bluuebunny/crossref_metadata_2025 huggingface dataset:
Coalescent Theory for a Partially Selfing Population
Authors: Fu Yun-Xin
Published: January 2021

A coalescent theory for a sample of DNA sequences from a partially selfing diploid population and an algorithm for simulating such samples are developed in this article. Approximate formulas are given for the expectation and the variance of the number of segregating sites in a sample of k sequences from n individuals. Several new estimators of the important parameters θ = 4Nμ and the selfing rate s, where N and μ are, respectively, the effective population size and the mutation rate per sequence per generation, are proposed and their sampling properties are studied.
Structured Coalescent Processes on Different Time Scales
Authors: Nordborg Magnus
Published: January 2021

It is demonstrated that the structured coalescent model can readily be extended to include phenomena such as partial selfing and background selection through the use of an approximation based on separation of time scales. A model that includes these phenomena, as well as geographic subdivision and linkage to a polymorphism maintained either by local adaptation or by balancing selection, is derived, and the expected coalescence time for a pair of genes is calculated. It is found that background selection reduces coalescence times within subpopulations and allelic classes, leading to a high degree of apparent differentiation. Extremely high levels of subpopulation differentiation are also expected for regions of the genome surrounding loci important in local adaptation. These regions will be wider the stronger the local selection, and the higher the selfing rate.
Synteny Conservation and Chromosome Rearrangements During Mammalian Evolution
Authors: Ehrlich Jason , Sankoff David , Nadeau Joseph H
Published: January 2021

An important problem in comparative genome analysis has been defining reliable measures of synteny conservation. The published analytical measures of synteny conservation have limitations. Nonindependence of comparisons, conserved and disrupted syntenies that are as yet unidentified, and redundant rearrangements lead to systematic errors that tend to overestimate the degree of conservation. We recently derived methods to estimate the total number of conserved syntenies within the genome, counting both those that have already been described and those that remain to be discovered. With this method, we show that ~65% of the conserved syntenies have already been identified for humans and mice, that rates of synteny disruption vary ~25-fold among mammalian lineages, and that despite strong selection against reciprocal translocations, inter-chromosome rearrangements occurred approximately fourfold more often than inversions and other intra-chromosome rearrangements, at least for lineages leading to humans and mice.
Roles for λ Orf and Escherichia coli RecO, RecR and RecF in λ Recombination
Authors: Sawitzke James A , Stahl Franklin W
Published: January 2021

Bacteriophage λ lacking its Red recombination functions requires either its own gene product, Orf, or the product of Escherichia coli's recO, recR and recF genes (RecORF) for efficient recombination in recBC sbcB sbcC mutant cells (the RecF pathway). Phage crosses under conditions of a partial block to DNA replication have revealed the following: (1) In the presence of Orf, RecF pathway recombination is similar to λ Red recombination; (2) Orf is necessary for focusing recombination toward the right end of the chromosome as λ is conventionally drawn; (3) RecORF-mediated RecF pathway recombination is not focused toward the right end of the chromosome, which may indicate that RecORF travels along the DNA; (4) both Orf- and RecORF-mediated RecF pathway recombination are stimulated by DNA replication; and (5) low level recombination in the simultaneous absence of Orf and RecORF may occur by a break-copy mechanism that is not initiated by a double strand break. Models for the roles of Orf and RecO, RecR and RecF in recombination are presented.
Hierarchical Analysis of Genetic Structure in Native Fire Ant Populations: Results From Three Classes of Molecular Markers
Authors: Ross Kenneth G , Krieger Michael J B , Shoemaker D DeWayne , Vargo Edward L , Keller Laurent
Published: January 2021

We describe genetic structure at various scales in native populations of the fire ant Solenopsis invicta using two classes of nuclear markers, allozymes and microsatellites, and markers of the mitochondrial genome. Strong structure was found at the nest level in both the monogyne (single queen) and polygyne (multiple queen) social forms using allozymes. Weak but significant microgeographic structure was detected above the nest level in polygyne populations but not in monogyne populations using both classes of nuclear markers. Pronounced mitochondrial DNA (mtDNA) differentiation was evident also at this level in the polygyne form only. These microgeographic patterns are expected because polygyny in ants is associated with restricted local gene flow due mainly to limited vagility of queens. Weak but significant nuclear differentiation was detected between sympatric social forms, and strong mtDNA differentiation also was found at this level. Thus, queens of each form seem unable to establish themselves in nests of the alternate type, and some degree of assortative mating by form may exist as well. Strong differentiation was found between the two study regions usinga all three sets of markers. Phylogeographic analyses of the mtDNA suggest that recent limitations on gene flow rather than longstanding barriers to dispersal are responsible for this large-scale structure.
SRO9, a Multicopy Suppressor of the Bud Gpowth Defect in the Saccharomyces cerevisiae rho3-Deficient Cells, Shows Strong Genetic Interactions With Tropomyosin Genes, Suggesting Its Role in Organization of the Actin Cytoskeleton
Authors: Kagami Mitsuhiro , Toh-e Akio , Matsui Yasushi
Published: January 2021

RHO3 encodes a Rho-type small GTPase in the yeast Saccharomyces cerevisiae and is involved in the proper organization of the actin cytoskeleton required for bud growth. SRO9 (YCL37c) was isolated as a multicopy suppressor of a rho3Δ mutation. An Sro9p domain required for function is similar to a domain in the La protein (an RNA-binding protein). Disruption of SRO9 did not affect vegetative growth, even with the simultaneous disruption of an SRO9 homologue, SRO99. However, sro9Δ was synthetically lethal with a disruption of TPM1, which encodes tropomyosin; sro9Δ tpm1Δ cells did not distribute cortical actin patches properly and lysed. We isolated TPM2, the other gene for tropomyosin, as a multicopy suppressor of a tpm1Δ sro9Δ double mutant. Genetic analysis suggests that TPM2 is functionally related to TPM1 and that tropomyosin is important but not essential for cell growth. Overexpression of SRO9 suppressed the growth defect in tpm1Δ tpm2Δ cells, disappearance of cables of actin filaments in both rho3Δ cells and tpm1Δ cells, and temperature sensitivity of actin mutant cells (act1-1 cells), suggesting that Sro9p has a function that overlaps or is related to tropomyosin function. Unlike tropomyosin, Sro9p does not colocalize with actin cables but is diffusely cytoplasmic. These results suggest that Sro9p is a new cytoplasmic factor involved in the organization of actin filaments.
Transgene Repeat Arrays Interact With Distant Heterochromatin and Cause Silencing in cis and trans
Authors: Dorer Douglas R , Henikoff Steven
Published: January 2021

Tandem repeats of Drosophila transgenes can cause heterochromatic variegation for transgene expression in a copy-number and orientation-dependent manner. Here, we demonstrate different ways in which these transgene repeat arrays interact with other sequences at a distance, displaying properties identical to those of a naturally occurring block of interstitial heterochromatin. Arrays consisting of tandemly repeated white transgenes are strongly affected by proximity to constitutive heterochromatin. Moving an array closer to heterochromatin enhanced variegation, and enhancement was reverted by recombination of the array onto a normal sequence chromosome. Rearrangements that lack the array enhanced variegation of white on a homologue bearing the array. Therefore, silencing of white genes within a repeat array depends on its distance from heterochromatin of the same chromosome or of its paired homologue. In addition, white transgene arrays cause variegation of a nearby gene in cis, a hallmark of classical position-effect variegation. Such spreading of heterochromatic silencing correlates with array size. Finally, white transgene arrays cause pairing-dependent silencing of a non-variegating white insertion at the homologous position.
The Yeast HRS1 Gene Is Involved in Positive and Negative Regulation of Transcription and Shows Genetic Characteristics Similar to SIN4 and GAL11
Authors: Piruat José I , Chávez Sebastián , Aguilera Andrés
Published: January 2021

We provide genetic evidence that HRS1/PGD1, a yeast gene previously identified as a suppressor of the hyper-recombination phenotype of hpr1, has positive and negative roles in transcriptional regulation. We have analyzed three differently regulated promoters, GAL1, PHO5 and HSP26, by β-galactosidase assays of lacZ-fused promoters and by Northern analysis of the endogenous genes. Transcription of these promoters was derepressed in hrs1Δ mutants under conditions in which it is normally repressed in wild type, Under induced conditions it was either strongly reduced or significantly enhanced depending on the promoter system analyzed. Constitutive transcription was not affected, as determined in ADH1 and TEF2. In addition, Hrs1p was required for mating-factor expression, telomere-linked DNA silencing and DNA supercoiling of plasmids. Furthermore, hrs1Δ suppressed Ty-insertion mutations and conferred a Gal−-phenotype. Many of these phenotypes also result from mutations in GAL11, SIN4 or RGR1, which encode proteins of the RNA polII mediator. We also show that gal11Δ and sin4Δ partially suppress the hyper-rec phenotype of hpr1 mutants, although to a lesser extent than hrs1Δ. Our results provide new evidence for the connection between hrs1Δ-induced deletions and transcription. We discuss the possibility that Hrs1p might be a component of the RNA polII transcription machinery.
The Accumulation of P-Element-Induced Recombinants in the Germline of Male Drosophila melanogaster
Authors: Tanaka Mark M , Liang Xu-Mei , Gray Yasmine H M , Sved John A
Published: January 2021

P-element-induced recombination in Drosophila melanogaster occurs premeiotically. Recombinants are therefore expected to accumulate in the stem cells of the germline of Pelement-carrying males. We show that both the recombination frequency and the incidence of “clustering” increase with the age of males carrying various P-element derivatives. The combination of end-deleted elements can lead to average recombination frequencies >50% with individual instances of 100% recombination. These elements also lowered the fertility of the carriers. We investigated these features by constructing an analytical and a computer simulation model of the course of events in the germline, incorporating the recently proposed hybrid element insertion (HEI) model of Pelement activity. The model is able to predict extreme recombination levels, segregation ratio biases and lowered fertility through cell death in a single analysis.
Geographic Structure of Mitochondrial and Nuclear Gene Polymorphisms in Australian Green Turtle Populations and Male-Biased Gene Flow
Authors: FitzSimmons Nancy N , Moritz Craig , Limpus Colin J , Pope Lisa , Prince Robert
Published: January 2021

The genetic structure of green turtle (Chelonia mydas) rookeries located around the Australian coast was assessed by (1) comparing the structure found within and among geographic regions, (2) comparing microsatellite loci vs. restriction fragment length polymorphism analyses of anonymous single copy nuclear DNA (ascnDNA) loci, and (3) comparing the structure found at nuclear DNA markers to that of previously analyzed mitochondrial (mtDNA) control region sequences. Significant genetic structure was observed over all regions at both sets of nuclear markers, though the microsatellite data provided greater resolution in identifying significant genetic differences in pairwise tests between regions. Inferences about population structure and migration rates from the microsatellite data varied depending on whether statistics were based on the stepwise mutation or infinite allele model, with the latter being more congruent with geography. Estimated rates of gene flow were generally higher than expected for nuclear DNA (nDNA) in comparison to mtDNA, and this difference was most pronounced in comparisons between the northern and southern Great Barrier Reef (GBR). The genetic data combined with results from physical tagging studies indicate that the lack of nuclear gene divergence through the GBR is likely due to the migration of sGBR turtles through the courtship area of the nGBR population, rather than male-biased dispersal. This example highlights the value of combining comparative studies of molecular variation with ecological data to infer population processes.
THE ISLAND MODEL OF POPULATION DIFFERENTIATION: A GENERAL SOLUTION
Authors: Latter B D H
Published: January 2021

The island model deals with a species which is subdivided into a number of discrete finite populations, races or subspecies, between which some migration occurs. If the number of populations is small, an assumption of equal rates of migration between each pair of populations may be reasonable approximation. Mutation at a constant rate to novel alleles may also be assumed.—A general solution is given for the process of population divergence under this model following subdivision of a single parental population, expressed in terms of the observed average frequency of heterozygotes within and between subpopulations at a randomly chosen set of independently segregating loci. No restriction is imposed on the magnitude of the migration or mutation rates involved, nor on the number of populations exchanging migrants.—The properties of two fundamental measures of genetic divergence are deduced from the theory. One is a parameter related to φ, the coefficient of kinship, and the other, γ, measures the rate of mutational divergence between the sub-populations.
THE GENETIC CONSTITUTION OF TANDEM DUPLICATIONS OF THE rII OF BACTERIOPHAGE T4D
Authors: Parma David H , Snyder Marlene
Published: January 2021

Methods for genetically mapping the end points of tandem duplicatictions of the rII region of bacteriophage T4D are presented. Analysis of ten duplications indicates (1) that the position of duplication end points and therefore the length of the duplicated segment differ in strains of independent origin; (2) that there is a direct relationship between segregation frequency and length; (3) that segregation is more frequent than expected on the basis of standard genetic mapping; and (4) that while duplications frequently include non-rII genetic material, frequently they do not include the entire rII region. The duplications studied range from less than two to about five cistrons in length.
THE PHYLOGENETIC RELATIONSHIPS OF THE MEMBERS OF THE DROSOPHILA ROBUSTA GROUP
Authors: Narayanan Yamuna
Published: January 2021

The phylogenetic relationships among the species of the D. robusta group were investigated by the analysis of chromosomal differences. Six of the ten known members of the D. robusta group were available for the study: D. colorata and D. robusta from the United States, and D. sordidula,  D. pseudosordidula,  D. lacertosa, and D, moriwakii from Japan. Analysis of the metaphase chromosomes from larval ganglion cells suggests that D. moriwakii and D. colorata, with rod-shaped X-chromosomes, are the more ancestral species, while D. sordidula,  D. pseudosordidula,  D. robusta, and D. lacertosa, with Vshaped X-chromosomes, are derived. The ancestral position of D. colorata and D. moriwakii is further strengthened by the fact that these are the two species in the D. robusta group that are cytologically closest to D. nigromelanica of the related D. melanica group. Of the four derived species, D. sordidula was found to be the closest to the ancestral species. The phylogeny based on the analysis of the gene sequences in the homologous chromosomes agreed with that indicated by the metaphase chromosomes. Since all attempts to obtain hybrids were unsuccessful except for the cross involving D. moriwakii females and D. colorata males, photographic maps of the salivary chromosomes were used to determine homology between the chromosomes of the different species. Evidence is presented to indicate that the D. robusta group originated in Asia (Japan), and that there were two migrations to the New World, the first leading to D. robusta, and the second to D. colorata. It is suggested that the route of migrations was across the Bering Land Bridge, and further, that the migrations occurred during the period from late Oligocene to middle Miocene, 20-25 million years ago.
A MEIOTIC MUTANT DEFECTIVE IN DISTRIBUTIVE DISJUNCTION IN DROSOPHILA MELANOGASTER
Authors: Carpenter Adelaide T C
Published: January 2021

The female meiotic mutant no distributive disjunction (symbol: nod) reduces the probability that a nonexchange chromosome will disjoin from either a nonexchange homolog or a nonhomolog; the mutant does not affect exchange or the disjunction of bivalents that have undergone exchange. Disjunction of nonexchange homologs was examined for all chromosome pairs; nonhomologous disjunction of the X chromosomes from the Y chromosome in XXY females, of compound chromosomes in females bearing attached-third chromosomes with and without a Y chromosome, and of the second chromosomes from the third chromosomes were also examined. The results suggest that the defect in nod is in the distributive pairing process. The frequencies and patterns of disjunction from a trivalent in nod females suggest that the distributive pairing process involves three separate events-pairing, orientation, and disjunction. The mutant nod appears to affect disjunction only.
RECOMBINATION IN DROSOPHILA MELANOGASTER MALE
Authors: Hiraizumi Yuichiro , Slatko Barton , Langley Charles , Nill Annegreth
Published: January 2021

T-007 strain of Drosophila melanogaster is known to show recombination in males. The present study established the following points: (1) Clustering occurrence of recombinant, unequal recovery of complementary products of recombination, relatively high frequency of recombination around centromeric region, and relatively frequent occurrence of mosaic phenontype flies—all of these seem to indicate that a considerable fraction of male recombination in the T-007 strain is of premeiotic, or somatic origin, although a fraction still could be of meiotic origin; (2) Male recombination occurs in the third as well as in the second chromosomes, and the frequencies of recombinations are comparable between these two chromosome pairs.
REGULATION OF GENE FUNCTION: A COMPARISON OF X-LINKED ENZYME ACTIVITY LEVELS IN NORMAL AND INTERSEXUAL TRIPLOIDS OF DROSOPHILA MELANOGASTER
Authors: Lucchesi John C , Rawls John M
Published: January 2021

We have measured gene function in normal and male-like intersexual triploids of Drosophila melanogaster by assaying crude extracts of whole flies or thoraces for levels of an X-linked (6-phosphogluconate dehydrogenase) and an autosomal (NADP-dependent isocitrate dehydrogenase) enzyme activity. Our observations lead us to conclude that each dose of the X-linked gene is more active in the cells of these intersexes than it is in normal triploid or diploid female cells. These results indicate that a level of activity intermediate between the normal male and female levels is possible for X-linked genes.
POPULATION GENETICS OF MARINE PELECYPODS. III. EPISTASIS BETWEEN FUNCTIONALLY RELATED ISOENZYMES OF MYTILUS EDULIS
Authors: Mitton Jeffry B , Koehn Richard K
Published: January 2021

The distribution of interlocus genotypic combinations was examined in Mytilus edulis for interdependence between two loci synthesizing functionally related isoenzymes. There is significant dependence between the Leucine Aminopeptidase and Aminopeptidase loci, which we attribute to epistasis, since the magnitude of dependency varies with age. Furthermore, dependency varies in magnitude with position in the intertidal zone from which samples were taken, suggesting that epistasis is a function of the combination of certain non-homologous alleles as well as of the environmental circumstance in which the combinations occur.
EFFECTS OF POPULATION SIZE AND SELECTION INTENSITY ON SHORT-TERM RESPONSE TO SELECTION FOR POSTWEANING GAIN IN MICE
Authors: Hanrahan J P , Eisen E J , Legates J E
Published: January 2021

The effects of population size and selection intensity on the mean response was examined after 14 generations of within full-sib family selection for postweaning gain in mice. Population sizes of 1, 2, 4, 8 and 16 pair matings were each evaluated at selection intensities of 100% (control), 50% and 25% in a replicated experiment. Selection response per generation increased as selection intensity increased. Selection response and realized heritability tended to increase with increasing population size. Replicate variability in realized heritability was large at population sizes of 1, 2 and 4 pairs. Genetic drift was implicated as the primary factor causing the reduced response and lowered repeatability at the smaller population sizes. Lines with intended effective population sizes of 62 yielded larger selection responses per unit selection differential than lines with effective population sizes of 30 or less.
BARLEY STRIPE MOSAIC VIRUS AND THE FREQUENCY OF TRIPLOIDS AND ANEUPLOIDS IN BARLEY
Authors: Sandfaer Jens
Published: January 2021

BSMV infection caused a pronounced increase in the frequency of triploid and aneuploid seeds in eleven barley varieties, but with considerable variation in frequency among varieties. In some of the varieties triploids exceeded three per cent. In virus-free material a few triploids were found in most of the varieties, but the frequency was very low. There was, however, a significant variation among varieties.
COMPLEMENTATION ANALYSIS OF MALE FERTILITY AMONG THE SEGREGATION DISTORTER CHROMOSOMES OF DROSOPHILA MELANOGASTER
Authors: Hartl D L
Published: January 2021

The fecundities of 55 genotypes of the form SDi/SDj, generated by 11 different SD chromosomes have been examined. Five of the genotypes are lethal The fecundities of the rest fall into a pattern of fertility and sterility that is highly suggestive of intracistranic complementation. The complementation leading to male fertility is only partial complementation: the fecundity of most fertile genotypes is less than half that of controls. The three components of the SD system, the Sd locus, the Ac locus, and the modifiers in 2R, were examined separately, and it appears that the complementation is a phenomenon associated with the Sd locus. A hypothesis of the molecular events involved in segregation distortion is formulated in the light of these observations. The model is based on the assumption that the Sd locus produces a multimeric molecule that regulates the activity of the Ac(=Rsp) locus during spermatogenesis.
CYTOGENETIC ANALYSIS OF PSEUDOLINKAGE OF LDH LOCI IN THE TELEOST GENUS SALVELINUS
Authors: Davisson Muriel Trask , Wright James E , Atherton Louisa M
Published: January 2021

Cytological and genetic analyses provide evidence that spontaneous centric fusion and fission can account for curious patterns of pseudolinkage of two LDH loci in males of brook trout (Salvelinus fonthalis) and in the F1, F2, and backcross generations of lake trout (S. namaycush) × brosk trout hybrids. Intraindividual polymorphisms for acrocentric and metacentric chromosomes in somatic and gonadal tissue of these fish have been related to the proposed polyploid evolution in Salmonidae.
BIOMETRICAL GENETICS WITH ONE OR TWO LOCI: THE INHERITANCE OF PHYSIOLOGICAL CHARACTERS IN MICE
Authors: Stewart John , Elston R C
Published: January 2021

Maximum likelihood methods have been used to compare the fit of twenty different genetic models to experimental data on fourteen characters, each measured on two parental strains, F1 hybrids and both backcrosses. Although variation in all characters was continuous, differentiation between the various models was meaningful, the mean likelihood ratio between the best and worst models for each character being greater than 1O4. Models with only one or two loci were adequate to account for the observed genetic variation in eleven of the fourteen characters. These results indicate that even in species without special genetic advantages, it may be possible to identify individually some of the genes responsible for naturally-occurring variation within the range of normality.
THE EFFECTS OF ENVIRONMENTAL HETEROGENEITY ON THE GENETICS OF FINITE POPULATIONS
Authors: Dickinson Heather , Antonovics Janis
Published: January 2021

The effects on a panmictic population of a patchy environment and stochastic selection were investigated by computer simulation. The model allowed for different patterns and intensities of selection and various densities of distribution of the offspring. It delineated the effects of these variables on the correlation between the genotype and the environment, the level of heterozygosity, the change in gene frequency from generation to generation and the divergence between similar populations due to random effects.
A TEMPERATURE-SENSITIVE MUTANT IN TETRAHYMENA PYRIFORMIS, SYNGEN 1
Authors: McCoy J Wynne
Published: January 2021

After treatment with nitrosoguanidine a mutation to temperature sensitivity was obtained in Tetrahymena pyriformis, syngen 1. The trait is controlled by a recessive allele, ts, at a locus linked to serotype locus T. IS is completely recessive, unlike any other allele studied in this organism, and the heterozygotes do not show vegetative assortment. The cross which revealed the linkage of ts and T failed to show evidence of the linkage of mt (mating type) and E-1 (esterase-I) which has been demonstrated in other crosses (ALLEN 1964; DOERDER 1972), but revealed a third case of linkage, involving mt and TO (tetrazolium oxidase). Taken together, these results are presumptive evidence for large interstrain differences in recombination properties within syngen 1.
GENETIC MAPPING IN SACCHAROMYCES IV. MAPPING OF TEMPERATURE-SENSITIVE GENES AND USE OF DISOMIC STRAINS IN LOCALIZING GENES
Authors: Mortimer R K , Hawthorne D C
Published: January 2021

Through use of tetrad, random spore, trisomic, and mitotic analysis procedures a large number of genes, including 48 new genetic markers, were studied for their locations on the genetic maps of the yeast Saccharomyces cerevisiae. Eighteen new centromere linked genes were discovered and all but one was located on various ones of the 16 previously-established chromosomes. Five fragments of linked genes were also assigned to chromosomes; four were located on known chromosomes while the fifth determined one arm of a new chromosome. The experiments indicate that seventeen is likely to be the haploid chromosome number in this yeast. Most chromosomes have been established by genetic means to be metacentric and their genetic lengths vary from 5 cM to approximately 400 cM. Functionally-related sets of genes generally were found to be dispersed over the genome.
GENETIC CONTROL OF RECOMBINATION IN SCHIZOPHYLLUM COMMUNE: LOCATION OF A GENE CONTROLLING B-FACTOR RECOMBINATION
Authors: Koltin Y , Stamberg Judith
Published: January 2021

In S. commune the frequency of recombination between the two subunits, α and β, of the B incompatibility factor is genetically controlled. Analysis of the progeny obtained from crosses between high- and low-recombining strains indicates that the gene controlling recombination frequency in the B factor is linked to the B factor itself, approximately nine map units from Bβ. This gene, called B-rec-1, does not affect the recombination frequency in an unlinked region (between the subunits of the A incompatibility factor) or in a region contiguous with the B factor (between Bα and the morphological marker dome-2).
DIRECTED EVOLUTION OF METABOLIC PATHWAYS IN MICROBIAL POPULATIONS II. A REPEATABLE ADAPTATION IN SACCHAROMYCES CEREVISIAE
Authors: Francis J C , Hansche P E
Published: January 2021

A selection experiment was conducted for approximately 1,000 generations in a chemostat population of 109 cells of the haploid yeast, S. cerevisiae. The experiment was designed to enhance genetically the rate at which the external enzyme acid phosphatase catalyzed the hydrolysis of very low concentrations of β-glycerophosphate at an unfavorably high pH. The observed genetic adaptation in this experiment consisted of a mutation (ACP-2) in the acid phosphatase structural gene which effected a shift in the pH optimum of the enzyme and incremented its activity. The effects of ACP-2 and a similar mutation, ACP-1, on acid phosphatase substrate specificity are also reported.
LINKAGE RELATIONSHIPS OF SIX ENZYME LOCI IN INTERSPECIFIC SUNFISH HYBRIDS (GENUS LEPOMIS)
Authors: Wheat T E , Whitt G S , Childers W F
Published: January 2021

Backcross hybrids produced from the bluegill, the red-ear sunfish, and their F1 interspecific hybrid have been analyzed for the inheritance of six enzyme phenotypes. Malate dehydrogenase A and B, tetrazolium oxidase, 6-phosphogluconate dehydrogenase, skeletal muscle esterase, and liver α-glycerophosphate dehydrogenase are all inherited in a mendelian manner as codominant alleles at nuclear loci. 6-phosphogluconate dehydrogenase and α-glycerophosphate dehydrogenase are encoded by linked loci, undergoing recombination at a frequency of 15%-22%. No other case of linkage was observed. The absence of linkage between the homologous malate dehydrogenase loci is of particular interest. These interspecific hybrids appear to be very useful for studies of biochemical genetics.
FERTILITY GENES IN NATURAL POPULATIONS OF DROSOPHILA MELANOGASTER. I. FREQUENCY, ALLELISM AND PERSISTENCE OF STERILITY GENES
Authors: Oshima Chozo , Watanabe Takao K
Published: January 2021

Three or four percent of the wild flies in natural populations of D. melanogaster have been found to be sterile. An analysis of sterility associated with the second chromosome revealed a much lower frequency of genetically sterile flies. The accumulation of sterility genes in a cage population was proportional to that of lethal genes, as were their equilibrium frequencies in several natural populations. Many sterile chromosomes were associated with low viability due to pleiotropic effects. The number of chromosomes leading to sterility in both sexes was larger than the expectation based on random combination of male and female sterility genes. This suggests that there is some linkage disequilibrium between male and female sterility genes, as well as a pleiotropic effect of single sterility genes. Some sterility genes were maintained in natural and cage populations, and the patterns of persistence of the sterility genes were very similar to those of lethal genes.
PROBABILITY OF FIXATION AND MEAN FIXATION TIME OF AN OVERDOMINANT MUTATION
Authors: Nei Masatoshi , Roychoudhury A K
Published: January 2021

The probability of fixation of an overdominant mutation in a finite population depends on the equilibrium gene frequency in an infinite population (m) and the product (A) of population size and selection intensity. If m < 0.5 (disadvantageous overdominant genes), the probability is generally much lower than that of neutral genes; but if m is close to 0.5 and A is relatively small, it becomes higher. If m > 0.5 (advantageous overdominant genes), the probability is largely determined by the fitness of heterozygotes rather than that of mutant homozygotes. Thus, overdominance enhances the probability of fixation of advantageous mutations. The average number of generations until fixation of an overdominant mutation also depends on m and A. This average time is long when m is close to 0.5 but short when m is close to 0 or 1. This dependence on m and A is similar to that of Robertson's retardation factor.
DELETION MAPPING OF THE Λ REX GENE
Authors: Gussin Gary N , Peterson Victoria , Loeb Nancy
Published: January 2021

Deletion mapping has been used to order 12 Λ rex- mutants. Correlation of recombination data with physically-determined positions of deletion end-points (SZYBALSKI 1971; BLATTNER et al. 1972) suggests that the left-most rex- mutation, rex209, is located about 260-300 nucleotide pairs from the PL mutation sex1 and abut 475 nucleotide pairs from the left end-paint of the region of nonhomology with Λimm434.
THE PRODUCT OF THE LEU-3 CISTRON AS A REGULATORY ELEMENT FOR THE PRODUCTION OF THE LEUCINE BIOSYNTHETIC ENZYMES OF NEUROSPORA
Authors: Polacco Joseph C , Gross S R
Published: January 2021

A class of intracistronic (or closely linked) partial reversions of leu-3 mutations has been found to be conditionally constitutive with respect to the synthesis of isopropylmalate isomerase (specified by the leu-2 cistron) and β-isopropylmalate dehydrogenase (specified by the leu-1 cistron), two of the enzymes of leucine biosynthesis in Neurospora. The intermediate level of enzyme production by these leu-3cc mutants is independent of the obligatory inducer effector, α-isopropylmalate, but dependent upon the presence of the branched-chain amino acids, isoleucine, valine and leucine. The properties of leu-3+, leu-3 and leu-3cc in heterokaryons indicate that the transnuclear regulatory activity of the leu-3 product varies specifically as a function of available effector molecules. The information presented suggests that the leu-3 cistron is responsible not only for the production of a "positive" regulatory substance necessary for the expression of the leu-1 and leu-2 cistrons, but that it probably serves also a coordinating role in the expression of many of the genes involved in branched-chain amino acid metabolism.
TEMPERATURE-SENSITIVE MUTATIONS IN DROSOPHILA MELANOGASTER. XVII. HEAT- AND COLD-SENSITIVE LETHALS ON CHROMOSOME 3
Authors: Tasaka S Elaine , Suzuki David T
Published: January 2021

Ethyl methanesulfonate-treated third chromosome of Drosophila melanogaster were tested for the presence of dominant and recessive temperature-sensitive lethal mutations at 17°, 22° and 29°C. Out of 1,176 chromosomes tested, no dominant ts lethals, 21 heat-sensitive, 22 cold-sensitive and 10 heat-cold-sensitive lethals were recovered. Heat-cold sensitivity was produced by a single mutation in all cases. Sixty-two percent of the ts lethals were fertile as homozygotes in both sexes. Surprisingly, 88% of the ts lethals mapped between st and Sb, a region straddling the centromere and estimated to comprise 12.9% of the genetic length and 55% of the physical length of chromosome 3. All but one of the heat- and cold-sensitive lethals complemented with each other at their respective restrictive temperatures.
GENE DOSAGE AND THE EXPRESSION OF ELECTROPHORETIC PATTERNS IN HETEROPLOID MOUSE CELL LINES
Authors: Farber Rosann A
Published: January 2021

Spontaneously transformed mouse cell lines heterozygous for electrophoretic markers have been studied to determine the relationship between gene dosage and phenotype. It is shown that a clone with an electrophoretic pattern for glucosephosphate isomerase of three bands in a ratio of 4A:4AB:1B contains three copies of chromosome 7, which carries the gene for this enzyme. A clone from a different line with a pattern of three bands in a ratio of 1A:6AB:9B for NADP-isocitrate dehydrogenase has four copies of the chromosome carrying this gene or three copies plus a rearrangement which apparently involves this chromosome. These results show that all of the alleles for each enzyme are expressed to an equal extent in these cells.
DIFFERENTIAL RESPONSE TO SELECTION ON THE TWO SEXES IN DROSOPHILA MELANOGASTER
Authors: Palenzona Domenico Lorenzo , Alicchio Rita
Published: January 2021

Artificial selection for short wing was performed in two Drosophila melanogaster populations with partially different gene pools: the C populations were derived from a Canton stock while the H lines were derived from a cross between Canton and a b, cn, vg strain. It is shown that in both populations selection on females (CF, HF) was more effective than selection on males (CM, HM). This difference cannot be explained in terms of differences in additive genetic variability between the two sexes because: (1) both sexes contribute to the genetic variability utilized by selection applied to one sex only, and (2) switching selection pressure on females in the M lines does not result in a response comparable to that obtained in the F populations; this rules out almost completely recombination as the responsible agent for the differences between the selection limits reached by M and F selections.—These results, together with several additional observations concerning sexual dimorphism, fitness and the effect of natural selection, suggest that a complex interaction should be involved in the differential response of M and F lines, controlling the wing length phenotype.
DNA FROM MAIZE WITH AND WITHOUT B CHROMOSOMES: A COMPARATIVE STUDY
Authors: Chilton Mary-Dell , McCarthy Brian J
Published: January 2021

DNA preparations from 5B and 0B maize seedlings are indistinguishable in their buoyant density distribution in CsCl gradients. Their renaturation kinetics are identical at several stringency criteria. DNA competition studies fail to detect any component in 5B DNA redundant sequences which is lacking in 0B DNA. Homologous and heterologous duplexes formed between 5B and 0B DNA have virtually identical melting profiles. The DNA of B chromosomes is concluded to be very closely related to that of A chromosomes.
EVIDENCE FOR A SEX-LINKED HAPLO-INVIABLE LOCUS IN THE CUT-SINGED REGION OF DROSOPHILA MELANOGASTER
Authors: Lefevre G , Johnson T K
Published: January 2021

Many cytologically normal and rearranged cut mutants have been reported, but no known deficiency involves both ct and its close neighbor, singed. This fact prompted an investigation of the mutational response of the ct-sn interval. Approximately 24,000 F1 female progeny of 7-day-old males given 2000 or 3000r X-ray exposures were examined for the presence of newly induced mutations at the Notch, carmine, ct, and sn loci. One sn, 2 cm-ct, 31 N, and 33 ct mutants were found, indicating that the frequency of recovery of ct mutants is much greater than that of either cm or sn, as high even as N. Among the F1 female progeny were two deficiency mutants that expressed both cm and ct (separated by 21 bands), but none expressed both ct and sn (separated by only 14 bands). Of the 18 cytologically analyzed ct mutants, two proved to be deficiencies; neither extended farther to the right than 7C1. No reported ct deficiency extends with certainty farther to the right than 7C4. This fact, together with the scarcity of sn deficiencies, suggests the presence of a haplo-insufficient locus between ct and sn that prevents recovery of ct-sn deficiencies. The analysis of the deficiency component of Tp snS93, a short transposition which moves most of the ct-sn interval from 7BC to 8D, proved the existence, just to the left of sn, of a haplo-inviable locus that prevents the development of females heterozygous for its deficiency.—A marked similarity between mutants at the N and ct loci was noted.
GENETIC RELATIONSHIP BETWEEN ARYL HYDROCARBON HYDROXYLASE INDUCIBILITY AND CHEMICAL CARCINOGEN INDUCED SKIN ULCERATION IN MICE
Authors: Thomas P E , Hutton J J , Taylor B A
Published: January 2021

Inbred strains of mice show differential skin inflammatory reactivity following the topical application of polycyclic hydrocarbons. Strains also differ in the extent to which hepatic aryl hydrocarbon hydroxylase activity is induced by these compounds. Differential inflammatory response and hydroxylase inducibility are genetically controlled by alleles at the In and Ahh loci, respectively. Genetic analyses and strain surveys indicate that the In and Ahh loci are identical, or very closely linked.
ASSIGNMENT OF THREE GENE LOCI (PGK, HGPRT, G6PD) TO THE LONG ARM OF THE HUMAN X CHROMOSOME BY SOMATIC CELL GENETICS
Authors: Ricciuti Florence C , Ruddle Frank H
Published: January 2021

The intrachromosomal localization of three X-linked gene loci (PGK, HGPRT and G6PD) has been determined using a somatic cell genetic approach. A human cell line possessing an X/14 translocation was used as one parent in the formation of human/mouse hybrids. The translocation separates the human X into two parts: Xp and t(Xq14q). The data indicate that all three X-linked loci segregate with the t(Xq14q) rearrangement product thus permitting their assignment to the X chromosome's long arm. Secondary rearrangements and data from other laboratories suggest that the order of the the three markers from the centromere to the distal end of the X long arm is PGK, HGPRT, G6PD. It was also observed that NP, an autosomal locus, segregated with the t(Xq14q) chromosome. This provides strong support for the assignment of NP to 14.
ANALYSES OF GENE FREQUENCIES
Authors: Cockerham C Clark
Published: January 2021

Models of variance components and their intraclass correlational equivalences are developed for genes falling into various categories of subdivisions within a population. Estimable functions are elaborated demonstrating that intraclass correlations can be estimated only relative to that for the least related genes in the informational system. The effects of different types of subdivisions-and of ignoring them-on the parameters are demonstrated. Small sample estimators are formulated for all of the parameters by three different methods, including both a weighted and an unweighted method of analysis of the variation among subpopulations. How estimators change with assumptions about the parameters is illustrated. Various tests of hypotheses are outlined in X2 and F-test terminology. Discussed are factors which may affect the correlations and the manner in which their effects are manifest, hopefully in clarification of some of the misconceptions that have arisen in this connection.
A COMPETITIVE SELECTION MODEL
Authors: Milkman Roger
Published: January 2021

The proportionate contribution of a genotype to the next generation is not independent of frequency and cannot always safely be equated with a constant. Survival potential (Haldane's viability) permits the use of a genetic selection model which deals more realistically with competition. A broader property than survival potential, called fitness potential, should be distinguished from fitness, which it determines in a competitive context.
GENETIC CONTROL OF QUANTITATIVE VARIATION IN SELF-INCOMPATIBILITY PROTEINS DETECTED BY IMMUNODIFFUSION
Authors: Nasrallah M E
Published: January 2021

Single radial immunodiffusion was used to study the self-incompatibility (S) proteins present in stigmas of two inbred lines of Brassica oleracea: a self-incompatible line and a self-compatible mutant derived from it. The genetic basis of observed quantitative differences in S proteins between the two inbreds was shown to be determined by a single gene with dosage effects. Self-pollination of individual plants with high, intermediate and low levels of S protein in the stigmas, respectively, resulted in low, intermediate and high seed set.
REGULATION OF NEWLY EVOLVED ENZYMES. I. SELECTION OF A NOVEL LACTASE REGULATED BY LACTOSE IN ESCHERICHIA COLI
Authors: Hall Barry G , Hartl Daniel L
Published: January 2021

Thirty-four lactose-utilizing strains of E. coli were selected from a lac Z deletion strain. In 31 of these, the synthesis of the newly evolved lactase is regulated by lactose. The lactase activity in all the strains is indistinguishable from the ebg  + activity identified by Campbell, Lengyel and Langridge (1973).
SOME IMPROVED METHODS IN P22 TRANSDUCTION
Authors: Ely Bert , Weppelman Roger M , Massey Holman C , Hartman Philip E
Published: January 2021

Recent refinements simplify methods for P22 transduction in Salmonella and allow improved recovery of phage-free transductional clones. The methods include use of: integration- and lysis-defective phage mutants, heat-killed bacteria to eliminate free phage, direct plating of phage and bacteria, replica-plating for detection of phage content of individual clones, improved broth for phage growth, and procurement of high titer phage from P22 lysogens.
GENETIC ANALYSIS OF THE ACTIVE SITES OF lac REPRESSOR
Authors: Pfahl Magnus , Stockter Christel , Gronenborn Bruno
Published: January 2021

Selection methods for the isolation of i  -d and i  s mutants are described. Two hundred and forty-seven i  -d and 98 i  s mutations have been localized by deletion mapping. All i  -d mutations map in the region of the i gene, which codes for the aminoterminal part of the lac repressor, whereas i  s mutations map in the middle of the i gene and at the proximal end of the i  -d cluster.
GENETICS OF CHEMICAL INDUCTION OF CONJUGATION IN PARAMECIUM AURELIA
Authors: Cronkite Donald L
Published: January 2021

Certain stocks of P. aurelia, syngen 8, could not be induced to conjugate in a solution (KCl + acriflavine + calcium-poor conditions) which was effective in inducing conjugation in other species of Paramecium as well as in other stocks of syngen 8. Both stocks could conjugate by interaction with cells of complementary mating type. Breeding analysis shows that each of the two stocks is homozygous for a recessive gene that blocks induction of conjugation by the KCl-acriflavine solution. These two genes are neither allelic nor linked. Analyses of the phenotypes of the two uninducibles and the wild type were carried out by attempting to induce mating in cells of a single mating type by exposing them to detached mating-reactive cilia from cells of complementary mating type and to the KCl-acriflavine solution, either sequentially or simultaneously. The results confirm the conclusions of others that there is at least one unique step in chemical induction not shared with induction by interaction of complementary mating types. But the results also indicate that there is more than one unique step in chemical induction and that the effects of the two genes described here operate during different periods of the hour required for chemical induction.
TEMPERATURE-SENSITIVE PLEIOTROPIC REVERTANTS FROM A MUTANT IN THE AROM GENE CLUSTER OF NEUROSPORA CRASSA
Authors: Case Mary E , Giles Norman H
Published: January 2021

Genetical and biochemical studies have been performed with revertants induced in a polyaromatic mutant (No. 58) in the arom gene cluster of Neurospora crassa. In addition to complete and partial revertants able to grow on minimal at both 25° and 35°, temperature-sensitive revertants capable of growth on minimal at 25° but not at 35° have been recovered. One of these revertants has been shown to lack biosynthetic dehydroquinase activity at both temperatures (utilizing the inducible catabolic isozyme for growth at 25°), to have dehydroshikimate reductase activity only at 25°, and to form an arom aggregate having a molecular weight approximately one-half that of wild type. These results are interpreted as indicating that pleiotropic mutants in the arom gene cluster can result from missense mutations, as well as from nonsense mutations as indicated in previous studies.
FINE STRUCTURE MAPPING IN YEAST WITH SUNLAMP RADIATION
Authors: Lawrence Christopher W , Christensen Roshan
Published: January 2021

The X-ray mapping procedure of Manney and Mortimer (1964) is the most widely applicable and convenient method for fine structure analysis in yeast, but suffers the disadvantage that suitable X-ray machines or gamma ray sources are very expensive. Although many other recombinogens are known, none gives a linear dose-response like X-rays and few are as convenient or give as reproducible results. Experiments with Saccharomyces cerevisiae reported in this paper show, however, that the near-ultraviolet radiation emitted by fluorescent sunlamps gives linear dose-response relations, as reproducible results as ionizing radiations, and map distances which correlate highly with those obtained by using 60Co gamma rays. It is suggested that this convenient recombinogen may be a suitable low-cost substitute for ionizing radiations in fine structure mapping.