bluuebunny/crossref_metadata_2025 huggingface dataset:
DCT4—A New Member of the Dicarboxylate Transporter Family in C4 Grasses
Authors: Weissmann Sarit , Huang Pu , Wiechert Madeline A , Furuyama Koki , Brutnell Thomas P , Taniguchi Mitsutaka , Schnable James C , Mockler Todd C
Published: January 2021

Malate transport shuttles atmospheric carbon into the Calvin–Benson cycle during NADP-ME C4 photosynthesis. Previous characterizations of several plant dicarboxylate transporters (DCT) showed that they efficiently exchange malate across membranes. Here, we identify and characterize a previously unknown member of the DCT family, DCT4, in Sorghum bicolor. We show that SbDCT4 exchanges malate across membranes and its expression pattern is consistent with a role in malate transport during C4 photosynthesis. SbDCT4 is not syntenic to the characterized photosynthetic gene ZmDCT2, and an ortholog is not detectable in the maize reference genome. We found that the expression patterns of DCT family genes in the leaves of Zea mays, and S. bicolor varied by cell type. Our results suggest that subfunctionalization, of members of the DCT family, for the transport of malate into the bundle sheath plastids, occurred during the process of independent recurrent evolution of C4 photosynthesis in grasses of the PACMAD clade. We also show that this subfunctionalization is lineage independent. Our results challenge the dogma that key C4 genes must be orthologues of one another among C4 species, and shed new light on the evolution of C4 photosynthesis.
EXCEPTIONALLY HIGH LEVELS OF RESTRICTION SITE POLYMORPHISM IN DNA NEAR THE MAIZE Adh1 GENE
Authors: Johns Mitrick A , Strommer Judith N , Freeling Michael
Published: January 2021

Restriction maps have been prepared for the chromosomal region near seven biochemically and genetically distinct maize alcohol dehydrogenase-1 (Adh1) alleles using a small cDNA probe for Adh1. Five restriction sites spanning about 4 kb in and near the Adh1 transcription unit appear identical in all seven alleles. Outside this conserved region, variation in restriction site position is the rule. Six of the seven alleles are distinguishable, and the alleles appear to fall into four groups. The DNA flanking the 1S-type alleles seems to share no restriction site homology with the DNA near the 1F-type alleles. Several hypotheses are put forward to explain how such high levels of polymorphism could have arisen in a species that has been domesticated for only about 10,000 years.
CHARACTERIZATION OF THE OPERATOR SITES OF THE exu REGULON IN ESCHERICHIA COLI K-12 BY OPERATOR-CONSTITUTIVE MUTATIONS AND REPRESSOR TITRATION
Authors: Mata-Gilsinger Mireille , Ritzenthaler Paul , Blanco Carlos
Published: January 2021

In Escherichia coli, the exu regulon of the hexuronate system involves the three exuT, uxaCA and uxaB operons and is under the negative control of the exuR regulatory gene product. The technique developed by Casadaban, Chou and Cohen was employed to construct two plasmids containing operon fusions in which the lactose genes were fused to the uxaCA and exuT operons. These fusions were transferred into the chromosome by a reciprocal recombination event, and the resulting strains were used for isolation of mutants defective in repression. Two types of operator-constitutive mutants were obtained: one specific for the uxaCA operon expression and the other affecting the exuT gene expression. This genetic evidence confirms that these two operons which are divergently transcribed each possess their own operator site.—The derepressed expression of the two exuT-lac and uxaCA-lac operons and the uxaB gene was also examined upon introduction of plasmids bearing various operators of the exu regulon. The results of testing exuR repressor titration by multiple copies of the exu operators allowed us to show a gradation in the affinity degrees for the three exu operators: uxaBo has the strongest affinity for the exuR repressor and uxaCo the weakest, although that of exuTo seems to be just slightly greater. This gradation may play a role in the control of the exu regulon expression.
ISOLATION AND CHARACTERIZATION OF SEX-LINKED FEMALE-STERILE MUTANTS IN DROSOPHILA MELANOGASTER WITH SPECIAL ATTENTION TO EGGSHELL MUTANTS
Authors: Komitopoulou Katia , Gans Madeleine , Margaritis Lukas H , Kafatos Fotis C , Masson Michele
Published: January 2021

To study genes that function mainly or exclusively during oogenesis, we have isolated and analyzed female-sterile mutations, with special emphasis on those that affect eggshell formation. Following treatment that induced 61 to 66% lethals, 8.1% of the 1071 X chromosomes tested carried recessive female sterility mutations (87 isolates), and 8.0% carried partial female-sterile mutations (86 isolates), respectively. In addition, three dominant female steriles were recovered. Some of the mutants had very low fecundity, and others laid morphologically normal eggs that failed to develop. A third category included 29 mutants that laid eggs with morphological abnormalities: 26 were female steriles, two were partial female steriles and one was fertile. Mutants of this third category were characterized in some detail and compared with 40 previously isolated mutants that laid similarly abnormal eggs. Approximately 28—31 complementation groups with morphological abnormalities were detected, some of which were large allelic series (11, 9, 7, 6 and 5 alleles). Twenty-four groups were mapped genetically or cytogenetically, and 21 were partially characterized by ultrastructural and biochemical procedures. Of the latter, one group showed clear deficiency of yolk proteins, and nine showed prominent ultrastructural defects in the chorion (at least eight accompanied by deficiencies in characterized chorion proteins). At least six groups with clear-cut effects were found at loci not previously identified with known chorion structural genes.
GENETIC COADAPTATION IN THE CHROMOSOMAL POLYMORPHISM OF DROSOPHILA SUBOBSCURA. I. SEASONAL CHANGES OF GAMETIC DISEQUILIBRIUM IN A NATURAL POPULATION
Authors: Fontdevila A , Zapata C , Alvarez G , Sanchez L , Méndez J , Enriquez I
Published: January 2021

Seasonal changes in gene arrangement and allozyme frequencies have been investigated in Drosophila subobscura for several years. Some arrangements (Ost and O  3+4+7) show seasonal variation, which suggests that chromosomal polymorphism is flexible in this species. Seasonal changes in allozyme frequencies for Lap and Pept-1 loci, both located within the same inversions of chromosome O, are significant only inside the Ost arrangement, but not inside O  3+4 arrangement. This arrangement-dependent response of allozyme generates variation in arrangement-allozyme disequilibrium. The historical hypothesis on the maintenance of disequilibria cannot explain these seasonal changes, and some kind of natural selection must be invoked. Association between Lap and Pept-1 is also seasonal inside Ost but not inside O  3+4. We propose that Ost probably consists of a finite array of supergenes that are differentially favored in each season by natural selection. The present evidence on this supergene selection and other genetic, biogeographic and phylogenetic data points to O  3+4 as the most primitive gene order among the present arrangements
LINKAGE DISEQUILIBRIUM, SELECTION AND RECOMBINATION AT THREE LOCI
Authors: Hastings Alan
Published: January 2021

Limits to the relationship among linkage disequilibrium, selection and recombination at equilibrium in three-locus, two-allele, deterministic, discrete generation models are determined using linear programming techniques. These results show that the commonly used measures of linkage disequilibrium are not appropriate for a multilocus setting. Additionally, interactions among three loci are important in reducing the strength of selection necessary to maintain a given level of disequilibrium, relative to a two-locus model.
CHROMOSOME-DESIGNATED MUTATION SELECTION IN TETRAHYMENA THERMOPHILA
Authors: Altschuler M I , Bruns P J
Published: January 2021

Two protocols are presented that allow the selection of mutations mapping to micronuclear chromosome 5 in Tetrahymena thermophilia. One protocol involves crossing mutagenized diploid cells directly to a strain nullisomic for chromosome 5 and screening the monosomic progeny for a mutant phenotype. The second protocol first takes the mutagenized diploid cells through round I of genomic exclusion to create useful and reusable mutant heterokaryons, which are then assayed for the presence of mutations on chromosome 5 by crossing to the nullisomic 5 strain. Of 14 putative chromosome 5 mutations obtained by these two methods, seven are shown by genetic analysis to be recessive mutations on chromosome 5; one mapped elsewhere in the genome; six were infertile or failed to yield progeny in some of the diagnostic crosses and, thus, their genetic nature could not be determined with certainty.
SEMIDOMINANCE OF rad18-2 FOR SEVERAL PHENOTYPIC CHARACTERS IN SACCHAROMYCES CEREVISIAE
Authors: Mayer Vernon W , Goin Carol J
Published: January 2021

Inbred diploid yeast strains heterozygous or homozygous for the rad18-2 allele and carrying markers for detection of mitotic recombination were constructed. The homozygous rad18-2/rad18-2 strain was highly sensitive to killing by UV light, showed greatly elevated frequencies of spontaneous and induced mitotic recombination and was more sensitive to trimethoprim than the wild-type diploid. The heterozygous strain RAD18/rad18-2 was intermediate in its response for these same phenotypic characters. These findings are discussed in the light of other studies in which incomplete dominance of genes involved in some aspect of DNA repair has been reported.
THE EFFECT OF INBREEDING ON COMPETITIVE MALE-MATING ABILITY IN DROSOPHILA MELANOGASTER
Authors: Sharp Paul M
Published: January 2021

The effect of full-sib inbreeding on competitive male-mating ability (CI♂) in Drosophila melanogaster was investigated in two experiments. In the first, five inbred lines (with reserves) were assessed up to 18 generations. Linear inbreeding depression, of 5.9% per 10% increase in homozygosity, was observed. In a second experiment, 21 inbred lines were tested after three generations of full-sib mating (without reserves), and the decline with inbreeding was more severe, the male competitive index (CI♂) decreasing by 10.7% per 10% increase in F. The difference between these results is attributed to natural selection acting on variation within the inbred lines in extent of homozygosity, which can arise because of the peculiarly strong influence of linkage in Drosophila. Furthermore, differentiation between the lines may have reflected this variation rather than the various effects of different alleles fixed.—These results imply that the genetic variation in male-mating ability is largely due to dominance (no epistasis was detected) and are consonant with the proposition that intermale sexual selection is a very important component of fitness in D. melanogaster. There was no evidence of a positive correlation between male body size and competitive mating ability.
THE NATURE OF NUCLEOTIDE SEQUENCE DIVERGENCE BETWEEN BARLEY AND MAIZE CHLOROPLAST DNA
Authors: Zurawski Gerard , Clegg Michael T , Brown Anthony H D
Published: January 2021

Analysis of a 2175-base pair (bp) SmaI-HindIII fragment of barley chloroplast DNA revealed that rbcL (the gene for the large subunit of ribulose 1,5-bisphosphate carboxylase) and atpB (the gene for the β subunit of ATPase) are transcribed divergently and are separated by an untranscribed region of 155-166 bp. The rbcL mRNA has a 320-residue untranslated leader region, whereas the atpB mRNA has a 296- to 309-residue leader region. The sequence of these regions, together with the initial 113 bp of the atpB-coding region and the initial 1279 bp of the rbcL-coding region, is compared with the analogous maize chloroplast DNA sequences. Two classes of nucleotide differences are present, substitutions and insertions/deletions. Nucleotide substitutions show a 1.9-fold bias toward transitions in the rbcL-coding region and a 1.5-fold bias toward transitions in the noncoding region. The level of nucleotide substitutions between the barley and maize sequences is about 0.065/bp. Seventy-one percent of the substitutions in the rbcL-coding region are at the third codon position, and 95% of these are synonymous changes. Insertion/deletion events, which are confined to the noncoding regions, are not randomly distributed in these regions and are often associated with short repeated sequences. The extent of change for the noncoding regions (about 0.093 events/bp) is less than the extent of change at the third codon positions in the rbcL-coding region (about 0.135 events/bp), including insertion/delection events. Limited sequence analysis of the analogous DNA from a wild line (Hordeum spontaneum) and a primitive Iranian barley (H. vulgare) suggested a low rate of chloroplast DNA evolution. Compared to spinach chloroplast DNA, the barley rbcL-atpB untranslated region is extremely diverged, with only the putative rbcL promoters and ribosome-binding site being extensively conserved.
TWO-STEP RESISTANCE BY ESCHERICHIA COLI B TO BACTERIOPHAGE T2
Authors: Lenski Richard E
Published: January 2021

Numerous authors have noted the difficulty in obtaining mutants of E. coli B that are resistant to bacteriophage T2 using standard procedures of plating large numbers of cells in the presence of excess phage. Yet, T2-resistant mutants appear in continuous culture at rates inconsistent with this difficulty. This paradoxical result derives from the fact that resistance to T2 usually arises as a consequence of two nonindependent mutations. Mutant bacteria resistant to phage T4 are very common and increase rapidly in continuous culture with phage T2 owing to an approximate halving of the rate at which T2 adsorbs to and kills these partially resistant mutants. The rate at which these partially resistant mutants then give rise to fully resistant mutants is approximately two orders of magnitude higher than the rate obtained by direct selection. These results are consistent with biochemical evidence that T2 adsorption to E. coli B involves both the bacterial lipopolysaccharide (to which phage T4 adsorbs) and a bacterial surface protein. However, this genetic evidence suggests that T2 can adsorb to either receptor type alone, whereas the biochemical evidence suggests that T2 requires a complex of the two receptors for adsorption to E. coli B. These results also indicate that the effects of genetic background can influence not only the selective advantage associated with particular mutations but also the rate at which certain selectively defined characteristics arise via mutation.
SELECTION WITH GENE-CYTOPLASM INTERACTIONS. I. MAINTENANCE OF CYTOPLASM POLYMORPHISMS
Authors: Gregorius H R , Ross M D
Published: January 2021

General conditions for the protectedness of gene-cytoplasm polymorphisms are considered for a biallelic model with two cytoplasm types and under the assumption that nuclear polymorphisms cannot be maintained in the presence of only one cytoplasm type. Analytical results involving male fertilities, female fertilities, viabilities and selfing rates are obtained, and numerical results show spiral and cyclic behavior of population trajectories. It is shown that a maternally inherited cytoplasmic polymorphism cannot be maintained in the absence of a nuclear polymorphism, and that a gene-cytoplasm polymorphism can only be maintained if the population shows sexual asymmetry, i.e., if the ratio of male to female fertility varies among genotypes. Thus, the classical viability selection model does not allow gene-cytoplasm polymorphisms.
RELATIONSHIPS BETWEEN A HYPER-REC MUTATION (rem1) AND OTHER RECOMBINATION AND REPAIR GENES IN YEAST
Authors: Malone Robert E , Hoekstra Merl F
Published: January 2021

Mutations in the REM1 gene of Saccharomyces cerevisiae confer a semidominant hyper-recombination and hypermutable phenotype upon mitotic cells (Golin and Esposito 1977). These effects have not been observed in meiosis. We have examined the interactions of rem1 mutations with rad6-1, rad50-1, rad52-1 or spo11-1 mutations in order to understand the basis of the rem1 hyper-rec phenotype. The rad mutations have pleiotropic phenotypes; spo11 is only defective in sporulation and meiosis. The RAD6, RAD50 and SPO11 genes are not required for spontaneous mitotic recombination; mutations in the RAD52 gene cause a general spontaneous mitotic Rec- phenotype. Mutations in RAD50, RAD52 or SPO11 eliminate meiotic recombination, and mutations in RAD6 prevent spore formation. Evidence for the involvement of RAD6 in meiotic recombination is less clear. Mutations in all three RAD genes confer sensitivity to X rays; the RAD6 gene is also required for UV damage repair. To test whether any of these functions might be involved in the hyper-rec phenotype conferred by rem1 mutations, double mutants were constructed. Double mutants of rem1 spo11 were viable and demonstrated rem1 levels of mitotic recombination, suggesting that the normal meiotic recombination system is not involved in producing the rem1 phenotype. The rem1 rad6 double mutant was also viable and had rem1 levels of mitotic recombination. Neither rem1 rad50 nor rem1 rad52 double mutants were viable. This suggests that rem1 causes its hyper-rec phenotype because it creates lesions in the DNA that are repaired using a recombination-repair system involving RAD50 and RAD52.
OMNIPOTENT SUPPRESSORS EFFECTIVE IN Ψ+ STRAINS OF SACCHAROMYCES CEREVISIAE: RECESSIVENESS AND DOMINANCE
Authors: Ono Bun-Ichiro , Moriga Nozomi , Ishihara Kiyomi , Ishiguro Junpei , Ishino Yumiko , Shinoda Sumio
Published: January 2021

We have characterized recessive and dominant omnipotent suppressor mutations obtained by conversion of the leu2-1 UAA mutation and the met8-UAG mutation in a ψ+ strain of Saccharomyces cerevisiae. The suppressors that act recessively upon these markers fell into two complementation groups; the sup47 and sup36 suppressors show linkage to the tyr1 locus and the aro1 locus, respectively. Of the suppressors acting dominantly upon both markers, those linked to the tyr1 locus are alleles of the SUP46 ribosomal mutation. The sup47 suppressors differ from the SUP46 suppressors not only in their suppressor activities in heterozygous diploids but also in their map positions relative to the tyr1 locus and their effects on the S11 ribosomal protein. The remaining dominant suppressors are not alleles of sup36 as judged by linkage analysis. The recessive suppressors and the dominant suppressors also differ in their effects on cell growth.
ON THE THEORY OF SPECIATION INDUCED BY TRANSPOSABLE ELEMENTS
Authors: Ginzburg Lev R , Bingham Paul M , Yoo Sinjae
Published: January 2021

A simple methematical model describes the invasion of panmictic, sexually reproducing populations by a newly introduced transposon. The model places important constraints on the properties that transposons must have to successfully invade a population and describes the kinetics with which such an invasion will occur. Invasibility conditions serve as a basis for new, detailed scenarios whereby transposon-mediated depression in fitness produces reproductive isolation of populations. These scenarios, in turn, lead to several speculations concerning the role of transposons in evolution.
ON THE COMPONENTS OF SEGREGATION DISTORTION IN DROSOPHILA MELANOGASTER. III. NATURE OF ENHANCER OF SD
Authors: Brittnacher John G , Ganetzky Barry
Published: January 2021

Analysis of X-ray-induced deletions in the Segregation Distorter (SD) chromosome, SD-5, revealed that this chromosome had a gene proximal to lt in the centric heterochromatin of 2L that strongly enhanced the meiotic drive caused by the SD chromosome. This Enhancer of Segregation Distortion [E(SD)] locus had not been characterized in earlier studies of SD chromosomes because it cannot be readily separated by recombination from the Responder (Rsp) locus in the proximal heterochromatin of 2R.—To determine whether E(SD) is a general component of all SD chromosomes and to examine further its effects on distortion, we produced deletions of E(SD) in three additional SD chromosomes. Analysis of these deletions leads to the following conclusions: (1) along with Sd and Rsp, E(SD) is common to all SD chromosomes; (2) the E(SD) allele on each SD chromosome enhances distortion by the same amount, which indicates that allelic variation at the E(SD) locus is not responsible for the different drive strengths seen among SD chromosomes; (3) E(SD) causes very little or no distortion by itself in the absence of Sd; (4) E(SD), like Sd, acts in a dosage-dependent manner; (5) E(SD) exerts its effect in cis or trans to Sd; and (6) if E(SD)  + exists, its function is not related to SD.
MEASUREMENT OF FITNESS AND ITS COMPONENTS IN SIX LABORATORY STRAINS OF DROSOPHILA MELANOGASTER
Authors: Yamazaki Tsuneyuki
Published: January 2021

Six laboratory strains of Drosophila melanogaster were used to measure "net fitness" and its components by interspecific competition with D. hydei using 100 experimental populations. The "total competitive ability," an estimate of net fitness measured in these competition experiments, was tightly correlated with another measure of net fitness, the population size, in single-species experiments (phenotypic correlation rp = 0.675 and genotypic correlation rg = 0.997). Other components of fitness were also measured simultaneously, and the correlation with the net fitness was calculated. The very high correlation between two measurements of net fitness and lower correlations between net fitness and components of fitness suggests that these net fitness measures are more reliable estimates of the "real net fitness" than the components of fitness.
THE GENETIC STRUCTURE OF NATURAL POPULATIONS OF DROSOPHILA MELANOGASTER. XVIII. CLINAL AND UNIFORM GENETIC VARIATION OVER POPULATIONS
Authors: Kusakabe Shinichi , Mukai Terumi
Published: January 2021

It has been reported in the previous papers of this series that in the eastern United States and Japan there is a north-to-south cline of additive genetic variance of viability and that the amount of the additive genetic variance in the northern population can be explained by mutation-selection balance. To determine whether or not the difference in the genetic variation in northern and southern populations can be explained by the differences in mutation rate and/or effective population size, numerical calculations were made using population genetic parameters. In addition, the average heterozygosities of the northern and southern populations at ten of 19 polymorphic structural loci surveyed were estimated in relation to the cline of additive genetic variance of viability, and the following findings were obtained. (1) The changes in mutation rate and population size cannot simultaneously explain the difference in additive genetic variance and inbreeding decline between the northern and southern populations. Thus, the operation of some kind of balancing selection, most likely diversifying selection, was suggested to explain the observed excess of additive genetic variance. (2) Estimates of the average heterozygosities of the southern population were not significantly different from those of the northern population. Thus, it was strongly suggested that the excess of additive genetic variance in the southern population cannot be caused by structural loci, but by factors outside the structural loci, and that protein polymorphisms are selectively neutral or nearly neutral.
RECOMBINATION AND ASSORTMENT IN THE MACRONUCLEUS OF TETRAHYMENA THERMOPHILA: A THEORETICAL STUDY BY COMPUTER SIMULATION
Authors: Doerder F P , Diblasi S L
Published: January 2021

The compound nature of the macronucleus of Tetrahymena thermophila presents multiple opportunities for recombination between genes on the same macronuclear chromosome. Such recombinants should be detectable through their assortment at subsequent amitotic macronuclear divisions. Thus, a macronucleus that is initially AB/ab should produce recombinant assortees of the genotypes Ab/aB. Computer simulation shows that, when the recombination frequency is two or fewer times per cell cycle, recombinant assortees are produced at experimentally measurable frequencies of less than 40%. At higher recombination frequencies, linked genes appear to assort independently. The simulations also show that recombination during macronuclear development can be distinguished from recombination in subsequent cell cycles only if the first appearance of recombinant assortees is 100 or more fissions after conjugation. The use of macronuclear recombination and assortment as a means of mapping macronuclear genes is severely constrained by the large variances in assortment outcomes; with experimentally small sample sizes, such mapping is impossible.
GENETIC STUDIES OF MEMBRANE EXCITABILITY IN DROSOPHILA: LETHAL INTERACTION BETWEEN TWO TEMPERATURE-SENSITIVE PARALYTIC MUTATIONS
Authors: Ganetzky Barry
Published: January 2021

Two mutants of Drosophila melanogaster, parats  1 (1-53.9) and napts (2-56.2) both display similar temperature-sensitive paralysis associated with blockage in the conduction of nerve action potentials, suggesting that the two gene products have a similar function. This idea is supported by the observation that the double mutant is unconditionally lethal. Genetic analysis of this synergistic interaction has revealed the following: 1) it specifically involves the para and nap loci; (2) all para alleles interact with napts, but the strength of the interaction varies in an allele-dependent fashion; (3) lethality of the double mutant occurs during the first larval instar with parats  1 but differs with other para alleles; (4) hypodosage of para  + causes lethality in a napts background. These results together with previous electrophysiological, behavioral and pharmacological studies of these mutants suggest that both para and nap affect sodium channels and possibly encode different subunits.
A GENETIC AND CYTOGENETIC ANALYSIS OF THE REGION SURROUNDING THE LSP-1 β-GENE IN DROSOPHILA MELANOGASTER
Authors: Roberts David B , Brock Hugh W , Rudden Nancy C , Evans-Roberts Susan
Published: January 2021

The region surrounding the gene coding for the β-polypeptide (21D-22C) of the major Drosophila melanogaster larval serum protein, LSP-1, has been studied in detail. Seven new γ-ray-induced deficiencies of the region have been used, together with the two extant deficiencies, to map the position of the β-gene and of the 55 newly induced ethyl methanesulfonate mutants uncovered by one of the largest deficiencies. No lethal mutation of the β-gene was found.
TRANSLOCATIONS IN DICTYOSTELIUM DISCOIDEUM
Authors: Welker D L , Williams K L
Published: January 2021

Fourteen translocations of independent origin were identified in Dictyostelium discoideum on the basis of segregation anomalies of diploids heterozygous for these chromosome rearrangements, all of which led to the cosegregation of unlinked markers. Many of these translocations were discovered in strains mutagenized with MNNG or in strains carrying mutations affecting DNA repair; however, spontaneous translocations were also obtained. Haploid mitotic recombinants of the rearranged linkage groups were produced from diploids heterozygous for the translocations at frequencies of up to 5% of viable haploid segregants; this is at least a ten-fold higher frequency than that seen with diploids not heterozygous for translocations (∼0.1%). These haploid recombinants included both translocated and nontranslocated strains. The T354(II,VII) translocation and possibly the T357(IV,VII) translocation reduce the chromosome number to n = 6; haploids carrying 11 other translocations all have karyotypes with n = 7. Genetic characterization of the T357(IV,VII) translocation showed that the bwnA and whiC loci normally found on linkage group IV were physically linked to the linkage group VII loci couA, phgA, bsgB and cobA.
EVOLUTION AND EXTINCTION OF TRANSPOSABLE ELEMENTS IN MENDELIAN POPULATIONS
Authors: Kaplan Norman , Darden Tom , Langley Charles H
Published: January 2021

A model of the evolution of a transposable element family in a Mendelian host population is proposed that incorporates heritable phenotypic mutations in the elements. The temporal behavior of the numbers of mutant and wild-type elements is studied, and the expected extinction time of the transposable element family is examined. Our results indicate that, if the mutant can be transposed equally well in the presence of the wild type, then it can be expected to be found in preponderance, whereas elements, such as retroviruses, where the transposing genome and its phenotypic expression are coupled, may be characterized by a low mutant frequency.
SON-KILLER: A THIRD EXTRACHROMOSOMAL FACTOR AFFECTING THE SEX RATIO IN THE PARASITOID WASP, NASONIA (=MORMONIELLA) VITRIPENNIS
Authors: Skinner Samuel Way
Published: January 2021

An extrachromosomal factor, termed son-killer (sk), affects the sex ratio in a parasitoid wasp, Nasonia (=Mormoniella) vitripennis. The factor is maternally transmitted and alters the secondary sex ratio of an infected female through mortality of approximately 80% of the male embryos. No effect on the primary (zygotic) sex ratio is observed. Ninety-five percent of the daughters of an infected female inherit son-killer. The factor can also be transmitted contagiously when the progeny of infected and uninfected females develop simultaneously on a single host. In newly infected strains, the sex ratio effects are equivalent to those in the original.
THE ROLE OF THE SPO11 GENE IN MEIOTIC RECOMBINATION IN YEAST
Authors: Klapholz Sue , Waddell Candace S , Esposito Rochelle Easton
Published: January 2021

Several complementary experimental approaches were used to demonstrate that the SPO11 gene is specifically required for meiotic recombination. First, sporulating cultures of spo11-1 mutant diploids were examined for landmark biochemical, cytological and genetic events of meiosis and ascosporogenesis. Cells entered sporulation with high efficiency and showed a near-doubling of DNA content. Synaptonemal complexes, hallmarks of intimate homologous pairing, and polycomplex structures appeared during meiotic prophase. Although spontaneous mitotic intra- and intergenic recombination occurred at normal levels, no meiotic recombination was observed. Whereas greater than 50% of cells completed both meiotic divisions, packaging of the four meiotic products into mature ascospores took place in only a small subset of asci. Haploidization occurred in less than 1% of viable colony-forming units. Second, the Rec- meiotic defect conferred by spo11-1 was confirmed by dyad analysis of spores derived from spo13-1 single-division meiosis in which recombination is not a requirement for viable ascospore production. Diploids homozygous for the spo13-1 mutation undergo meiotic levels of exchange followed by a single predominantly equational division and form asci containing two near-diploid spores. With the introduction of the spo11-1 mutation, high spore viability was retained, whereas intergenic recombination was reduced by more than 100-fold.
MICROGEOGRAPHIC AND TEMPORAL GENETIC DIFFERENTIATION IN NATURAL POPULATIONS OF DROSOPHILA SUBOBSCURA
Authors: Cabrera V M , González A M , Hernández M , Larruga J M , Martell M
Published: January 2021

Evidence of microgeographic and temporal genetic differentiation in natural populations of Drosophila subobscura is presented. The alcohol dehydrogenease locus was used as a genetic marker. Behavioral differences among the sexes and genotypes may explain these observations, although the molecular basis remains obscure.
APPARENT GENETIC COMPLEXITY GENERATED BY DEVELOPMENTAL THRESHOLDS: THE APTEROUS LOCUS IN DROSOPHILA MELANOGASTER
Authors: Stevens Mary E , Bryant Peter J
Published: January 2021

Mutations at the apterous (ap) locus in Drosophila melanogaster give rise to three distinct phenotypes: aberrant wings, female sterility and precocious adult death. The wing phenotype includes five types of abnormality: blistering, deficiencies, duplications, high-order repetitions and transformation of structures. The mildest phenotype is seen with homozygous apblt animals which have either normal or slightly blistered wings. Most alleles produce, in the homozygote, a deficient wing in which part or all of the wing margin and wing blade is missing, but wing hinge and notum regions are normal. Animals hemizygous for each of 20 ap alleles, as well as apID/apXa heterozygotes, show duplication of parts of the notum associated with complete wing deficiency. Animals heterozygous for apc and the other tested ap alleles show repetitions of parts of the anterior wing margin, an engrailed-like transformation of posterior wing margin into anterior margin or both. Both apblt and apc show similar phenotypes in homozygotes and hemizygotes, yet both produce a less extreme phenotype than that of the other hemizygotes, suggesting that neither mutation causes loss of the entire ap  + function. The 15 alleles that cause precocious death and female sterility occur in six complementation groups based on complementation for these phenotypes. This supports the previous conclusion that the effects of apterous mutations on the wing do not correlate with their effects on viability and fertility. We propose an explanation for the effects of apterous mutations on the wing in which quantitative reductions in the activity of gene product give rise to qualitatively different phenotypes because of different threshold requirements of the ap  + function for critical events in wing disc development.
MOLECULAR CLONING OF α-AMYLASE GENES FROM DROSOPHILA MELANOGASTER. I. CLONE ISOLATION BY USE OF A MOUSE PROBE
Authors: Gemmill Robert M , Levy Jack N , Doane Winifred W
Published: January 2021

A cloned ä-amylase cDNA sequence from the mouse is homologous to a small set of DNA sequences from Drosophila melanogaster under appropriate conditions of hybridization. A number of recombinant lambda phage that carry homologous Drosophila genomic DNA sequences were isolated using the mouse clone as a hybridization probe. Putative amylase clones hybridized in situ to one or the other of two distinct sites in polytene chromosome 2R and were assigned to one of two classes, A and B. Clone λDm32, representing class A, hybridizes within chromosome section 53CD. Clone λDm65 of class B hybridizes within section 54A1-B1. Clone λDm65 is homologous to a 1450- to 1500-nucleotide RNA species, which is sufficiently long to code for α-amylase. No RNA homologous to λDm32 was detected. We suggest that the class B clone, λDm65, contains the functional Amy structural gene(s) and that class A clones contain an amylase pseudogene.
GENE GENEALOGY AND VARIANCE OF INTERPOPULATIONAL NUCLEOTIDE DIFFERENCES
Authors: Takahata Naoyuki , Nei Masatoshi
Published: January 2021

A mathematical theory is developed for computing the probability that m genes sampled from one population (species) and n genes sampled from another are derived from l genes that existed at the time of population splitting. The expected time of divergence between the two most closely related genes sampled from two different populations and the time of divergence (coalescence) of all genes sampled are studied by using this theory. It is shown that the time of divergence between the two most closely related genes can be used as an approximate estimate of the time of population splitting (T) only when T ≡ t/(2 N) is small, where t and N are the number of generations and the effective population size, respectively. The variance of Nei and Li's estimate (d) of the number of net nucleotide differences between two populations is also studied. It is shown that the standard error (sd) of d is larger than the mean when T is small (T << 1). In this case, sd is reduced considerably by increasing sample size. When T is large (T > 1), however, a large proportion of the variance of d is caused by stochastic factors, and increase in the sample size does not help to reduce sd. To reduce the stochastic variance of d, one must use data from many independent unlinked gene loci.
ALTERED FIDELITY OF MITOTIC CHROMOSOME TRANSMISSION IN CELL CYCLE MUTANTS OF S. CEREVISIAE
Authors: Hartwell Leland H , Smith David
Published: January 2021

Thirteen of 14 temperature-sensitive mutants deficient in successive steps of mitotic chromosome transmission (cdc2, 4, 5, 6, 7, 8, 9, 13, 14, 15, 16, 17 and 20) from spindle pole body separation to a late stage of nuclear division exhibited a dramatic increase in the frequency of chromosome loss and/or mitotic recombination when they were grown at their maximum permissive temperatures. The increase in chromosome loss and/or recombination is likely to be due to the deficiency of functional gene product rather than to an aberrant function of the mutant gene product since the mutant alleles are, with one exception, recessive to the wild-type allele for this phenotype. The generality of this result suggests that a delay in almost any stage of chromosome replication or segregation leads to a decrease in the fidelity of mitotic chromosome transmission. In contrast, temperature-sensitive mutants defective in the control step of the cell cycle (cdc28), in cytokinesis (cdc3) or in protein synthesis (ils1) did not exhibit increased recombination or chromosome loss.—Based upon previous results with mutants and DNA-damaging agents in a variety of organisms, we suggest that the induction of mitotic recombination in certain mutants is due to the action of a repair pathway upon nicks or gaps left in the DNA. This interpretation is supported by the fact that the induced recombination is dependent upon the RAD52 gene product, an essential component in the recombinogenic DNA repair pathway. Gene products whose deficiency leads to induced recombination are, therefore, strong candidates for proteins that function in DNA metabolism. Among the mutants that induce recombination are those known to be defective in some aspect of DNA replication (cdc2, 6, 8, 9) as well as some mutants defective in the G2 (cdc13 and 17) and M (cdc5 and 14) phases of the mitotic cycle. We suggest that special aspects of DNA metabolism may be occurring in G2 and M in order to prepare the chromosomes for proper segregation.
MUTATIONS IN GENES ENCODING ESSENTIAL MITOTIC FUNCTIONS IN DROSOPHILA MELANOGASTER
Authors: Smith David A , Baker Bruce S , Gatti Maurizio
Published: January 2021

Temperature-sensitive mutations at 15 loci that affect the fidelity of mitotic chromosome behavior have been isolated in Drosophila melanogaster. These mitotic mutants were detected in a collection of 168 EMS-induced X-linked temperature-sensitive (ts) lethal and semilethal mutants. Our screen for mutations with mitotic effects was based upon the reasoning that under semirestrictive conditions such mutations could cause an elevated frequency of mitotic chromosome misbehavior and that such events would be detectable with somatic cell genetic techniques. Males hemizygous for each ts lethal and heterozygous for the recessive autosomal cell marker mwh were reared under semirestrictive conditions, and the wings of those individuals surviving to adulthood were examined for an increased frequency of mwh clones. Those mutations producing elevated levels of chromosome instability during growth of the wing imaginal disc were also examined for their effects on chromosome behavior in the cell lineages producing the abdominal cuticle. Fifteen mutations affect chromosome behavior in both wing and abdominal cells and thus identify loci generally required for the fidelity of mitotic chromosome transmission. Mapping and complementation tests show that these mutations represent 15 loci. One mutant is an allele of a locus (mus-101) previously identified by mutagensensitive mutants and a second mutant is an allele of the lethal locus zw10.—The 15 mutants were also examined cytologically for their effects on chromosomes in larval neuroblasts. Taken together, the results of our cytological and genetical studies show that these mutants identify loci with wild-type functions necessary for either (1) maintenance of chromosome integrity or (2) regular disjunction of chromosomes or (3) chromosome condensation. Thus, these mutations define a broad spectrum of genes required for the normal execution of the mitotic chromosome cycle.
A MOUSE β-GLOBIN MUTANT THAT IS AN EXACT MODEL OF HEMOGLOBIN RAINIER IN MAN
Authors: Peters J , Andrews S J , Loutit J F , Clegg J B
Published: January 2021

A mutation induced by ethylnitrosourea in a spermatogonial stem cell of a 101/H mouse has resulted in a structurally altered β-diffuse major globin in one of his offspring. The mutant hemoglobin is associated with polycythemia, rubor, increased oxygen affinity and decreased hem-hem interaction. The mutant haplotype has been designated Hbbd  4, polycythemia. Amino acid analysis of the mutant globin has shown that a single substitution β145 Tyr → Cys has occurred, and it is proposed that ethylnitrosourea induced an A → G transition in the tyrosine codon (TAC → TGC). This murine polycythemia is homologous with hemoglobin Rainier in man, in which the amino acid substitution is also β145 Tyr → Cys and which is associated with similar physiological consequences.
THE LOCUS ENCODING αA-CRYSTALLIN IS CLOSELY LINKED TO H-2K ON MOUSE CHROMOSOME 17
Authors: Skow Loren C , Donner Maria E
Published: January 2021

We have used a complementary DNA (cDNA) for mouse αA-crystallin to probe genomic DNA for restriction fragment length polymorphisms which could be used to map the αA-crystallin gene locus (Acry-1) in the mouse genome. Ten of 12 restriction endonucleases produced fragment polymorphism among various inbred strains of mice. A comprehensive strain survey conducted with six endonucleases resulted in the discovery of six allelic forms of Acry-1. Linkage analysis was conducted on DNA from three sets of recombinant inbred strains of mice and demonstrated close linkage of Acry-1 with the major histocompatibility complex (H-2) on chromosome 17. Analysis of congenic and recombinant congenic strains of mice confirmed the linkage of Acry-1 and H-2 and located the αA gene to the region between glyoxylase (Glo-1) and H-2K.
ON THE DEVELOPMENT OF ECTOPIC EYES IN DROSOPHILA MELANOGASTER PRODUCED BY THE MUTATION EXTRA EYE (EE)
Authors: Baker William K , Marcey David J , McElwain M Catharine
Published: January 2021

The mutation ee often produces an ectopic eye on the vertex that is a mirror image partial duplication of the normal eye on the ipsilateral side of the head. The pattern of the duplication and a clonal analysis by mitotic recombination indicate that the duplications are of dorsal eye and orbital structures. Large ectopic eyes (more than 100 ommatidia) and their surrounding bristles may be produced without cuticular deficiencies. The penetrance of ee is temperature dependent with penetrance higher (72%) at 25° and 29° than at 19° (43%). Temperature shift experiments show two temperature-sensitive periods: one at midembryogenesis, the other at mid-first larval instar. Microscopic examination of ee late-second and third instar imaginal cephalic discs show no indication of growth of the extra tissue needed to produce the duplication until after mid-third instar. This was confirmed by cell counts of ee and wild-type discs. There is no evidence of differential cell death in the two types of discs at this stage, although much earlier cell death is postulated. Tests for cell autonomy of the mutation by the production of morphogenetic clones suggest nonautonomy. Formation of pattern duplications by mutant genes is discussed in terms of cell death that eliminates whole developmental compartments, restricted cell death that occurs within a compartment, extensive cell death within a compartment and proliferative growth unassociated with cell lethality.
GENETIC ANALYSIS OF MUTANTS WITH A REDUCED Ca2+-DEPENDENT K+ CURRENT IN PARAMECIUM TETRAURELIA
Authors: Hinrichsen Robert D , Amberger Ed , Saimi Yoshiro , Burgess-Cassler Anthony , Kung Ching
Published: January 2021

Two mutants of Paramecium tetraurelia with greatly reduced Ca2+-dependent K+ currents have been isolated and genetically analyzed. These mutants, designated pantophobiac, give much stronger behavioral responses to all stimuli than do wild-type cells. Under voltage clamp, the Ca2+-dependent K+ current is almost completely eliminated in these mutants, whereas the Ca2+ current is normal. The two mutants, pntA and pntB, are recessive and unlinked to each other. pntA is not allelic to several other ion-channel mutants of P. tetraurelia. The microinjection of a high-speed supernatant fraction of wild-type cytoplasm into either pantophobiac mutant caused a temporary restoration to the wild-type phenotype.
GENETIC ANALYSIS OF THE HAIRY LOCUS IN DROSOPHILA MELANOGASTER
Authors: Ingham P W , Pinchin S M , Howard K R , Ish-Horowicz D
Published: January 2021

Mutations of the hairy locus in Drosophila may affect both adult chaeta differentiation and embryonic segmentation. In an effort to understand this phenotypic complexity, we have analyzed 30 mutant alleles of the locus. We find that the alleles fall into four groups according to their complementation properties, suggesting a structurally complex locus in which two distinct functions share a common coding region.
A DETAILED DEVELOPMENTAL AND STRUCTURAL STUDY OF THE TRANSCRIPTIONAL EFFECTS OF INSERTION OF THE COPIA TRANSPOSON INTO THE WHITE LOCUS OF DROSOPHILA MELANOGASTER
Authors: Zachar Zuzana , Davison Dan , Garza Dan , Bingham Paul M
Published: January 2021

The copia insertion responsible for the wamutation is 3' to the white promotor and in the same transcriptional orientation as white. First, we have analyzed the effects of the wa copia insertion on levels of polyadenylated white transcripts and find large, developmentally programmed effects. Second, we have isolated and sequenced an LTR-excision event involving the copia insertion at wa. This represents the first documented case of an LTR-excision event in Drosophila. This single copia LTR has developmentally programmed effects on white transcript levels qualitatively similar to the intact copia element. Third, we have characterized the structures of white transcripts from wa. We find polyadenylated white transcripts apparently having 3' termini in or near the 3' LTR of the wa copia insertion, as has been reported in limited studies of wa transcription in adults by others. These earlier studies also revealed wa transcripts apparently corresponding to polyadenylated terminus formation in the 5' LTR of the copia transposon; however, our more detailed studies reveal that these transcripts probably have other origins and that little, if any, polyadenylated terminus formation for white transcripts occurs in the 5' LTR of the wa copia insertion. Moreover, we find no polyadenylated terminus formation for white transcripts occurring in the single LTR of the wa LTR-excision product. Fourth, we find that each of three mutant alleles at su(wa) produces elevated levels of several classes of RNAs apparently corresponding to transcriptional readthrough of the wa copia transposon. Elevated levels of one presumptive readthrough transcript were observed previously in one su(wa)1 mutant strain. Fifth, we have confirmed the existence of a transcript initiated in the 3' LTR of the wa copia insertion and find the levels of this transcript to be strongly influenced by developmental stage and genetic background. Lastly, we have analyzed white transcripts produced by the whd  81b11 allele, which carries an insertion of copia in the opposite transcriptional orientation and in a different position than the wa copia insertion. In contrast to the wa copia insertion allele, the whd  81b11 allele produces polyadenylated white transcript levels very similar to the w  + case at the stages examined. Moreover, the whd  81b11  copia element apparently produced polyadenylated terminus formation in white transcripts and we observe no effect of the allelic state of su(wa) on apparent readthrough of this stop site. We discuss some possible implications of our results for the properties of retrotransposons as developmentally complex insertional mutagens and for the functional organization of the copia transcription unit.