ddc  + and amd  + gene doses are varied show that increasing DDC activity does not lead to a measurable increase in resistance to dietary alphamethyldopa. This suggests that the increased resistance to dietary alpha-methyldopa is not the result of increased DDC activity but, rather, results from increased l(2)amd  + activity. Both cytogenetic and molecular analyses indicate that these overproduction variants are not the result of small duplications of the Ddc and amd genes, nor are they associated with small (?100 bp) insertions or deletions. Measurements of DDC activity in wild-type strains of Drosophila reveal a unimodal distribution of activity levels with the Canton-S and RE strains at the high end of the scale, the Oregon-R control at the low end and RS near the modal value. We conclude that accumulated changes in a genetic element (or elements) in close proximity to the Ddc  + and amd  + genes lead to the coordinated changes in the expression of the Ddc and amd genes in these strains.
β-GLUCURONIDASE MUTANTS OF THE NEMATODE CAENORHABDITIS ELEGANS
Authors: Sebastiano Marisa , D'Alessio Marina , Bazzicalupo Paolo
Published: January 2021

Using a screening procedure that is based on a histochemical stain for the enzyme β-glucuronidase, we have isolated several mutants of the nematode Caenorhabditis elegans affected in β-glucuronidase activity. All of the mutations fall into one complementation group and identify a new gene, gus-1, which has been mapped on the right arm of linkage group I (LG I), 1.1 map units to the left of unc-54. The mutants have no visible phenotype, and their viabilities and fertilities are unaffected. Linked revertants of two of the mutations have been isolated. They restore enzyme activity to almost wild-type levels; the β-glucuronidase that one of the revertants produces differs from that of the wild type. We propose that gus-1 is the structural locus for β-glucuronidase.
INTERACTIONS BETWEEN WHITE GENES CARRIED BY A LARGE TRANSPOSING ELEMENT AND THE ZESTE
1 ALLELE IN DROSOPHILA MELANOGASTER
Authors: Gubb D , Roote J , McGill S , Shelton M , Ashburner M
Published: January 2021

TE146, a large transposing element of Drosophila melanogaster, carries two copies of the white and roughest genes in tandem. In consequence, z  1  w  11E4; TE146(Z)/+ flies have a zeste (lemon-yellow) eye color. However, one in 103  TE146 chromosomes mutates to a red-eyed form. The majority of these "spontaneous red" (SR) derivatives of TE146 have only one copy of the white gene and are, cytologically, two- to three-banded elements, rather than six-banded as their progenitor. The SR forms of TE146 are also unstable and give zeste-colored forms with a frequency of about one in 104. One such "spontaneous zeste" (SZ) derivative carries duplicated white genes as an inverted, rather than a tandem, repeat. The genetic instability of this inverted repeat form of TE146 is different from that of the original tandem repeat form. In particular, the inverted repeat form frequently produces derivatives with internal rearrangements of the TE and gives a much lower frequency of SR forms. In addition, two novel features of the interaction between w  + alleles in a zeste background have been found. First, copies of w  + can become insensitive to suppression by zeste even when paired. Second, an inversion breakpoint may disrupt the pairing between two adjacent w  + alleles, necessary for their suppression by zeste, without physically separating them.
EVOLUTIONARY CHANGE OF RESTRICTION CLEAVAGE SITES AND PHYLOGENETIC INFERENCE
Authors: Li Wen-Hsiung
Published: January 2021

Mathematical formulas are developed for the evolutionary change of restriction cleavage sites in a DNA sequence, allowing unequal rates between transitional and transversional types of nucleotide substitution. Formulas are also developed for the probability of having a particular pattern of site changes among evolutionary lineages, such as parallel gains or losses of sites, and for inferring the presence or absence of a restriction site in an ancestral sequence from data on the present-day sequences. The unordered compatibility method is proposed for inferring the phylogenetic relationships among relatively closely related organisms, treating restriction sites as cladistic characters. Formulas are derived for the probability (P  +) of obtaining the correct network for a given number (N) of informative sites for the cases of four and five species. These formulas are applied to evaluate the performance of the method and to estimate the N value required for P  + to be 95% or larger. The method performs well when the branches between ancestral nodes and the branches leading to the two most recent species are more or less equal in length, but performs poorly when the latter two branches are considerably longer than the former.
GENETIC AND MOLECULAR ANALYSIS OF THE GAL3 GENE IN THE EXPRESSION OF THE GALACTOSE/MELIBIOSE REGULON OF SACCHAROMYCES CEREVISIAE
Authors: Torchia Timothy E , Hopper James E
Published: January 2021

During the galactose adaptation period of a Saccharomyces cerevisiae strain bearing a naturally occurring gal3 allele, we found a longer induction lag and slower rate of accumulation of GAL10 and MEL1 RNAs compared to wild-type strains. A strain of genotype gal3 gal1 gal7 is noninducible for MEL1 gene expression, but this expression block is bypassed by overexpression of the GAL4 gene or by deletion of the GAL80 gene, either of which causes a constitutive phenotype. An otherwise wild-type strain that bears a chromosomal gal3 gene disruption mutation does not produce wild-type GAL3 RNA and exhibits induction comparable to a strain bearing the naturally occurring gal3. Based on this array of results, we conclude that the GAL3 gene product executes its function at a point before GAL4 mediated transcription of the GAL1-10-7 and MEL1 genes. Thus, the data are consistent with the previously advanced hypothesis that the GAL3 gene product functions to synthesize the inducer or coinducer molecule. In experiments in which the presence of either the plasmid-carried cloned GAL3 gene or the plasmid-carried cloned GAL1-10-7 genes allows MEL1 induction of a gal3 gal1 gal7 cell, we find that loss of the plasmid results in the shutoff of MEL1 expression even when galactose is continuously present. Either GAL3 function or GAL1-10-7 functions are therefore required for both the initiation and the maintenance of the induced state. Since the strains bearing either the naturally occurring gal3 allele or the gal3 disruption (null) allele do induce, the plasmid loss experiments indicate the existence of two completely independent induction initiation-maintenance pathways, one requiring GAL3 function, the other requiring GAL1-10-7 function. Finally, Northern blot analysis reveals two major GAL3 transcripts that differ in size by approximately 500 nucleotides.
AN EXPERIMENTAL TEST OF THE RELATIONSHIP BETWEEN GENETIC VARIATION AND ENVIRONMENTAL VARIATION IN TRIBOLIUM FLOUR BEETLES
Authors: Riddle Russel A , Dawson Peter S , Zirkle Dave F
Published: January 2021

The hypothesis that a component of genetic variation for polygenic fitness traits is maintained by environmental heterogeneity was tested using an experimental system involving two species of flour beetles, Tribolium castaneum and T. confusum. Replicated populations of each species from a number of environmental treatments were analyzed for various fitness components following almost 60 generations of natural selection. Environmental differences consisted of flours of cereals commonly invaded by natural populations of these insects.—Tests for adaptation to environments were based on experiments in which populations were reared factorially on each flour, such that population treatment x flour interactions could be detected. Measurements were made of survival, growth rate, larval weight, pupal weight, developmental time, fecundity of individuals at low density and fecundity and cannibalism at high density in both fresh and conditioned media.—Flour differences were found to have significant effects on most traits. Evidence for significant genetic variation and significant genotype x environment interaction was also found. However, no evidence could be found to support the hypothesis that genetic variation was maintained by environmental heterogeneity in food resources. The absence of adaptation to the experimental treatments despite the presence of genetic variation in fitness components suggests that pleiotropy may assume an important role in determining net fitness values of polygenes.
THE GENETICS OF THE DORSAL-BICAUDAL-D REGION OF DROSOPHILA MELANOGASTER
Authors: Steward Ruth , Nüsslein-Volhard Christiane
Published: January 2021

The chromosomal region 36C on 2L contains two maternal-effect loci, dorsal (dl) and Bicaudal-D (Bic-D), which are involved in establishing polarity of the Drosophila embryo along the dorsal-ventral and anterior-posterior axes, respectively. To analyze the region genetically, we isolated X-ray-induced dorsal alleles, which we recognized by virtue of the haplo-insufficient temperature-sensitive dorsal-dominant phenotype in progeny of single females heterozygous for a mutagenized chromosome. From the 20,000 chromosomes tested, we isolated three deficiencies, two inversions with breakpoint in dl and one apparent dl point mutant. One of the deficiencies, Df(2L)H20 (36A6,7; 36F1,2) was used to screen for EMS-induced lethal- and maternal-effect mutants mapping in the vicinity of dl and Bic-D. We isolated 44 lethal mutations defining 11 complementation groups. We also recovered as maternal-effect mutations four dl alleles, as well as six alleles of quail and one allele of kelch, two previously identified maternal-effect genes. Through complementation tests with various viable mutants and deficiencies in the region, a total of 18 loci were identified in an interval of about 30 cytologically visible bands. The region was subdivided into seven subregions by deficiency breakpoints. One lethal complementation group as well as the two maternal loci, Bic-D and quail, are located in the same deficiency interval as is dl.
MOLECULAR ZOOGEOGRAPHY OF FRESHWATER FISHES IN THE SOUTHEASTERN UNITED STATES
Authors: Bermingham Eldredge , Avise John C
Published: January 2021

Restriction fragment length polymorphisms in mitochondrial DNA (mtDNA) were used to reconstruct evolutionary relationships of conspecific populations in four species of freshwater fish—Amia calva, Lepomis punctatus, L. gulosus, and L. microlophus. A suite of 14-17 endonucleases was employed to assay mtDNAs from 305 specimens collected from 14 river drainages extending from South Carolina to Louisiana. Extensive mtDNA polymorphism was observed within each assayed species. In both phenograms and Wagner parsimony networks, mtDNA clones that were closely related genetically were usually geographically contiguous. Within each species, major mtDNA phylogenetic breaks also distinguished populations from separate geographic regions, demonstrating that dispersal and gene flow have not been sufficient to override geographic influences on population subdivision.—Importantly, there were strong patterns of congruence across species in the geographic placements of the mtDNA phylogenetic breaks. Three major boundary regions were characterized by concentrations of phylogenetic discontinuities, and these zones agree well with previously described zoogeographic boundaries identified by a different kind of data base—distributional limits of species—suggesting that a common set of historical factors may account for both phenomena. Repeated episodes of eustatic sea level change along a relatively static continental morphology are the likely causes of several patterns of drainage isolation and coalescence, and these are discussed in relation to the genetic data.—Overall, results exemplify the positive role that intraspecific genetic analyses may play in historical zoogeographic reconstruction. They also point out the potential inadequacies of any interpretations of population genetic structure that fail to consider the influences of history in shaping that structure.
GENERAL SELECTION FOR SPECIFIC DNA-BINDING ACTIVITIES
Authors: Benson Nicholas , Sugiono Paul , Bass Steven , Mendelman Lynn V , Youderian Philip
Published: January 2021

We present a general strategy for the selection of bacterial clones that express DNA-binding activities corresponding to particular DNA recognition sites. The selection uses a "challenge phage" vector, P22 Kn9 arc-am H1605, into which is substituted a synthetic DNA-binding site for a site that controls transcription of the P22 antirepressor (ant) gene. Constitutive synthesis of antirepressor channels a challenge phage into lytic development and efficiently kills an infected host, unless the substituted site is bound by a specific protein; in this case, the challenge phage prefers lysogenic development, and the host survives and acquires an antibiotic-resistance phenotype. Infections with challenge phages carrying the E. coli Lac operator, phage λOL1 operator, or synthetic, "idealized" E. coli Trp and Tn10 Tet operators select clones that express each of the corresponding binding activities. The use of challenge phage vectors may be extended to select clones that express eukaryotic DNA-binding activities.
DETECTION OF Rsp AND MODIFIER VARIATION IN THE MEIOTIC DRIVE SYSTEM SEGREGATION DISTORTER (SD) OF DROSOPHILA MELANOGASTER
Authors: Lyttle Terrence W , Brittnacher John G , Ganetzky Barry
Published: January 2021

Identification of allelic variability at the two major loci (Sd and Rsp) that interact to cause sperm dysfunction in Segregation distorter (SD) males of D. melanogaster has been hampered by the difficulty in separating the elements recombinationally. In addition, small differences in the strength of Sd alleles or sensitivities of Rsp alleles to Sd are difficult to measure against background genetic or environmental variation. Viability effects of the markers used to score progeny classes may also introduce a bias. Removal of Sd and E(SD) from their second chromosome location to create a Dp(2;Y)Sd E(SD) chromosome eliminates these problems, since any combination of Rsp alleles can be easily tested without resorting to recombinational techniques. Further, since these pairs of Rsp alleles are compared in their response to Dp Sd E(SD) in the same individual males, background variation and viability effects can be easily removed to allow finescale resolution of Rsp differences. Tests of all possible pairwise combination of six laboratory chromosomes in this way revealed at least three and possibly four different Rsp allelic classes. In addition, the hierarchical nature of the tests further allowed for determination of the presence of linked suppressors or enhancers of Sd activity. A sample of 11 second chromosomes selected from a group recently isolated from a natural population was also unambiguously ordered as to Rsp allelic status using this approach. The resultant pattern was similar to that obtained for the laboratory chromosomes, except for the not unexpected observation that the natural population apparently harbored more drive suppressors. The pattern of results obtained from these pairwise combinations of Rsp alleles supports the notion that there are no dominance interactions within the group, but that each responds more or less independently to Sd in giving sperm dysfunction.
EXPERIMENTAL ANALYSIS OF A PATERNALLY INHERITED EXTRACHROMOSOMAL FACTOR
Authors: Werren John H , van den Assem Johannes
Published: January 2021

Virtually all known cases of extrachromosomal inheritance involve cytoplasmic inheritance through the maternal line. Recently, a paternally transmitted factor that causes the production of all-male families has been discovered in a parasitic wasp. The wasp has haplodiploid sex determination: male offspring are haploid and usually develop from unfertilized eggs, whereas females are diploid and usually develop from fertilized eggs. It has been postulated that this paternal sex-ratio factor (psr) is either (1) an infectious agent (a venereal disease) that is transmitted to the female reproductive tract during copulation with an infected male and, subsequently, causes all-male families or (2) a male cytoplasmic factor that is transmitted by sperm to eggs upon egg fertilization and, somehow, causes loss of the paternal set of chromosomes.—Experimental evidence is presented which shows that the factor requires egg fertilization for transmission to the next generation; therefore, it is likely to be a cytoplasmic factor. Significant potential intragenomic conflict results from the presence of this factor and two other sex-ratio distorters in this wasp species.
GENETICS OF PARTHENOGENESIS IN DROSOPHILA MELANOGASTER. II. CHARACTERIZATION OF A GYNOGENETICALLY REPRODUCING STRAIN
Authors: Fuyama Yoshiaki
Published: January 2021

A strain of Drosophila melanogaster, named gyn-F9, can reproduce by gynogenesis. On mating with a male sterile mutant, ms(3)K81, gyn-F9 females produced impaternate progeny at a rate of about 15 flies per female, which was almost 2000 times as frequent as that of the control. When the females were mated with normally fertile males, the number of offspring varied extremely from parent to parent, with average fertility being much lower than that of normal females. Nearly one-third of these bisexual progeny were either triploid females or intersexes. Among the rest of the progeny, some were diploid impaternates having developed without syngamy. The gynogenetic property of gyn-F9 is primarily governed by a few genes, most likely two recessive genes, one each located on the second and third chromosomes. The impaternates were found to restore their diploidy by the fusion of two nonsister nuclei out of the four egg pronuclei which result from the second meiotic division (central fusion). Although nondisjunction occurs frequently in the meiosis of gyn-F9, this is unlikely to bring about an appreciable number of diploid gametes developing into impaternates. Possible mechanisms of the evolutionary origin of parthenogenesis are discussed in relation to these findings.
THE ORGANIZATION OF GENETIC VARIATION FOR RECOMBINATION IN DROSOPHILA MELANOGASTER
Authors: Brooks Lisa D , Marks R William
Published: January 2021

The amount and form of natural genetic variation for recombination were studied in six lines for which second chromosomes were extracted from a natural population of Drosophila melanogaster. Multiply marked second, Χ and third chromosomes were used to score recombination. Recombination in the second chromosomes varied in both amount and distribution. These second chromosomes caused variation in the amount and distribution of crossing over in the Χ chromosome and also caused variation in the amount, but not the distribution, of crossing over in the third chromosome. The total amount of crossing over on a chromosome varied by 12-14%. One small region varied twofold; other regions varied by 16-38%. Lines with less crossing over on one chromosome generally had less crossing over on other chromosomes, the opposite of the standard interchromosomal effect. These results show that modifiers of recombination can affect more than one chromosome, and that the variation exists for fine-scale response to selection on recombination.
CHARACTERIZATION OF THE HETEROKARYOTIC AND VEGETATIVE DIPLOID PHASES OF MAGNAPORTHE GRISEA
Authors: Crawford Mark S , Chumley Forrest G , Weaver Carolyn G , Valent Barbara
Published: January 2021

The heterokaryotic and vegetative diploid phases of Magnaporthe grisea, a fungal pathogen of grasses, have been characterized. Prototrophic heterokaryons form when complementary auxotrophs are paired on minimal medium. Hyphal tip cells and conidia (vegetative spores) taken from these heterokaryons are auxotrophs with phenotypes identical to one or the other of the parents. M. grisea heterokaryons thus resemble those of other fungi that have completely septate hyphae with a single nucleus per cell. Heterokaryons have been utilized for complementation and dominance testing of mutations that affect nutritional characteristics of the fungus. Heterokaryons growing on minimal medium spontaneously give rise to fast-growing sectors that have the genetic properties expected of unstable heterozygous diploids. In fast-growing sectors, most hyphal tip cells are unstable prototrophs. The conidia collected from fast-growing sectors include stable and unstable prototrophs, as well as auxotrophs that exhibit a wide range of phenotypes, including many recombinant classes. Genetic linkage in meiosis has been detected between two auxotrophic mutations that recombine in vegetatively growing unstable diploids. The appearance of recombinants suggests that homologous recombination occurs during vegetative growth of M. grisea. No interstrain barriers to heterokaryosis and diploid formation have been detected. The mating type of the strains that are paired does not influence the formation of heterokaryons or diploids.
STERILITY AND HYPERMUTABILITY IN THE P-M SYSTEM OF HYBRID DYSGENESIS IN DROSOPHILA MELANOGASTER
Authors: Kocur Gordon J , Drier Eric A , Simmons Michael J
Published: January 2021

Inbred wild strains of Drosophila melanogaster derived from the central and eastern United States were used to make dysgenic hybrids in the P-M system. These strains possessed P elements and the P cytotype, the condition that represses P element transposition. Their hybrids were studied for the mutability of the P element insertion mutation, snw, and for the incidence of gonadal dysgenesis (GD) sterility. All the strains tested were able to induce hybrid dysgenesis by one or both of these assays; however, high levels of dysgenesis were rare. Sets of X chromosomes and autosomes from the inbred wild strains were more effective at inducing GD sterility than were sets of Y chromosomes and autosomes. In two separate analyses, GD sterility was positively correlated with snw mutability, suggesting a linear relationship. However, one strain appeared to induce too much GD sterility for its level of snw destabilization, indicating an uncoupling of these two manifestations of hybrid dysgenesis.