bluuebunny/crossref_metadata_2025 huggingface dataset:
GENETICS OF MANDIBLE FORM IN THE MOUSE
Authors: Atchley William R , Plummer A Alison , Riska Bruce
Published: January 2021

The underlying determination of phenotypic variability and covariability is described for 14 traits that define the morphological size and shape of the mature mouse mandible. Variability is partitioned into components due to direct additive and dominance genetic effects, indirect maternal additive genetic effects, genetic covariance between direct additive and indirect maternal additive effects and common and residual environmental effects. Multivariate analyses of the dimensionality of genetic variability indicate several complex and independent genetic components underlie the morphological form of the mandible. The multidimensional nature of the genetic components suggests a complex picture with regard to the consequences of selection on mandibular form.
DEVELOPMENTAL GENETICS OF MUTANTS THAT SPECIFY KNOTTED LEAVES IN MAIZE
Authors: Freeling Michael , Hake Sarah
Published: January 2021

Of seven dominant knotted-leaf mutants tested, six mapped at or near Kn1 on the long arm of chromosome 1, and one was not linked to Kn1. Comparisons of phenotypes among these mutants allowed us to focus on a systematic abnormality: the parenchyma cells associated with lateral veins do not fully differentiate into bundle sheath, mesophyll or upper sclerenchyma. The more dramatic expression of Kn1 mutants–knots, ligule alterations and twisting–is sporadic and dependent on the time when the mutant acts in leaf primordium development. Using lw to mark leaf sectors that lose Kn1 following X-irradiation, we show that the knotted-leaf phenotype encoded by chromosome 1L is autonomous. Analysis of sectors lacking a particular Kn1 gene (Kn1-N2) suggests that Kn1 itself, rather than a linked modifier gene, is autonomous in the leaf primordium. Aneuploid studies using various translocations involving 1L and marked by Adh1 allozymes are compared. The Kn1 mutant appears to encode a "new" function or a considerable overproduction of an extant product in the leaf. Kn1/- 1L hypoploids either express knotted poorly or not at all; transvection is ruled out, but the cause for this modification of Kn1 expression is not yet known.—Our working hypothesis is that Kn1 mutants permit the expression of a product that is usually not produced in leaf primordial cells. We suggest that this product interferes with the early cell-type commitments of cells near lateral veins. Thus, relatively uncommitted cells are present in more mature blades, where they may divide unexpectedly into knots or may induce bits of ligule.
GENE ACTIONS INVOLVED IN DETERMINING THE NUMBER OF OVARIOLES AND STERNITE CHAETAE IN FRESHLY COLLECTED STRAINS OF DROSOPHILA MELANOGASTER
Authors: Thomas-Orillard Michele , Jeune Bernard
Published: January 2021

The nature of gene action involved in the mode of determination of two quantitative traits of Drosophila melanogaster, e.g., number of ovarioles and sternite chaetae, was studied in freshly captured strains and their crosses, using the biomodel built up by Cockerman and Weir. The results proved to be similar to those obtained with laboratory populations. The genome is by far the most important source of variation for the two traits. Extragenetic interactions are far more important in freshly captured stock than in flies which have already been propagated for several years in the laboratory. We can now interpret neutrality of a quantitative character as a state of equilibrium between medium and population. Since there are extragenetic interactions (type k) in the case of the neutral character, we could even think of possible future variations able to alter its mean value in such a way as to make it selective.
ESCHERICHIA COLI GENE INDUCTION BY ALKYLATION TREATMENT
Authors: Volkert Michael R , Nguyen Dinh C , Beard K Christopher
Published: January 2021

Searches for alkylation-inducible (aid) genes of Escherichia coli have been conducted by screening random fusions of the Mu-dl(ApR  lac) phage for fusions showing increased β-galactosidase activity after treatment with methylating agents, but not after treatments with UV-irradiation. In this report we describe gene fusions that are specifically induced by alkylation treatments. Nine new mutants are described, and their properties are compared with the five mutants described previously. The total of 14 fusion mutants map at five distinct genetic loci. They can be further subdivided on the basis of their induction by methyl methanesulfonate (MMS) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). alkA, aidB and aidD are induced by both agents and appear to be regulated by ada. Neither aidC nor aidI is regulated by ada. Moreover, since aidC is induced only by MNNG and aidI is induced only by MMS, these two genes are likely to be individually regulated. Thus, there appear to be at least three different regulatory mechanisms controlling aid genes.
PERSISTENCE OR RAPID GENERATION OF DNA LENGTH POLYMORPHISM AT THE ZETA-GLOBIN LOCUS OF HUMANS
Authors: Chapman Barbara S , Vincent Karen A , Wilson Allan C
Published: January 2021

Extensive restriction mapping of 76 human genomic DNAs defines multiple sites of length and point mutation near the zeta-globin locus, which codes for an embryonic alpha-like globin chain. There are two major sites of DNA length variation: one in the intergenic region with three alleles and one in the first intron of the zeta 1 gene with at least four alleles. Our mapping establishes that the intronic polymorphism is associated with a tandem array of short, repeated sequences. The length alleles occur in each of four human populations sampled, suggesting an ancient origin with persistence of several length alleles, or rapid regeneration of these particular variants. Four polymorphic restriction sites were also found; the frequency of polymorphic sites is comparable to that found in the human beta-globin gene region. Analysis of haplotypes indicates either that multiple recombinations have occurred near the 5' end of the zeta 1 gene or that this region is prone to recurrent length mutation.
LOCALIZATION IN THE TOMATO GENOME OF DNA RESTRICTION FRAGMENTS CONTAINING SEQUENCES HOMOLOGOUS TO THE rRNA (45S), THE MAJOR CHLOROPHYLL a/b BINDING POLYPEPTIDE AND THE RIBULOSE BISPHOSPHATE CARBOXYLASE GENES
Authors: Vallejos C E , Tanksley S D , Bernatzky R
Published: January 2021

DNA restriction fragments containing sequences homologous to the ribosomal RNA (45s), the major chlorophyll a/b binding polypeptide (CAB) and the small subunit of ribulose bisphosphate carboxylase (RBCS) genes have been localized and mapped in the tomato nuclear genome by linkage analysis. Ribosomal RNA genes map to a single locus, R45s, which resides in a terminal position on the short arm of chromosome 2 and corresponds to the Nucleolar Organizer Region. The size of the 45s repeating unit is estimated to be approximately 9 kb in Lycopersicon esculentum and 11 kb in Lycopersicon pennellii. Five loci were found to contain CAB sequences. Two of the loci, Cab-1 (chromosome 2) and Cab-3 (chromosome 8), together accounted for more than 80% of the hybridization signal. These loci contain more than one CAB structural gene. The other three loci, Cab-2 (chromosome 8), Cab-4 (chromosome 7) and Cab-5 (chromosome 12), each account for <10% of the total signal and may contain only a single copy of the CAB structural sequence. Three loci were found to contain RBCS sequences. Rbcs-2 (chromosome 3) and Rbcs-3 (chromosome 2) were responsible for >80% of the signal, with the remainder being associated with Rbcs-1 (chromosome 2). Rbcs-2 and Rbcs-3 may contain more than one copy of the gene.
NEGATIVE DOMINANT MUTATIONS OF THE uidR GENE IN ESCHERICHIA COLI: GENETIC PROOF FOR A COOPERATIVE REGULATION OF uidA EXPRESSION
Authors: Blanco Carlos , Ritzenthaler Paul , Mata-Gilsinger Mireille
Published: January 2021

The uidA gene is the first gene involved in the hexuronide-hexuronate pathway in Escherichia coli K-12 and is under the dual control of the uidR and uxuR encoded repressors. Point mutations affecting the uidR regulatory gene were sought to investigate the regulation of uidA. When the uidR mutant allele was on a multicopy plasmid and the wild-type allele was on the chromosome, some of the mutant phenotypes were dominant to the wild-type phenotype, indicating that the active form of the UidR repressor is multimeric. We have demonstrated that expression of the mutant phenotype is dependent on gene dosage. The dominance of the uidR allele was also sensitive to the presence of the wild-type uxuR allele in the cell. This behavior probably results from UidR-UxuR repressor interactions. A mechanism is proposed: we suggest that the UidR and UxuR repressors interact after their binding to the operator site of uidA; the binding of one regulatory molecule may facilitate the binding of the other one in a cooperative process.
SEGREGATION ANALYSES AND GENE-CENTROMERE DISTANCES IN ZEBRAFISH
Authors: Streisinger George , Singer Fred , Walker Charline , Knauber Donna , Dower Nancy
Published: January 2021

The gol-1, gol-2, alb-1 and spa-1 mutations affect pigment pattern in the zebrafish. We show here that these loci are unlinked to each other. In addition, gene-centromere distances were determined for these loci by analysis of halftetrads obtained by the inhibition of the second meiotic division. The fractions of tetratype (second-division segregation) tetrads range from 0.24 (spa-1) to 0.89 (gol-1). The observation of >0.67 second-division segregation indicates that the zebrafish has high chiasma interference.
A GENETIC ANALYSIS OF PRIMARY PRODUCTS OF BACTERIOPHAGE LAMBDA RECOMBINATION
Authors: Huisman Olivier , Fox Maurice S
Published: January 2021

Primary products of bacteriophage lambda recombination that display heterozygosity as a consequence of the presence of regions of heteroduplex DNA are rare in standard λ crosses. Phage manifesting heterozygosity at a given allele are evident when recombinants, emerging from a cross, are selected for an exchange in a neighboring interval. We show that the abundance of such heterozygotes can be increased 10- to 20-fold by selection on an E. coli indicator that is defective in methyl-directed mismatch repair (mutL). Thus, the activity of the methyl-directed mismatch repair system is, at least in part, responsible for the low frequency of detectably heterozygous phage emerging from a standard cross. In a mutL indicator, many primary products of recombination are replicated without the intervention of mismatch repair.—The products of a six-factor phage cross have been plated on a mutL indicator allowing visual detection of those phage products heterozygous for one of the allelic pairs, cI. By genetic analysis, we show that the heteroduplex regions of these primary products of recombination are on the average about 4 kb in length and can include as much as half of the lambda genome.
DNA REPAIR DEPENDENCE OF SOMATIC MUTAGENESIS OF TRANSPOSON-CAUSED WHITE ALLELES IN DROSOPHILA MELANOGASTER AFTER TREATMENT WITH ALKYLATING AGENTS
Authors: Fujikawa Kazuo , Kondo Sohei
Published: January 2021

DNA repair-defective alleles of the mei-9, mei-41, mus-104 and mus-101 loci of Drosophila melanogaster were introduced into stocks bearing the UZ and SZ marker sets. Males with the UZ marker set, z  1 (zeste allele) and w  +(TE) (genetically unstable white allele presumably caused by a transposable element), or the SZ marker set, z  1 and w  +R (semistable white allele caused by partial duplication of the w  + locus plus transposon insert), were exposed to EMS at the first instar. After emergence, adult males bearing red spots on lemon-yellow eyes were scored as flies with somatic reversions of w  +(TE) or w  +R. The relative mutabilities (relative values of reversion frequency at an equal EMS dose) of either w  +(TE) or w  +R in a repair-proficient strain and in mei-9, mei-41, mus-104 and mus-101 strains were 1:?1.2:0.3:0.3:0.7, despite the fact that w  +(TE) reverted two to three times as frequently as w  +R under both the repair-proficient and repair-deficient genetic conditions. Similarly, after treatment with MMS, MNNG and ENNG, w  +(TE) was somatically more mutable in the mei-9 strain and less mutable in the mei-41 and mus-104 strains than in the repair-proficient strain. From these results, we propose that mutagenic lesions produced in DNA by treatment with these chemicals are converted to mutant DNA sequences via the error-prone repair mechanisms dependent on the products of the genes mei-41  + (mei-41 and mus-104 being alleles of the same locus) and mus-101  +, whereas they are eliminated by mei-9  +-dependent excision repair. In contrast to the approximately linear responses of induced reversions of w  +(TE) with ENNG in the repair-proficient, mei-9, and mei-41 strains, seemingly there were dosage insensitive ranges for induced reversion with MNNG in the repair-proficient and mei-41 strains, but not for reversion in the mei-9 strain; w  +(TE) in the mus-104 strain was virtually nonmutable with MNNG and ENNG. These results suggest that O  6-methylguanine (O  6MeG) produced in DNA with MNNG, but not O  6-ethylguanine produced with ENNG, is almost completely repaired in a low dose range by constitutive activity of DNA O  6MeG transmethylase. From the distribution of clone sizes of spontaneous revertant spots and other data, we propose that both w  +(TE) and w  +R have a similar tendency to spontaneously revert more frequently at early rather than at late developmental stages, probably reflecting a common property of their inserted transposons.
DEFICIENCY ANALYSIS OF THE TIP OF CHROMOSOME 3R IN DROSOPHILA MELANOGASTER
Authors: Kongsuwan Kritaya , Dellavalle Robert P , Merriam John R
Published: January 2021

Region 98EF-100F in chromosome 3 is interesting for genetic analysis because it contains a number of genes of developmental importance. Although there are no preexisting simple deficiency stocks, this region is amenable to genetic manipulation using other types of rearrangements. In the present investigation we obtained deficiencies by combining the terminal deficiencies formed by segregation of Y;3 translocations with a series of duplications of the tip of 3R, both from Y;3 translocations with different breakpoints and from 3;1 duplications in which the 3R tip is carried as a second arm on the X chromosome. Analysis of such synthetic deficiencies reveals five haplo-abnormal loci in the 98A-100F interval. These include a haplolethal site, a newly described Minute and three previously reported Minute mutations. The newly discovered Minute has been designated M(3)99D and is localized cytologically to bands 99D1-9. The three previously reported Minute loci in the region have been localized more precisely: M(3)1 to bands 99B5-9, M(3)f to bands 99E4-F1 and M(3)g to region 100C-F. In addition, we have been able to obtain synthetic deficiencies uncovering all of the intervals from 99B5 to 100B. These deficiencies will be useful for future genetic and molecular analyses of the genes that map within the right tip of chromosome 3.
SELECTION AND BIASED GENE CONVERSION IN A MULTIGENE FAMILY: CONSEQUENCES OF INTERALLELIC BIAS AND THRESHOLD SELECTION
Authors: Walsh James Bruce
Published: January 2021

In a previous paper, I investigated the interactions in a gene family of additive selection and biased gene conversion in a finite population when conversion events are rare. Here I extend my "weak-conversion limit" model by allowing biased interallelic conversion (conversion between alleles at the same locus) of arbitrary frequency and various threshold selection schemes for rare interlocus conversion events. I suggest that it is not unreasonable for gene families to experience threshold fitness functions, and show that certain types of thresholds can greatly constrain the rate at which advantageous alleles are fixed as compared to other fitness schemes, such as additive selection. It is also shown that the double sampling process operating on a gene family in a finite population (sampling over the number of genes in the gene family and over the number of individuals in the population) can have interesting consequences. For selectively neutral alleles that experience interallelic bias, the probability of fixation at each single locus may be essentially neutral, but the cumulative effects on the entire gene family of small departures from neutrality can be significant, especially if the gene family is large. Thus, in some situations, gene families can respond to directional forces that are weak in comparison to drift at single loci.
THE EVOLUTION OF RESTRICTED RECOMBINATION AND THE ACCUMULATION OF REPEATED DNA SEQUENCES
Authors: Charlesworth Brian , Langley Charles H , Stephan Wolfgang
Published: January 2021

We suggest hypotheses to account for two major features of chromosomal organization in higher eukaryotes. The first of these is the general restriction of crossing over in the neighborhood of centromeres and telomeres. We propose that this is a consequence of selection for reduced rates of unequal exchange between repeated DNA sequences for which the copy number is subject to stabilizing selection: microtubule binding sites, in the case of centromeres, and the short repeated sequences needed for terminal replication of a linear DNA molecule, in the case of telomeres. An association between proximal crossing over and nondisjunction would also favor the restriction of crossing over near the centromere. The second feature is the association between highly repeated DNA sequences of no obvious functional significance and regions of restricted crossing over. We show that highly repeated sequences are likely to persist longest (over evolutionary time) when crossing over is infrequent. This is because unequal exchange among repeated sequences generates single copy sequences, and a population that becomes fixed for a single copy sequence by drift remains in this state indefinitely (in the absence of gene amplification processes). Increased rates of exchange thus speed up the process of stochastic loss of repeated sequences.
DNA SYNTHESIS AT THE SITE OF A Red-MEDIATED EXCHANGE IN PHAGE Λ
Authors: Stahl Franklin W , Stahl Mary M
Published: January 2021

In phage λ, progeny particles bearing unreplicated chromosomes are recombinant by action of λ's Red system only near the right end of the chromosome. These recombinants are frequently heterozygous (heteroduplex) for markers located there. In replication-blocked crosses involving two heavy-labeled parents we find that particles in the solitary peak, containing progeny with fully conserved DNA, vary in density. Those on the heavy side of this peak are more apt to be heterozygous than are those on the light side. The data fit a model in which a double chain cut at cos, λ's packaging origin, is followed by partial exonucleolytic degradation of λ's r chain from the right end leftward. The exposed l chain, which thereby constitutes a 3′ overhang, invades an intact, circular homologue afrter itself suffering some degradation. Completion of the recombinant chromosome sometimes involves DNA synthesis primed by the invading chain.
HYPER-RECOMBINING RECIPIENT STRAINS IN BACTERIAL CONJUGATION
Authors: Feinstein Sheldon I , Low K Brooks
Published: January 2021

Using a direct enrichment and screening procedure, mutants of Escherichia coli have been isolated in which recombination frequencies for several intragenic Hfr × F- crosses are significantly higher (twofold to sixfold) than in the parental strains. These hyper-recombination mutations comprised five new mutS  - and one new mutL  - allele. Together with other known mut  - alleles, they were analyzed for effects on intragenic recombination using several types of crosses. Hyper-recombination was found for mutS  -, mutL  -, mutH (=mutR)- and mutU (=uvrD)-, with the largest effects seen for certain alleles of uvrD; these resulted in over 20-fold excesses in recombinant production for Hfr × F- crosses and F'-chromosome homogenotization. Spontaneous mutator ability was not always correlated with degree of hyper-recombination.
ENHANCEMENT AND SUPPRESSION OF A EUCHROMATIC POSITION EFFECT AT NOTCH IN DROSOPHILA
Authors: Welshons W J , Welshons H J
Published: January 2021

The recessive visible rough-eye mutant facet-strawberry, faswb, is caused by the deletion of 0.8 kb of base sequences from the 5' end of the Notch locus. Visible deficiencies adjacent to faswb suppress this mutant effect of the Notch locus, and in the same region (between salivary bands 3C1 and 3C7), we have demonstrated the presence of at least one partial suppressor and one enhancer of the faswb position effect at Notch.—The enhancer seems to be a small inversion approximately equal to the salivary-band doublet 3C2, 3, and the partial suppressor lies between the inversion in 3C2, 3 and the small deletion in faswb immediately distal to 3C7. Neither the enhancer, e(faswb), nor the partial suppressor, su(faswb), can be detected except when linked in cis to faswb. The e(faswb) and the su(faswb), in unison, act antagonistically on the faswb position effect.—The faswb mutant is interpreted to be a nonvariegating position effect at the Notch locus resulting from a novel euchromatic—euchromatic association of base sequences caused by the small deletion.
TWO ALLELES OF MAIZE ALCOHOL DEHYDROGENASE 1 HAVE 3' STRUCTURAL AND POLY(A) ADDITION POLYMORPHISMS
Authors: Sachs M M , Dennis E S , Gerlach W L , Peacock W J
Published: January 2021

Two standard electrophoretic alleles of the maize alcohol dehydrogenase 1 locus (Adh1-1S and Adh1-1F) have been isolated and characterized. Restriction endonuclease mapping shows that a region of less than 5 kb is conserved in both alleles and is flanked both 5' and 3' by regions highly polymorphic for restriction sites. Nucleotide sequence comparison of these two alleles reveals that polymorphism in the 3' flanking region is due to rearrangements including tandem duplications, a transposable element-like insertion and a deletion. S1 nuclease analysis shows that both the Adh1-1S and the Adh1-1F alleles contain multiple poly(A) addition sites; four sites are observed for the Adh1-1S alleles and seven sites for the Adh1-1F allele. Only two of these poly(A) addition sites appear to be identical in the two alleles. No consensus signal for poly(A) addition is observed near any of these sites.
GENETIC VARIATION IN THE SHAPE OF THE MOUSE MANDIBLE AND ITS RELATIONSHIP TO GLUCOCORTICOID-INDUCED CLEFT PALATE ANALYZED BY USING RECOMBINANT INBRED LINES
Authors: Lovell D P , Erickson R P
Published: January 2021

Variation in mandible shape has been investigated in a set of recombinant inbred (RI) lines of mice, the C57BL/6J × A/J (BXA;AXB) RI lines. Considerable genetic variation was detected between the RI lines, but most lines were intermediate in shape when compared with the parent lines. Variation in mandible shape could not be explained by any single gene differences known between the parent lines including the H-2 locus. Some RI lines had mandible shapes unlike either parent, and one in particular, line BXA1, had an unusual shape with a pronounced condyloid process. It was concluded that mandible shape has a complex inheritance involving a number of genes, each with small effects. In some cases, recombination of the genes can produce bone shapes quite different from those of the original parent line.—There was no evidence that the variability in steroid-induced palate incidence in the BXA;AXB RI lines is related to the variation in adult mandible shape as detected in this study.
ON THE DIVERGENCE OF ALLELES IN NESTED SUBSAMPLES FROM FINITE POPULATIONS
Authors: Hudson Richard R , Kaplan Norman L
Published: January 2021

Within-population variation at the DNA level will rarely be studied by sequencing of loci of randomly chosen individuals. Instead, individuals will usually be chosen for sequencing based on some knowledge of their genotype. Data collected in this way require new sampling theory. Motivated by these observations, we have examined the sampling properties of a finite population model with two mutation processes and with no selection or recombination. One mutation process generates new alleles according to an infinite-alleles model, and the other generates polymorphisms at sites according to an infinite-sites model. A sample of n genes is considered. The stationary distribution of the number of segregating sites in a subsample from one of the allelic classes in the sample conditional on the allelic configuration of the sample is studied. A recursive scheme is developed to compute the moments of this distribution, and it is shown that the distribution is functionally independent of the number of additional alleles in the sample and their respective frequencies in the sample. For the case in which the sample contains only two alleles, the distribution of the number of segregating sites in a subsample containing both alleles conditional on the sample frequencies of the alleles is studied. The results are applied to the analysis of DNA sequences of two alleles found at the Adh locus of Drosophila melanogaster. No significant departure from the neutral model is detected.
GLUCOSE REPRESSION OF AMYLASE GENE EXPRESSION IN DROSOPHILA MELANOGASTER
Authors: Benkel Bernhard F , Hickey Donal A
Published: January 2021

We have previously shown that dietary glucose can reduce amylase activity in both adults and larvae of Drosophila; this reduction in enzyme activity reflects a reduction in the quantity of amylase protein, rather than an inhibition of enzyme activity. Here, we report that we have now defined conditions in which the repressive effect of glucose can be greater than 100-fold. Moreover, this repression is partially counteracted by the addition of exogenous cyclic AMP. We also show that there is a direct correlation between changes in amylase activity and changes in the amount of translatable mRNA as assayed in microinjected Xenopus oocytes. This means that the glucose repression is occurring at a pretranslational stage.
GENETIC ANALYSIS OF LIVER NEURAMINIDASE ISOZYMES IN RATTUS NORVEGICUS: INDEPENDENT CONTROL OF NEU-1 AND NEU-2 PHENOTYPES
Authors: Samollow Paul B , Vandeberg John L , Ford Allen L , Kunz Heinz W , Gill Thomas J
Published: January 2021

Two recently identified isozymes of neuraminidase in rat liver were examined for transmission patterns and linkage relationships, and for variation among inbred strains. The isozymes, designated neuraminidase-1 (NEU-1) and neuraminidase-2 (NEU-2), exhibited no electrophoretic mobility variants among the 22 inbred strains examined, but did possess striking interstrain variation in activity phenotypes on electrophoretic gels. The results of a backcross analysis involving the KGH and ACP strains revealed that NEU-1 and NEU-2 phenotypes are independently controlled, each by a single autosomal locus with additively acting alleles. The two loci are unlinked to one another, but the gene controlling NEU-1 is tightly linked to RT1, the rat major histocompatibility complex. This gene is almost certainly identical to Neu-1, a gene identified previously through its effect on "total" activity levels of liver neuraminidase as determined by fluorometric assay of tissue homogenates. NEU-2 and the gene controlling its phenotype were not detected by the fluorometric technique. We designate the genes controlling the NEU-1 and NEU-2 phenotypes as Neu-1 and Neu-2, respectively. Data from this and other studies place Neu-1 between Glo-1 and dw-3. The location of Neu-2 is unknown.
CHROMOSOMAL TRANSLOCATIONS GENERATED BY HIGH-FREQUENCY MEIOTIC RECOMBINATION BETWEEN REPEATED YEAST GENES
Authors: Jinks-Robertson Sue , Petes Thomas D
Published: January 2021

We have examined meiotic and mitotic recombination between repeated genes on nonhomologous chromosomes in the yeast Saccharomyces cerevisiae . The results of these experiments can be summarized in three statements. First, gene conversion events between repeats on nonhomologous chromosomes occur frequently in meiosis. The frequency of such conversion events is only 17-fold less than the analogous frequency of conversion between genes at allelic positions on homologous chromosomes. Second, meiotic and mitotic conversion events between repeated genes on nonhomologous chromosomes are associated with reciprocal recombination to the same extent as conversion between allelic sequences. The reciprocal exchanges between the repeated genes result in chromosomal translocations. Finally, recombination between repeated genes on nonhomologous chromosomes occurs much more frequently in meiosis than in mitosis.
STUDIES OF NORMAL AND POSITION-AFFECTED EXPRESSION OF ROSY REGION GENES IN DROSOPHILA MELANOGASTER
Authors: Clark Stephen H , Chovnick Arthur
Published: January 2021

Transformant complementation, intragenic deletions and Northern blot analyses provide unambiguous localization of the l (3) S12 gene immediately proximal to the 5' end of the rosy locus. We have characterized an array of transformants with respect to l (3) S12 and rosy expression. The l (3) S12 gene is exceedingly sensitive to euchromatic site-specific position effects. Unlike the rosy locus, l (3)S12 is insensitive to heterochromatic position effect in rearrangements, as well as in a transformant located in heterochromatin. Cotransformants for both l(3)S12 and rosy elicit no apparent pattern of concordance with respect to euchromatic site-specific position effects. Heterochromatic-euchromatic rearrangements are examined with respect to position effects on expression of the rosy region genes l(3)12, rosy, snake and piccolo, as well as suppressor effects. Clear distinction is seen between euchromatic and heterochromatic effects.
COINCIDENT GENE CONVERSION EVENTS IN YEAST THAT INVOLVE A LARGE INSERTION
Authors: Golin John E , Falco S Carl , Margolskee Jeanne P
Published: January 2021

In yeast, spontaneous gene conversion events involving sites that are far apart (16 cM) occur 1000 times more frequently in mitotic cells than is expected for two independent acts of recombination. It has been proposed that a major portion of these could be due to a long, continuous heteroduplex intermediate. We have examined this possibility in further detail by introducing, via transformation, a large plasmid insertion between the LEU1 and TRP5 loci and studying its behavior among coincident convertants involving the flanking sites. Among such convertants, there is frequent loss of the plasmid when it is present in hemizygous or homozygous configuration. Our results could support the long heteroduplex model for coincident recombination events, but only if novel assumptions regarding the formation and fate of mismatched DNA are made. Therefore, an alternative model that proposes multiple, concerted recombination events is discussed.
Genetic Functions Promoting Homologous Recombination in Escherichia coli: A Study of Inversions in Phage Λ
Authors: Ennis Don G , Amundsen Susan K , Smith Gerald R
Published: January 2021

We have studied homologous recombination in a derivative of phage λ containing two 1.4-kb repeats in inverted orientation. Inversion of the intervening 2.5-kb segment occurred efficiently by the Escherichia coli RecBC pathway but markedly less efficiently by the λ Red pathway or the E. coli RecE or RecF pathways. Inversion by the RecBCD pathway was stimulated by Chi sites located to the right of the invertible segment; this stimulation decreased exponentially by a factor of about 2 for each 2.2 kb between the invertible segment and the Chi site. In addition to RecA protein and RecBCD enzyme, inversion by the RecBC pathway required single-stranded DNA binding protein, DNA gyrase, DNA polymerase I and DNA ligase. Inversion appeared to occur either intra- or intermolecularly. These results are discussed in the framework of a current molecular model for the RecBC pathway of homologous recombination.
On Recombination Among In(2L)t, α-Gpdh and Adh in Drosophila melanogaster
Authors: Malpica J-M , Vassallo J M , Frías A , Fuentes-Bol F
Published: January 2021

The occurrence and patterns of linkage disequilibrium between an inversion and allozymic loci within it or nearby have been used in attempts to discriminate among different hypotheses for the maintenance of variability. The interpretation of the data on the best-documented case, that of the nonrandom association between In(2L)t and ?-Gpdh or Adh in the second chromosome of Drosophila melanogaster, has been done on the basis that recombination between ?-Gpdh and Adh is almost entirely due to the recombination between In(2L)t and the locus within it (?-Gpdh), the recombination between the inversion and the nearby locus (Adh) being negligible. In this paper, we show that the pattern of recombination is just the opposite.
Distribution and Abundance of Insertion Sequences Among Natural Isolates of Escherichia coli
Authors: Sawyer Stanley A , Dykhuizen Daniel E , DuBose Robert F , Green Louis , Mutangadura-Mhlanga T , Wolczyk David F , Hartl Daniel L
Published: January 2021

A reference collection of 71 natural isolates of Escherichia coli (the ECOR collection) has been studied with respect to the distribution and abundance of transposable insertion sequences using DNA hybridization. The data include 1173 occurrences of six unrelated insertion sequences (IS 1, IS2, IS3, IS4, IS5 and IS 30). The number of insertion elements per strain, and the sizes of DNA restriction fragments containing them, is highly variable and can be used to discriminate even among closely related strains. The occurrence and abundance of pairs of unrelated insertion sequences are apparently statistically independent, but significant correlations result from stratifications in the reference collection. However, there is a highly significant positive association among the insertion sequences considered in the aggregate. Nine branching process models, which differ in assumptions regarding the regulation of transposition and the effect of copy number on fitness, have been evaluated with regard to their fit of the observed distributions. No single model fits all copy number distributions. The best models incorporate no regulation of transposition and a moderate to strong decrease in fitness with increasing copy number for IS1 and IS5, strong regulation of transposition and a negligible to weak decrease in fitness with increasing copy number for IS3, and less than strong regulation of transposition for IS2, IS 4 and IS30.
Meiotic Gene Conversion and Crossing Over Between Dispersed Homologous Sequences Occurs Frequently in Saccharomyces cerevisiae
Authors: Lichten Michael , Borts Rhona H , Haber James E
Published: January 2021

We have examined meiotic recombination between two defined leu2 heteroalleles present at the normal LEU2 locus and in leu2-containing plasmids inserted at four other genomic locations. In diploids where the two leu2 markers were present at allelic locations on parental homologs, the frequency of Leu2+ spores varied 38-fold, in a location-dependent manner. These results indicate that recombination in a genetic interval can be modulated by sequences at least 2.7 kb outside that interval. Leu2+ meiotic segregants were also recovered from diploids where LEU2 was marked with one heteroallele, and the other leu2 heteroallele was inserted at another genomic location. These products of ectopic interactions, between dispersed copies of leu2 sharing only 2.2 kb of homology, were recovered at a frequency comparable to that observed in corresponding allelic crosses. This high frequency of ectopic meiotic recombination was observed in crosses where both recombining partners could potentially pair with sequences at an allelic position. In addition, a significant fraction (22-50%) of these ectopic recombinants were associated with crossing over of flanking sequences.
Use of the Multinomial Dirichlet Model for Analysis of Subdivided Genetic Populations
Authors: Jiang C J , Cockerham C Clark
Published: January 2021

The distribution found by compounding the multinomial distribution with the Dirichlet distribution has been suggested as a basis for the estimation of parameters in subdivided populations, in particular of the "correlation between genotypes" within subpopulations. It is shown that the estimators deriving from these procedures perform poorly when the data are generated by the classical Wright drift model of subdivided populations. This conclusion suggests that the compound distribution estimation approach does not provide a good estimation procedure for real populations which are reasonably described by the Wright model.
Mutations that Affect the Efficiency of Translation of mRNA for the cII Gene of Coliphage Lambda
Authors: Dul Ed , Mahoney Michael E , Wulff Daniel L
Published: January 2021

Starting with the λ p  RE  -strain λctr1 cy3008, which forms clear plaques, we have isolated two mutant strains, λdya2 ctr1 cy3008 and λdya3 ctr1 cy3008, that form plaques with very slightly turbid centers. The dya2 and dya3 mutations lie in the region of overlap between the PRE promoter and the ribosome recognition region of the cII gene, and have nucleotide alterations at positions -1 and +5 of pRE, and alterations of cII mRNA at -16 and -21 nucleotides before the initial AUG codon of the gene. Both mutations destabilize a stem structure that may be formed by cII mRNA, and dya2 also changes the sequence on cII mRNA that is complementary to the 3′-end of 16 S rRNA from 5′-UAAGGA-3′ to 5′-UGAGGA-3′.—The dya2 and dya3 mutations, along with the ctr1 mutation, which destabilizes either of two alternate stem structures which may be formed by cII mRNA (these being more stable stem structures than the one affected by dya2 and dya3), were tested for their ability to reverse two cII  - mutations that are characterized by inefficient translation of cII mRNA. These are cII3088, an A → G mutation four bases before the initial AUG codon, and cII3059, a GUU → GAU (Val2 → Asp) second codon mutation. It was found that ctr1 completely reverses the translation defects of these two mutations, while dya2 partially reverses these translation defects. The dya3 mutation has no effect on translation efficiency under any condition tested. However neither the ctr1 mutation nor the dya2 mutation has much effect on translation efficiency in an otherwise cII  + background, indicating that other factors must limit the rate of translation of cII mRNA under these conditions.
Cross-Specificities Between cII-like Proteins and pRE-like Promoters of Lambdoid Bacteriophages
Authors: Wulff Daniel L , Mahoney Michael E
Published: January 2021

We have investigated the activation of transcription from the pRE promoters of phages λ, 21 and P22 by the λ and 21 cII proteins and the P22 c1 (cII-like) protein, using an in vivo system in which cII protein from a derepressed prophage activates transcription from a pRE DNA fragment on a multicopy plasmid. We find that each protein is highly specific for its own cognate pRE promoter, although measureable cross-reactions are observed. The primary recognition sequence for cII protein on λ pRE is a pair of TTGC repeat sequences in the sequence 5′-TTGCN6TTGC-3′ at the -35 region of the promoter. This same sequence is found in 21 pRE, while P22 pRE has the sequence 5′-TTGCN6TTGT-3′, which is the same as that of λctr1, a pRE  + variant of λ. λctr1 pRE is half as active as λ+  pRE when assayed with either the λ cII or the P22 c1 proteins. Therefore, the single base change in the P22 repeat sequence cannot explain why the P22 c1 protein is much more active with P22 pRE than λ pRE. The dya5 mutation, a G→A change at position -43 of pRE, makes pRE a stronger promoter when assayed with either the λ or 21 cII proteins or the P22 c1 protein. We conclude that efficient activation of a cII-dependent promoter by a cII protein requires sequence information in addition to the TTGC repeat sequences. We do not know the characteristics of the proteins which are responsible for the specificity of each protein for its own cognate promoter. However, λdya8, which has a Glu27→Lys alteration in the λ cII protein and a cII  + phenotype, results in a mutant cII protein that is much more highly specific than wild-type cII protein for its own cognate λ pRE promoter. This is especially remarkable because the dya8 amino acid alteration makes the helix-2 region (the region of the protein predicted to make contact with the phosphodiester backbone of the DNA) of λ cII protein conform exactly with the helix-2 region of the P22 c1 protein in both charge and charge distribution.
PET111, a Saccharomyces cerevisiae Nuclear Gene Required for Translation of the Mitochondrial mRNA Encoding Cytochrome c Oxidase Subunit II
Authors: Poutre Candace G , Fox Thomas D
Published: January 2021

Mutations in the nuclear gene PET111 are recessive and specifically block accumulation of cytochrome c oxidase subunit II (coxII), the product of a mitochondrial gene. However, the coxII mRNA is present in pet111 mutants at a level approximately one-third that of wild type. The simplest explanation for this phenotype is that PET111 is required for translation of the coxII mRNA. The reduced steady-state level of this mRNA is probably a secondary effect, caused by increased degradation of the untranslated transcript. Mitochondrial suppressors of pet111, carried on rho- mtDNAs, bypass the requirement for PET111 in coxII translation. Three suppressors are fusions between the coxII structural gene and other mitochondrial genes, that encode chimeric proteins consisting of the N-terminal portions of other mitochondrially coded proteins fused to the coxII precursor protein. When present together with rho  + mtDNA in a heteroplasmic state, these suppressors allow coxII synthesis in pet111 mutants. Thus in wild type, the PET111 product, or something under its control, probably acts at a site coded in the proximal portion of the gene for coxII to promote translation of the mRNA. PET111 was isolated by molecular cloning and genetically mapped to a position approximately midway between rna1 and SUP8 on chromosome XIII.
MMS Sensitivity of All Amino Acid-Requiring Mutants in Aspergillus and Its Suppression by Mutations in a Single Gene
Authors: Käfer Etta
Published: January 2021

All available amino acid-requiring mutants of Aspergillus nidulans were found to be hypersensitive to MMS (methyl methanesulfonate) to various degrees. On MMS media, secondary mutations could be selected which suppress this MMS sensitivity but do not affect the requirement. Many such mutations were analyzed and found to be alleles of one gene, smsA (=suppressor of MMS sensitivity), which mapped distal on the right arm of chromosome V. This gene is more likely to be involved in general regulation of amino acid biosynthesis than MMS uptake, since a variety of pathway interactions were clearly modified by smsA suppressors in the absence of MMS.
Definition and Properties of Disequilibrium Statistics for Associations Between Nuclear and Cytoplasmic Genotypes
Authors: Asmussen Marjorie A , Arnold Jonathan , Avise John C
Published: January 2021

We define and establish the interrelationships of four components of statistical association between a diploid nuclear gene and a uniparentally transmitted, haploid cytoplasmic gene: an allelic (gametic) disequilibrium (D), which measures associations between alleles at the two loci; and three genotypic disequilibria (D  1, D  2, D  3), which measure associations between two cytotypes and the three respective nuclear backgrounds. We also consider an alternative set of measures, including D and the residual disequilibrium (d). The dynamics of these disequilibria are then examined under three conventional models of the mating system: (1) random mating; (2a) assortative mating without dominance (the "mixed-mating model"); and (2b) assortative mating with dominance ("O'Donald's model"). The trajectories of gametic disequilibria are similar to those for pairs of unlinked nuclear loci. The dynamics of genotypic disequilibria exhibit a variety of behaviors depending on the model and the initial conditions. Procedures for statistical estimation of cytonuclear disequilibria are developed and applied to several real and hypothetical data sets. Special attention is paid to the biological interpretations of various categories of allelic and genotypic disequilibria in hybrid zones. Genetic systems for which these statistics might be appropriate include nuclear genotype frequencies in conjunction with those for mitochondrial DNA, chloroplast DNA, or cytoplasmically inherited microorganisms.
Single-Locus Inheritance in the Tetraploid Treefrog Hyla versicolor With an Analysis of Expected Progeny Ratios in Tetraploid Organisms
Authors: Marsden J Ellen , Schwager Steven J , May Bernie
Published: January 2021

The recently evolved autotetraploid frog, Hyla versicolor, was examined electrophoretically for evidence of genomic restructuring leading to diploidization. Loci were tested against the progeny ratios expected if inheritance was disomic vs. tetrasomic. Two loci (Mpi and Sod-2) appeared to be inherited tetrasomically, one (Mdh-2) appeared to be inherited disomically, and one (Tpi) appeared to be inherited disomically in one family and tetrasomically in another family, when tested conventionally against 1:2:1 and 1:4:1 segregation ratios. The minimum number of progeny required for this type of analysis for codominant alleles is shown to be 92. Progeny resulting from double reduction were observed, and the occurrence of a null allele class at Mpi was noted. A reexamination of expected progeny ratios in tetraploid organisms reveals that tetrasomic inheritance patterns cannot be predicted without adequate knowledge of the amount of crossing-over, the proportion of tetravalents vs. random bivalents that are formed, and the ratio and types of centromere segregation (alternate and adjacent) that occur from tetravalents in the species being studied. However, disomic inheritance can be unambiguously confirmed only by the production of all heteroallelic gametes from homobivalent, symmetrically heterozygous individuals. In addition, a method is described for estimating genecentromere distances using the ratio of progeny genotypes in certain crosses in tetraploid species.
Transmission of Duplication-Deficiencies from Cotton Translocations Is Unrelated to Map Lengths of the Unbalanced Segments
Authors: Menzel Margaret Y , Dougherty Brian J
Published: January 2021

Adjacent-1 duplication-deficiencies (dp-dfs) are readily recovered from most heterozygous translocations in Gossypium hirsutum L., but frequencies of specific cytotypes differ widely in progenies from heterozygote (♀) x standard crosses. Surprisingly, these frequencies seem to be unrelated to the primary (postmeiotic) frequencies predicted by metaphase I configurations or to the proportion of the chromosome arm that is duplicate or deficient. Deficiencies and duplications from different translocations involving the same arm, as well as the two complementary dp-dfs from the same translocation, seldom exhibit similar frequencies. We conclude that the frequency of each of 101 different adjacent-1 cytotypes is largely idiosyncratic and may depend in part on interactions between the specific chromosome regions that are respectively trisegmental and monosegmental. Few, if any, of these interactions can be between homoeologues of the Ah and Dh genomes. Adjacent-2 dp-dfs are seldom recovered, even if they involve chromosomes that are readily tolerated in monosomic condition. Comparison of monosomes and telosomes with deficiencies suggests that some chromosomes and chromosome regions may be more dosage-sensitive than others, but their identification is not strongly supported by these data.