bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonparametric confidence interval estimators for heritability and expected selection response.
Authors: Knapp S J , Bridges-Jr W C , Yang M H
Published: April 2021

Statistical methods have not been described for comparing estimates of family-mean heritability (H) or expected selection response (R), nor have consistently valid methods been described for estimating R intervals. Nonparametric methods, e.g., delete-one jackknifing, may be used to estimate variances, intervals, and hypothesis test statistics in estimation problems where parametric methods are unsuitable, nonrobust, or undefinable. Our objective was to evaluate normal-approximation jackknife interval estimators for H and R using Monte Carlo simulation. Simulations were done using normally distributed within-family effects and normally, uniformly, and exponentially distributed between-family effects. Realized coverage probabilities for jackknife interval (2) and parametric interval (5) for H were not significantly different from stated probabilities when between-family effects were normally distributed. Coverages for jackknife intervals (3) and (4) for R were not significantly different from stated coverages when between-family effects were normally distributed. Coverages for interval (3) for R were occasionally significantly less than stated when between-family effects were uniformly or exponentially distributed. Coverages for interval (2) for H were occasionally significantly less than stated when between-family effects were exponentially distributed. Thus, intervals (3) and (4) for R and (2) for H were robust. Means of analysis of variance estimates of R were often significantly less than parametric values when the number of families evaluated was 60 or less. Means of analysis of variance estimates of H were consistently significantly less than parametric values. Means of jackknife estimates of H calculated from log transformed point estimates and R calculated from untransformed or log transformed point estimates were not significantly different from parametric values. Thus, jackknife estimators of H and R were unbiased. Delete-one jackknifing is a robust, versatile, and effective statistical method when applied to estimation problems involving variance functions. Jackknifing is especially valuable in hypothesis test estimation problems where the objective is comparing estimates from different populations.
Analysis of the GAL3 signal transduction pathway activating GAL4 protein-dependent transcription in Saccharomyces cerevisiae.
Authors: Bhat P J , Oh D , Hopper J E
Published: April 2021

The Saccharomyces cerevisiae GAL/MEL regulon genes are normally induced within minutes of galactose addition, but gal3 mutants exhibit a 3-5-day induction lag. We have discovered that this long-term adaptation (LTA) phenotype conferred by gal3 is complemented by multiple copies of the GAL1 gene. Based on this result and the striking similarity between the GAL3 and GAL1 protein sequences we attempted to detect galactokinase activity that might be associated with the GAL3 protein. By both in vivo and in vitro tests the GAL3 gene product does not appear to catalyze a galactokinase-like reaction. In complementary experiments, Escherichia coli galactokinase expressed in yeast was shown to complement the gal1 but not the gal3 mutation. Thus, the complementation activity provided by GAL1 is not likely due to galactokinase activity, but rather due to a distinct GAL3-like activity. Overall, the results indicate that GAL1 encodes a bifunctional protein. In related experiments we tested for function of the LTA induction pathway in gal3 cells deficient for other gene functions. It has been known for some time that gal3gal1, gal3gal7, gal3gal10, and gal3 rho- are incapable of induction. We constructed isogenic haploid strains bearing the gal3 mutation in combination with either gal15 or pgi1 mutations: the gal15 and pgi1 blocks are not specific for the galactose pathway in contrast to the gal1, gal7 and gal10 blocks. The gal3gal5 and gal3pgi1 double mutants were not inducible, whereas both the gal5 and pgi1 single mutants were inducible. We conclude that, in addition to the GAL3-like activity of GAL1, functions beyond the galactose-specific GAL1, GAL7 and GAL10 enzymes are required for the LTA induction pathway.
ret1-1, a yeast mutant affecting transcription termination by RNA polymerase III.
Authors: James P , Hall B D
Published: April 2021

In eukaryotes, extended tracts of T residues are known to signal the termination of RNA polymerase III transcription. However, it is not understood how the transcription complex interacts with this signal. We have developed a selection system in yeast that uses ochre suppressors weakened by altered transcription termination signals to identify mutations in the proteins involved in termination of transcription by RNA polymerase III. Over 7600 suppression-plus yeast mutants were selected and screened, leading to the identification of one whose effect is mediated transcriptionally. The ret1-1 mutation arose in conjunction with multiple rare events, including uninduced sporulation, gene amplification, and mutation. In vitro transcription extracts from ret1-1 cells terminate less efficiently at weak transcription termination signals than those from RET1 cells, using a variety of tRNA templates. In vivo this reduced termination efficiency can lead to either an increase or a further decrease in suppressor strength, depending on the location of the altered termination signal present in the suppressor tRNA gene. Fractionation of in vitro transcription extracts and purification of RNA polymerase III has shown that the mutant effect is mediated by highly purified polymerase in a reconstituted system.
An unusual Y chromosome of Drosophila simulans carrying amplified rDNA spacer without rRNA genes.
Authors: Lohe A R , Roberts P A
Published: April 2021

The X and Y chromosomes of Drosophila melanogaster each contain a cluster of several hundred ribosomal RNA genes (rDNA). A nontranscribed spacer region separates adjacent rRNA genes and contains tandem copies of 240 bp repeats that include the initiation site for RNA polymerase I transcription. We show here that Drosophila simulans, a sibling species of D. melanogaster, contains few, if any, rRNA genes on its Y chromosome but carries instead a large block (3,000 kb or 12,500 copies) of 240 bp nontranscribed spacer repeats. The repeats are located at the tip of the long arm of the simulans Y chromosome, in contrast to their location among rRNA genes on the short arm of the Y chromosome of D. melanogaster. The bobbed mutation in homozygous females of D. melanogaster shortens and thins the bristles, owing to a partial deletion of rRNA genes on the X chromosome. The bristles of bobbed/Y males are normal owing to the presence of a full complement of rRNA genes on the Y chromosome. Peculiarly, in bobbed/Y males of D. simulans the short bristle phenotype does not return to normal but is enhanced by the presence of the Y chromosome. We propose that the 12,500 nontranscribed spacer repeats on the Y chromosome are responsible for this biological effect by competition for a protein factor(s) essential for normal levels of rDNA transcription at the X-linked locus.
Interaction of the murine dilute suppressor gene (dsu) with fourteen coat color mutations.
Authors: Moore K J , Swing D A , Copeland N G , Jenkins N A
Published: April 2021

The murine dilute suppressor gene, dsu, was previously shown to suppress the dilute coat color phenotypes of mice homozygous for the dilute (d), leaden (ln), and ashen (ash) mutations. Each of these mutations produce adendritic melanocytes, which results in an abnormal transportation of pigment granules into the hair shaft and a diluted coat color. The suppression of each mutation is associated with the restoration of near normal melanocyte morphology, indicating that dsu can compensate for the absence of normal d, ln and ash gene products. In experiments described here, we have determined whether dsu can suppress the coat color phenotype of 14 additional mutations, at 11 loci, that affect coat color by mechanisms other than alterations in melanocyte morphology. In no case was dsu able to suppress the coat color phenotype of these 14 mutations. This suggests that dsu acts specifically on coat color mutations that result from an abnormal melanocyte morphology. Unexpectedly, dsu suppressed the ruby eye color of ruby-eye (ru) and ruby-eye-2 (ru-2) mice, to black. The exact nature of the defect producing these two mutant phenotypes is unknown. Histological examination of the pigmented tissues of the eyes of these mice indicated that dsu suppresses the eye color by increasing the overall level of pigmentation in the choroid but not the retinal pigmented epithelium. Choroid melanocytes, like those in the skin, are derived from the neural crest while melanocytes in the retinal pigmented epithelium are derived from the optic cup. This suggests that dsu may act specifically on neural crest-derived melanocytes. These studies have thus identified a second group of genes whose phenotypes are suppressed by dsu and have provided new insights into the mechanism of action of dsu.
Properties of a class of genes required for ray morphogenesis in Caenorhabditis elegans.
Authors: Baird S E , Emmons S W
Published: April 2021

We have identified eight mutations that define at least five terminal differentiation genes (ram genes) whose products are required during the extension of the male-specific ray sensilla in Caenorhabditis elegans. ram gene mutations result in morphological abnormalities in the sensory rays but do not appear to interfere with ray functions. A similar ray morphology phenotype was observed in males harboring mutations in three previously defined genes, dpy-11, dpy-18 and sqt-1, that also affect body shape. One of these genes, sqt-1, is known to encode a collagen. Mutations in different ram genes failed to complement, from which we infer that their gene products functionally interact. For one ram gene, failure to complement was shown to result from haploinsufficiency. Intergenic noncomplementation did not extend to the body morphology genes. The temperature-sensitive periods of both ram and body morphology mutations corresponded to the period of development in which ray extension occurs. We propose that ram gene products act together in a critical interaction between the rays and the cuticle required for wild-type ray morphology.
Genetic analysis of transvection effects involving cis-regulatory elements of the Drosophila Ultrabithorax gene.
Authors: Micol J L , Castelli-Gair J E , García-Bellido A
Published: April 2021

The Ultrabithorax (Ubx) gene of Drosophila melanogaster contains two functionally distinguishable regions: the protein-coding Ubx transcription unit and, upstream of it, the transcribed but nonprotein-coding bxd region. Numerous recessive, partial loss-of-function mutations which appear to be regulatory mutations map within the bxd region and within the introns of the Ubx transcription unit. In addition, mutations within the Ubx unit exons are known and most of these behave as null alleles. Ubx1 is one such allele. We have confirmed that, although the Ubx1 allele does not produce detectable Ubx proteins (UBX), it does retain other genetic functions detectable by their effects on the expression of a paired, homologous Ubx allele, i.e., by transvection. We have extended previous analyses made by E. B. Lewis by mapping the critical elements of the Ubx gene which participate in transvection effects. Our results show that the Ubx1 allele retains wild-type functions whose effectiveness can be reduced (1) by additional cis mutations in the bxd region or in introns of the Ubx transcription unit, as well as (2) by rearrangements disturbing pairing between homologous Ubx genes. Our results suggest that those remnant functions in Ubx1 are able to modulate the activity of the allele located in the homologous chromosome. We discuss the normal cis regulatory role of these functions involved in trans interactions between homologous Ubx genes, as well as the implications of our results for the current models on transvection.
copia expression is variable among natural populations of Drosophila.
Authors: Csink A K , McDonald J F
Published: April 2021

A survey of copia (retroviral-like element) expression in flies representing 37 populations worldwide of Drosophila melanogaster, Drosophila simulans and Drosophila mauritiana demonstrates that, although copia elements are present in all three species, copia-encoded transcripts are detectable only in D. melanogaster. Levels of copia transcripts vary nearly 100-fold among flies representing geographically diverse populations of D. melanogaster and this variation is not correlated with variability in copia copy number. Analysis of transcript levels in interpopulation hybrids demonstrates that much of this variability may be attributable to the action of trans-acting controls. The geographic and phylogenetic pattern of copia expression suggests that moderate to high levels of copia expression may be a relatively recent evolutionary acquisition. The potential evolutionary significance of these findings is discussed.
Characterization of the FB-NOF transposable element of Drosophila melanogaster.
Authors: Harden N , Ashburner M
Published: April 2021

FB-NOF is a composite transposable element of Drosophila melanogaster. It is composed of foldback sequences, of variable length, which flank a 4-kb NOF sequence with 308-bp inverted repeat termini. The NOF sequence could potentially code for a 120-kD polypeptide. The FB-NOF element is responsible for unstable mutations of the white gene (wc and wDZL) and is associated with the large TEs of G. Ising. Although most strains of D. melanogaster have 20-30 sites of FB insertion, FB-NOF elements are usually rare, many strains lack this composite element or have only one copy of it. A few strains, including wDZL and Basc have many (8-21) copies of FB-NOF, and these show a tendency to insert at "hot-spots." These strains also have an increased number of FB elements. The DNA sequence of the NOF region associated with TE146(Z) has been determined.
Evidence of extensive genetic exchange in the rp49 region among polymorphic chromosome inversions in Drosophila subobscura.
Authors: Rozas J , Aguadé M
Published: April 2021

Restriction map variation in 107 lines extracted from two natural populations of Drosophila subobscura was investigated with seven four-nucleotide-recognizing enzymes in a 1.6-kb region including the rp49 gene, that is located very close to the proximal breakpoint of inversion O3. Fourteen restriction site and 8 length polymorphisms, resulting in 73 haplotypes, have been identified. Estimated heterozygosity per nucleotide, pi = 0.0045, is comparable to the average nucleotide variation observed in Drosophila melanogaster. Because of the location of the rp49 region in D. subobscura, variation in three different gene arrangements-Ost, O3 + 4 and O3 + 4 + 8-has been compared. Out of 14 restriction site polymorphisms, 3 are shared by Ost, O3 + 4 and O3 + 4 + 8, and 3 additional ones are shared by Ost and O3 + 4, evidencing extensive genetic exchange among these polymorphic inversions. In agreement with previous data, the higher level of variation of O3 + 4 (as measured by haplotype diversity and nucleotide variation) suggests that O3 + 4 may be ancestral in relationship to extant gene arrangements.
The molecular basis of brown, an old mouse mutation, and of an induced revertant to wild type.
Authors: Zdarsky E , Favor J , Jackson I J
Published: April 2021

The murine b locus encodes the tyrosinase related protein, TRP-1, a putative membrane-bound, copper-containing enzyme having about 40% amino acid identity with tyrosinase. The protein is essential for production of black rather than brown hair pigment. We show that skin of mutant brown mice contains the same amount of TRP-1 mRNA as wild type. On sequencing the coding region of the mutant mRNA we find four nucleotide differences from the wild-type (Black) sequence. Two of these differences result in different amino acid residues encoded by the brown allele. By sequencing the TRP-1 gene from a mouse in which a reversion from brown to Black has been induced by ethylnitrosourea we are able to show that only one of these amino acid changes, which substitutes a tyrosine for a conserved cysteine, is the cause of the brown phenotype. This mutation is adjacent to another cysteine at which, in the analogous position in tyrosinase a mutation results in the albino phenotype. The sequence of the revertant is the first report of DNA sequence of an ethylnitrosourea-induced genetic change in mouse.
The expression of additive and nonadditive genetic variation under stress.
Authors: Blows M W , Sokolowski M B
Published: April 2021

Experimental lines of Drosophila melanogaster derived from a natural population, which had been isolated in the laboratory for approximately 70 generations, were crossed to determine if the expression of additive, dominance and epistatic genetic variation in development time and viability was associated with the environment. No association was found between the level of additive genetic effects and environmental value for either trait, but nonadditive genetic effects increased at both extremes of the environmental range for development time. The expression of high levels of dominance and epistatic genetic variation at environmental extremes may be a general expectation for some traits. The disruption of the epistatic gene complexes in the parental lines resulted in hybrid breakdown toward faster development and there was some indication of hybrid breakdown toward higher viability. A combination of genetic drift and natural selection had therefore resulted in different epistatic gene complexes being selected after approximately 70 generations from a common genetic base. After crossing, the hybrid populations were observed for 10 generations. Epistasis contributed on average 12 hr in development time. Fluctuating asymmetry in sternopleural bristle number also evolved in the hybrid populations, decreasing by > 18% in the first seven generations after hybridization.
DNA synthesis errors associated with double-strand-break repair.
Authors: Strathern J N , Shafer B K , McGill C B
Published: April 2021

Repair of a site-specific double-strand DNA break (DSB) resulted in increased reversion frequency for a nearby allele. Site-specific DSBs were introduced into the genome of Saccharomyces cerevisiae by the endonuclease encoded by the HO gene. Expression of the HO gene from a galactose-inducible promoter allowed efficient DNA cleavage at a single site in large populations of cells. To determine whether the DNA synthesis associated with repair of DSBs has a higher error rate than that associated with genome duplication, HO-induced DSBs were generated 0.3 kb from revertible alleles of trp1. The reversion rate of the trp1 alleles was approximately 100-fold higher among cells that had experienced an HO cut than among uninduced cells. The reverted allele was found predominantly on the chromosome that experienced the DNA cleavage.
Host and phi X 174 mutations affecting the morphogenesis or stabilization of the 50S complex, a single-stranded DNA synthesizing intermediate.
Authors: Ekechukwu M C , Oberste D J , Fane B A
Published: April 2021

The morphogenetic pathway of bacteriophage phi X 174 was investigated in rep mutant hosts that specifically block stage III single-stranded DNA synthesis. The defects conferred by the mutant rep protein most likely affect the formation or stabilization of the 50S complex, a single-stranded DNA synthesizing intermediate, which consists of a viral prohead and a DNA replicating intermediate (preinitiation complex). phi X 174 mutants, ogr (rep), which restore the ability to propagate in the mutant rep hosts, were isolated. The org (rep) mutations confer amino acid substitutions in the viral coat protein, a constituent of the prohead, and the viral A protein, a constituent of the preinitiation complex. Four of the six coat protein substitutions are localized on or near the twofold axis of symmetry in the atomic structure of the mature virion.
Genetics of the synthesis of serine from glycine and the utilization of glycine as sole nitrogen source by Saccharomyces cerevisiae.
Authors: Sinclair D A , Dawes I W
Published: April 2021

Saccharomyces cerevisiae can grow on glycine as sole nitrogen source and can convert glycine to serine via the reaction catalyzed by the glycine decarboxylase multienzyme complex (GDC). Yeast strains with mutations in the single gene for lipoamide dehydrogenase (lpd1) lack GDC activity, as well as the other three 2-oxoacid dehydrogenases dependent on this enzyme. The LPD1 gene product is also required for cells to utilize glycine as sole nitrogen source. The effect of mutations in LPD1 (L-subunit of GDC), SER1 (synthesis of serine from 3-phosphoglycerate), ADE3 (cytoplasmic synthesis of one-carbon units for the serine synthesis from glycine), and all combinations of each has been determined. The results were used to devise methods for isolating mutants affected either in the generation of one-carbon units from glycine (via GDC) or subsequent steps in serine biosynthesis. The mutants fell into six complementation groups (gsd1-6 for defects in conversion of glycine to serine). Representatives from three complementation groups were also unable to grow on glycine as sole nitrogen source (gsd1-3). Assays of the rate of glycine uptake and decarboxylation have provided insights into the nature of the mutations.
Construction and analysis of yeast RNA polymerase II CTD deletion and substitution mutations.
Authors: West M L , Corden J L
Published: April 2021

The carboxyl-terminal domain (CTD) of the RNA polymerase II largest subunit plays an essential but poorly understood role in transcription. The CTD is highly phosphorylated in vivo and this modification may be important in the transition from transcription initiation to elongation. We report here the development of a strategy for creating novel yeast CTDs. We have used this approach to show that the minimum viable CTD in yeast contains eight consensus (Tyr1Ser2Pro3Thr4Ser5Pro6Ser7) heptapeptide repeats. Substitution of alanine or glutamate for serines in positions two or five is lethal. In addition, changing tyrosine in position one to phenylalanine is lethal. The effects of mutations that alter potential phosphorylation sites are consistent with a requirement for CTD phosphorylation in vivo.
The role of cdc2 and other genes in meiosis in Schizosaccharomyces pombe.
Authors: Iino Y , Hiramine Y , Yamamoto M
Published: April 2021

The requirement of the cdc2, cdc13 and cdc25 genes for meiosis in Schizosaccharomyces pombe was investigated using three different conditions to induce meiosis. These genes were known to be required for meiosis II. cdc13 and cdc25 are essential for meiosis I. The cdc2 gene, which is required for the initiation of both mitotic S-phase and M-phase, is essential for premeiotic DNA synthesis and meiosis II. The requirement of cdc2 for meiosis I was unclear. This contrasts with Saccharomyces cerevisiae, where CDC28, the homolog of cdc2, is required for meiosis I but not for premeiotic DNA synthesis. Expression of cdc13 and cdc25 was induced after premeiotic DNA synthesis, reaching a sharp peak before the first nuclear division. Expression of cdc22, encoding the large subunit of ribonucleotide reductase, was also induced but the peak was before premeiotic DNA synthesis. The induction of cdc13 and cdc25 was largely dependent on DNA synthesis and the function of the mei4 gene. The mei4 gene itself was also induced in a DNA synthesis-dependent manner. The chain of gene expression activating cdc25 may be important as part of the mechanism that ensures the dependency of nuclear division on DNA replication during meiosis.
Ribosomal RNA multigene loci: nomads of the Triticeae genomes.
Authors: Dubcovsky J , Dvorák J
Published: April 2021

The nucleolus organizing regions (NORs) on the short arms of chromosomes 1A(m) and 5A(m) of diploid wheat, Triticum monococcum L., are at the most distal loci in the linkage maps of these two chromosome arms. This distal location differs from the interstitial location of the Nor loci on chromosome arms 1BS of tetraploid Triticum turgidum L. and hexaploid T. aestivum L., 5DS of T. aestivum and diploid Ae. tauschii Coss., and 5HS of barley. Moreover, the barley 5HS locus is at a different location than the 5DS locus. However, other markers, including the centromeres, are colinear. These findings showed that the major Nor loci have repeatedly changed position in the chromosome arms during the radiation of species in the tribe Triticeae without rearrangements of the linkage groups. It is suggested that Nor loci may change position via dispersion of minor loci, that are shown here to exist in the T. monococcum genome, magnification of gene copy numbers in these minor loci, and subsequent deletion of the original major loci. Implications of these findings for the use of rRNA nucleotide sequences in phylogenetic reconstructions are pointed out.
Synonymous substitution rates in enterobacteria.
Authors: Eyre-Walker A , Bulmer M
Published: April 2021

It has been shown previously that the synonymous substitution rate between Escherichia coli and Salmonella typhimurium is lower in highly than in weakly expressed genes, and it has been suggested that this is due to stronger selection for translational efficiency in highly expressed genes as reflected in their greater codon usage bias. This hypothesis is tested here by comparing the substitution rate in codon families with different patterns of synonymous codon use. It is shown that the decline in the substitution rate across expression levels is as great for codon families that do not appear to be subject to selection for translational efficiency as for those that are. This implies that selection on translational efficiency is not responsible for the decline in the substitution rate across genes. It is argued that the most likely explanation for this decline is a decrease in the mutation rate. It is also shown that a simple evolutionary model in which synonymous codon use is determined by a balance between mutation, selection for an optimal codon, and genetic drift predicts that selection should have little effect on the substitution rate in the present case.
MUTATION-SELECTION BALANCE WITH STOCHASTIC SELECTION
Authors: Hartl Daniel L
Published: April 2021

Diffusion theory has been used to analyze a model of mutation-selection balance in which the selection process is assumed to be stochastic in time. The limiting outcome of the mutation-stochastic selection process is determined qualitatively by the geometric mean fitnesses of the genotypes, and the conditions for fixation or polymorphism are similar to those that determine the outcome of the mutation-selection process when selection is constant. However, in the case of a completely recessive allele, detailed numerical study of the polymorphism associated with stochastic selection has shown that the average allele frequency maintained is greater than the equilibrium frequency expected when selection is constant, even when the geometric mean fitness of the recessive homozygotes is identical in the stochastic and deterministic models. Thus, allele frequencies in natural populations that are too high to be plausibly explained by a balance between mutation and constant selection can be accounted for if selection is stochastic.
RECOMBINATION PATHWAY SPECIFICITY OF CHI
Authors: Stahl Franklin W , Stahl Mary M
Published: April 2021

Chi in phage λ is a genetic element increasing the rate of recombination in its vicinity. Chi activity requires the wild-type functions of both the recA and the recB genes of E. coli. In terms of the pathway concept for recombination, Chi is active in the RecBC pathway and inactive in the Red, RecE, and RecF pathways.
GENETICS OF YEAST HEXOKINASE
Authors: Lobo Zita , Maitra P K
Published: April 2021

Two independent isolates of Saccharomyces cerevisiae lacking hexokinase activity (EC 2.7.1.1) are described. Both mutant strains grow on glucose but are unable to grow on fructose, and contain two mutant genes h×k1 and h×k2 each. The mutations are recessive and noncomplementing. Genetic analysis suggests that these two unlinked genes h×k1 and h×k2 determine, independently of each other, the synthesis of hexokinase isozymes P1 and P2, respectively. h×k1 is located on chromosome VIR distal to met10, and h×k2 is on chromosome IIIR distal to MAL2. Of four hexokinase-positive spontaneous reversions, one is very tightly linked to h×k1 and the other three to the h×k2 locus. The reverted enzymes are considerably more thermolabile than the respective wild-type enzymes, and in one case show altered immunological properties. Data are presented which suggest that the h×k1 and h×k2 mutations are missense mutations in the structural genes of hexokinase P1 and hexokinase P2, respectively. These are presumably the only enzymes that allow S. cerevisiae to grow on fructose.
A NEW GENE AFFECTING THE EFFICIENCY OF MATING-TYPE INTERCONVERSIONS IN HOMOTHALLIC STRAINS OF SACCHAROMYCES CEREVISIAE
Authors: Haber James E , Garvik Barbara
Published: April 2021

Homothallic strains of Saccharomyes cerevisiae are able to switch efficiently from one mating genotype to another. From a single haploid spore arise both a and α mating type cells, which then self-mate to produce a colony consisting almost exclusively of nonmating a/α diploid cells. We have isolated a mutant homothallic strain that gives rise to colonies that show bisexual mating behavior. The mating reaction is always asymmetric, that is, in some colonies a mating is much stronger than α mating, while others show greater α than a mating.—This mating phenotype arises from the presence of three cell types in a colony: some a/α nonmating diploids and an unequal number of a and α haploid cells. The predominant haploid type is that of the original cell that gives rise to the colony. This mixture of cell types arises from a very reduced efficiency of homothallic mating-type interconversions in the mutant strain.—The mutation, designated switch (swi1-1), behaves as a single genetic locus. The mutation is centromere linked, but not linked to the mating type locus or to any of the homothallism genes: HO, HM  a and HMα. The switch mutation does not affect the efficiency of self-mating, but rather directly affects the frequency of interconversion of mating types.
LOCATION AND UNDERREPLICATION OF SATELLITE DNA IN DROSOPHILA MELANOGASTER
Authors: Wollenzien Paul , Barsanti Paolo , Hearst John E
Published: April 2021

The two light nuclear satellites (ρCsCl = 1.672 and ρCsCl = 1.687) have been quantified in DNA isolated from the larvel imaginal discs and brains of Drosophila melanogaster with the genotypes X/O, X/X and X/Y. By comparing the results from these different genotypes, the amounts of the two satellites in the X and Y chromosomes and in the autosomes have been determined. The lightest satellite is not located to any appreciable extent in the X chromosome. The heterochromatic regions are not completely filled by these satellites.—Satellite DNA has also been quantified in DNA isolated from adults containing different genotypes. The two satellites are underreplicated to different extents. The apparent amount of underreplication for one of the satellites is different in different parts of the genome.
GENE FREQUENCY CHANGES AT THE α-AMYLASE LOCUS IN EXPERIMENTAL POPULATIONS OF DROSOPHILA PSEUDOOBSCURA
Authors: Yardley Darrell G , Anderson Wyatt W , Schaffer Henry E
Published: April 2021

The frequencies of alleles at the α-Amylase locus of D. pseudoobscura were followed in both large and small experimental populations. No evidence for balancing or directional selection was found, although our ability to detect weak selection is limited. The gene frequency changes in our experimental populations were consistent with the hypothesis of selective neutrality and genetic drift due to sampling error.
DELETION OF MITOCHONDRIAL DNA BYPASSING A CHROMOSOMAL GENE NEEDED FOR MAINTENANCE OF THE KILLER PLASMID OF YEAST
Authors: Wickner Reed B
Published: April 2021

Strains of Saccharomyces cerevisiae carrying a 1.4 × 106 dalton double-stranded (ds) RNA in virus-like particles (the killer plasmid or virus) secrete a toxin that is lethal to strains not carrying this plasmid (virus). The mak10 gene is one of 24 chromosomal genes (called pets, mak1, mak2,…) that are needed to maintain and replicate the killer plasmid. We report here isolation of spontaneous and induced mutants in which the killer plasmid is maintained and replicated in spite of a defect in the mak10 gene. The bypass (or suppressor) mutations in these strains are in the mitochondrial genome. Respiratory deficiency produced by various chromosomal pet mutations, by chloramphenicol, or by antimycin A, does not bypass the mak10-1 mutation. Several spontaneous mak10-1 killer strains have about 12-fold more of the killer plasmid ds RNA than do wild-type killers. Although the absence of mitochondrial DNA bypasses mak10-1, it does not bypass pets-1, mak1-1, mak3-1, mak4-1, mak5-1, mak6-1, mak7-1, or mak8-1.
A COMPARISON OF SURVIVAL AND REPAIR OF UV-INDUCED DNA DAMAGE IN CULTURED INSECT VERSUS MAMMALIAN CELLS
Authors: Koval Thomas M , Hart Ronald W , Myser Willard C , Hink Walter F
Published: April 2021

Survival and unscheduled DNA synthesis (UDS) were measured in a cultured insect cell line, TN-368, and a cultured mammalian cell line, V-79-4, following exposure to several fluences of ultraviolet light. TN-368 cells were approximately seven times more resistant to the lethal effects of UV than V-79 cells, as determined by colony formation. The amount of UDS per unit amount of DNA is about the same in both cell types 4 hr after 10-50 J/m2 UV irradiations.
SPONTANEOUS AND ETHYL METHANESULFONATE-INDUCED MUTATIONS CONTROLLING VIABILITY IN DROSOPHILA MELANOGASTER. II. HOMOZYGOUS EFFECT OF POLYGENIC MUTATIONS
Authors: Ohnishi Ohmi
Published: April 2021

Polygenic mutations affecting viability were accumulated on the second chromosome of Drosophila melanogaster by treating flies with EMS in successive generations. The treated chromosomes were later made homozygous and tested for their effects on viability by comparison of the frequency of such homozygotes with that of other genotypes in the same culture. The treated wild-type chromosomes were kept heterozygous in Pm/+ males by mating individual males in successive generations to Cy/Pm females. The number of generations of accumulation was 1 to 30 generations, depending on the concentration of EMS. A similar experiment for spontaneous polygenic mutations was also conducted by accumulating mutations for 40 generations. The lower limit of the spontaneous mutation rate of viability polygenes is estimated to be 0.06 per second chromosome per generation, which is about 12 times as high as the spontaneous recessive lethal mutation rate, 0.005. EMS-induced polygenic mutations increase linearly with the number of treated generations and with the concentration of EMS. The minimum mutation rate of viability polygenes is about 0.017 per 10-4 m, which is only slightly larger than the lethal rate of 0.013 per 10-4 m. The maximum estimate of the viability reduction of a single mutant is about 6 to 10 percent of the normal viability. The data are consistent with a constant average effect per mutant at all concentrations, but this is about three times as high as that for spontaneous mutants. It is obvious that one can obtain only a lower limit for the mutation rate, since some mutants may have effects so near to zero that they cannot be detected. The possibility of measuring something other than the lower limit is discussed. The ratio of the load due to detrimental mutants to that caused by lethals, the D/L ratio, is about 0.2 to 0.3 for EMS-induced mutants, as compared to about 0.5 for spontaneous mutants. This is to be expected if EMS treatment produces a large fraction of small deletions and other chromosome rearrangements which are more likely to be lethal.
GENETIC ANALYSIS OF MATING-TYPE DIFFERENTIATION IN PARAMECIUM TETRAURELIA
Authors: Brygoo Yves
Published: April 2021

Whereas each of the two complementary mating types, O and E, of Paramecium tetraulrelia normally shows cytoplasmic inheritance, an abnormal heredity of mating type was observed in the progeny of crosses between two stocks of different geographical origin of Paramecium tetraurelia(stock 51 and stock 32). The modified pattern of mating-type inheritance was shown to result from the interaction of the two wild-type alleles at the locus mtD (mtD51 and mtD32), leading to a new differentiated state O*, different from the normal O and E states observed in both stock 51 and stock 32 cells. The genetic analysis of O* clones showed that the O* phenotype involves both a new heritable cytoplasmic state and possibly a nuclear change which can be transmitted through conjugation and segregates in a Mendelian fashion. All the data can be interpreted if the assumption is made that mating-type determination is achieved only by the commitment or noncommitment to the expression of mating-type E, and that this commitment may simply reflect the activation or nonactivation of the locus mtD, under the influence of one or two "cytoplasmic factors" including the product of the gene mtD itself.
THE MEIOTIC EFFECT OF A DEFICIENCY IN DROSOPHILA MELANOGASTER WITH A MODEL FOR THE EFFECTS OF ENZYME DEFICIENCY ON RECOMBINATION
Authors: Robbins Leonard G
Published: April 2021

The meiotic effects of heterozygosity for a deficiency of the zeste-white region of the X chromosome include reduced recombination and increased non-disjunction of the entire chromosome complement. Reduced dosage of a gene or genes in the zeste-white interval, rather than structural heterozygosity, is responsible for the meiotic effect. A model for the recombination effects of reduced enzyme concentration has been developed, and its consequences are comparable with the results obtained for deficiency heterozygosity. Thus, all of the observations can be accounted for by imagining a dosage-sensitive locus in the zeste-white region that codes for an enzyme involved in the recombination process. The interaction of the interchromosomal effect of heterozygous inversions with the deficiency has been examined, and the possibility of using the model for the analysis of other meiotic phenomena is considered.
HETEROSIS AS AN EXPLANATION FOR LARGE AMOUNTS OF GENIC POLYMORPHISM
Authors: Lewontin R C , Ginzburg L R , Tuljapurkar S D
Published: April 2021

By using both numerical and analytical approaches, we have shown that heterosis alone is not a mechanism for maintaining many alleles segregating at a locus. Even when all heterozygotes are more fit than all homozygotes, the proportion of fitness arrays that will lead to a stable, feasible equilibrium of more than 6 or 7 alleles is vanishingly small. More alleles can be maintained if, in addition to heterosis, it is assumed that there is very little variation in fitness from heterozygote to heterozygote, with the ratio of mean heterosis to standard deviation of fitness among heterozygotes in the neighborhood of 10. When such conditions hold, the allelic frequency distribution and equilibrium will be very uniform, with all alleles very close to equal frequency p = - . It is much more likely that stable equilibria for multiple alleles will be best explained by multiple niche selection. 1 n
AFFINITY DISTANCE VALUES AMONG SOMATIC METAPHASE CHROMOSOMES IN MAIZE
Authors: Horn J D , Walden D B
Published: April 2021

In maize root-tip metaphase preparations, all distances between two chromosomes were measured in 50 cells from each of seven stocks and in 30 from one stock; four were arrested with cold, two with 8-hydroxyquinoline, one with colchicine and one with monobromonaphthalene Standardized, affinity-distance values were calculated for all pairs of homologues and pairs of nonhomologues from each preparation. The homologues of pair X were the least separated, those of pair I the most separated in the cold-arrested stocks. All but pairs I and VIII were shown to be significantly different from the observed mean. The observed mean was less than but not significantly different from the theoretical value for a random distribution. The use of chemical agents for metaphase arrest increased the separation of homologues, except for pair I.—Eleven percent of the comparisons of nonhomologues from cold-arrested, as contrasted to none of the comparisons from the c-metaphase treatments, were significantly different from the theoretical talue for a random distribution. This was considered evidence for limited primary nonhomologue association in maize. Although there were specific, differential responses to the two arrest agents, the population of homologous pairs approached a random distribution only in chemically arrested stocks.—Primary homologue association was considered to be maintained by two mechanisms. the more common involving the micro-tubules and the second involving the nucleolus.—Interpretations are offered regarding the claims of somatic association in other species, especially man. The opportunity in maize for experimentally modifying distance values by cytogenetic techniques is discussed.
SPONTANEOUS CHROMOSOME BREAKAGE AT MALE MEIOSIS ASSOCIATED WITH MALE RECOMBINATION IN DROSOPHILA MELANOGASTER
Authors: Henderson S A , Woodruff R C , Thompson J N
Published: April 2021

An inbred line (OKI) of Drosophila melanogaster, recently derived from a natural population in Oklahoma, has been found by WOODRUFF and THOMPSON to exhibit a low frequency of spontaneous male recombination when outcrossed to marker stocks. There is also a reciprocal-cross effect, such that recombination is found only if OK1 males are used in the initial cross. When OK1 females are used, however, male recombinatioii is again found if their male progeny are used for a subsequent cross,-In the present cytological analysis, chromosome behavior at male meiosis was studied in reciprocal crosses between the OK1 line and both a marker gene stock and an inversion stock. If the recombination events were "conventional" and premeiotic (gonial) in origin, no chromosome aberrations would be expected during meiosis. If they were "conventional" and meiotic, some dicentric bridges with free fragments would be expected in the inversion heterozygote, but none should be present in the marker gene cross.—The results demonstrated that the occurrence of recombination in males is most likely a meiotic event, though the occurrence of some limited premeiotic recombination can not be disproven. Meiosis was found to be perfectly normal in all crosses lacking male recombination. In all of the inversion stock and noninversion marker stock crosses that showed male recombination, however, anaphase bridges were found at both first and second meiotic divisions. These were often accompanied by more than the single fragment expected from a conventional inversion bridge and fragment situation. In extreme cases, almost complete pulverization of one or more autosomes was found.—All metaphase I stages were perfectly normal, suggesting that no comparable breakage occurs in premeiotic gonial mitoses. The form of chromosome damage is similar in many ways to that produced by some DNA synthesis inhibitors, or by some viral or mycoplasma infections. This possibility is discussed, and some of the evolutionary implications of the system are briefly considered.
MODES OF SELECTION MAINTAINING AN INVERSION POLYMORPHISM IN DROSOPHILA PAULISTORUM
Authors: Gromko Mark H , Richmond Rollin C
Published: April 2021

The possibility that fitness relationships associated with an inversion polymorphism in D. paulistorum were frequency dependent was investigated. Using allozymes of tetrazolium oxidase to mark inversions, the effects of genotype frequency, larval density, and culture conditions on fitness were assessed. The proportions of genotypes among egg-laying females were varied, thus changing the expected proportions of progeny produced in the absence of fecundity or viability selection. The genotypes of progeny were determined by electrophoresis and comparisons of the ratio of the numbers of the different genotypes produced to the expected ratio was used to evaluate fitness relationships. Fitness relationships were dependent on genotype frequency, larval density, and culture conditions. Selection was either absent, directional, frequency dependent (favoring rare types), or heterotic depending on density and culture conditions. It is implied that the adaptive value of genetic variants need not be apparent in all environments, or may change with changing conditions. There is evidence for different criteria for selection in the two sexes. These results add to the evidence supporting the importance of frequency-dependent selection. It is argued that for frequency dependence to be of general importance, selection must act on genes in groups, either as an inversion or as lengths of chromosome with integrity maintained by disequilibrium.
INFLUENCE OF MATERNAL PHENOTYPE ON METABOLIC DIFFERENTIATION OF AGOUTI LOCUS MUTANTS IN THE MOUSE
Authors: Wolff George L
Published: April 2021

The results of extensive breeding experiments indicate that the phenotypic differentiation of embryos carrying the viable yellow, Avy, or mottled, am, mutations is influenced to a major extent by the agouti locus genotype and the strain genome of the dam. The Avy/a and am/a genotypes are each expressed in a spectrum of coat color phenotypes. These can be grouped into two classes, mottled and pseudoagouti.—In a reciprocal cross of C57BL/6JNIcrWf and AM/Wf-am/am mice, 29.5% of the offspring of C57BL/6 dams were of the pseudoagouti phenotype, whereas no pseudoagouti offspring were produced by AM strain dams.—Mottled yellow Avy/a mice become obese and tumor formation is enhanced in these mice in comparison with the lean pseudoagouti Avy/a siblings.—In two different reciprocal crosses using four different inbred strains, the proportion of pseudoagouti Avy/a offspring differed according to the strain of the dam. Regardless of strain, mottled yellow Avy/a dams produced significantly fewer pseudoagouti Avy/a offspring than did black a/a dams.—The data suggest that metabolic differentiation of Avy/a zygotes into phenotypic classes with different susceptibilities to obesity and tumor formation is influenced to a considerable degree by the metabolic characteristics of the oviductal and uterine environment of the dam.
INHERITANCE OF SEMIDWARFISM IN RICE, ORYZA SATIVA L
Authors: Foster K W , Rutger J N
Published: April 2021

The inheritance of plant height was investigated in a ten-parent diallel cross of diverse rice cultivars. Parents included two tall japonica lines and eight semidwarf lines. Data from parent, F1, F2, and F3 generations indicated that the majority of height variation among the ten parents could be accounted for by three major genes with additive loci effects. D51, 72/2234-11, and G33 (derived from the known major-gene indica semidwarf Dee-geo-woo-gen) all were found to possess an allelic, partially recessive semidwarfing gene (sd1). Additional semidwarfing genes were detected in D66 (sd2, fully recessive) and in CI 9858 (sd3, partially to fully recessive). Relative magnitudes of additive effects were sd1 > sd2 ≥ sd3. Hokuriki 76, Tedoriwase, and IV 29-4 were found to be dwarfed by a multiple-gene system. Hayman-Jinks diallel cross analysis on parent and F1 information (1974 and 1975) and on parent and F2 information demonstrated the presence of significant additive and dominance variation, but epistasis was not detected. A preponderance of dominant alleles with partial dominance for increased plant height was observed. Since diallel statistics reflect properties of genes with larger effects, the genetic model proposed from segregation analysis was in substantial agreement with predictions of the Hayman-Jinks analysis.