bluuebunny/crossref_metadata_2025 huggingface dataset:
THE GENETIC FACTORS ALTERED IN HOMOZYGOUS abo STOCKS OF DROSOPHILA MELANOGASTER
Authors: Sullivan William , Pimpinelli Sergio
Published: January 2021

Females homozygous for the maternal-effect mutation abo (2-44.0) produce a large fraction of eggs which arrest during embryogenesis. Increasing doses of defined heterochromatic regions inherited by offspring of abo mothers from their fathers function zygotically to bring about a partial rescue of the abo-induced embryonic lethality. Another property of the abo mutation is that the severity of the maternal effect decreases when an abo stock is maintained in homozygous condition for a number of generations. Here, we show that the factors which change in homozygous abo stocks to result in the decrease in maternally induced embryonic lethality, act zygotically, dominantly and additively. More importantly, we show that the X and second chromosomes, but not the Y and third chromosomes, derived from homozygous abo stocks are, when inherited from males, more effective in promoting zygotic rescue of the abo-induced lethality than are the equivalent chromosomes derived from an abo stock maintained in heterozygous condition. The chromosomal locations of the factors altered in the homozygous stock, as well as their behavior, strongly suggest that the same heterochromatic elements that are responsible for rescuing embryos from the abo-induced maternal effect are altered in homozygous abo flies in such a way that the maternal effect itself is less severe.
THE INTERACTION OF GENETIC AND ENVIRONMENTAL FACTORS IN THE CONTROL OF AMYLASE GENE EXPRESSION IN DROSOPHILA MELANOGASTER
Authors: Benkel Bernhard F , Hickey Donal A
Published: January 2021

A number of previous studies have established that amylase activity can vary between Drosophila strains which are maintained under identical laboratory conditions. In addition, we have recently shown that all strains examined so far are subject to glucose repression of amylase activity. In this study, we show that the degree of glucose repression can vary between strains. Moreover, the glucose repression effect is much more pronounced in larvae than in adult flies. Our results lead to the conclusion that the strain-specific differences in activity and the dietary effects are not independent phenomena. These results have implications for the interpretation of many studies on amylase activity variation, including those experiments which have been designed to link amylase activity variations with fitness differences in nature. A question that naturally arises concerns the molecular basis for these strain-specific variations in the degree of glucose repression of this eukaryotic gene.
SEVERAL GALACTOSYLTRANSFERASE ACTIVITIES ARE ASSOCIATED WITH MOUSE CHROMOSOME 17
Authors: Furukawa Kiyoshi , Roth Stephen , Sawicki Janet
Published: January 2021

Indirect evidence suggests that some major histocompatibility complex (MHC) proteins are glycosyltransferases. No sequence or mapping information is available for transferases, although ganglioside variations in mice are linked to the H-2 complex on chromosome 17, and one galactosyltransferase activity on mouse sperm varies with T/t complex genotypes, also on chromosome 17. In the present experiments, diploid and trisomy 17 mouse embryos were assayed for four different galactosyltransferase activities. The same preparations were assayed for isocitrate dehydrogenase (Id-1, chromosome 1) and glyoxalase-1 (Glo-1, chromosome 17). Galactosyltransferase specific activities in trisomy 17 embryos are almost 1.5 times higher than in diploid embryos. The correlation between galactosyltransferase activities and chromosome 17 dosage indicates that the structural or regulatory gene for these enzymes are located on chromosome 17.
Sexual Hyperactivity and Reduced Longevity of dunce Females of Drosophila melanogaster
Authors: Bellen Hugo J , Kiger John A
Published: January 2021

The dunce gene of Drosophila melanogaster codes for a cyclic adenosine-3',5'-monophosphate-specific phosphodiesterase. Mutations of dunce alter or abolish the activity of this enzyme, produce elevated cAMP levels, cause recessive female sterility, and produce learning deficiencies in both sexes. Aberrant male sexual behavior has also been associated with the memory defects of dunce mutants. Here we show that the longevity of dunce mutant females, homozygous for null-enzyme alleles, is reduced by 50% in the presence of males compared to control dunce females kept without males. Mutant dunce females mate on average every 14 hours whereas wild type revertants of dunce, and Canton-S females, mate every 22-24 hr. We propose a cause-effect relationship between mating and reduced longevity. Pheromones or peptides transferred during mating may activate adenylate cyclase and create an increase in cAMP levels that cannot be damped in dunce females. This increase may affect basic physiological functions and lead to reduced longevity
Patterns of Somatic Mutations in Immunoglobulin Variable Genes
Authors: Golding G Brian , Gearhart Patricia J , Glickman Barry W
Published: January 2021

The mechanism responsible for somatic mutation in the variable genes of antibodies is unknown and may differ from previously described mechanisms that produce mutation in DNA. We have analyzed 421 somatic mutations from the rearranged immunoglobulin variable genes of mice to determine (1) if the nucleotide substitutions differ from those generated during meiosis and (2) if the presence of nearby direct and inverted repeated sequences could template mutations around the variable gene. The results reveal a difference in the pattern of substitutions obtained from somatic mutations vs. meiotic mutations. An increased frequency of T:A to C:G transitions and a decreased frequency of mutations involving a G in the somatic mutants compared to the meiotic mutants is indicated. This suggests that the mutational processes responsible for somatic mutation in antibody genes differs from that responsible for mutation during meiosis. An analysis of the local DNA sequences revealed many direct repeats and palindromic sequences that were capable of templating some of the known mutations. Although additional factors may be involved in targeting mutations to the variable gene, mistemplating by nearby repeats may provide a mechanism for the enhancement of somatic mutation.
Molecular Nature of Spontaneous Mutations in Mouse Lactate Dehydrogenase-A Processed Pseudogenes
Authors: Fukasawa Kayoko M , Tanimura Masako , Sakai Ikuya , Sharief Farida S , Chung Fu-Zon , Li Steven S-L
Published: January 2021

The presence of at least ten mouse LDH-A pseudogenes was demonstrated in the genomic blot analysis, and four different processed pseudogenes have thus far been isolated and characterized. In this report, the nucleotide sequences of two different mouse lactate dehydrogenase-A processed pseudogenes, M11 and M14, were determined and compared with the protein-coding sequences of the mouse and rat LDH-A functional genes. In the pseudogene M11, the sequence of 64 nucleotides from codon no. 257 to 278 was tandemly duplicated. In the pseudogene M14, the sequence of 22 nucleotides from codon no. 68 to 75 was replaced by an inserted repetitive sequence of 242 nucleotides homologous to a mouse truncated R element. The pattern of nucleotide substitutions accumulated in mouse LDH-A pseudogenes M11 and M14, as well as that of pseudogene M10 identified previously, was analyzed, and the substitution frequencies of the C or G at the CG dinucleotide were found to be high.
Metabolic Flux and Fitness
Authors: Dykhuizen Daniel E , Dean Antony M , Hartl Daniel L
Published: January 2021

Studies of Escherichia coli under competition for lactose in chemostat cultures have been used to determine the selective effects of variation in the level of the β-galactoside permease and the β-galactosidase enzyme. The results determine the adaptive topography of these gene products relative to growth in limiting lactose and enable predictions concerning the selective effects of genetic variants found in natural populations. In the terms of metabolic control theory, the β-galactosidase enzyme at wild-type-induced levels has a small control coefficient with respect to fitness (C = 0.018), and hence genetic variants resulting in minor changes in enzyme activity have disproportionately small effects on fitness. However, the apparent control coefficient of the β-galactoside permease at wild-type-induced levels is large (C = 0.551), and hence even minor changes in activity affect fitness. Therefore, we predict that genetic polymorphisms in the lacZ gene are subject to less effective selection in natural populations than are those in the lacY gene. The β-galactoside permease is also less efficient than might be expected, and possible forces resulting in selection for an intermediate optimum level of permease activity are considered. The selective forces that maintain the lactose operon in a regulated state in natural populations are also discussed.
Mutations Causing Constitutive Invertase Synthesis in Yeast: Genetic Interactions with snf Mutations
Authors: Neigeborn Lenore , Carlson Marian
Published: January 2021

We have selected 210 mutants able to grow on sucrose in the presence of 2-deoxyglucose. We identified recessive mutations in three major complementation groups that cause constitutive (glucose-insensitive) secreted invertase synthesis. Two groups comprise alleles of the previously identified HXK2 and REG1 genes, and the third group was designated cid1 (constitutive invertase derepression). The effect of cid1 on SUC2 expression is mediated by the SUC2 upstream regulatory region, as judged by the constitutive expression of a SUC2-LEU2-lacZ fusion in which the LEU2 promoter is under control of SUC2 upstream sequences. A cid1 mutation also causes glucose-insensitive expression of maltase. The previously isolated constitutive mutation ssn6 is epistatic to cid1, reg1 and hxk2 for very high level constitutive invertase expression. Mutations in SNF genes that prevent derepression of invertase are epistatic to cid1, reg1 and hxk2; we have previously shown that ssn6 has different epistasis relationships with snf mutations. The constitutive mutation tup1 was found to resemble ssn6 in its genetic interactions with snf mutations. These findings suggest that CID1, REG1 and HXK2 are functionally distinct from SSN6 and TUP1.
Construction of an Unstable Ring-X Chromosome Bearing the Autosomal Dopa Decarboxylase Gene in Drosophila melanogaster and Analysis of Ddc Mosaics
Authors: Gailey Donald A , Bordne Deborah L , Vallés Ana Maria , Hall Jeffrey C , White Kalpana
Published: January 2021

An unstable Ring-X chromosome, Ddc  +- Ring-X carrying a cloned Dopa decarboxylase (Ddc) encoding segment was constructed. The construction involved a double recombination event between the unstable Ring-X, R(1)wvC and a Rod-X chromosome which contained a P-element mediated Ddc  + insert. The resulting Ddc  +-Ring-X chromosome behaves similarly to the parent chromosome with respect to somatic instability. The Ddc  +-Ring-X chromosome was used to generate Ddc mosaics. Analyses of Ddc mosaics revealed that while there was no absolute requirement for the Ddc  + expression in either the epidermis or the nervous system, very large mutant clones did affect the viability of the mosaic.
A Comprehensive Study of Genic Variation in Natural Populations of Drosophila melanogaster. I. Estimates of Gene Flow from Rare Alleles
Authors: Singh Rama S , Rhomberg Lorenz R
Published: January 2021

In order to assess the evolutionary significance of molecular variation in natural populations of Drosophila melanogaster, we have started a comprehensive genetic variation study program employing a relatively large number of gene-protein loci and an array of populations obtained from various geographic locations throughout the world. In this first report we provide estimates of gene flow based on the spatial distributions of rare alleles at 117 gene loci in 15 worldwide populations of D. melanogaster . Estimates of Nm (number of migrants exchanged per generation among populations) range from 1.09 in East-Asian populations (Taiwan, Vietnam and Australia) to 2.66 in West-Coast populations of North America. These estimates, among geographic populations separated by hundreds or even thousands of miles, suggest that gene flow among neighboring populations of D. melanogaster is quite extensive. This means that, for selectively neutral genes, we should expect little differentiation among neighboring populations. A survey of eight West-Coast populations of D. melanogaster (geographically comparable to Drosophila pseudoobscura) showed that in spite of extensive gene flow, populations of D. melanogaster show much more geographic differentiation than comparable populations of D. pseudoobscura. From this we conclude that migration in combination with natural selection rather than migration alone is responsible for the geographic uniformity of molecular polymorphisms in D. pseudoobscura.
Genetic Evidence of Mutator-Induced Deletions in the Short Arm of Chromosome 9 of Maize
Authors: Robertson Donald S , Stinard Philip S
Published: January 2021

Evidence is presented that at least 12 of the Mu-induced yg2 mutants found in an extensive mutation analysis of this locus are the result of deletions in the region of the yg2 locus on the short arm of chromosome 9. Twelve of these putative deletions were characterized genetically, and in every instance, they were confirmed to be deletions involving chromosomal segments that include the yg2 and wd loci as well as additional portions of the short arm of chromosome 9.
Allosuppressors that Enhance the Efficiency of Omnipotent Suppressors in Saccharomyces cerevisiae
Authors: Song Jae Mahn , Liebman Susan W
Published: January 2021

Two recessive Mendelian-allosuppressors have been isolated and have been shown to enhance the efficiency of omnipotent suppressors thought to be translational ambiguity mutations. These allosuppressors are unlinked to each other or to the omnipotent suppressors on which they act. They also increase the efficiency of the serine-inserting UAA-suppressor, SUP16 . One allosuppressor is allelic or tightly linked to the previously isolated sal2. Another allosuppressor, called sal6, represents a new locus, unlinked to the previously isolated sal1-sal5 that enhance the efficiency of the UAA-suppressors. When present singly in the absence of suppressors or other modifiers the sal2 and sal6 mutations do not have suppressor activity. However, when sal2 and sal6 are combined together in a haploid cell they do suppress weakly. In addition sal2 becomes a weak suppressor in the presence of the [η+] modifying factor.
Ddcde1, a Mutant Differentially Affecting Both Stage and Tissue Specific Expression of Dopa Decarboxylase in Drosophila
Authors: Bishop Clifton P , Wright Theodore R F
Published: January 2021

The isolation and characterization of a unique Dopa decarboxylase (Ddc) mutant in Drosophila melanogaster is reported. This mutant, Ddcde1, exhibits stage- and tissue-specific altered Ddc expression. Homozygous Ddcde1 embryos, central nervous systems (CNSs) at pupariation and newly eclosed adult epidermis all have approximately 5% as much specific dopa decarboxylase (DDC) activity as the pr control stock in which Ddcde1 was induced. In contrast, the Ddcde1 epidermis at pupariation has roughly 50% as much DDC activity as controls, a 10-fold increase over the relative activity detected in other tissues and stages. Although the adult cuticle lacks proper pigmentation as expected in flies with low DDC activity (?5%), the bristles unexpectedly have wild-type black pigmentation. This implies that the bristle forming cells have more DDC activity than the rest of the adult epidermis. This variegated phenotype, black bristles and pale cuticle, plus the fact that Ddcde1 was originally isolated in a reciprocal translocation between proximal X heterochromatin and the euchromatic left arm of the second chromosome, 42 bands from the Ddc locus, suggested that the mutant might be an example of position-effect variegation. All tests for position-effect variegation, including persistence of the mutant phenotype when Ddcde1 was removed from the translocation, were negative. At pupariation DDC cross-reacting material (CRM) levels are similar in Ddcde1 and wild-type controls, but in newly eclosed adults CRM levels are approximately 35% of wild-type controls. This suggests that DDC produced by Ddcde 1 adults has less activity per DDC molecule than the DDC produced at pupariation by Ddcde1. If the DDC enzyme produced by Ddcde1 at adult eclosion had full DDC activity (35% DDC CRM = 35% DDC activity) then no mutant phenotype would be exhibited by Ddcde1 since flies with as little as 10% activity have a wild-type phenotype. DDC thermolability assays clearly demonstrate that DDC from Ddcde1 is more thermolabile than control DDC at both pupariation and adult eclosion. Furthermore, DDC from adults in both Ddcde1 and the pr control is more thermolabile than DDC from white prepupae. Mixing experiments indicate the difference in DDC thermolability between pr white prepupae and pr adults is not due to a difference in the white prepupal and adult supernatants. This suggests that in wild-type different isoforms of DDC are produced either by differences in post-translational modification or as a result of a different primary amino acid sequence. The lesion in Ddcde1 may be in a translated sequence which is more important for proper Ddc expression in embryos, CNSs at pupariation and adult epidermis than it is in white prepupal epidermis and the bristle-forming cells.
Polymorphism and Gene Conversion in Mouse α-Globin Haplotypes
Authors: Erhart Mark A , Piller Kenneth , Weaver Steven
Published: January 2021

We have cloned and characterized three distinct α-globin haplotypes obtained from inbred strains of the mouse, Mus domesticus. We report here the complete nucleotide sequence of the six α-globin genes that the haplotypes contain. Our analysis of these genes and those from one other previously described haplotype indicates that recurrent gene conversion events have played a major role in their history. The pattern of nucleotide substitutions suggests that conversions have occurred both within and between haplotypes. Limited segments of coding and noncoding DNA have been involved in these gene conversion events. In two of the haplotypes, the nonallelic genes of each maintain DNA sequence identity over discrete intervals and encode the same α-globin polypeptide. On the other hand, the coding regions of some genes have accumulated replacement changes that result in distinct α-globins. In one instance, these changes appear to reflect positive selection of advantageous mutations.
Natural Selection and Y-Linked Polymorphism
Authors: Clark Andrew G
Published: January 2021

Several population genetic models allowing natural selection to act on Y-linked polymorphism are examined. The first incorporates pleiotropic effects of a Y-linked locus, such that viability, segregation distortion, fecundity and sexual selection can all be determined by one locus. It is shown that no set of selection parameters can maintain a stable Y-linked polymorphism. Interaction with the X chromosome is allowed in the next model, with viabilities determined by both X- and Y-linked factors. This model allows four fixation equilibria, two equilibria with X polymorphism and a unique point with both X- and Y-linked polymorphism. Stability analysis shows that the complete polymorphism is never stable. When X- and Y-linked loci influence meiotic drive, it is possible to have all fixation equilibria simultaneously unstable, and yet there is no stable interior equilibrium. Only when viability and meiotic drive are jointly affected by both X- and Y-linked genes can a Y-linked polymorphism be maintained. Unusual dynamics, including stable limit cycles, are generated by this model. Numerical simulations show that only a very small portion of the parameter space admits Y polymorphism, a result that is relevant to the interpretation of levels of Y-DNA sequence variation in natural populations.
Short-Flagella Mutants of Chlamydomonas reinhardtii
Authors: Kuchka Michael R , Jarvik Jonathan W
Published: January 2021

Six short-flagella mutants were isolated by screening clones of mutagenized Chlamydomonas for slow swimmers. The six mutants identify three unlinked Mendelian genes, with three mutations in gene shf-1, two in shf-2 and one in shf-3. shf-1 and shf-2 have been mapped to chromosomes VI and I, respectively. Two of the shf-1 mutations have temperature-sensitive flagellar-assembly phenotypes, and one shf-2 mutant has a cold-sensitive phenotype. shf shf double mutants were constructed; depending on the alleles present they showed either flagellaless or short-flagella phenotypes. Phenotypic revertants of shf-1 and shf-2 mutants were isolated, and certain of them were found to carry extragenic suppressors, some dominant and some recessive. We suspect that the shf mutations affect components of a specific flagellar size-control system, the existence of which has been suggested by a variety of physiological experiments.
The P-M Hybrid Dysgenesis Cline in Eastern Australian Drosophila melanogaster: Discrete P, Q and M Regions Are Nearly Contiguous
Authors: Boussy Ian A , Kidwell Margaret G
Published: January 2021

The dramatic latitudinal cline in P-M hybrid dysgenesis characteristics along the east coast of Australia is not smooth. Tests of recent collections of Drosophila melanogaster from the southeastern coast define the previously described cline as comprising three discrete, apparently contiguous regions of P, Q and M phenotypes, respectively. Northern populations from Cairns (16.9°SLat) to Ourimbah (33.4°SLat) are phenotypically P; populations from Wollongong (34.4°SLat) to Eden (37.1°SLat) are Q; and populations from Genoa (37.5°SLat) to Cygnet (43.2°SLat) are M. The decline in P activity from northern Queensland (55-60% gonadal dysgenesis (GD) in cross A) to mid-New South Wales (20-30% GD in cross A) is gradual; proceeding south, there then is a sharp drop to Q populations (<10% GD in crosses A and A*). This drop in P activity occurs in only 150 km, across the urban and suburban area of Sydney. Q populations are then found south to Eden, but Genoa, only about 50 km further southeast, is clearly M (48% GD in cross A*), as are two populations further south. The two discontinuities in the P-M cline do not correspond to obvious climatic differences along the coast, nor to obvious barriers to dispersal of D. melanogaster. The cline has apparently not moved between 1983 and 1985-1986.
Large Heterologies Impose Their Gene Conversion Pattern Onto Closely Linked Point Mutations
Authors: Hamza H , Nicolas A , Rossignol J L
Published: January 2021

We have studied the meiotic non-Mendelian segregation (NMS) pattern of seven large heterologous combinations located in the b2 ascospore gene of Ascobolus. The NMS patterns of these aberration heterozygotes widely differ from each other and from those of point mutations located in the same genetic region. They give lower gene conversion frequencies than point mutations, no postmeiotic segregations (PMS), and either parity or disparity that favors the wild type allele. Two related deletions, G234 and G40, were studied for their effects on the conversion behavior of closely linked point mutations. We found that, when heterozygous, the deletions impose their own NMS pattern onto close mutations. These effects occur on both sides of the heterologies. The effects upon PMS and disparity of linked point mutations gradually disappear as point mutations become more distant. The effects on NMS frequencies and on aberrant 4:4 are polar. They persist for all mutations located downstream from the high conversion end of the gene. This last effect can reflect a blockage of symmetric hDNA formation by large heterologies, whereas the epistasis of the NMS pattern of large heterologies over that of closely linked point mutations suggests that large heterologies and point mutations undergo conversion by means of distinct pathways.
A Genetic Map of Lettuce (Lactuca sativa L.) With Restriction Fragment Length Polymorphism, Isozyme, Disease Resistance and Morphological Markers
Authors: Landry Benoit S , Kesseli Rick V , Farrara Barry , Michelmore Richard W
Published: January 2021

A detailed linkage map of lettuce was constructed using 53 genetic markers including 41 restriction fragment length polymorphism (RFLP) loci, five downy mildew resistance genes, four isozyme loci and three morphological markers. The genetic markers were distributed into nine linkage groups and cover 404 cM which may be 25-30% of the lettuce genome. The majority (31 of 34) of the RFLP probes detected single segregating loci, although seven of these may have been homologous to further monomorphic loci. When several loci were detected by a single probe, the loci were generally linked, suggesting tandem duplications. One probe, however, detected loci in three linkage groups suggesting translocations. The five downy mildew resistance genes (Dm1, Dm3, Dm4, Dm5/8 and Dm13), segregating in the Calmar × Kordaat cross, represented each of the four resistance gene linkage groups. Dm5/8 is flanked by two cDNA loci, each located 10 cM away. These flanking markers will be used to study the source of variation in downy mildew genes and are also part our strategy to clone resistance genes.
High Fitness of Heterokaryotypic Individuals Segregating Naturally Within a Long-Standing Laboratory Population of Drosophila silvestris
Authors: Carson Hampton L
Published: January 2021

Natural populations of Drosophila silvestris are polymorphic for inversions in one or more of four of the five major chromosome arms; laboratory stocks tend to retain this heterozygosity. A laboratory stock, U28T2, was started from a single naturally inseminated wild female caught at Kilauea Forest Reserve, Hawaii, in January 1977. Polytene analysis in 1980 showed the presence of three natural inversions in chromosome 4: k  2 is distal, t is central and l  2 is proximal. The inversions are short but only short uncovered euchromatic sections exist at the distal and proximal ends. Periodic examinations through 1986 showed all three inversions to be persistent at moderately high frequencies. In 1984, a series of tests of mating performance of caged, mature males, taken at random as they eclosed from the stock, were followed by cytological testcrosses to females from a homokaryotypic stock. Only three of the eight possible haplotypes, k  2/t/+ (A), +/+/l  2 (a) and +/+/+ (a′) were present. Tests of crossing over show none in males; in females, there is about 1% in each of the two regions between the inversions. Only one such apparent crossover haplotype was found among 1084 examined in samples from this stock. Thus, chromosome arrangements A, a and a′ virtually behave as wholechromosome alleles in both sexes. Of 146 males marked and tested in cages, 61 produced progeny; the others failed to reproduce. Of 58 males and 80 females producing progeny and analyzed cytologically, there were, respectively, 49 and 59 heterokaryotypes. On the basis of frequencies calculated for fertilized eggs, 33.6 males and 46.3 females are expected. The facts suggest that individual males with the Aa karyotype are particularly successful in production of offspring. Adult females show an excess of Aa′ as well as Aa. Such high fitness of heterokaryotypes in the effective breeding adults could be a major factor in the maintenance of stable chromosomal polymorphisms both in laboratory stocks and in nature. Although some of this heterosis is clearly ascribable to differential survival, the facts suggest that there is a substantial opportunity, indeed a likelihood, for a contribution from differential mating among surviving adults.
Average Number of Nucleotide Differences in a Sample From a Single Subpopulation: A Test for Population Subdivision
Authors: Strobeck Curtis
Published: January 2021

Unbiased estimates of θ = 4Nµ in a random mating population can be based on either the number of alleles or the average number of nucleotide differences in a sample. However, if there is population structure and the sample is drawn from a single subpopulation, these two estimates of θ behave differently. The expected number of alleles in a sample is an increasing function of the migration rates, whereas the expected average number of nucleotide differences is shown to be independent of the migration rates and equal to 4N  Tµ for a general model of population structure which includes both the island model and the circular stepping-stone model. This contrast in the behavior of these two estimates of θ is used as the basis of a test for population subdivision. Using a Monte-Carlo simulation developed so that independent samples from a single subpopulation could be obtained quickly, this test is shown to be a useful method to determine if there is population subdivision.
A New Type of Fusion Analysis Applicable to Many Organisms: Protein Fusions to the URA3 Gene of Yeast
Authors: Alani Eric , Kleckner Nancy
Published: January 2021

We have made constructs that join the promoter sequences and a portion of the coding region of the Saccharomyces cerevisiae HIS4 and GAL1 genes and the E. coli lacZ gene to the sixth codon of the S. cerevisiae URA3 gene (encodes orotidine-5′-phosphate (OMP) decarboxylase) to form three in frame protein fusions. In each case the fusion protein has OMP decarboxylase activity as assayed by complementation tests and this activity is properly regulated. A convenient cassette consisting of the URA3 segment plus some immediately proximal amino acids of HIS4C is available for making URA3 fusions to other proteins of interest. URA3 fusions offer several advantages over other systems for gene fusion analysis: the URA3 specified protein is small and cytosolic; genetic selections exist to identify mutants with either increased or decreased URA3 function in both yeast (S. cerevisiae and Schizosaccharomyces pombe) and bacteria (Escherichia coli and Salmonella typhimurium); and a sensitive OMP decarboxylase enzyme assay is available. Also, OMP decarboxylase activity is present in mammals, Drosophila and plants, so URA3 fusions may eventually be applicable in these other organisms as well.
Analysis of the Functional Significance of Linkage Group Conservation in Drosophila
Authors: Hilliker Arthur J , Trusis-Coulter Silvija N
Published: January 2021

Linkage groups, as defined by chromosome arms in Drosophila melanogaster, appear to have remained largely intact within the genus Drosophila and, possibly, within the higher Diptera per se. We hypothesized that linkage group conservation might have a functional basis (possibly related to interphase chromosome arrangement). To test this hypothesis, a series of autosomal 2-3 translocations were synthesized, creating many new linkage groups. A total of 167 2-3 translocations were recovered, cytologically analyzed to determine their polytene chromosome breakpoints, and tested for homozygous viability and fertility. The breakpoints associated with homozygous viable translocations were randomly distributed throughout the genome, indicating that the linear continuity of the linkage groups could be disrupted quite extensively. Inter se complementation crosses between homozygous lethal translocations having similar breakpoints further confirmed this result, documenting that, at least with respect to homozygous viability, the linear integrity of the autosomal linkage groups was not of major functional significance. Fertility analysis of the homozygous translocations also indicated that sterility could not be a single major factor. Having concluded that linkage group conservation is not based on important functional interactions between specific linked chromosomal segments, or due principally to the sterility of new linkages, the problem of linkage group conservation remains unsolved. Several possible selective factors are discussed, principally segregational load and inbreeding depression, which may contribute to the elimination of new linkage rearrangements.
The Allelic Correlation Structure of Gainj- and Kalam-Speaking People. II. The Genetic Distance Between Population Subdivisions
Authors: Long Jeffrey C , Smouse Peter E , Wood James W
Published: January 2021

The patterning of allele frequency variability among 18 local groups of Gainj and Kalam speakers of highland Papua New Guinea is investigated using new genetic distance methods. The genetic distances proposed here are obtained by decomposing Sewall Wright's coefficient FST into a set of coefficients corresponding to all pairs of population subdivisions. Two statistical methods are given to estimate these quantities. One method provides estimates weighted by sample sizes, while the other method does not use sample size weighting. Both methods correct for the within-individual and between-individual-within-groups sums of squares. Genetic distances among the Gainj and Kalam subdivisions are analyzed with respect to demographic, geographic, and linguistic variables. We find that a demographic feature, group size, has the greatest demonstrable association with the patterning of genetic distances. The pattern of geographic distances among groups displays a weak congruence with the pattern of genetic distances, and the association of genetic and linguistic diversity is very low. An effect of differences in group size on genetic distances is not surprising, from basic theoretical considerations, but genetic distances have not often been analyzed with respect to these variables in the past. The lack of correspondence between genetic distances and linguistic and geographic differences is an unusual feature that distinguishes the Gainj and Kalam from most other tribal populations.
A Novel P22 Prophage in Salmonella typhimurium
Authors: Downs Diana M , Roth John R
Published: January 2021

Under several sets of conditions, all of which seem to perturb purine metabolism, Salmonella typhimurium releases a variety of phages which were not known to be present in the strain. These cryptic phages are not induced by UV irradiation. Furthermore, the induction process does not require a functional recA gene product. While phages of several phenotypic classes have been recovered, including both turbid and clear plaque formers, all appear to be variants of P22 because all show DNA restriction patterns indistinguishable from that of P22. The variety of types suggests that the cryptic prophage is mutagenized as a consequence of the induction process. All the temperate phages tested are capable of transducing a variety of chromosomal markers with high efficiency. The phages induced in this novel way are capable of forming plaques on the strains that gave rise to them. Since the strains releasing phage are not immune to P22, the parental lysogens must not express immunity and the phage must be held in a cryptic state by a novel mechanism. The released phage possess an intact P22 immunity system because many can form standard immune lysogens after reinfection of Salmonella. These results raise the possibility that Salmonella typhimurium harbors cryptic phages that are subject to a novel system of global control related to purine metabolism. Preliminary evidence suggests that the regulation system may involve DNA modification.
Genetic Analysis of Adult-Specific Surface Antigenic Differences Between Varieties of the Nematode Caenorhabditis elegans
Authors: Politz Samuel M , Chin Karl J , Herman Daniel L
Published: January 2021

We have studied developmental stage-specificity and genetic specification of surface antigens in the nematode Caenorhabditis elegans. Rabbit antisera directed against the adult C. elegans cuticle were used in conjunction with antiserum adsorption experiments to obtain antibody reagents with specificity for the adult surface. Adult-specific antibodies were used to identify several varietal strains of C. elegans that display antigen-negative phenotypes as adults. Genetic mapping results using the surface antigen phenotype as a marker indicated that a single gene (designated srf-1) or cluster of genes on linkage group II determines the adult surface antigen phenotype.
Effect of the Molecular Nature of Mutation on the Efficiency of Intrachromosomal Gene Conversion in Mouse Cells
Authors: Letsou Anthea , Liskay R Michael
Published: January 2021

With the intent of further exploring the nature of gene conversion in mammalian cells, we systematically addressed the effects of the molecular nature of mutation on the efficiency of intrachromosomal gene conversion in cultured mouse cells. Comparison of conversion rates revealed that all mutations studied were suitable substrates for gene conversion; however, we observed that the rates at which different mutations converted to wild-type could differ by two orders of magnitude. Differences in conversion rates were correlated with the molecular nature of the mutations. In general, rates of conversion decreased with increasing size of the molecular lesions. In comparisons of conversion rates for single base pair insertions and deletions we detected a genotype-directed path for conversion, by which an insertion was converted to wild-type three to four times more efficiently than was a deletion which maps to the same site. The data are discussed in relation to current theories of gene conversion, and are consistent with the idea that gene conversion in mammalian cells can result from repair of heteroduplex DNA (hDNA) intermediates.
Autocorrelation of Gene Frequencies Under Isolation by Distance
Authors: Barbujani Guido
Published: January 2021

Spatial autocorrelation statistics are used for description of geographic variation of gene frequencies, but the relationship of these indices with the parameters describing the genetic structure of populations is not established. A simple relation is derived here between kinship coefficient and a measure of spatial autocorrelation, Moran's I. The autocorrelation coefficient of gene frequencies at a given distance is a direct function of the kinship at that distance, and an inverse function of the standardized gene frequency variance, Fst. Under isolation by distance, the expected values of Moran's I for any allele may be calculated by means of Malkcot-Morton function, which predicts an exponential decline of genetic similarity in space. This allows comparison of observed gene frequency patterns with the patterns that should be caused by interaction of short range migration and random genetic drift.
Effects of DNA heterologies on bacteriophage lambda recombination.
Authors: Pearson R K , Fox M S
Published: January 2021

Previous studies of bacteriophage lambda recombination have provided indirect evidence that substantial sequence nonhomologies, such as insertions and deletions, may be included in regions of heteroduplex DNA. However, the direct products of heterology-containing heteroduplex DNA--heterozygous progeny phage--have not been observed. We have constructed a series of small insertion and deletion mutations in the cI gene to examine the possibility that small heterologies might be accommodated in heterozygous progeny phage. Genetic crosses were carried out between lambda cI- Oam29 and lambda cI+ Pam80 under replication-restricted conditions. Recombinant O+P+ progeny were selected on mutL hosts and tested for cI heterozygosity. Heterozygous recombinants were readily observed with crosses involving insertions of 4 to 19 base pairs (bp) in the cI gene. Thus, nonhomologies of at least 19 bp can be accommodated in regions of heteroduplex DNA during lambda recombination. In contrast, when a cI insertion or deletion mutation of 26 bp was present, few of the selected recombinants were heterozygous for cI. Results using a substitution mutation, involving a 26-bp deletion with a 22-bp insertion, suggest that the low recovery of cI heterozygotes containing heterologies of 26 bp or more is due to a failure to encapsulate DNA containing heterologies of 26 bp or more into viable phage particles.
H-2 polymorphisms are more uniformly distributed than allozyme polymorphisms in natural populations of house mice.
Authors: Nadeau J H , Britton-Davidian J , Bonhomme F , Thaler L
Published: January 2021

Patterns of H-2 and allozyme polymorphism in natural populations of house mice from Europe, North Africa and South America were analyzed. The purpose of the analysis was to determine whether H-2 and allozyme polymorphisms were similarly distributed both geographically and temporally in wild mice. Two subspecies of house mice, Mus musculus domesticus and M. m. musculus were sampled and the polymorphisms of two H-2 class I genes, H-2K and H-2D, and 34 allozyme-encoding genes were surveyed. The three kinds of analyses that were conducted included a hierarchical gene diversity analysis, an analysis of the effects of barriers to gene flow, and an analysis of similarity networks. Each of the comparisons demonstrated that H-2 polymorphisms were more uniformly distributed than allozyme polymorphisms and provided additional evidence that H-2 and allozyme polymorphisms are subject to different evolutionary pressures. The analysis of similarity networks also demonstrated that H-2 genes provide little information about the phylogeny of wild mice.
UGA suppressors in Saccharomyces cerevisiae: allelism, action spectra and map positions.
Authors: Ono B I , Fujimoto R , Ohno Y , Maeda N , Tsuchiya Y , Usui T , Ishino-Arao Y
Published: January 2021

Sixty independent UGA suppressors of Saccharomyces cerevisiae have been studied. They are dominant and are divided into 16 groups (loci) by recombination. Suppressors representing these loci are divided into two classes by action spectra; four in class 1 (a broad action spectrum) and 12 in class 2 (a narrow action spectrum). Class 1 suppressors are less frequent in terms of not only total number but also number per locus than class 2 suppressors, indicating difference in either or both mutation frequency and selective pressure between suppressors of the two classes. Two of the class 1 suppressors, SUP152 and SUP161, do not recombine with SUP28 and SUP33, leucine-inserting UAA suppressors, respectively, indicating that they are mutations in genes coding for tRNA(Leu)UUA. Of the remaining two class 1 suppressors, SUP160 which causes lethality in the psi+ cytoplasm is mapped on chromosome XV very close to the centromere, and SUP165 on the right arm of chromosome XIV 44 cM distal to lys9. Of the class 2 suppressors, ten do not recombine with one or another of previously known UGA suppressors. The remaining two class 2 suppressors, SUP154 and SUP155, are mapped on the left and right arms of chromosome VII, respectively.
The influence of whole-arm trisomy on gene expression in Drosophila.
Authors: Devlin R H , Holm D G , Grigliatti T A
Published: January 2021

The biochemical consequences of extensive aneuploidy in Drosophila have been examined by measuring the levels of specific proteins in larvae trisomic for entire chromosome arms. By far the most common effect is a reduction in gene product levels (per gene template) by one-third from the diploid quantity, consistent with the model that concentration-dependent repressors of these loci reside on the duplicated chromosome arms. Most loci appear sensitive to such repression in one or more of the trisomies examined, suggesting that such regulatory loci might be quite common. Repression of gene-product levels in trisomies may significantly contribute to their inviability. Few loci are activated in trisomies implying that most factors necessary for gene expression are in excess. While autosomal trisomies can repress the expression of both X-linked and autosomal loci, X-chromosomal trisomies have little effect on most autosomal genes. A family of genes coding for larval serum proteins do not respond similarly in trisomies, suggesting that regulation operates on a process which is not common to their coordinate regulation. Finally, Adh genes transposed to new chromosomal positions maintain their ability to be repressed in 3L trisomies suggesting that this response to regulation involves a closely linked cis-acting regulatory element.
Patterns of mating and mitochondrial DNA inheritance in the agaric Basidiomycete Coprinus cinereus.
Authors: May G , Taylor J W
Published: January 2021

Patterns of mating and mitochondrial DNA (mtDNA) inheritance were investigated for the Basidiomycete, Coprinus cinereus in order to better understand the relationship of reproductive biology and mtDNA evolution in fungi. Results showed that the unique mating system of basidiomycetes can lead to the formation of mitochondrial mosaics (i.e., colonies composed of sectors differing in mtDNA). Mitochondria do not migrate along with nuclei during mating. Intracellular mixed or recombinant mtDNA molecules were not observed. Interestingly, it was found that mating asymmetry, caused by nonreciprocal nuclear migration, may be an important part of the reproductive biology of C. cinereus.
Physical lengths of meiotic and mitotic gene conversion tracts in Saccharomyces cerevisiae.
Authors: Judd S R , Petes T D
Published: January 2021

Physical lengths of gene conversion tracts for meiotic and mitotic conversions were examined, using the same diploid yeast strain in all experiments. This strain is heterozygous for a mutation in the URA3 gene as well as closely linked restriction site markers. In cells that had a gene conversion event at the URA3 locus, it was determined by Southern analysis which of the flanking heterozygous restriction sites had co-converted. It was found that mitotic conversion tracts were longer on the average than meiotic tracts. About half of the tracts generated by spontaneous mitotic gene conversion included heterozygous markers 4.2 kb apart; none of the meiotic conversions included these markers. Stimulation of mitotic gene conversion by ultraviolet light or methylmethanesulfonate had no obvious effect on the size or distribution of the tracts. Almost all conversion tracts were continuous.
Maintenance of the 2 micron circle plasmid of Saccharomyces cerevisiae by sexual transmission: an example of a selfish DNA.
Authors: Futcher B , Reid E , Hickey D A
Published: January 2021

Many eukaryotic mobile elements have been identified, but few have any obvious function. This has led to the proposal that many such elements may be parasitic DNA. We have used the 2 micron circle plasmid of Saccharomyces cerevisiae as a model system to investigate the maintenance of a cryptic genetic element. We find that under certain conditions this plasmid can spread through experimental populations despite demonstrable selection against it. This spread is dependent upon outbreeding, suggesting that cell to cell transmission of the plasmid during the yeast sexual cycle can counterbalance selection, and maintain the plasmid in populations. This result provides experimental support for the idea that some mobile elements may be parasitic DNA.
motA1552, a mutation of Dictyostelium discoideum having pleiotropic effects on motility and discoidin I regulation.
Authors: Kayman S C , Birchman R , Clarke M
Published: January 2021

The Dictyostelium discoideum mutant MC2 exhibits temperature-sensitive growth, temperature-sensitive motility, and temperature induction of discoidin I synthesis. These three phenotypes of MC2 were not separated in the genetic experiments reported here. They were therefore assigned to the mutation motA1552, which was mapped to linkage group II by segregation analysis and by analysis of mitotic recombinant diploids. In one motA1552 strain, loss of motility preceded accumulation of discoidin I by 3 hr, indicating that discoidin I is not involved in generation of the motility defect. Expression of motA1552 phenotypes varied both among strains carrying the mutation, and among different clones of a particular strain. MC2 and its derivatives displayed elevated levels of recombination between whiA and acrA on linkage group II, and yielded highly unstable mutations at the acrA locus. Accumulation of large amounts of discoidin I during axenic growth of strain AX3 was found to depend on the presence of a second linkage group II mutation, daxA1551. This mutation was already present in the strain mutagenized to isolate motA1552, complicating explication of motA1552 action.