bluuebunny/crossref_metadata_2025 huggingface dataset:
CHARACTERIZATION OF A RECOMBINANT MOUSE t HAPLOTYPE THAT EXPRESSES A DOMINANT LETHAL MATERNAL EFFECT
Authors: Winking Heinz , Silver Lee M
Published: January 2021

The twLub  2 chromosome was generated by rare recombination between a complete t haplotype and a wild-type form of mouse chromosome 17. This recombinant chromosome expresses a dominant lethal effect in all embryos that inherit the mutant chromosome from their mothers. The phenotype of this maternal effect is indistinguishable from that expressed by the previously described Thp deletion chromosome. It appears likely that the crossing over event that gave rise to twLub  2 was unequal and resulted in the alteration or deletion of a gene (which is named the T-associated maternal effect locus, Tme) that must be inherited from the mother in order for normal development to proceed through late stages of gestation. The results presented here allow a mapping of the Tme locus between the quaking and tufted loci which are 3 cM apart within the proximal region of chromosome 17.
LOCATION OF THE GENES THAT CONTROL INDUCTION OF THE ALLANTOIN-DEGRADING ENZYMES IN SACCHAROMYCES CEREVISIAE
Authors: Turoscy Vanessa , Chisholm George , Cooper Terrance G
Published: January 2021

In an effort to understand the regulation of allantoin degradation in Saccharomyces cerevisiae, we isolated two classes of mutants, each defective in the induction process associated with production of the pathway enzymes. Mutation at one locus (DAL80) results in constitutive expression of the genes involved in allantoin catabolism. Mutation at the second locus (DAL-81) results in the loss of ability to induce these enzymes. This report describes genetic data indicating that the DAL80 and DAL81 loci are situated approximately 13 cM from the centromere on the right arm of chromosome XI and 9 cM proximal to the DAL1 locus on chromosome IX, respectively.
DYSGENESIS-INDUCED INSTABILITY OF ROSY LOCUS TRANSFORMATION IN DROSOPHILA MELANOGASTER: ANALYSIS OF EXCISION EVENTS AND THE SELECTIVE RECOVERY OF CONTROL ELEMENT DELETIONS
Authors: Daniels Stephen B , McCarron Margaret , Love Carol , Chovnick Arthur
Published: January 2021

Utilizing the method of P-M hybrid dysgenesis-mediated gene transfer to insert rosy locus DNA into various chromosomal locations, we recovered a transformed strain that carries an ry  + transposon inserted in or near the scalloped locus in polytene section 13F on the Χ chromosome. The resultant product, when stabilized, behaves as a homozygous and hemizygous viable and fertile extreme scalloped allele associated with wild-type expression of the rosy locus. We have labeled this allele, sdry+  +. This allele has been destabilized by subsequent P-M hybrid dysgenesis, and mutations were recovered that exhibit alterations in the rosy and/or scalloped phenotypes. Representative samples of all phenotypic classes have been characterized by Southern blot analyses of restricted DNA. The most common events are excisions of DNA wholly internal to the transposon and representing sections of rosy DNA. In addition to loss of rosy locus function, such excisions affect the scalloped locus expression.—A second dysgenesis experiment was carried out involving an ry  + transposon inserted in polytene section 16D on the Χ chromosome. A minimal estimate of the relative frequency of imprecise excisions, determined in this experiment is 75%.—A successful pilot experiment is described that utilizes dysgenic perturbation of the sdryry  + allele to select for small deletions of the 5' noncoding region of the rosy locus.
MUTAGENESIS IN CAENORHABDITIS ELEGANS. II. A SPECTRUM OF MUTATIONAL EVENTS INDUCED WITH 1500 R OF γ-RADIATION
Authors: Rosenbluth Raja E , Cuddeford Cheryl , Baillie David L
Published: January 2021

We previously established a γ-ray dose-response curve for recessive lethal events (lethals) captured over the eT1 balancer. In this paper we analyze the nature of lethal events produced, with a frequency of 0.04 per eT1 region, at a dose of 1500 r. To do so, we developed a protocol that, in the absence of cytogenetics, allows balanced lethals to be analyzed for associated chromosomal rearrangements. A set of 35 lethal strains was chosen for the analysis. Although the dosage was relatively low, a large number of multiple-break events were observed. The fraction of lethals associated with rearrangements was found to be 0.76. Currently most X- and γ-ray dosages used for mutagenesis in C. elegans are 6000-8000 r. From our data we conservatively estimated that 43% of rearrangements induced with 8000 r would be accompanied by additional chromosome breaks in the genome. With 1500 r the value was 5%.—The 35 lethals studied were derived from 875 screened F1's. Among these lethals there were (1) at least two unc-36 duplications, (2) at least four translocations, (3) at least six deficiencies of chromosome V (these delete about 90% of the unc-60 to unc-42 region) and (4) several unanalyzed rearrangements. Thus, it is possible to recover desired rearrangements at reasonable rates with a dose of only 1500 r.—We suggest that the levels of ionizing radiation employed in most published C. elegans studies are excessive and efforts should be made to use reduced levels in the future.
MECHANISMS OF SPONTANEOUS AND INDUCED FRAMESHIFT MUTATION IN BACTERIOPHAGE T4
Authors: Streisinger George , Owen Joyce Emrich
Published: January 2021

Frequencies of spontaneous and proflavine-induced frameshift mutations increase dramatically as a function of the number of reiterated base pairs at each of two sites in the lysozyme gene of bacteriophage T4. At each site, proflavine induces addition mutations more frequently than deletion mutations. We confirm that the steroidal diamine, irehdiamine A, induces frameshift addition mutations. At sites of reiterated bases, we propose that base pairing is misaligned adjacent to a gap. The misaligned configuration is stabilized by the stacking of mutagen molecules around the extrahelical base, forming a sandwich. Proflavine induces addition mutations efficiently at a site without any reiterated bases. Mutagenesis at such sites may be due to mutagen-induced stuttering of the replication complex.
SEQUENCE EVOLUTION OF DROSOPHILA MITOCHONDRIAL DNA
Authors: Wolstenholme David R , Clary Douglas O
Published: January 2021

We have compared nucleotide sequences of corresponding segments of the mitochondrial DNA (mtDNA) molecules of Drosophila yakuba and Drosophila melanogaster, which contain the genes for six proteins and seven tRNAs. The overall frequency of substitution between the nucleotide sequences of these protein genes is 7.2%. As was found for mtDNAs from closely related mammals, most substitutions (86%) in Drosophila mitochondrial protein genes do not result in an amino acid replacement. However, the frequencies of transitions and transversions are approximately equal in Drosophila mtDNAs, which is in contrast to the vast excess of transitions over transversions in mammalian mtDNAs. In Drosophila mtDNAs the frequency of C ↔ T substitutions per codon in the third position is 2.5 times greater among codons of two-codon families than among codons of four-codon families; this is contrary to the hypothesis that third position silent substitutions are neutral in regard to selection. In the third position of codons of four-codon families transversions are 4.6 times more frequent than transitions and A ↔ T substitutions account for 86% of all transversions. Ninety-four percent of all codons in the Drosophila mtDNA segments analyzed end in A or T. However, as this alone cannot account for the observed high frequency of A ↔ T substitutions there must be either a disproportionately high rate of A ↔ T mutation in Drosophila mtDNA or selection bias for the products of A ↔ T mutation.—Consideration of the frequencies of interchange of AGA and AGT codons in the corresponding D. yakuba and D. melanogaster mitochondrial protein genes provides strong support for the view that AGA specifies serine in the Drosophila mitochondrial genetic code.
GENETIC DIFFERENTIATION OF TRANSPOSABLE ELEMENTS UNDER MUTATION AND UNBIASED GENE CONVERSION
Authors: Slatkin Montgomery
Published: January 2021

A model is developed to predict the extent of genetic differentiation in a family of transposable elements under the combined effects of genetic drift, transposition, mutation and unbiased gene conversion. The model is based on simplifying assumptions that are valid when transposition is always to new sites and copy number per site is low. In the absence of gene conversion, the degree of differentiation as measured by the probability of identity of different elements is the same as at a single locus with the same mutation rate but in a population of effective size Nc/2, where N is the population size and c is the number of copies per individual. The inclusion of unbiased gene conversion does not significantly change this result. If, as seems to be the case, families of transposable elements are relatively homogeneous, then the model implies either that mutation rates for transposable elements are much lower than at comparable single-copy loci or that some other force, such as natural selection or biased gene conversion, is at work. Transposition is a very ineffective force for homogenizing a family of transposable elements.
SUPPRESSION OF THE FACET-STRAWBERRY POSITION EFFECT IN DROSOPHILA BY LESIONS ADJACENT TO NOTCH
Authors: Welshons W J , Welshons H J
Published: January 2021

The recessive visible rough eye mutant effect of faswb, a small deletion at the 5' end of the Notch locus, is suppressed when faswb is coupled to five different closely linked deficiencies distal to salivary band 3C7. In addition, an inversion with a proximal breakpoint between 3C3 and 3C5 similarly suppresses the mutant effect. The data support the position effect interpretation of faswb: The small deletion allows functions distal to Notch to interfere with functions at Notch, and when the interference is eliminated, the faswb-mutant effect disappears.—The faswb deletion also interacts with another recessive visible rough-eye mutant at Notch called fag. In the cis condition, faswb fag double mutants have a mutant-eye phenotype like fag (similar to the mutant effect of faswb) and, in addition, express an accessory phenotype (thickened wing veins). Although the mutant-eye effect of faswb can be suppressed by lesions adjacent to Notch, the accessory phenotype of the coupled mutants is not suppressed. It is suggested that the faswb deletion has two observable effects: One is a modifiable position effect causing the faswb rough-eye phenotype; the other is a stable effect exerted upon a 5-kb insertion that is the probable cause of the fag mutant expression, thus resulting in a wing effect that accompanies the eye effect of fag.
LENGTH VARIATION AND HETEROPLASMY ARE FREQUENT IN MITOCHONDRIAL DNA FROM PARTHENOGENETIC AND BISEXUAL LIZARDS (GENUS CNEMIDOPHORUS)
Authors: Densmore Llewellyn D , Wright John W , Brown Wesley M
Published: January 2021

Samples of mtDNA isolated from each of 92 lizards representing all color pattern classes of Cnemidophorus tesselatus and two populations of C. tigris marmoratus were digested with the restriction endonucleases MboI, TaqI, RsaI and MspI. The mtDNA fragment sizes were compared after radioactive labeling and gel electrophoresis. Three features were notable in the comparisons: (1) there was little variation due to gain or loss of cleavage sites, (2) two fragments varied noticeably in length among the samples, one by a variable amount up to a maximum difference of ∼370 base pairs (bp) and the other by a discrete amount of 35 bp, (3) these two fragments occasionally varied within, as well as between, samples. Two regions that corresponded in size to these variants were identified by restriction endonuclease cleavage mapping. One of these is adjacent to the D-loop. Heteroplasmy, heretofore rarely observed, occurred frequently in these same two regions. Variability in the copy number of a tandemly repeated 64-bp sequence appears to be one component of the variation, but others (e.g., base substitutions or small additions/deletions) must also be involved. The frequent occurrence of these length variations suggests either that they can be generated rapidly or that they were inherited from a highly polymorphic ancestor. The former interpretation is favored.
TWO RECESSIVE SUPPRESSORS OF SACCHAROMYCES CEREVISIAE CHO1 THAT ARE UNLINKED BUT FALL IN THE SAME COMPLEMENTATION GROUP
Authors: Atkinson Katharine D
Published: January 2021

Phenotypic reversion of ethanolamine-requiring Saccharomyces cerevisiae cho 1 mutants is predominantly due to recessive mutations at genes unlinked to the chromosome V cho 1 locus. The recessive suppressors do not correct the primary cho 1 defect in phosphatidylserine synthesis but circumvent it with a novel endogenous supply of ethanolamine. One suppressor (eam1) was previously mapped to chromosome X, and 135 suppressor isolates were identified as eam1 alleles by complementation analysis. Additional meiotic recombination studies have identified a second genetic locus, eam2, that falls in the eam1 complementation group but maps close to the centromere of chromosome IV. Although the normal EAM1 and EAM2 alleles are fully dominant over recessive mutant alleles, their dominance fails in diploids heterozygous for defects in both genes simultaneously. The unusual complementation pattern could be explained by interaction of the gene products in formation of the same enzyme.
COUPLED INSTABILITY OF TWO X-LINKED GENES IN DROSOPHILA MAURITIANA: GERMINAL AND SOMATIC MUTABILITY
Authors: Jacobson James W , Hartl Daniel L
Published: January 2021

A highly unstable allele has been isolated at the white locus of Drosophila mauritiana, a sibling species of D. melanogaster. This allele, white-peach (wpch), mutates spontaneously in males and females to give both wild-type and bleached-white derivatives. The mutation frequency is about 10-3 mutations/generation. There is no evidence for clustering among mutant progeny, and phenotypically wpch flies with mosaic patches of wild-type tissue in the eyes are frequently recovered. Another X-linked locus, plum, is destabilized when wpch is on the same X chromosome.
THE EFFECT OF TRANSFORMER, DOUBLESEX AND INTERSEX MUTATIONS ON THE SEXUAL BEHAVIOR OF DROSOPHILA MELANOGASTER
Authors: McRobert Scott P , Tompkins Laurie
Published: January 2021

We have identified the effects of genes that regulate sex determination on female-specific tissues in the abdomen that produce sex pheromones and parts of the central nervous system that function when a male performs courtship. To do this, we monitored the sexual behaviors of flies with mutations in the transformer (tra), doublesex (dsx) and intersex (ix) genes. Except for tra, which transforms diplo-X flies so that they look and function like normal males, these mutations do not have the same effect on pheromone-producing tissues and the central nervous system as they do on the appearance of the fly. The dsx and ix mutations, which make diplo-X-flies look like intersexes, do not transform the flies so that they can perform courtship, suggesting that these genes do not regulate the development of sex-specific parts of the central nervous system. Conversely, the ix mutation, which has no effect on the appearance of haplo-X flies, makes the flies sexually attractive and impairs their ability to perform courtship, which implies that the ix gene is active in internal tissues of males.
JOINT DISTRIBUTION OF INSERTION ELEMENTS IS4 AND IS5 IN NATURAL ISOLATES OF ESCHERICHIA COLI
Authors: Dykhuizen Daniel E , Sawyer Stanley A , Green Louis , Miller Raymond D , Hartl Daniel L
Published: January 2021

A reference collection of natural isolates of Escherichia coli has been studied in order to determine the distribution, abundance and joint occurence of DNA insertion elements IS4 and IS5. Among these isolates, 36% were found to contain IS4 and 30% were found to contain IS5. Among strains containing IS4 the mean number of copies per strain was 4.4 ± 0.8; the comparable figure for IS5 was 3.7 ± 1.0. Although the presence of the elements among the isolates was independent, among those isolates containing both IS4 and IS5, there was a significant negative correlation in the number of copies of the elements.— The reference collection was also studied for the presence of the DNA sequences flanking the single copy of IS4 in the chromosome of E. coli K12. Homologous sequences were found in only 26% of the isolates. The sequences flanking the IS4 invariably occur together, and their presence is significantly correlated with the presence of IS4. In eight of the strains that carry these flanking sequences, an IS4 is located between them, and the sequences are present at the homologous position as in the K12 strain. We suggest that IS4 and its flanking sequences share a common mechanism of dissemination, such as plasmids, and we present evidence that they are included in a much larger transposable element.
AMYLASE VARIATION IN THE SALT MARSH AMPHIPOD, GAMMARUS PALUSTRIS
Authors: Borowsky Richard , Borowsky Betty , Milani Haleh , Greenberg Pietra
Published: January 2021

There are two common alleles at the Amylase-2 locus in populations of Gammarus palustris, the salt marsh amphipod. Intensive sampling of individuals from two localities at Jamaica Bay revealed a consistent pattern of heterozygote deficiency.ߝFive possible sources of heterozygote deficiency were examined in this study. Four of themߝselection against heterozygotes, null alleles at the locus, assortative mating for amylase genotype and inbreedingߝare inconsistent with the evidence and are rejected. The fifth possibility, Wahlund effects due to genetic differentiation of the population, is tentatively accepted. Although there is no direct evidence for differentiation within this population, separate populations along the Eastern seaboard are highly differentiated in a nonclinal pattern. Furthermore, the Wahlund hypothesis is consistent with observations on differences in degree of deficiency exhibited among collections at Jamaica Bay.ߝAnimals from this population exhibit feeding preferences correlated with genotype. Given the choice of two green algae, Enteromorpha or Ulva, the frequency of the slow allele among individuals choosing Enteromorpha was higher than among those choosing Ulva. This suggests that the animals assort themselves in the field into subpopulations with different allelic frequencies. This assortment could contribute to the maintenance of the polymorphism and to the observed heterozygote deficiency. We hypothesize that genotype influences behavior in this system through the action of enzyme on substrate, which determines the nature of the oligosaccharide pool liberated early in amylolysis.
TRANSPOSABLE ELEMENT-INDUCED RESPONSE TO ARTIFICIAL SELECTION IN DROSOPHILA MELANOGASTER
Authors: Mackay Trudy F C
Published: January 2021

The P family of transposable elements in Drosophila melanogaster transpose with exceptionally high frequency when males from P strains carrying multiple copies of these elements are crossed to females from M strains that lack P elements, but with substantially lower frequency in the reciprocal cross. Transposition is associated with enhanced mutation rates, caused by insertion and deletion of P elements, and chromosome rearrangements. If P element mutagenesis creates additional variation for quantitative traits, accelerated response to artificial selection of progeny of M♀♀ × P♂♂ strain crosses is expected, compared with that from progeny of P♀♀ × M♂♂ strain crosses.—Divergent artificial selection for number of bristles on the last abdominal tergite was carried out for 16 generations among the progeny of P–strain males (Harwich) and M–strain females (Canton-S) and also of M–strain males (Canton-S) and P-strain females (Harwich). Each cross was replicated four times. Average realized heritability of abdominal bristle score for the crosses in which P transposition was expected was 0.244 ± 0.017, 1.5 times greater than average heritability estimated from crosses in which transposition was expected to be rare (0.163 ± 0.010). Phenotypic variance of abdominal bristle score increased by a factor of four in lines selected from M♀♀ × P♂♂ crosses when compared with those selected from P♀♀ × M♂♂ hybrids. Not all quantitative genetic variation induced by P elements is additive. A substantial fraction of nonadditive genetic variation is implicated by chromosomal analysis, which demonstrates deleterious fitness effects of the mutations when homozygous.—Several putative "quantitative" mutations were identified from chromosomes extracted from the selected lines; these will form the basis for further investigation at the molecular level of the genes controlling quantitative inheritance.
POPULATION BOTTLENECKS AND NONEQUILIBRIUM MODELS IN POPULATION GENETICS. III. GENIC HOMOZYGOSITY IN POPULATIONS WHICH EXPERIENCE PERIODIC BOTTLENECKS
Authors: Maruyama Takeo , Fuerst Paul A
Published: January 2021

The amount of variability in a population that experiences repeated restrictions in population size has been calculated. The restrictions in size occur cyclically with a fixed cycle length. Analytical formulas for describing the gene identity at any specific time in the expanded and restricted phases of the cycle, and for the average and second moment of the gene identity, have been derived. It is shown that the level of genetic diversity depends critically on the two parameters that account for the population size, mutation rate and the time of duration for each of the two phases in the cycle. If one or both of these composite parameters are small, the gene diversity will be much reduced, and population gene diversity will then be predictable from knowledge of the harmonic mean population size over the entire cycle. If these parameters take on intermediate values, diversity changes constantly during the cycle, fluctuating steadily from a high to a low value and back again. If these parameters are large, gene diversity will fluctuate rapidly between extreme values and will stay at the extremes for long periods of time.
GENETIC VARIABILITY OF FLIGHT METABOLISM IN DROSOPHILA MELANOGASTER. II. RELATIONSHIP BETWEEN POWER OUTPUT AND ENZYME ACTIVITY LEVELS
Authors: Laurie-Ahlberg C C , Barnes P T , Curtsinger J W , Emigh T H , Karlin B , Morris R , Norman R A , Wilton A N
Published: January 2021

The major goal of the studies reported here was to determine the extent to which genetic variation in the activities of the enzymes participating in flight metabolism contributes to variation in the mechanical power output of the flight muscles in Drosophila melanogaster. Isogenic chromosome substitution lines were used to partition the variance of both types of quantitative trait into genetic and environmental components. The mechanical power output was estimated from the wingbeat frequency, wing amplitude and wing morphology of tethered flies by applying the aerodynamic models of Weis-Fogh and Ellington. There were three major results. (1) Chromosomes sampled from natural populations provide a large and repeatable genetic component to the variation in the activities of most of the 15 flight metabolism enzymes investigated and to the variation in the mechanical power output of the flight muscles. (2) The mechanical power output is a sensitive indicator of the rate of flight metabolism (i.e., rate of oxygen consumption during tethered flight). (3) In spite of (1) and (2), no convincing cases of individual enzyme effects on power output were detected, although the number and sign of the significant enzyme-power correlations suggests that such effects are not totally lacking.
CHROMOSOMAL EFFECTS ON MUTABILITY IN THE P-M SYSTEM OF HYBRID DYSGENESIS IN DROSOPHILA MELANOGASTER
Authors: Simmons Michael J , Raymond John D , Laverty Todd R , Doll Rhonda F , Raymond Nancy C , Kocur Gordon J , Drier Eric A
Published: January 2021

Two manifestations of hybrid dysgenesis were studied in flies with chromosomes derived from two different P strains. In one set of experiments, the occurrence of recessive X-linked lethal mutations in the germ cells of dysgenic males was monitored. In the other, the behavior of an X-linked P-element insertion mutation, snw, was studied in dysgenic males and also in dysgenic females. The chromosomes of one P strain were more proficient at causing dysgenesis in both sets of experiments. However, there was variation among the chromosomes of each strain in regard to the ability to induce lethals or to destabilize snw. The X chromosome, especially when it came from the stronger P strain, had a pronounced effect on both measures of dysgenesis, but in combination with the major autosomes, these effects were reduced. For the stronger P strain, the autosomes by themselves contributed significantly to the production of X-linked lethals and also had large effects on the behavior of snw, but they did not act additively on these two characters. For this strain, the effects of the autosomes on the X-linked lethal mutation rate suggest that only 1/100 P element transpositions causes a recessive lethal mutation. For the weaker P strain, the autosomes had only slight effects on the behavior of snw and appeared to have negligible effects on the X-linked lethal mutation rate. Combinations of chromosomes from either the strong or the weak P strain affected both aspects of dysgenesis in a nonadditive fashion, suggesting that the P elements on these chromosomes competed with each other for transposase, the P-encoded function that triggers P element activity. Age and sex also influenced the ability of chromosomes and combinations of chromosomes to cause dysgenesis.
PAIRING COMPETITION BETWEEN IDENTICAL AND HOMOLOGOUS CHROMOSOMES IN AUTOTETRAPLOID RYE. I. SUBMETACENTRIC CHROMOSOMES
Authors: Orellana J , Santos J L
Published: January 2021

Meiotic pairing preferences between identical and homologous but not identical chromosomes were analyzed in ten induced tetraploid/diploid chimaeral rye plants (Secale cereale) heterozygous for telomeric heerochromatin C-bands in both arms of chromosome 1R. These plants were the progeny of two crosses between only one plant of cv. Petkus, used as male, and two plants of the inbred lines E and R, respectively. Different pairing preferences for chromosome 1R were found: (1) between plants, (2) between chromosome arms within the same plant and (3) between bivalents and multivalents within the same plant. The possible influence in the preferences of several factors such as differences in C-heterochromatin content in the chromosomes analyzed, specific genetic control and independence in pairing behavior between both arms and partner exchange is discussed.
THE Mu TRANSPOSABLE ELEMENTS OF MAIZE: EVIDENCE FOR TRANSPOSITION AND COPY NUMBER REGULATION DURING DEVELOPMENT
Authors: Alleman Mary , Freeling Michael
Published: January 2021

The Mu transposon of maize exists in a highly mutagenic strain called Robertson's Mutator. Plants of this strain contain 10-50 copies of the Mu element, whereas most maize strains and other plants have none. When Mutator plants are crossed to plants of the inbred line 1S2P, which does not have copies of Mu, the progeny plants have approximately the same number of Mu sequences as did their Mutator parent. Approximately one-half of these copies have segregated from their parent and one-half have arisen by transposition and are integrated into new positions in the genome. This maintenance of copy number can be accounted for by an extremely high rate of transposition of the Mu elements (10-15 transpositions per gamete per generation). When Mutator plants are self-pollinated, the progeny double their Mu copy number in the first generation, but maintain a constant number of Mu sequences with subsequent self-pollinations. Transposition of Mu and the events that lead to copy number maintenance occur very late in the development of the germ cells but before fertilization. A larger version of the Mu element transposes but is not necessary for transposition of the Mu sequences. The progeny of crosses with a Mutator plant occasionally lack Mutator activity; these strains retain copies of the Mu element, but these elements no longer transpose.
A TWO-LOCUS NEUTRALITY TEST: APPLICATIONS TO HUMANS, E. COLI AND LODGEPOLE PINE
Authors: Hedrick Philip W , Thomson Glenys
Published: January 2021

The expected disequilibrium between two loci with k alleles at one locus and l alleles at the other is given for a sample of size n drawn from a population under neutrality equilibrium. Three different measures of disequilibrium with 95% intervals are tabulated for combinations of n, k, l and 4Nc, where N is the effective population size and c is the amount of recombination between the loci. The extent and pattern of disequilibrium are strongly dependent upon 4Nc and are somewhat dependent on n, k and l. The 95% intervals are large, particularly for low numbers of alleles and low values of 4Nc. As examples, observed disequilibrium from histocompatibility loci in humans (HLA) and electrophoretic data in E. coli and lodgepole pine were compared to these theoretical values. Using information about recombination rates, the HLA data showed more disequilibrium than neutrality expectations, whereas electrophoretic data from E. coli and lodgepole pine had somewhat less disequilibrium than neutrality expectations.
THE USE OF RESTRICTION FRAGMENT LENGTH POLYMORPHISMS AND DNA DUPLICATIONS TO STUDY THE ORGANIZATION OF THE ACTIN MULTIGENE FAMILY IN DICTYOSTELIUM DISCOIDEUM
Authors: Welker Dennis L , Hirth K Peter , Romans Patricia , Noegel Angelika , Firtel Richard A , Williams Keith L
Published: January 2021

The techniques of restriction fragment length polymorphism analysis and examination of gene copy number in duplication-bearing Dictyostelium discoideum strains have been used to map four actin genes of the wild-type strain NC4 to specific linkage groups. In part, this was accomplished by identification of restriction fragments corresponding to particular cloned actin genes using genespecific probes from unique sequence 5' and 3' untranslated regions. Cloned gene Actin 8 (designation act-8) maps to linkage group I; Actins 12 (act-12) and M6 (actM6) to linkage group II. An uncloned gene (act-100) also maps to linkage group II in the same region as actM6, as defined by a chromosomal duplication. From analysis of other wild isolates of D. discoideum, it was determined that in these isolates at least two actin genes map to linkage group I and at least four map to linkage group II. These results demonstrate the utility of molecular techniques in genetic analysis of Dictyostelium, particularly for developmentally regulated genes that have been cloned but that have no identified mutant phenotypes.
MOLECULAR GENETIC ANALYSIS OF THE DILUTE-SHORT EAR (d-se) REGION OF THE MOUSE
Authors: Rinchik Eugene M , Russell Liane B , Copeland Neal G , Jenkins Nancy A
Published: January 2021

Genes of the dilute-short ear (d-se) region of mouse chromosome 9 comprise an array of loci important to the normal development of the animal. Over 200 spontaneous, chemically induced and radiation-induced mutations at these loci have been identified, making it one of the most genetically well-characterized regions of the mouse. Molecular analysis of this region has recently become feasible by the identification of a dilute mutation that was induced by integration of an ecotropic murine leukemia virus genome. Several unique sequence cellular DNA probes flanking this provirus have now been identified and used to investigate the organization of wild-type chromosomes and chromosomes with radiation-induced d-se region mutations. As expected, several of these mutations are associated with deletions, and, in general, the molecular and genetic complementation maps of these mutants are concordant. Furthermore, a deletion break-point fusion fragment has been identified and has been used to orient the physical map of the d-se region with respect to the genetic complementation map. These experiments provide important initial steps for analyzing this developmentally important region at the molecular level, as well as for studying in detail how a diverse group of mutagens acts on the mammalian germline.
ON THE IDENTIFICATION OF THE ROSY LOCUS DNA IN DROSOPHILA MELANOGASTER: INTRAGENIC RECOMBINATION MAPPING OF MUTATIONS ASSOCIATED WITH INSERTIONS AND DELETIONS
Authors: Clark S H , McCarron M , Love C , Chovnick A
Published: January 2021

DNA extracts of several rosy-mutation-bearing strains were associated with large insertions and deletions in a defined region of the molecular map believed to include the rosy locus DNA. Large-scale, intragenic mapping experiments were carried out that localized these mutations within the boundaries of the previously defined rosy locus structural element. Molecular characterization of the wild-type recombinants provides conclusive evidence that the rosy locus DNA is localized to the DNA segment marked by these lesions.—One of the mutations, ry  2101, arose from a P-M hybrid dysgenesis experiment and is associated with a copia insertion. Experiments are described which suggest that copia mobilizes in response to P-M hybrid dysgenesis.—Relevance of the data to recombination in higher organisms is considered.
TOWARD A SATURATED LINKAGE MAP IN TOMATO BASED ON ISOZYMES AND RANDOM cDNA SEQUENCES
Authors: Bernatzky Robert , Tanksley Steven D
Published: January 2021

A linkage map in tomato has been developed based on isozyme and random cDNA clones derived from mRNA. Interspecific backcross and F2 populations of Lycopersicon esculentum and L. pennellii were employed in the linkage analysis. Allelic differences in cDNA markers were based on restriction fragment length polymorphisms detected through Southern analysis. A total of 57 unique cDNA clones have been analyzed. The majority of cDNA markers correspond to single loci and are dispersed throughtout the genome. Of those clones that hybridize to two or more loci, most show genetic independence (ie., they are unlinked). The combination of isozyme, cDNA and previously mapped DNA markers total 112 loci. It is estimated that approximately 92% of the genome can be monitored during segregation with these markers. Molecular maps, such as the one being constructed in tomato, may allow genetic and breeding experiments that previously were not possible.
ON THE FREQUENCY OF UNDETECTABLE RECOMBINATION EVENTS
Authors: Stephens J Claiborne
Published: January 2021

Simple analytical results show that many recombination events occur in such a way as to have no effect on the resultant DNA sequence. The proportion of these undetectable events depends on the population size, mutation rate and recombination rate and is quite large for reasonable values of these quantities. Efforts to estimate recombination rates and frequencies directly from DNA sequence data must, therefore, take this undetectable fraction into account.
DIRECTION OF TRAVEL OF RecBC RECOMBINASE THROUGH BACTERIOPHAGE LAMBDA DNA
Authors: Stahl Franklin W , Kobayashi Ichizo , Thaler David , Stahl Mary M
Published: January 2021

We examined linkage relationships for RecBC-mediated recombination in lytic cycle crosses of λ phages bearing two cohesive end sites (cos) oriented in the same direction. The relationships obtained imply that a given recombinant tends to be packaged from the cos site that is the nearer one to the right of the exchange. In view of the previously established coupling of entry of a recombinase at a cos cut and initiation of DNA packaging by that cos cut, these results imply that the recombinase (presumably the RecBC gene product) enters λ's chromosome at the right end.
NICHE EXPANSION IN BACTERIA: CAN INFECTIOUS GENE EXCHANGE AFFECT THE RATE OF EVOLUTION?
Authors: Evans Ralph
Published: January 2021

Recombination occurs by infectious gene transfer in bacteria, at rates much lower than recombination by sexual reproduction in other organisms. Thus, recombination may accelerate evolution in bacteria only under restricted conditions, such as occur when mutations at several loci are required for the evolution of an expanded ecological niche. Mathematical ("chemostat") models of several such cases—evolution of independence from three limiting essential or "interactive-essential" resources; evolution of the ability to use three new substitutable resources; and evolution of resistance to three growth inhibitors—were analyzed by computer simulation. All combinations of three mutation rates (U) and four values for the "infectious gene transfer rate parameter" (χ) were considered. Recombination accelerated evolution most when U was low and χ was high, but was unlikely to have large effects when χ was low enough to be realistic for natural populations of Escherichia coli. Recombination had the largest effects when resources were substitutable, and in that case could have substantially reduced the chance of random loss of the favored "triple mutant" while it was still rare. The simulations also revealed some interesting features of selection for an expanded niche. Evolution of independence from essential resources occurred more rapidly when the resources were weakly complementary than when they did not interact. Selection for the ability to use all substitutable resources was weak after all intermediate types that used only one or two of the resources had arisen.
VARIABILITY OF EVOLUTIONARY RATES OF DNA
Authors: Gillespie John H
Published: January 2021

A statistical analysis of DNA sequences from four nuclear loci and five mitochondrial loci from different orders of mammals is described. A major aim of the study is to describe the variation in the rate of molecular evolution of proteins and DNA. A measure of rate variability is the statistic R, the ratio of the variance in the number of substitutions to the mean number. For proteins, R is found to be in the range 0.16 < R < 35.55, thus extending in both directions the values seen in previous studies. An analysis of codons shows that there is a highly significant excess of double substitutions in the first and second positions, but not in the second and third or first and third positions. The analysis of the dynamics of nucleotide evolution showed that the ergodic Markov chain models that are the basis of most published formulas for correcting for multiple substitutions are incompatible with the data. A bootstrap procedure was used to show that the evolution of the individual nucleotides, even the third positions, show the same variation in rates as seen in the proteins. It is argued that protein and silent DNA evolution are uncoupled, with the evolution at both levels showing patterns that are better explained by the action of natural selection than by neutrality. This conclusion is based primarily on a comparison of the nuclear and mitochondrial results.
HYBRID DYSGENESIS-INDUCED REVERTANTS OF INSERTIONS AT THE 5' END OF THE RUDIMENTARY GENE IN DROSOPHILA MELANOGASTER: TRANSPOSON-INDUCED CONTROL MUTATIONS
Authors: Tsubota Stuart , Schedl Paul
Published: January 2021

Mutations in the 5' control region of the rudimentary (r) gene of Drosophila melanogaster were generated by using hybrid dysgenesis to mobilize P elements that were already inserted within this region. Eighteen new mutations out of 7793 chromosomes were isolated. Among the mutations were small insertions, deletions and inversions. All five of the deletions deleted into the 5' coding region of the r gene resulting in a severe mutant phenotype. The inversions and small insertions left the coding region intact, but altered the 5' control region. Northern analyses of the message levels in adult females indicated that these mutations alter the amount of the wild-type rudimentary message. These data also indicated that there is a region about 800 bp upstream of the start of transcription which is necessary for normal r expression. This region is not involved with the temporal and spatial regulation of r gene expression, but with the quantitative expression. An analysis of the DNA changes associated with each of the mutations demonstrates that P elements usually mobilize in an imprecise manner. Of the 22 mutations that have been isolated to date, only three are precise excisions. This means that P elements are potent mutators of the genome.
THE INFLUENCE OF GENETIC BACKGROUND AND THE HOMOLOGOUS CHROMOSOME 17 ON t-HAPLOTYPE TRANSMISSION RATIO DISTORTION IN MICE
Authors: Gummere Gregory R , McCormick Paulette J , Bennett Dorothea
Published: January 2021

Transmission ratio distortion is a characteristic of complete t-haplotypes, such that heterozygous males preferentially transmit the t-haplotype bearing chromosome 17 to the majority of their progeny. At least two genes contained within the t-haplotype have been identified as being required for such high transmission ratios. In this study we examine the effects of the genetic background and the chromosome homologous to the t-haplotype on transmission ratio distortion. We use two different congenic lines: (1) BTBRTF/Nev.Ttf/t12, in which the t12 haplotype has a transmission ratio of 52%, and (2) C3H/DiSn.Ttf/t12, in which the t12 haplotype has a transmission ratio of 99%. By intercrossing these two strains to produce reciprocal F1 and F2 generations, we have isolated the effects of the homologous chromosome 17 from the effects of the genetic background. We demonstrate that both the homologous chromosome and the genetic background have profound effects on t-haplotype transmission ratio distortion. Furthermore, it is evident that the t-haplotype transmission ratio behaves as a quantitative character rather than an intrinsic property of t-haplotypes.
THE MOLECULAR EVOLUTION OF ACTIN
Authors: Hightower Robin C , Meagher Richard B
Published: January 2021

We have investigated the molecular evolution of plant and nonplant actin genes comparing nucleotide and amino acid sequences of 20 actin genes. Nucleotide changes resulting in amino acid substitutions (replacement substitutions) ranged from 3-7% for all pairwise comparisons of animal actin genes with the following exceptions. Comparisons between higher animal muscle actin gene sequences and comparisons between higher animal cytoplasmic actin gene sequences indicated <3% divergence. Comparisons between plant and nonplant actin genes revealed, with two exceptions, 11-15% replacement substitution. In the analysis of plant actins, replacement substitution between soybean actin genes SAc1, SAc3, SAc4 and maize actin gene MAc1 ranged from 8-10%, whereas these members within the soybean actin gene family ranged from 6-9% replacement substitution. The rate of sequence divergence of plant actin sequences appears to be similar to that observed for animal actins. Furthermore, these and other data suggest that the plant actin gene family is ancient and that the families of soybean and maize actin genes have diverged from a single common ancestral plant actin gene that originated long before the divergence of monocots and dicots. The soybean actin multigene family encodes at least three classes of actin. These classes each contain a pair of actin genes that have been designated kappa (SAc1, SAc6), lambda (SAc2, SAc4) and mu (SAc3, SAc7). The three classes of soybean actin are more divergent in nucleotide sequence from one another than higher animal cytoplasmic actin is divergent from muscle actin. The location and distribution of amino acid changes were compared between actin proteins from all sources. A comparison of the hydropathy of all actin sequences, except from Oxytricha, indicated a strong similarity in hydropathic character between all plant and nonplant actins despite the greater number of replacement substitutions in plant actins. These protein sequence comparisons are discussed with respect to the demonstrated and implicated roles of actin in plants and animals, as well as the tissue-specific expression of actin.
DEVELOPMENTALLY REGULATED RNA TRANSCRIPTS CODING FOR ALCOHOL DEHYDROGENASE IN DROSOPHILA AFFINIDISJUNCTA
Authors: Rowan Robert G , Brennan Mark D , Dickinson W J
Published: January 2021

The organization of the gene coding for alcohol dehydrogenase (Adh) in Drosophila affinidisjuncta has been determined by physically mapping Adh RNA transcripts to cloned genomic DNA. Two distinct transcript types accumulate with developmental specificity. Because only a single genomic Adh locus is detected in D. affinidisjuncta, and since all Adh transcripts appear to be identical except at their termini, the two Adh RNA types are products of the same gene. One type of transcript, abundant in adults, contains a small 5' terminal exon that is completely lacking in the other type of transcript, which accumulates in larvae. This 5' end difference suggests that the D. affinidisjuncta Adh gene, like the homologous gene from the distantly related species D. melanogaster, is expressed from two promoters. According to the transcription map, these D. affinidisjuncta promoters are separated by approximately 560 base pairs of genomic DNA sequence. D. affinidisjuncta Adh transcripts also resemble D. melanogaster Adh transcripts in both their overall organization and their developmental distribution. Multiple 3' ends are responsible for the size heterogeneity of both types of D. affinidisjuncta Adh RNA, and some of these also appear with stage specificity.
A QUANTITATIVE MODEL FOR NONRANDOM GENERALIZED TRANSDUCTION, APPLIED TO THE PHAGE P22–SALMONELLA TYPHIMURIUM SYSTEM
Authors: Mandecki W , Krajewska-Grynkiewicz K , Klopotowski T
Published: January 2021

A mathematical model for nonrandom generalized transduction is proposed and analyzed. The model takes into account the finite number of transducing particle classes for any given marker. The equations for estimation of the distance between markers from cotransduction frequency data are derived and standard errors of the estimates are given. The obtained relationships depend significantly on the number of classes of transducing fragments. The model was applied to estimate the number of transducing fragment classes for a given marker in transduction with phage P22 of Salmonella typhimurium. It was found that the literature data on frequencies of cotransduction in crosses with mutual substitution of selective and nonselective markers can be rationalized most accurately by assuming that the mean number of classes is equal to 2. An improved method for analysis of cotransduction data is proposed on the basis of our model and the results of calculation. The method relies on solving a set of algebraic equations for cotransduction frequencies of markers located within one phage length. The method allows a relatively precise determination of distances between markers, positions of transducing particle ends and deletion or insertion lengths. The approach is applied to the trp-cysB-pyrF and aroC-hisT-purF-dhuA regions of the Salmonella typhimurium chromosome.
STABLE NON-MUTATOR STOCKS OF MAIZE HAVE SEQUENCES HOMOLOGOUS TO THE Mu1 TRANSPOSABLE ELEMENT
Authors: Chandler Vicki , Rivin Carol , Walbot Virginia
Published: January 2021

Mutator stocks of maize produce mutants at many loci at rates 20- to 50-fold above spontaneous levels. Current evidence suggests that this high mutation rate is mediated by an active transposable element system, Mu. Members of this transposable element family are found in ~10-60 copies in Mutator stocks. We report here an initial characterization of previously undetected sequences homologous to Mu elements in eight non-Mutator inbred lines and varieties of maize that have a normal low mutation rate. All stocks have ~40 copies of sequences homologous only to the terminal repeat and show weak homology to an internal probe. In addition, several of the stocks contain an intact Mu element. One intact Mu element and two terminal-specific clones have been isolated from one non-Mutator line, B37. The cloned sequences have been used to demonstrate that in genomic DNA the intact element, termed Mu1.4B37, is modified, such that restriction sites in its termini are not accessible to cleavage by the HinfI restriction enzyme. This modification is similar to that observed in Mutator lines that have lost activity. We hypothesize that the DNA modification of the Mu-like element may contribute to the lack of Mutator activity in B37.