bluuebunny/crossref_metadata_2025 huggingface dataset:
ANALYSIS OF THE ALBINO-LOCUS REGION OF THE MOUSE. III. TIME OF DEATH OF PRENATAL LETHALS
Authors: Russell Liane B , Raymer G D
Published: April 2021

The stage at which homozygotes die was determined for 28 mutations (general symbol c*) at the albino (c) locus, of which 26 had earlier been found to be probably prenatally lethal. Within each of the mutant stocks, the uterine contents of c*/cch females, made pregnant either by c*/cch males ("Ex" series) or by cch/cch males ("CO" series), were examined between 13 and 17 days postconception. Altogether, 743 females were dissected and 7197 corpora lutea (representing ovulations) counted. In selected stocks, an additional 40 and 13 females were dissected on days seven or nine, respectively.— In each of the 26 presumed prenatally lethal mutants, there was a deficiency of living fetuses in the Ex, as compared with the CO, group. Overall, this deficiency was 23.6% (expectation, 25% c*/c*). All meaningful excesses were in numbers either of moles (death shortly before, during, or just after implantation), or of early preimplantation losses. Homozygotes in none of the mutant stocks die between days nine and 19 postconception. Of 24 c-locus mutants known to be deficiencies since they lack the closely linked Mod-2, 13 clearly kill before implantation, ten around implantation, and me neonatally. The c and Mod-2 loci and the region between them are not needed for intrauterine survival.—There are indications that the distinction between early-preim-plantation death and implantation death may, in a general way, be related to length of the deficiency.
AN UNSTABLE NUCLEAR GENE IN PHYCOMYCES
Authors: Delbrück M , Ootaki T
Published: April 2021

A gentic instability in Phycomyces is described that appears to be associated with a single nuclear gene, dar. The wild type is able to take up riboflavin and its toxic analogue, deaza-riboflavin, from nanomolar concentrations in the medium. The mutants are unable to take up riboflavin and are resistant to deaza-riboflavin. Forward and reverse mutation rates are estimated to be 4 × 10-5 and 2 × 10-3 per nuclear division. Independently arisen dar mutants do not complement in heterokaryons. The mutant alleles are almost completely recessive. The phenotype of spores is not determined cell-autonomously, but is strongly influenced by the allele ratio among the nuclei in the sporangium of origin.
LETHALS, STERILES AND DEFICIENCIES IN A REGION OF THE X CHROMOSOME OF CAENORHABDITIS ELEGANS
Authors: Meneely Philip M , Herman Robert K
Published: April 2021

Twenty-one X-linked recessive lethal and sterile mutations balanced by an unlinked X-chromosome duplication have been identified following EMS treatment of the small nematode, Caenorhabditis elegans. The mutations have been assigned by complementation analysis to 14 genes, four of which have more than one mutant allele. Four mutants, all alleles, are temperature-sensitive embryonic lethals. Twelve mutants, in ten genes, are early larval lethals. TWO mutants are late larval lethals, and the expression of one of these is influenced by the number of X chromosomes in the genotype. Two mutants are maternal-effect lethals; for both, oocytes made by mutant hermaphrodites are rescuable by wild-type sperm. One of the maternal-effect lethals and two larval lethals are allelic. One mutant makes defective sperm. The lethals and steriles have been mapped by recombination and by complementation testing against 19 deficiencies identified after X-ray treatment. The deficiencies divide the region, about 15% of the X-chromosome linkage map, into at least nine segments. The deficiencies have also been used to check the phenotypes of hemizygous lethal and sterile hermaphrodites.
THE GENETICS OF MELANISM IN MALACOSOMA DISSTRIA HÜBNER (LEPIDOPTERA: LASIOCAMPIDAE)
Authors: Lorimer Nancy
Published: April 2021

The forest tent caterpillar is polymorphic far two melanic genes affecting wing color of moths. These are the first genetically determined morphological traits reported for the genus. Dark (D) is a sex-limited, autosomal dominant with a phenotype of dark brown males. Frequencies in population samples varied from 8 to 44%. Characteristics of Dark and nonmelanic males were compared. Larval development times, larval survival and pupal weights were not significantly different, but mean fecundity was higher for females with Dark progeny. Band (b), a darkened area across the forewings, occurred in low frequency in both sexes.
MUTATIONS OF CHINESE HAMSTER SOMATIC CELLS FROM 2-DEOXYGALACTOSE SENSITIVITY TO RESISTANCE
Authors: Claverie Jean-Michel , De Souza Aristide Comlan , Thirion Jean-Paul
Published: April 2021

In Chinese hamster somatic cells, the spontaneous change of phcnotype from 2-deoxygalactose sensitivity to resistance was studied using fluctuation test experiments à la LURIA and DELBRUCK (1943) for four Chinese hamster cell strains derived from V79. The results are consistent with true mutational events. The mutation rates are in the range of 1 to 3.5 × 10-5 per cell per generation. The relationship between the 2-deoxygalactose resistance and the galactokinase markers is discussed.
INTERFERENCE IN GENETIC CROSSING OVER AND CHROMOSOME MAPPING
Authors: Stam P
Published: April 2021

This paper proposes a general model for interference in genetic crossing over. The model assumes serial Occurrence of chiasmata, visualized as a renewal process along the paired (or pairing) chromosomes. This process is described as an underlying Poisson process in which the Ist, n + 1th, 2n + 1th, etc., events are to be interpreted as realized chiasmata. Chromatid interference is described in terms of the probabilities that two successive chiasmata involve two, three or four different chromatids. Several characteristics of this model, e.g., the cytological and genetic mapping function and the density of chiasmata along the chromosomes, are discussed. Some aspects of other interference models are briefly discussed.
GENE CONVERSION OF THE MATING-TYPE LOCUS IN SACCHAROMYCES CEREVISIAE
Authors: Klar Amar J S , Fogel Seymour , Lusnak Karin
Published: April 2021

Tetrad analysis of MAT  a/MATα diploids of Saccharomyces cerevisiae generally yields 2 MATa:2MATα meiotic products. About 1 to 1.8% of the tetrads yield aberrant segregations for this marker. Described here are experiments that determine whether the aberrant meiotic segregations at the mating-type locus are ascribable to gene conversions or to MAT switches, that is, to mating-type interconversions. Diploid strains incapable of switching MAT  a to MATα, or the converse, nevertheless display changes of MAT  a to MATα, or the reverse. These events must be attributed to gene conversion. Further, we suggest that MAT  a and MATα alleles may represent nonhomologous sequences of DNA since they fail to display postmeiotic segregations.
THE EFFECTS OF MUTAGEN-SENSITIVE MUTANTS OF DROSOPHILA MELANOGASTER IN NONMUTAGENIZED CELLS
Authors: Baker Bruce S , Smith David A
Published: April 2021

The effects of 13 mutagen-sensitive (mus) mutants (representing seven loci) on mitotic chromosome stability in nonmutagenized cells have been examined genetically. To do this, mus-bearing flies heterozygous for the recessive somatic-cell marker, multiple wing hairs (mwh), were examined for increased frequencies of mwh clones in the wing blade. Mutants at the mus-103, mus-104 and mus-106 loci do not affect the frequency of mwh clones, while mus-101, mus-102, mus-105 and mus-109 alleles cause increases in the frequency of mwh clones. These data show that the wild-type alleles of latter four loci specify functions that are required for chromosome stability in nonmutagenized cells. Analysis of the size distribution of mwh clones produced by these mutants suggests that most chromosome instability caused by these mutants is the consequence of chromosome breakage; in the presence of mus-105 and mus-109 alleles a small fraction of the mwh clones are produced by an event (mitotic recombination, mutation, nondisjunction) that produces euploid clones. To inquire whether any of the extant alleles of the mus-101, mus-102, mus-105 and mus-209 loci might be leaky alleles of loci that carry out essential mitotic functions, chromosome stability in females homozygous for alleles of these loci has been compared to that of females carrying one dose of a mutant over a deficiency for that mus locus. These comparisons show that the extant alleles at the mus-102, mus-1O9 and mus-105 loci are all leaky mutants. It is suggested that all three of these loci may specify essential mitotic functions.
THE EFFECT OF ABO PHENOTYPIC EXPRESSION ON RIBOSOMAL DNA INSTABILITIES IN DROSOPHILA MELANOGASTER
Authors: Krider Hallie M , Yedvobnick Barry , Levine Bryan I
Published: April 2021

The recessive maternal-effect mutation, abnormal oocyte (abo:2-38), reduces viability in the offspring of homozygous mutant females. Zygotes lacking specific heterochromatic segments of the X or Y chromosomes are most severely affected. We have shown that abo/abo lines can lose the capacity to express the mutant phenotype, and that elevated rDNA redundancies can be observed in such stocks (KRILIER and LEVINE 1975). In this study, we describe a microhybridization procedure that facilitates the measurement of rDNA redundancy, using a small number of adult Drosophila. We show that instability of the rDNA content persists in an abo/abo line after loss of the capacity to express the phenotype, and that changes in rDNA amounts occur between successive generations of the stock. Further, we show that the rDNA content of XO progeny from abo/abo females is elevated. The effect is directly correlated with the expression of the abo phenotype, and it is not observed in the XO progeny of abo heterozygous females or abo homozygotes from lines that do not show abo expression.
ISOLATION AND CHARACTERIZATION OF dnaX AND dnaY TEMPERATURE-SENSITIVE MUTANTS OF ESCHERICHIA COLI
Authors: Henson Joan M , Chu Herman , Irwin Carleen A , Walker James R
Published: April 2021

Escherichia coli mutants with temperature-sensitive (ts) mutations in dnaX and dnaY genes have been isolated. Based on transduction by phage PI, dnaX and Y have been mapped at minutes 10.4-10.5 and 12.1, respectively, in the sequence dnaX purE dnaY. Both dnaXts36 and YtslO are recessive to wild-type alleles present on episomes. F13 carries both dnaX  + and Y  +; the shorter F210 carries dnaY  +, but not X  +. Lambda transducing phages that carry dnaX  + or Y  + have been isolated, and hybrid plasmids of Col E1 and E. coli DNA from the CLARKE and CARBON (1976) collection also carry portions of the dnaX purE dnaY region. Results obtained with the λ transducing phages and the hybrid plasmids suggest that dnaX is a different gene from the previously characterized dnaZ gene, which is also near minute 10.5.—The dnaXts36 mutant, after a shift to 42°, stopped DNA synthesis gradually, and the total amount of DNA increased two-fold. When this mutant was shifted to M°, the rate of DNA synthesis dropped immediately and the final increment of DNA was only 10% of the initial amount. Replicative DNA synthesis in toluene-treated cells was completely inhibited at 42° and was partially in-hibited even at 30°.—When the dnaYtslO mutant was shifted to 42°, DNA synthesis gradually stopped, and the amount of DNA increased 3.6-fold. At 44°, residual DNA synthesis amounted to a two-fold increase. Replicative DNA synthesis in vitro in toluene-treated cells was inactivated after 20 minutes at 42° or by "preincubation" of cells at 42° before toluene treatment.— The dnaX and dnaY products probably function in polymerization of DNA, although participation also in initiation cannot be excluded.
AN ENRICHMENT FOR TEMPERATURE-SENSITIVE MUTANTS IN TETRAHYMENA THERMOPHILA
Authors: Martindale Duane W , Pearlman Ronald E
Published: April 2021

The parameters for the killing of Tetrahymena by 5-bromodeoxyuridine (BUdR) and near-ultraviolet light have been determined. Significant preferential killing by UV* of cells that have incorporated BUdR was obtained when the cells were irradiated in a nonnutrient buffer. UV alone was found to be toxic to cells irradiated in growth medium. Mutants defective in division at a restrictive temperature were isolated from mutagenized cultures that had been treated with BUdR and UV and from mutagenized cultures that had no such treatment. Results indicate that the number of temperature sensitive (ts) growth mutants can be increased five to six times using the BUdR/UV treatment. Data are presented that indicate differences in the frequency of occurrence of various types of ts mutants, with and without enrichment. A mutant that immediately stopped macromolecular synthesis and cell division upon being placed at the restrictive temperature was more resistant to BUdR/UV treatment than wild type by 1000-fold. Using the above techniques, BUdR-resistant mutants altered in the phosphorylation of thymidine have been isolated.
A NEUROSPORA MUTATION THAT ARRESTS PERITHECIAL DEVELOPMENT AS EITHER MALE OR FEMALE PARENT
Authors: Johnson Thomas E
Published: April 2021

A mutant of Neurospora crassa fails to produce perithecia when crossed as either the male (fertilizing) parent or the female (protoperithecial) parent. This mutant is unique in that it appears to be due to a single mutation that blocks sexual development when crossed as either parent. As either a male or female parent, the mutant, fmf-1, produces perithecia blocked at a diameter of 120 microns and containing no meiotic figures; normal perithecia are over 4.00 microns in diameter. The mutant maps to linkage group IL near arg-1. Forced heterokaryons have been made between fmf-1 and fmf-1  + nuclei. These heterokaryons are fertile when crossed, and fmf-1 can participate as either the male or female component; the mutation is thus heterokaryon recessive and nuclear nonautonomous. Homokaryotic fmf-1 conidia were purified from a mixed conidial population derived from such a heterokaryon; these conidia failed to function as the male parent, suggesting that the fmf-1  + gene product is not contained in the conidium. In mixed mating-type heterokaryons, formed using tol, fmf-1 participates in ascospore formation and triggers perithecial development. Moreover, to1 suppreses the action of fmf-1 if present in both components of a cross.——These data suggest that (1) fmf-1 acts in the perithecium at some time between fusion of the conidium with the trichogyne and the onset of meiosis; (2) the fmf-1 gene product is not contained in conidia; and (3) both mating types may enter the protoperithecium when a mixed mating-type heterokaryon is used as the male parent.
THE Ah LOCUS: BIOCHEMICAL BASIS FOR GENETIC DIFFERENCES IN BRAIN TUMOR FORMATION IN MICE
Authors: Levitt Roy C , Fysh Jacquelene M , Jensen Nancy M , Nebert Daniel W
Published: April 2021

Allelic differences at the Ah locus are shown to exist in the mouse brain. This finding probably explains inbred mouse strain differences in polycyclic hydrocarbon tumorigenesis of the brain described more than 35 years ago and may be important in understanding the etiology of genetic differences in certain human intracranial neoplasms.
SOME PROPERTIES OF SITE-SPECIFIC AND GENERAL RECOMBINATION INFERRED FROM INT-INITIATED EXCHANGES BY BACTERIOPHAGE LAMBDA
Authors: Echols Harrison , Green Linda
Published: April 2021

The site-specific recombination at the attachment site for prophage integration might proceed by two general mechanisms: (1) a concerted reaction with-out a free intermediate; (2) a sequential mechanism differing from typical general recombination only by an inability of the cross-strand intermediate structure to migrate into the region of nonhomology adjacent to the attachment site. The blocked-migration, sequential model predicts frequent genetic exchange in the int xis region near the attachment site if Int-mediated recombination occurs between λ phage with homologous attachment sites. We fiid such additional int xis exchanges, but only at very low frequency (1% of the Int-mediated recombination). We conclude that the resolution point only rarely moves away from the initial crossover point specified by Int and, therefore, that the Int reaction is mainly concerted. We interpret the rare additional int xis recombinants as indicative of occasional branch migration from an initial Int-mediated crossover. The frequency of the rare int xis recombinants is not simply related to distance from thp attachment site to an int  - or xis  - mutation, suggesting that the heteroduplex distance is often at least a gene in length. The frequency of these additional exchanges is also not a strong function of distance between two mutations; from this we conclude that the resolution to the observed recombinant structure in the sequential cases occurs often by mismatch repair. We have found no marked effect of mutations in the bacterial recA, recB, recC, recF, or recL genes on the frequency of the int xis recombinants; this may indicate that none of these genes specifies a product uniquely required for resolution of a cross-strand intermediate.
ESTIMATION OF GENETIC COVARIANCE FROM JOINT OFFSPRING-PARENT AND SIB-SIB STATISTICS
Authors: Gianola Daniel
Published: April 2021

Formulae for calculating the variances and covariances of estimates of genetic variance or covariance from offspring-parent and sib covariance data are presented. The model consists of a one-way classification of families with unequal numbers of offspring, where normally distributed traits x (a parental measure), y and z (offspring measures) are recorded. Procedures for pooling offspring-parent and sib covariance estimators are discussed. An application of the results to estimating genetic variance is presented, and the offspring-parent and sib covariance estimators and a pooled statistic are compared in terms of exact and asymptotic formulae. Implications for experimental design and allocation of experimental resources are also reported.
REARRANGEMENT OF THE BACTERIAL CHROMOSOME USING Tn10 AS A REGION OF HOMOLOGY
Authors: Chumley Forrest G , Roth John R
Published: April 2021

The transposable tetracycline resistance element, TnlO, can serve as a region of homology to promote rec-dependent deletion, duplication and directed transposition of bacterial genes. TnlO insertions in regions of the chromosome near the histidine operon (his) have been isolated and characterized in Salmonella typhimurium. When strains are constructed containing two TnlO insertions flanking the his operon in the same orientation (TniO-his-TnZO), recombination can occur between TnZO sequences resulting in the deletion of the intervening his region. The sites of the TnZO insertions determine the endpoints of the deletion. In crosses designed toconstruct strains carrying Tn10-his-TnZO, another class of unstable recombinants arises in which the his region exists in tandem duplication, with a TnlO insertion joining the duplicated copies (his-TnlO-his). The sites of the parental TnZO insertions mark the endpoints of the duplication. When a strain carrying TnIO-his-TnZO is used as a donor of his+ in conjugation or P22-mediated transduction, recombinants can arise in which the his region has been transposed to the site of any Tn1O insertion, far from the normal location of his in the recipient chromosome. In this manner, the his operon has been moved to the site of a pyrB::TdO insertion and has been placed on F' plasmids. At these new locations, the his+ character shows the rec-dependent deletion of his+ expected for a TnZO-his-TnlO duplication. These methods should be generally useful for the manipulatioo of bacterial genes.
A MUTANT OF E. COLI THAT RESTRICTS GROWTH OF BACTERIOPHAGE T4 AT ELEVATED TEMPERATURES
Authors: Jensen Jean L , Susman Millard
Published: April 2021

After nitrosoguanidine mutagenesis, a Phage Host Defective (phd) mutant of E. coli HfrH was isolated that supported the growth of T4D wild-type bacteriophage at 30",but not at 40"or higher. Eleven independent spontaneous mutants of T4 (go mutants) were isolated that overcame the growth restriction at high temperature. All of these mutants were located within three percent recombination of a gene 39 amber mutation in the clockwise direction on the standard map. In mixed infections, the representative go mutant chosen for further study seems to be recessive to its wild-type allele. Temperature-shift experiments suggested that the mutated host function involved in phage growth is a "late" function, beginning in mid-eclipse.—Electrophoresis of phage proteins labelled early and late in infection showed that under restrictive conditions early protein synthesis was normal, but that certain late proteins were absent. However, measurements ofDNA synthesis showed that under restrictive conditions the amount of phage DNA synthesized, and especially the amount of DNA sedimenting as high molecular weight replicative intermediate, was reduced. Pulse-chase experiments showed that the phage DNA made under restrictive conditions was not rapidly degraded.
THE POPULATION BIOLOGY OF BACTERIAL PLASMIDS: A PRIORI CONDITIONS FOR THE EXISTENCE OF MOBILIZABLE NONCONJUGATIVE FACTORS
Authors: Levin Bruce R , Stewart Frank M
Published: April 2021

A mathematical model for the population dynamics of nonconjugative plasmids that can be mobilized by conjugative factors is presented. In the analysis of the properties of this model, primary consideration is given to the conditions under which these nonself-transmissible extrachromosomal elements could become established and would be maintained in bacterial populations. The results of this analysis demonstrate the existence of conditions where, as a consequence of infectious transmission via mobilization, nonconjugative plasmids could become established and be maintained even when the bacteria carrying them have lower reproductive fitnesses than plasmid-free members of the population. However, these existence conditions are stringent and suggest, therefore, that it is highly unlikely that plasmids of this type would become established and maintained without some direct selection favoring their carriage. The general implications of these results and limitations of the model are discussed. Brief consideration is also given to the implications of these theoretical findings to the problems of the spread of multiple antibiotic resistance plasmids (R-factors) and the risk of contaminating natural populations of bacteria with chimeric plasmids produced by work with recombinant DNA.
MATING-TYPE FUNCTIONS FOR MEIOSIS AND SPORULATION IN YEAST ACT THROUGH CYTOPLASM
Authors: Klar Amar J S
Published: April 2021

Given a nutritional regime marked by a low nitrogen level and the absence of fermentable carbon sources, conventional a/α diploid cells of Saccharomyces cerevisiue exhibit a complex developmental sequence that includes a round of premeiotic DNA replication, commitment to meiosis and the elaboration of mature tetrads containing viable ascospores. Ordinarily, haploid cells and diploid cells af genotype a/a and α/α fail to display these reactions under comparable conditions. Here, we describe a simple technique for sporulation of α/α and a/a cells. Cells of genotype α/α are mated to haploid a cells carrying the karl (karyogamy defective) mutation to yield heterokaryons containing the corresponding diploid and haploid nuclei. The karl strains mate normally, but nuclei in the resultant zygotes do not fuse. When heterokaryotic cells are inoculated into sporulation media, they produce asci with six spores. Four spores carry genotypes derived from the diploid nucleus and the other two posses the markers originating from the haploid nucleus, i.e., the diploid nucleus divides meiotically while the haploid nucleus apparently divides mitotically. Similarly, the a/a genome is "helped" to sporulate as a consequence of mating with α karl strains. The results allow us to conclude that the mating-type functions essential for meiosis and sporulation are communicated and act through the cytoplasm and that sporulation can be dissociated from typical meiosis. This procedure will facilitate the genetic analysis of strains that are otherwise unable to sporulate.
THE CYTOGENETIC LOCALIZATION OF THE ALCOHOL DEHYDROGENASE-1 LOCUS IN MAIZE
Authors: Birchler James A
Published: April 2021

The alcohol dehydrogenase-I (Adh) locus in maize has been positioned relative to thirteen reciprocal translocations that have breakpoints in the long arm of chromosome I (1L). The methods of GOPINATH and BURNHAM (1956) to produce interstitial segmental trisomy with overlapping translocations and of RAKHA and ROBERTSON (1970) to produce compound B-A translocations were coupled with the co-dominant nature of the ADH isozymes to allow the cytological placement. The results of several crosses are consistent with Adh being in the region of 0.80-0.90 of 1L.—The duplication that results from the overlap of translocations 1-3 (5267) and 2-3 (5242) and that includes Adh was studied with respect to meiotic segregation and pollen transmission. When heterozygous with normal chromosomes, a low level of recombination within the duplicated regions is detectable and the duplication and normals are recovered with equal frequencies through the female. In the pollen, the hyperploid grains cannot compete equally with the euploids in achieving fertilization.—The use of co-dominant heteromultimeric isozymes as genetic markers for the development of a series of interstitial segmental trisomics in maize is discussed.
ANALYSIS OF SOME TWO-LOCUS SYSTEMS FOR TRAITS EXHIBITING CONTINUOUS VARIATION
Authors: Carmelli Dorit
Published: April 2021

Some generalized two-locus, major-gene models for traits exhibiting continuous expression are investigated. Conditions of gametic equilibria are stated as functions of the parameters characterizing the within phenotypic-genotypic distributions. Selection is stabilizing in favor of an optimum phenotype. It is established that an increase in the phenotypic variance facilitates stability of a central polymorphic state with tighter linkage. Also, with increased phenotypic variance in an additive two-locus selection model, a HARDY-WEINBERG type of equilibrium will be less central. The rate d convergence, in this case, is slowed down with an augmented environmental background.
STATISTICAL STUDIES ON PROTEIN POLYMORPHISM IN NATURAL POPULATIONS. III. DISTRIBUTION OF ALLELE FREQUENCIES AND THE NUMBER OF ALLELES PER LOCUS
Authors: Chakraborty Ranajit , Fuerst Paul A , Nei Masatoshi
Published: April 2021

With the aim of understanding the mechanism of maintenance of protein polymorphism, we have studied the properties of allele frequency distribution and the number of alleles per locus, using gene-frequency data from a wide range of organisms (mammals, birds, reptiles, amphibians, Drosophila and non-Drosophila invertebrates) in which 20 or more loci with at least 100 genes were sampled. The observed distribution of allele frequencies was U-shaped in all of the 138 populations (mostly species or subspecies) examined and generally agreed with the theoretical distribution expected under the mutation-drift hypothesis, though there was a significant excess of rare alleles (gene frequency, 0 ~ 0.05) in about a quarter of the populations. The agreement between the mutation-drift theory and observed data was quite satisfactory for the numbers of polymorphic (gene frequency, 0.05 ~ 0.95) and monomorphic (0.95 ~ 1.O) alleles.—The observed pattern of allele-frequency distribution was incompatible with the prediction from the overdominance hypothesis. The observed correlations of the numbers of rare alleles, polymorphic alleles and monomorphic alleles with heterozygosity were of the order of magnitude that was expected under the mutation-drift hypothesis. Our results did not support the view that intracistronic recombination is an important source of genetic variation. The total number of alleles per locus was positively correlated with molecular weight in most of the species examined, and the magnitude of the correlation was consistent with the theoretical prediction from mutation-drift hypothesis. The correlation between molecular weight and the number of alleles was generally higher than the correlation between molecular weight and heterozygosity, as expected.
SELECTION-MIGRATION REGIMES CHARACTERIZED BY A GLOBALLY STABLE EQUILIBRIUM
Authors: Karlin Samuel , Campbell R B
Published: April 2021

The principle that a subdivided population subject to overdominance viability selection in each habitat will manifest a unique, globally attractng polymorphic equilibrium is posited. This follows as a corollary to the stronger principle that, if haploid selection or submultiplicative diploid selection (definition: the geometric mean of the homozygote viabilities is less than or equal to the heterozygote viability) is operating in each habitat,there is a unique, globally attracting stable equilibrium that may be monomorphic or polymorphic. These principles are proven for a broad spectrum of migration patterns. In all such migration selection systems, multiple fixation states cannot be simultaneously stable under submultiplicative viability regimes. Contrasting examples where sub-multiplicative viabilities are not in force are given.
GENES AFFECTING THE EXPRESSION OF CYTOCHROME c IN YEAST: GENETIC MAPPING AND GENETIC INTERACTIONS
Authors: Rothstein Rodney J , Sherman Fred
Published: April 2021

The four mutant genes, cyc2, cyc3, cycl and cyc9, that affect the levels of the two iso-cytochromes c in the yeast Saccharomyces cerevisiae have been characterized and mapped. Both cyc2 and cyc3 lower the amount of iso-l-cytochrome c and iso-2-cytochrome c; whereas, cyc8 and cyc9 increase the amount of iso-2-cytochrome c. The cyc2, cyc3, cyc8 and cyc9 genes are located, respectively, on chromosomes XV, I, II and III, and are, therefore, unlinked to each other and unlinked to CYCI, the structural gene of iso-I-cytochrome c and to CYC7, the structural gene of iso-2-cytochrome c. While some cyc3 mutants are completely or almost completely deficient in cyotchromes c, none of the cyc2 mutants contained less than 10% of parental level of cytochrome c even though over one-half of the mutants contain UAA or UAG nonsense mutations. Thus, it appears as if a complete block of the cyc2 gene product still allows the formation of a residual fraction of cytochrome c. The cyc2 and cyc3 mutant genes cause deficiencies even i n the presence of CYC7, cyc8 and cycY, which normally cause overproduction of iso-2-cytochrome c. We suggest that cyc2 and cyc3 may be involved with the regulation or maturation of the iso-cytochromes c. In addition to having high levels of iso-2-cytochromes c, the cyc8 and cyc9 mutants are associated with flocculent cells and other abnormal phenotypes. The cyc9 mutant was shown to be allelic with the tup1 mutant and to share its properties, which include the ability to utilize exogenous dTMP, a characteristic flocculent morphology, the lack of sporulation of homozygous diploids and low frequency of mating and abnormally shaped cells Df a strains. The diverse abnormalities suggest that cyc8 and cyc9 are not simple regulatory mutants controlling iso-2-cytochrome C.
PLEIOTROPIC MUTATIONS AT THE TUP1 LOCUS THAT AFFECT THE EXPRESSION OF MATING-TYPE-DEPENDENT FUNCTIONS IN SACCHAROMYCES CEREVISIAE
Authors: Lemontt Jeffrey F , Fugit Donna R , Mackay Vivian L
Published: April 2021

The umr7-1 mutation, previously identified in a set of mutants that had been selected for defective UV-induced mutagenesis at CAN1, affects other cellular functions, including many of those regulated by the mating-type locus (MAT) in heterothallic Saccharomyces cereuisiae. The recessive umr7-1 allele, mapping approximately 20 cM distal to thr4 on chromosome III, causes clumpy growth in both a and α cells and has no apparent effect on a mating functions. However, α umr7 meiotic segregants fail to express several α-specific functions (e.g., high-frequency conjugation with a strains, secretion of the hormone α-factor and response to the hormone a-factor). In addition, α umr7 cells exhibit some a-specific characteristics, such as the barrier phenotype (Bar+) that prevents diffusion of α-factor and an increased mating frequency with α strains. The most striking property of α umr7 strains is their altered morphology, in which mitotic cells develop an asymmetric pear shape, like that of normal a cells induced to form "shmoos" by interaction with α-factor. Some a/α-specific diploid functions are also affected by umr7; instead ofpolar budding patterns, a/α umr7/umr7 diploids have medial budding like a/a,α/α and haploid strains. Moreover, a/α umr7/umr7 diploids have lost the ability to sporulate and are Bar+ like a or a/a strains. Revertant studies indicate that umr7-1 is a single point mutation. The umr7 mutant fails to complement mutants of both tup1 (selected for deoxythymidine monophosphate utilization) and cyc9 (selected for high iso-2-cytochrome c levels), and all three isolates have similar genetic and phenotypic properties. It is suggested that the product of this gene plays some common central role in the complex regulation of the expression of both MAT-dependent and MAT-independent functions.
CYTOGENETICS OF DISOMICS, MONOTELO- AND MONOISODISOMICS AND ml1 st1 MUTANTS OF CHROMOSOME 4 OF COTTON
Authors: Endrizzi J E , Bray R
Published: April 2021

The linkage relationships and arm locations of the ml1 and st1 mutants of cotton were determined with the use of monotelodisomics, a monoisodisomic and disomics. The ml1, st1 mutants are more than 50 cM apart on chromosome 4. The ml1 locus is in the short arm and 16 cM from the centromere, and st1 is in the long arm and 48 or more CM from the centromere. Recombination in the monoisodisomic was twice the expected value and higher, but not significantly, than in its monotelodisomic counterpart. It was concluded that the increase indicates a greater frequency of proximal exchange in the mono-isodisomic than in the monotelodisomic.
SERIAL-SECTION ANALYSIS OF CLUSTERING WITHIN ANTHERS OF MAIZE MICROSPOROCYTES WITH SPECIFIC CROSSOVERS
Authors: Maguire Majorie P
Published: April 2021

The distribution within anthers of maize plants of microsporocytes of differing crossover class was studied by application of the serial-sectioning technique to plants heterozygous for a paracentric inversion. In such material, cells with four-strand double crossovers within the inversion are distinguishable from cells with other classes of crossovers within the inverted region and from cells with no crossovers within the inversion. Evidence was found for coarse clustering of cells with four-strand double crossovers within the inversion and for coarse clustering of cells of other crossover classes (with at least one crossover within the inversion). The local frequencies of these two major categories of crossover cells appeared to vary independently of each other, with regional increases in each occurring at the expense of noncrossover cells. There is also some suggestion that cells with four-straqd doubles within the inversion may he clustered independently of other double-crossover classes within the inversion, but these other classes are not directly scorable.
RATE OF GENE SILENCING AT DUPLICATE LOCI: A THEORETICAL STUDY AND INTERPRETATION OF DATA FROM TETRAPLOID FISHES
Authors: Li Wen-Hsiung
Published: April 2021

A large-scale simulation has been conducted on the rate of gene loss at duplicate loci under irreversible mutation. It is found that tight linkage does not provide a strong sheltering effect, as thought by previous authors; indeed, the mean loss time for the case of tight linkage is of the same order of magnitude as that for no linkage, as long as Nu is not much larger than 1, where N is the effective population size and u the mutation rate. When Nu is 0.01 or less, the two loci behave almost as neutral loci, regardless of linkage, and the mean loss time is about only half the mean extinction time for a neutral allele under irreversible mutation. However, the former becomes two or more times larger than the latter when Nu ≥ 1.—In the simulation, the sojourn times in the frequency intervals (0, 001) and (0.99, 1) and the time for the frequency of the null allele to reach 0.99 at one of the two loci have also been recorded. The results show that the populatian is monomorphic for the normal allele most of the time if Nu ≤ 0.01, but polymorphic for the null and the normal alleles most of the time if Nu ≥ 0.1.—The distribution of the frequency of the null allele in an equilibrium tetraploid population has been studied analytically. The present results have been applied to interpret data from some fish groups that are of tetraploid origin, and a model for explaining the slow rate of gene loss in these fishes is proposed.
AN ANTISUPPRESSOR THAT ACTS ON OMNIPOTENT SUPPRESSORS IN YEAST
Authors: Liebman Susan W , Cavenagh Margaret
Published: April 2021

Six partially dominant antisuppressors were obtained that reduce the efficiency of two omnipotent yeast suppressors, sup45 and sup35, thought to be ribosomal ambiguity mutations. Each of these six antisuppressors was shown to fall within a single Mendelian locus, named asu9. The mu9 mutations are specific for omnipotent suppressors; they have no effect on several dominant tRNA-like suppressors. In the absence of suppressors, mu9 causes sensitivity to the aminoglycoside antibiotic, paromomycin. The properties of mu9 are consistent with the hypothesis that mu9 alters yeast ribosomal proteins.
CYTOGENETIC ANALYSIS OF THE CHROMOSOMAL REGION IMMEDIATELY ADJACENT TO THE ROSY LOCUS IN DROSOPHILA MELANOGASTER
Authors: Hilliker Arthur J , Clark Stephen H , Chovnick Arthur , Gelbart William M
Published: April 2021

This report describes the genetic analysis of a region of the third chromosome of Drosophila melanogaster extending from 87D2-4 to 87E12-F1, an interval of 23 or 24 polytene chromosome bands. This region includes the rosy (ry, 3-52.0) locus, carrying the structural information for xanthine dehydrogenase (XDH). We have, in recent years, focused attention on the genetic regulation of the rosy locus and, therefore, wished to ascertain in detail the immediate genetic environmcnt of this locus. Specifically, we question if rosy is a solitary genetic unit or part of a larger complex genetic unit encompassing adjacent genes. Our data also provide opportunity to examine further the relationship between euchromatic gene distrihution and polytene chromosome structure.—The results of our genetic dissection of the rosy microregion substantiate the conclusion drawn earlier (SCHALET, KERNAGHAN and CHOVNICK 1964) that the rosy locus is the only gene in this region concerned with XDH activity and that all adjacent genetic units are functionally, as well as spatially, distinct Erom the rosy gene. Within the rosy micro-region, we observed a close correspondence between the number of complementation groups (21) and the number of polytene chromosome bands (23 or 24). Consideration of this latter observation in conjunction with those of similar studies of other chhromosomal regions supports the hypothesis that each polytene chromosome band corresponds to a single genetic unit.
THE SELECTION OF S. CEREVISIAE MUTANTS DEFECTIVE IN THE START EVENT OF CELL DIVISION
Authors: Reed Steven I
Published: April 2021

Thirty-three temperature-sensitive mutations defective in the start event of the cell division cycle of Saccharomyces cereuisiae were isolated and subjected to preliminary characterization. Complementation studies assigned these mutations to four complementation groups, one of which, cdc28, has been described previously. Genetic analysis revealed that these complementation groups define single nuclear genes, unlinked to one another. One of the three newly identified genes, cdc37, has been located in the yeast linkage map on chromosome IV, two meiotic map units distal to hom2.—Each mutation produces stage-specific arrest of cell division at start, the same point where mating pheromone interrupts division. After synchronization at start by incubation at the restrictive temperature, the mutants retain the capacity to enlarge and to conjugate.
ANALYSIS OF THE AUTOSOMAL MUTATION abo AND ITS INTERACTION WITH THE RIBOSOMAL DNA OF DROSOPHILA MELANOGASTER: THE ROLE OF X-CHROMOSOME HETEROCHROMATIN
Authors: Yedvobnick Barry , Krider Hallie M , Levine Bryan I
Published: April 2021

The autosomal recessive, maternal-effect mutation abnormal oocyte (abo: 2-38) preferentially lowers the viability of XO progeny. The severity of the sex-ratio distortion is reduced by duplications of maternal or zygotic heterochromatin chromatin (SANDLER 1970, 1977; PARRY and SANDLER 1974). Utilizing X-chromosome inversions that contain modifications in the quantity and arrangement of the heterochromatic functions, Xhabo and cr  +, we have extended our investigations of nbo's influence on XO male recovery and rDNA redundancy (KRIDER,YEDVOBNICK and LEVINE 1979).——XO males bearing In(1)scs1Lsc4R or In(1)wm4Lsc4R are recovered twice as frequently as X chromosomes containing a single Xh region, implying that these inversions possess a duplication of Xhabo. abo mutant females heterozygous for In(1)scs1Lsc4R and wild-type X chromosomes generate XO progeny that do not contain elevated rDNA redundancies. XO males containing In(1)wm4 exhibit male recoveries and rDNA elevations similar to those of males bearing a wild-type X chromosome, when both derive from a common abo/abo mother. Reciprocal crosses between In(1)wm4 and Canton-S males to attached-X abo females show significant, though reduced, sex ratios in the absence of an rDNA effect. The observation that abo can elevate the rDNA redundancy of In(1)wm4, a chromosome that does not compensate, suggests that abo and cr+ functions are not directly related.
EVIDENCE FOR A COMPLEX CLASS OF NONADENYLATED mRNA IN DROSOPHILA
Authors: Zimmerman J Lynn , Fouts David L , Manning Jerry E
Published: April 2021

The amount, by mass, of poly(A+) mRNA present in the polyribosomes of third-instar larvae of Drosophila melanogaster, and the relative contribution of the poly(A+) mRNA to the sequence complexity of total polysomal RNA, has been determined, Selective removal of poly(A+) mRNA from total polysoma1 RNA by use of either oligo-dT-cellulose, or poly (U)-sepharose affinity chromatography, revealed that only 0.15% of the mass of the polysomal RNA was present as poly(A+) mRNA. The present study shows that this RNA hybridized at saturation with 3.3% of the single-copy DNA in the Drosophila genome. After correction for asymmetric transcription and reactability of the DNA, 7.4% of the single-copy DNA in the Drosophila genome is represented in larval poly(A+) mRNA. This corresponds to 6.73 × 1O6 nucleotides of mRNA coding sequences, or approximately 5,384 diverse RNA sequences of average size 1,250 nucleotides. However, total polysomal RNA hybridizes at saturation to 10.9% of the single-copy DNA sequences. After correcting this value for asymmetric transcripti0n and tracer DNA reactability, 24% of the single-copy DNA in Drosophila is represented in total polysomal RNA. This corresponds to 2.18 × 107 nucleotides of RNA coding sequences or 17,440 diverse RNA molecules of size 1,250 nucleotides. This value is 3.2 times greater than that observed for poly(A+) mRNA, and indicates that ≃69% of the polysomal RNA sequence complexity is contributed by n0nadenylated RNA. Furthermore, if the number of different structural genes represented in total polysomal RNA is ≃1.7 × 104, then the number of genes expressed in thirdinstar larvae exceeds the number of chromomeres in Drosophila by about a factor of three. This numerology indicates that the number of chromomeres observed in polytene chromosomes does not reflect the number of structural gene sequences in the Drosophila genome.
A MODIFIED MODEL OF SEGREGATION DISTORTION IN DROSOPHILA MELANOGASTER
Authors: Hiraizumi Yuichiro , Martin Diana W , Eckstrand Irene A
Published: April 2021

Elements of the Segregation Distorter (SD) system of Drosophila melanogaster, Sd and Rsp, were analyzed and the following points were established: (1) The model of multiple alleles at the Rsp  s locus proposed by MARTIN and HIRAIZUMI (1979) is supported by our observations. (2) A modifier of SD, tentatively symbolized M(SD), was found close to cn (2R-57.5). (3) Sd heterozygous males were found to show, under certain genotypic condition, almost complete sterility.——Based upon these observations, the following modified model of segregation distortion is proposed: (1) The M(SD) locus produces a multimeric repressor protein that binds to the Rsp locus as a necessary condition for normal spermiogenesis. M(SD) homozygotes produce a repressor M(SD)/M(SD); whereas, a homozygote for its normal allele M+(SD) produces a M+(SD)/M+(SD) repressor. M(SD)/M+(SD) heterzygotes produce a M(SD)/M+(SD) repressor. (2) The Sd locus produces a certain product that, like an inducer in the lactose system of E. coli, tends to bind with the repressor complexed with the Rsp locus. This binding disrupts the repressor-Rsp complex, causing Rsp locus to be turned on. The product of Rsp transcription, in turn, results in sperm dysfunction. (3) Rsp  i, an allele of Rsp, has a strong complexing affinity with the repressor such that the Rsp  i-repressor complex is "resistant" to the inducing activity of Sd product. Rsp  s, on the other hand, has a weaker complexing affinity than that of Rsp  i, and the degree of affinity varies among different Rsp  s alleles.——A possible extension of the above model is discussed.
THE INFLUENCE OF SEXUAL AND LARVAL SELECTION ON THE MAINTENANCE OF POLYMORPHISM AT THE SEPIA LOCUS IN DROSOPHILA MELANOGASTER
Authors: Anxolabehere D
Published: April 2021

Sexual selection is measured between two strains of Drosophila melanogaster: a wild strain and a strain mutant at the sepia locus. Frequencydependent male mating was found to be successful, whereas the female genotype exerted no influence. The rarer the male genotype becomes, the greater is its mating success. A selection model is built for this behavior characteristic in which selection operates differently in the two sexes. The genetic consequencies of this model upon the maintenance of genetic polymorphism at the sepia locus are compared to experimental data from previous population cage studies. The fit obtained with this sexual selection model is compared to that of the larval selection model previously investigated. A model composed of both sexual and larval components of fitness is presented. The role that each major selection component is expected to play in experimental populations as the gene frequency changes is discussed. Sexual selection leads to an equilibrium level higher than larval selection, and the combined model is very close to the experimental values.
THE DISTRIBUTION OF INDIVIDUAL HETEROZYGOSITY IN NATURAL POPULATIONS
Authors: Mitton Jeffry B , Pierce Benjamin A
Published: April 2021

Estimation of the distribution of the level of individual heterozygosity within natural populations is explored with both Monte-Carlo simulation studies and data from natural populations. Simulations indicate that heterozygosities estimated from as few as a dozen randomly chosen loci may, to some degree, reflect (r = 0.35) heterozygosity determined by 100 independent loci. The shape of the expected distribution of heterozygosity is heavily dependent upon levels of heterozygosity at the loci. Complete genetic data for 12 loci from 997 Fundulus heteroclitus are used to describe the distributions of heterozygosity for different localities, for age classes and for sexes. The distributions deviate from normality. Distributions from different localities are not different, but the distributions are heterogeneous among age classes at one of two localities and are heterogeneous between the sexes.