bluuebunny/crossref_metadata_2025 huggingface dataset:
EFFECTS OF THE RAD52 GENE ON RECOMBINATION IN SACCHAROMYCES CEREVISIAE
Authors: Prakash Satya , Prakash Louise , Burke William , Montelone Beth A
Published: April 2021

Effects of the rad52 mutation in Saccharomyces cerevisiae on meiotic, γ-ray-induced, UV-induced and spontaneous mitotic recombination were studied. The rad52/rad52 diploids undergo premeiotic DNAsynthesis; sporulation occurs hut inviable spores are produced. Both intra and intergenic recombination during meiosis were examined in cells transferred from sporulation medium to vegetative medium at different time intervals. No intragenic recombination was observed at the hisl-ljhis1-315 and trp5-2/trp5-48 hetero-alleles. Gene-centromere recombination also was not observed in rad52/rad52 diploids. No γ-ray- or UV-induced intragenic mitotic recombination is seen in rad52/rad52 diploids. The rate of spontaneous mitotic recombination is lowered five-fold at the hisf -1/hisf-315 and leu1-c/leu1-12 heteroalleles. Spontaneous reversion rates of both hisf-1 and hisf-315 were elevated 10to 20 fold in rad52/rad52 diploids.—The RAD52 gene function is required for spontaneous mitotic recombination, UV- and γ-ray-induced mitotic recombination and meiotic recombination.
SEX AND THE SINGLE CELL. I. ON THE ACTION OF MAJOR LOCI AFFECTING SEX DETERMINATION IN DROSOPHILA MELANOGASTER
Authors: Baker Bruce S , Ridge Kimberly A
Published: April 2021

Sex determination in Drosophila melanogaster is under the control of the X chrom0some:autosome ratio and at least four major regulatory genes: transformer (tra), transformer-2 (tra-2), doublesex (dsx) and intersex (ix) . Attention is focused here on the roles of these four loci in sex determination. By examining the sexual phenotype of clones of homozygous mutant cells produced by mitotic recombination in flies heterozygous for a given recessive sex-determination mutant, we have shown that the tra, tra-2 and dsx loci determine sex in a cell-autonomous manner. The effect of removing the wild-type allele of each locus (by mitotic recombination) at a number of times during development has been used to determine when the wild-type alleles of the tra, tra-2 and dsx loci have been transcribed sufficiently to support normal sexual development. The wild-type alleles of all three loci are needed into the early pupal period for normal sex determination in the cells that produce the sexually dimorphic (in pigmentation) cuticle of the fifth and sixth dorsal abdominal segments. tra+ and tra-2+ cease being needed shortly before the termination of cell division in the abdomen, whereas dsx+ is required at least until the end of division. By contrast, in the foreleg, the wild-type alleles of tra+ and tra-2  + have functioned sufficiently for normal sexual differentiation to occur by about 24 to 48 hours before pupariation, but dsx+ is required in the foreleg at least until pupariation—A comparison of the phenotypes produced in mutant/deficiency and homozygous mutant-bearing flies shows that dsx, tra-2 and tra mutants result jn a loss of wild-type function and probably represent null alleles at these genes.—All passible homozygous doublemutant combinations of ix, tra-2 and dsx have been constructed and reveal a clear pattern of epistasis: dsx > tra, tra-2 > ix. We conclude that these genes function in a single pathway that determines sex. The data suggest that these mutants are major regulatory loci that control the batteries of genes necessary for the development of many, and perhaps all, secondary sexual characteristics.—The striking similarities between the properties of these loci and those of the homeotic loci that determine segmental and subsegmental specialization during development suggest that the basic mechanisms of regulation are the same in the two situations. The phenotypes and interactions of these sex-determination mutants provide the basis for the model of how the wild-type alleles of these loci act together to effect normal sex determination. Implications of these observations for the function of other homeotic loci are discussed.
EXPERIMENTAL AND THEORETICAL ANALYSIS OF THE "SEX-RATIO" POLYMORPHISM IN DROSOPHILA PSEUDOOBSCURA
Authors: Curtsinger James W , Feldman Marcus W
Published: April 2021

The Sex-ratio chromosome (SR) is a widespread, multiply inverted rearrangement of the X chromosome present in several species of Drosophila. Male carriers transmit mostly X-bearing sperm. In the absence ofstrong counteracting selection, SR is expected to increase rapidly to fixation, causing extinction. The present study incorporates a selection-components analysis of SR in laboratory populations, using the closely linked Esterase-5 locus as a marker. Estimated fitnesses show directional viability selection against SR in both males and females, heterosis for fertility and no significant effects on virility, the male adult component of fitness. Estimated fitnesses satisfy conditions for protected polymorphism and accurately predict gene-frequency trajectories in experimental populations. A model of SR gene-frequency evolution is developed, which incorporates sex-linkage, meiotic drive, viability, fertility and virility selecton. We show that conditions for protected polymorphisms are not unduly restrictive and that differential fitness among males is not sufficient for protected polymorphism, irrespective of the degree ofmeiotic drive.
STRUCTURAL ANALYSIS OF THE dur LOCI IN S. CEREVISIAE: TWO DOMAINS OF A SINGLE MULTIFUNCTIONAL GENE
Authors: Cooper Terrance G , Lam Christine , Turoscy Vanessa
Published: April 2021

In Saccharomyces cerevisiae, the degradation of urea to carbon dioxide and ammonia is catalyzed byurea carboxylase and albphanate hydrolase. The loci coding for these enzymes (dur1 and dur2) are very tightly linked an the right arm of chromosome II between pet11 and met8. Pleiotropic mutations that fail to complement mutations in either of the dur loci were found to be predominantly located in or near the dur2 locus. We interpret these data as suggesting that the two dur loci might in reality be domains of a single gene that codes fora multifunctional polypeptide. In view OIthis conclusion, we have renamed the dur loci as the durl,2 locus.
PREFERENTIAL OCCURRENCE OF NONSISTER SPORES IN TWO-SPORED ASCI OF SACCHAROMYCES CEREVISIAE: EVIDENCE FOR REGULATION OF SPORE-WALL FORMATION BY THE SPINDLE POLE BODY
Authors: Davidow Lance S , Goetsch Loretta , Byers Breck
Published: April 2021

Yeast cells subjected to a reversible thermal arrest of meiosis yielded progressively fewer spores per ascus as the arrest was extended. Dissection of two-spored asci by a newly developed method that prevents selection of false asci revealed that the spores were not a random sample of the haploid meiotic products. Most, if not all, pairs of spores contain nonsister products of the reductional division. Electron microscopic examination of the meiotic cells revealed the cytological basis for this bias. All four spindle pole bodies (SPBs) present at the second meiotic division normally gain a structural modification (the outer plaque) upon which the initiation of the prospore wall occurs. In the formation of a two-spored ascus, only one spindle pole body on each meiosis I1 spindle was so modified. These observations suggest that the morphogenesis of spcires is regulated at meiosis 11 by limiting the number of SPBs gaining the outer plaque. The enhancement of spore yield upon addition of fresh medium suggests that this morphogenetic regulation responds more directly to nutrient deprivation arising during the thermal arrest, rather than to elevated temperature per se.
CHROMOSOMAL SITES NECESSARY FOR NORMAL LEVELS OF MEIOTIC RECOMBINATION IN DROSOPHILA MELANOGASTER. I. EVIDENCE FOR AND MAPPING OF THE SITES
Authors: Hawley R Scott
Published: April 2021

Meiotic exchange was measured in females heterozygous for a normal sequence X chromosome and for each of eleven T(1;4)s and each of sixteen T(1;Y)s. The results indicate that the X chromosome can be divided into five intervals, such that heterozygosity for a breakFoint in one interval strongly suppresses exchange within that interval, but has little or no effect on exchange in other intervals. The boundaries between these intervals are identified and mapped to regions 3C4-6/7, 7A-7E, 11Aand proximal to 18Con the standard salivary map; each boundary is located at (or within a small region containing) a major constriction (i.e., a block of intercalary heterochromatin) .αExchange was examined in females heterozygous for translocations broken within the constriction at IIA.The results imply that a boundary occupies only a subregion of the entire constriction and issubdivisible by translocation breakpoints. Several other properties of boundaries have been elucidated. Finally, the relationship of these data to a simple model of meiotic pairing proposed by I. SANDLER(1956)and to the role of intercalary heterochromatin in the meiotic process is discussed.
GENETIC ANALYSIS OF AUDIOGENIC SEIZURE SUSCEPTIBILITY IN C57BL/6J x DBA/2J RECOMBINANT INBRED STRAINS OF MICE
Authors: Seyfried Thomas N , Yu Robert K , Glaser Gilbert H
Published: April 2021

The inheritance of susceptibility to audiogenic seizures (ASS) was studied in the C57BW6J (B6) and DBA/2j (D2) progenitor strains, their reciprocal F1 hybrids, backcross generations and in 21 B6 × D2 recombinant inbred (RI) strams of mice at 21 days of age. All of the D2 mice tested experienced ASS, whereas none of the B6 mice responded to the sound. Although 23% of the F1 mice experienced wild running, they were generally as resistant to ASS as their B6 parents. Mice of the F1 × B6 backcross generation were also resistant to ASS. In the F1 × D2 backcross generation, however, a significant pre-ponderance (72%) of AS-susceptible mice was found. No significant association was observed between any of the four coat-color phenotypes that were segregating in this generation and susceptibility to ASS. A continuous distribution of mean seizure severity scores and several new audiogenic response phenotypes, distinctly different from the phenotypes of either progenitor strain, were found among the 21 RI strains. These and the results from the F1 × D2 backcross generation suggest that the difference in AS susceptibility between 21-day-old B6 and D2 mice cannot be under the control of a single locus. In addition, no association was found between AS susceptibility and the chromosome 4 markers Lyb-2, Mup-1 and b among the 21 RI strains. An association was observed, however, between AS susceptibility and the Ah locus. Several of the RI strains that were AS resistant at 21 days of age became AS susceptible as adults. One RI strain was susceptible to ASS at both young and adult ages. The B6, D2 and F, mice were completely resistant to ASS at adult ages. Genetic differences were found among the RI strains for the incidence, onset, duration, and type of severity of ASS. A remarkable amount of phenotypic variability in the audiogenic response, which can be attributed only to the influence of environmental factors, occurred within several of the RI strains. A multiple-factor mode of inheritance involving a physiological threshold can account for our observations.
THE THEORY OF SPECIATION VIA THE FOUNDER PRINCIPLE
Authors: Templeton Alan R
Published: April 2021

The founder principle has been used to explain many instances of rapid speciation. Advances from theoretical population genetics are incorporated into MAYR'S original founder-effect genetic-revolution model to yield a newer model called the genetic transilience. The basic theoretical edifice lies upon the fact that founder event can sometimes lead to an accumulation of inbreeding and an induction of gametic disequilibrium. This, in turn, causes alleles to be selected more for their homozygous fitness effects and for their effects on a more stable genetic background. Selection occurring in multi-locus systems controlling integrated developmental, physiological, behavioral, etc., traits is particularly sensitive to these founder effects. If sufficient genetic variability exists in the founder population, such multilocus genetic systems can respond to drift and the altered selective forces by undergoing a rapid shift to a new adaptive peak known as the genetic transilience. A genetic transilience is, therefore, most likely to occur when the founder event causes a rapid accumulation of inbreeding without a severe reduction in genetic variability. The implications of this model are then examined for three aspects of the founder-effect genetic-transilience model: the attributes of the ancestral population, the nature of the sampling process used t o generate the founders and the attributes of the founder population. The model is used to explain several features of the evolution of the Hawaiian Drosophila, and experimental designs are outlined to test the major predictions of the theory. Hence, this theory of speciation can be tested in the laboratory, using systems and techniques that already exist—a rare attribute of most models of speciation.
ALCOHOL DEHYDROGENASE IN THE DIPLOID PLANT STEPHANOMERIA EXIGUA (COMPOSITAE): GENE DUPLICATION, MODE OF INHERITANCE AND LINKAGE
Authors: Roose M L , Gottlieb L D
Published: April 2021

Study of the biochemical genetics of alcohol dehydrogenase (ADH) in the annual plant Stephanameria exigua (Compositae) revealed that the isozymes are specified by a small family of tightly linked structural genes. One set of ADH isozymes (ADH-1) was induced in roots by flooding, and was also expressed in thickened unflooded tap roots, stems, ovaries and seeds. As in other plants, the enzymes are dimeric and form homo- and heterodimers. An electrophoretic survey of ADH-1 phenotypes in two natural populations revealed seven different ADH-1 homodimers in various phenotypes having one to eight enzyme bands. Genetic anaIysis of segregations from crosses involving 59 plants showed that the ADH-1 isozymes are inherited as a single Mendelian unit, Adhl. Adhl is polymorphic for forms that specify one, two, or three different ADH-1 subunits (which combine to form homo- and heterodimers), and are expressed co-dominantly in all genotypic combinations. Staining intensity of enzymes extracted from various homozygous and heterozygous plants indicated that the different subunit types specified by Adhl are produced in approximately equal amounts. These observations suggest that Adhl is a compound locus consisting of one to several tightly linked (0 recombinants among 579 testcross progeny), coordinately expressed structural genes. The genes in the two triplications also occur in various duplicate complexes and thus could have originated via unequal crossing over. The ADH-2 isozyme found in pollen and seeds is apparently specified by a different gene, Adh2. Adhl and Adh2 are tightly linked (0 recombinants among 81 testcross progeny).
ALLOZYME FREQUENCY CHANGES ASSOCIATED WITH SELECTION FOR INCREASED GRAIN YIELD IN MAIZE (ZEA MAYS L.)
Authors: Stuber C W , Moll R H , Goodman M M , Schaffer H E , Weir B S
Published: April 2021

Frequency changes of alleles at eight enzyme loci were monitored in four long-term maize selection experiments. The results indicate that changes in frequencies of the alleles at these loci are associated with changes due to selection for improved grain yield. The frequencies changed more than is consistent with the hyFothesis of selective neutrality. In addition, significant deviations from a random-drift model were nearly always accompanied by significant linear tiends as would result ii allozyme frequencies respond to directional selection. Evaluations of linkages aiid linkage disequilibria in the selected populations indicate that the eight enzyme loci responded independently as selection progressed.
INTERCONVERSION OF YEAST CELL TYPES BY TRANSPOSABLE GENES
Authors: Klar Amar J S
Published: April 2021

The a and α cell types of budding yeast Saccharomyces cerevisiae are controlled by alternate alleles of the mating-type locus (MAT), MATa and MATα. The cell types can be interconverted by switching alleles of MAT. The loci HMRa and HMLα, which are loosely linked to MAT, are involved in mating-type switching. Experimental evidence for their role in MAT interconversion is presented. As a result of switching, the homothallic and heterothallic strains containing the amber and ochre mutations within the HMRa locus yield corresponding amber and ochre mutant mata loci. Similarly, the hmlα mutant strain generates mata mutant alleles. That is, specific mutations from HMRa and HMLα are transmitted to MAT. A replica of the mating-type coding information originating from these loci is transposed to MAT, where it replaces the existing information. Furthermore, "Hawthorne deletions" in strains containing hmra-ambe/ochre result in production of mata-ambedochre alleles, Therefore, genetic information for MATa resides at HMRa. The switches occur in a defined set of clonally related cells. Thus, the efficient interconversion of yeast cell types is mediated by an unidirectional transfer of genetic information between nonallelic sites in a nonrandom and programmed fashion. The results are inconsistent with the "flipflop" models, but satisfy a key prediction of the general controlling element and the specific cassette models proposed for mating-type interchange.
THE GENETICS OF DROSOPHILA SUBOBSCURA POPULATIONS. XIV. FURTHER DATA ON LINKAGE DISEQUILIBRIA
Authors: Loukas M , Krimbas C B , Morgan K
Published: April 2021

Data coming from one natural population of D. subobscura, that of Crete, are presented in detail and examined for nonrandom associations of genes and gene arrangements. This population and four others previously studied are reanalyzed for the detection of higher than first-order interactions. Only firstorder interactions are important and statistically significant, especially those concerning genes and inversions in which these genes are included. The paucity of linkage disequilibria detected is remarkable, and we argue that it does not depend on the methods of study, rather it is genuine. We further argue that most of the disequilibria detected are probably due to mechanisms based on epistatic selection.
DEVELOPMENTAL STABILITY OF DROSOPHILA MELANOGASTER UNDER ARTIFICIAL AND NATURAL SELECTION IN CONSTANT AND FLUCTUATING ENVIRONMENTS
Authors: Bradley Brian P
Published: April 2021

Populations of Drosophila melanogaster in constant 25λ and fluctuating 20/29λ environments showed increases in developmental stability, indicated by decreases in bilateral asymmetry of sterno-pleural chaeta number. In both environments, rates of decrease in asymmetry were greater under natural selection (control lines) than under artificial stabilizing selection. Overall mean asymmetry was greater in the fluctuating environment.—There was no evidence that decreased asymmetry was due to heterozygosity, and the decline in asymmetry was not explained by the decline in chaeta number in the lines under only natural selection. However, the decline was consistent with changes in total phenotypic variance and environmental variance.— The divergence between lines after 39 generations of selection was seen in differences in asymmetry and also in the genotype-environment interaction expressed in cross-culturing experiments.
ASSEMBLY OF THE MITOCHONDRIAL MEMBRANE SYSTEM: NUCLEAR SUPPRESSION OF A CYTOCHROME b MUTATION IN YEAST MITOCHONDRIAL DNA
Authors: Coruzzi Gloria , Tzagoloff Alexander
Published: April 2021

In a previous study, a mitochondrial mutant expressing a specific enzymatic deficiency in co-enzyme QH2-cytochrome c reductase was described (Tzagoloff, Foury and Akai 1976). Analysis of the mitochondrially translated proteins revealed the absence in the mutant of the mitochondrial product corresponding to cytochrome b and the presence of a new low molecular weight product. The premature chain-termination mutant was used to obtain suppressor mutants with wild-type properties. One such revertant strain was analyzed genetically and biochemically. The revertant was determined to have a second mutation in a nuclear gene that is capable of partially suppressing the original mitochondrial cytochrome b mutation. Genetic data indicate that the nuclear mutation is recessive and is probably in a gene coding for a protein involved in the mitochondrial translation machinery.
THE EVOLUTION OF MULTIPLE MATING BEHAVIOR BY HONEY BEE QUEENS (APIS MELLIFERA L.)
Authors: Page Robert E
Published: April 2021

A model is presented showing that natural selection operating at the individual level can adequately explain the evolution of multiple mating behavior by honey bee queens. Group selection need not be invoked. The fitness of a given female genotype is a function of the number of sex alleles in the population, the number of matings by an individual female and the specific parameters that determine the relationship of brood viability to individual fitness. Even though the exact relationship is not known, it is almost certainly not linear. A nonlinear relationship between worker brood viability and fitness and a significant genetic load associated with the sex-determination system in honey bees are the essential components of this model.
A NEW MAP LOCATION FOR THE ilvB LOCUS OF ESCHERICHIA COLI
Authors: Newman Thomas C , Levinthal Mark
Published: April 2021

We isolated, in E. coli K12, new alleles of the ilvB locus, the structural gene for acetolactate synthase isoenzyme I, and showed them to map at or near the ilvB619 site. The map position of the ilvB locus was redetermined because plasmids containing the ilvC-cya portion of the chromosome did not complement mutations at the ilvB locus. Furthermore, diploids for the ilvEDAC genes formed with these plasmids in an ilvHI background facilitated the isolation of the new ilvB alleles. The ilvB locus was remapped and found to be located at 81.5 minutes, between the uhp and dnaA loci. This location was determined by two- and three-point transductional crosses, deletion mapping and complementation with newly isolated plasmids. One of the new alleles of the ilvB gene is a mu-1 insertion. When present in the donor strain, this allele interferes with the linkage of genes flanking the mu-1 insertion, as well as the linkage of genes to either side of the mu-1 insertion.
CHARACTERIZATION OF AN AUTOSOMAL RUDIMENTARY-SHAPED WING MUTATION IN DROSOPHILA MELANOGASTER THAT AFFECTS PYRIMIDINE SYNTHESIS
Authors: Lastowski Donna M , Falk D R
Published: April 2021

A new autosomal mutation, rudimental (ral), which causes rudimentary-shaped wings in Drosophila melanogaster, has been isolated following ethyl methanesulfonate (EMS) mutagenesis. The wing phenotype of rudimental is identical to that of the X-linked rudimentary (r) mutation, which affects the first three enzymes in the pyrimidine biosynthetic pathway. The autosomal mutant maps very close to ebony (3—70.7) at 70.42 on the right arm of chromosome 3. Analysis of the enzyme activities of orotate phosphoribosyltransferase (OPRTase) and orotidylate decarboxylase (ODCase) indicates that the rala26a allele has less than wild-type activity for both enzymes. This result is discussed in light of the fact that the OPRTase and ODCase activities are part of an enzyme complex, as are the carbamyl phosphate synthetase (CPSase), aspartate transcarbamylase (ATCase) and dihydroorotase (DHOase) activities, which are encoded by the complex rudimentary locus. We suggest that rudimental is also a complex locus.
SMALL-SIZED MUTANTS OF SACCHAROMYCES CEREVISIAE
Authors: Carter Bruce L A , Sudbery Peter E
Published: April 2021

The isolation of mutants of Saccharomyces cerevisiae that divide at approximately half the size of the wild type is described. Three mutants have been isolated in which the small size at bud initiation is due to a mutation in a single nuclear gene.
MORE SEX-DETERMINATION MUTANTS OF CAENORHABDITIS ELEGANS
Authors: Hodgkin Jonathan
Published: April 2021

Sex determination in Caenorhabditis elegans is controlled by the X chromosome: autosome ratio, i.e. 2A;XX animals are hermaphrodite, and 2A;XO animals are male. A procedure for isolating 2A;XO animals that are transformed into hermaphrodites has been developed. Nine mutations causing this transformation have been obtained: eight are recessive, and all of these fall into a new autosomal complementation group, her-1 V. The remaining mutation (her-2) is dominant and has a genetic map location similar to that of tra-1 III. Recessive mutations of tra-1 cause the reverse transformation, transforming 2A;XX animals into males. Therefore, the her-2 mutation may result in constitutive expression of tra-1. Mutations in her-1 are without effect on XX animals, but the her-2 mutation prevents sperm production in both XX and XO animals, in addition to its effect on the sexual phenotype of XO animals. The epistatic relationships between tra and her genes are used to deduce a model for the action of these genes in controlling sex determination.
THE ORIGIN OF SPONTANEOUS MUTATION IN SACCHAROMYCES CEREVISIAE
Authors: Quah Siew-Keen , von Borstel R C , Hastings P J
Published: April 2021

Characterization of two antimutator loci in yeast shows that both are members of the same mutagenic repair system known to be responsible for almost all induced mutation (Lawrence and Christensen 1976, 1979a,b; Prakash 1976). One of the these newly isolated antimutator mutations is an allele of rev3 (Lemontt 1971b). Two other alleles of rev3 were tested and were also found to be antimutators. Double mutants carrying rev3 and mutator mutations of rad3, rad51 or rad18 are like rev3 single mutants with respect to spontaneous mutation rate, supporting the hypothesis (Hastings, Quah and von Borstel 1976) that many mutators in yeast act by channelling spontaneous lesions from accurate to mutagenic repair. However, the enhanced mutation rate seen in a radiation-resistant mutator mutant mut1 is not dependent on REV3, but is dependent on another gene designated ANT1. An additive effect on the reduction in spontaneous mutation, seen in the ant1 rev3 double-mutant strain, leads to the conclusion that at least 90% of spontaneous mutations seen in the wild type are caused by mutagenic repair of spontaneous lesions.
MATERNAL AND ZYGOTIC SEX-SPECIFIC GENE INTERACTIONS IN DROSOPHILA MELANOGASTER
Authors: Cline Thomas W
Published: April 2021

Sex-lethal (Sxl) is a vital, X-chromosome gene involved in Drosophila sex determination. The most striking aspect of the phenotype of daughterless (da), an autosomal maternal-effect mutation, may be explained by effects on the functioning of the Sxl gene in the zygote. In this paper, new aspects of interactions between various combinations of Sxl and da alleles are explored in order to understand better the complex da phenotype. The study focuses on the relationship between maternal and zygotic da  + gene functions, and on the relationship between aspects of the da phenotype that are sex-specific and aspects that are not. The SxlM#1 allele, which counteracts the female-specific maternal effect of da, is shown to have no effect on two other aspects of the da phenotype (one maternal, one primarily zygotic) that are not sex-specific. The female-lethal da maternal effect is shown to kill daughters even when the progeny are entirely wild-type with respect to da. Recessive mutant alleles of the two genes can interact synergistically when both are heterozygous with their wild-type alleles, disrupting the development of most of the daughters. Surprisingly, even a deficiency of the da  + locus can produce a dominant, temperature-sensitive, female-lethal maternal effect. A new class of subliminal Sxlf alleles is described. These spontaneous mutations can confuse analysis of both da and Sxl if their presence is not appreciated. Finally, conditions are described that facilitate the study of the Enhancer of daughterless mutation.
THE DETECTION OF MUTANTS IN MICE BY ELECTROPHORESIS: RESULTS OF A MODEL INDUCTION EXPERIMENT WITH PROCARBAZINE
Authors: Johnson F M , Roberts G T , Sharma R K , Chasalow Fred , Zweidinger Ruth , Morgan Ann , Hendren R Wayne , Lewis Susan E
Published: April 2021

Male mice of the DBA/2J strain were treated with the mutagen procarbazine and mated with C57BL/6J females. Offspring and parents were then analyzed for electrophoretically expressed mutations. A control group, not mutagen treated, was also examined. Two mutants probably due to induction were identified, and several of spontaneous origin were also found.
AN ACETYLCHOLINESTERASE-DEFICIENT MUTANT OF THE NEMATODE CAENORHABDITIS ELEGANS
Authors: Johnson Carl D , Duckett John G , Culotti Joseph G , Herman Robert K , Meneely Philip M , Russell Richard L
Published: April 2021

Within a set of five separable molecular forms of acetylcholinesterase found in the nematode Caenorhabditis elegans, previously reported differences in kinetic properties identify two classes, A and B, likely to be under separate genetic control. Using differences between these classes in sensitivity to inactivation by sodium deoxycholate, a screening procedure was devised to search for mutants affected only in class A forms. Among 171 previously isolated behavioral and morphological mutant strains examined by this procedure, one (PR946) proved to be of the expected type, exhibiting a selective deficiency of class A acetylcholinesterase forms. Although originally isolated because of its uncoordinated behavior, this strain was subsequently shown to harbor mutations in two genes; one in the previously identified gene unc-3, accounting for its behavior, and one in a newly identified gene, ace-1, accounting for its selective acetylcholinesterase deficiency. Derivatives homozygous only for the ace-1 mutation also lacked class A acetylcholinesterase forms, but were behaviorally and developmentally indistinguishable from wild type. The gene ace-1 has been mapped near the right end of the X chromosome. Gene dosage experiments suggest that it may be a structural gene for a component of class A acetylcholinesterase forms.
B CHROMOSOME NONDISJUNCTION IN CORN: CONTROL BY FACTORS NEAR THE CENTROMERE
Authors: Carlson Wayne R , Chou Tau-San
Published: April 2021

B chromosomes of corn are stable at all mitotic and meiotic divisions of the plant except the second pollen mitosis. In the latter division, B chromosomes undego mitotic nondisjunction at rates as high as 98%. Studies by several workers on B-A translocation chromosomes have provided evidence for the existence of four factors on the B chromosome that control nondisjunction and are separable from the centromere. Two of these factors, referred to here as factors 3 and 4, flank the B chromosome centromere. Factor 3 is the centromere-adjacent heterochromatin in the long arm of the B chromosome; factor 4 is located in the minute short arm. Evidence is presented here supporting the existence of factors 3 and 4. Deficiencies that include each factor were identified following centromeric misdivision events, with breaks at or near the centromere of a B-translocation chromosome. B chromosomes lacking factors 3 or 4 show much less nondisjunction than do chromosomes containing them. The possible function of factor 4 in nondisjuntion is also discussed.
NONSTRUCTURAL CHROMOSOME DIFFERENTIATION AMONG WHEAT CULTIVARS, WITH SPECIAL REFERENCE TO DIFFERENTIATION OF CHROMOSOMES IN RELATED SPECIES
Authors: Dvořák Jan , McGuire Patrick E
Published: April 2021

Wheat cultivar Chinese Spring (Triticum aestivum L. em. Thell.) was crossed with cultivars Hope, Cheyenne and Timstein. In all three hybrids, the frequencies of pollen mother cells (PMCs) with univalents at metaphase I (MI) were higher than those in the parental cultivars. No multivalents were observed in the hybrids, indicating that the cultivars do not differ by translocations. Thirty-one Chinese Spring telosomic lines were then crossed with substitution lines in which single chromosomes of the three cultivars were substituted for their Chinese Spring homologues. The telosomic lines were also crossed with Chinese Spring. Data were collected on the frequencies (% of PMCs) of pairing of the telesomes with their homologues at MI and the regularity of pairing of the remaining 20 pairs of Chinese Spring chromosomes in the monotelodisomics obtained from these crosses. The reduced MI pairing in the intercultivar hybrids was caused primarily by chromosome differentiation, rather than by specific genes. Because the differentiation involved a large part of the chromosome complement in each hybrid, it was concluded that it could not be caused by structural changes such as inversions or translocations. In each case, the differentiation appeared to be unevenly distributed among the three wheat genomes. It is proposed that the same kind of differentiation, although of greater magnitude, differentiates homoeologous chromosomes and is responsible, together with structural differentiation, for poor chromosome pairing in interspecific hybrids.
RESPONSE TO SELECTION AT TWO TEMPERATURES FOR FAST AND SLOW GROWTH FROM FIVE TO NINE WEEKS OF AGE IN POULTRY
Authors: Bohren B B , Carson J R , Rogler J C
Published: April 2021

Cornell Control White Leghorn chicks were grown in a common environment to five weeks of age and selected for fast and slow gain in body weight from five to nine weeks of age at two temperatures, 21.1° (cold) and 32.2° (hot), during which time a constant 50% relative humidity was maintained. All lines were tested each generation in both temperature environments. Selection continued for four generations, with a second replicate started six weeks after the first replicate in each generation. In the hot environment, a 20% reduction (104 g) in five-to-nine-week weight gain was found. The responses to selection for fast and slow growth were symmetrical except in the first generation, when an outbreak of bronchitis confounded selection for body weight with selection for disease resistance and allowed little gain in the slow lines. No genotype-by-environment interactions were found, indicating that selection in either direction in either selection temperature produced equal responses in either test temperature. This suggests that any interactions observed between the growth of strains in tropical vs. temperate climates must be due to some difference between these environments other than the temperature differences studied.
THE MOLECULAR BASIS OF DOMINANCE
Authors: Kacser Henrik , Burns James A
Published: April 2021

The best known genes of microbes, mice and men are those that specify enzymes. Wild type, mutant and heterozygote for variants of such genes differ in the catalytic activity at the step in the enzyme network specified by the gene in question. The effect on the respective phenotypes of such changes in catalytic activity, however, is not defined by the enzyme change as estimated by in vitro determination of the activities obtained from the extracts of the three types. In vivo enzymes do not act in isolation, but are kinetically linked to other enzymes via their substrates and products. These interactions modify the effect of enzyme variation on the phenotype, depending on the nature and quantity of the other enzymes present. An output of such a system, say a flux, is therefore a systemic property, and its response to variation at one locus must be measured in the whole system. This response is best described by the sensitivity coefficient, Z, which is defined by the fractional change in flux over the fractional change in enzyme activity.
GAMETIC FREQUENCY OF SECOND CHROMOSOMES OF THE T-007 TYPE IN A NATURAL POPULATION OF DROSOPHILA MELANOGASTER IN TEXAS
Authors: Hiraizumi Yuichiro , Gerstenberg Mary V
Published: April 2021

The T-007 second chromosome, which was isolated from a natural population of Drosophila melanogaster in south Texas in 1970, is known to show, when made heterozygous in males with a standard cn bw second chromosome, a transmission frequency (k) of 0.35—much lower than the theoretically expected 0.5. Natural populations of this species in Texas contain second chromosomes that, against the standard cn bw genetic background, are associated with distorted transmission frequencies comparable to that of the T-007 chromosome. In order to explain how such chromosomes can persist in natural populations in nontrivial frequencies, it has been postulated that, although such chromosomes show reduced k values when tested under the genetic background of a laboratory stock such as cn bw, they may show, on the average, k values larger than 0.5 under natural genetic backgrounds. If this were true, the frequency of chromosomes of the T-007 type (T chromosomes) should be higher in male than in female gametes under natural genetic backgrounds. The present study was conducted to examine this possibility. The results clearly showed that the frequency of such chromosomes was much higher among male than among female gametes, and that the transmission frequency of this type of chromosome was higher than 0.5 under natural genetic backgrounds. These results suggest that T chromosomes behave like Segregation Distorter (SD) chromosomes in natural populations of this species in Texas. A possible relationship between T-007 and SD chromosomes is suggested.
GENETIC CHARACTERIZATION OF THE REGION OF THE DROSOPHILA GENOME KNOWN TO INCLUDE THE HISTONE STRUCTURAL GENE SEQUENCES
Authors: Siegel Jacqueline G
Published: April 2021

This report describes a genetic study of salivary map region 39DE of the Drosophila genome, which is known to include the histone gene sequences (Pardue 1975; Lifton et al. 1977). Small deficiences extending proximally into 39DE were constructed by the segmental aneuploid method of Lindsley et al. (1972). The translocational deficiencies obtained in this manner were γ-irradiated to remove the Y translocational arms. One of these newly reconstituted deficiencies was then used to screen 10,000 γ-irradiated second chromosomes for lethal mutations. The 32 lethals recovered from the screen were tested against several deficiencies and markers, crossed inter se and categorized according to their genetic properties. From these data, a preliminary complementation map was constructed of salivary region 39A-39F. The salivary map positions of certain of the complementation groups suggest that the mutants in these groups may affect histone gene functions.
TEMPORAL STABILITY OF ALLOZYME FREQUENCIES IN A NATURAL POPULATION OF DROSOPHILA MELANOGASTER
Authors: Cavener Douglas R , Clegg Michael T
Published: April 2021

A Kamuela, Hawaii, population of Drosophila mercatorum was surveyed for enzyme variability. The mean heterozygosity and the proportion of polymorphic loci were estimated as 0.1255 and 0.37, respectively. Neither deviates more than one standard error from their respective means for 43 Drosophila species (Nevo 1978). Heterozygosity was distributed across enzyme categories in much the same manner as observed in other species (Gillespie and Kojima 1968; Johnson 1974), and enzymes associated with glycolysis were about as variable as other enzymes of central metabolism.——The levels of heterozygosity and polymorphism in this population do not seem to have been affected by a low-level capacity for parthenogenesis. The observed parthenogenetic reproduction is not strongly associated with particular allelic variants among viable parthenogenetic adults; however, the capacity to establish a self-sustaining parthenogenetic clone is strongly associated with the phenotype with the most frequent allele at every locus studied. We interpret these results to mean that isozyme variants do not strongly influence viability under total homozygosity (the genetic condition imposed by parthenogenesis), but they do have an impact upon the reproductive biology of parthenogenetic adults.
LAC4 IS THE STRUCTURAL GENE FOR β-GALACTOSIDASE IN KLUYVEROMYCES LACTIS
Authors: Sheetz R Michael , Dickson Robert C
Published: April 2021

Using genetic and biochemical techniques, we have determined that β-galactosidase in the yeast Kluyveromyces lactis is coded by the LAC4 locus. The following data support this conclusion: (1) mutations in this locus result in levels of β-galactosidase activity 100-fold lower than levels in uninduced wild type and all other lac- mutants; (2) three of five lac4 mutations are suppressible by an unlinked suppressor whose phenotype suggests that it codes for a nonsense suppressor tRNA; (3) a Lac+ revertant, bearing lac4–14 and this unlinked suppressor, has subnormal levels of β-galactosidase activity, and the Km for hydrolysis of o-nitrophenyl-β, D-galactoside and the thermal stability of the enzyme are altered; (4) the level of β-galactosidase activity per cell is directly proportional to the number of copies of LAC4; (5) analysis of cell-free extracts of strains bearing mutations in LAC4 by two-dimensional acryl-amide gel electrophoresis shows that strains bearing lac4–23 and lac4–30 contain an inactive β-galactosidase whose subunit co-electrophoreses with the wild-type subunit, while no subunit or fragment of the subunit is obs0ervable in lac4–8, lac4–14 or lac4–29 mutants; (6) of all lac4 mutants, only those bearing lac4–23 or lac4–30 contain a protein that cross-reacts with anti-β-galactosidase antibody, a finding consistent with the previous result; and (7) β-galactosidase activity in several Lac+ revertants of strains carrying lac4–23 or lac4–30 has greatly decreased thermostability.
GENETIC CHARACTERIZATION OF THE REGION BETWEEN 86F1,2 AND 87B15 ON CHROMOSOME 3 OF DROSOPHILA MELANOGASTER
Authors: Gausz J , Gyurkovics H , Bencze G , Awad A A M , Holden J J , Ish-Horowicz D
Published: April 2021

The region between 86F1,2 and 87B15 on chromosome 3 of Drosophila melanogaster, which contains about 27 polytene chromosome bands including the 87A7 heat-shock locus, has been screened for EMS-induced visible and lethal mutations. We have recovered 268 lethal mutations that fall into 25 complementation groups. Cytogenetic localization of the complementation groups by deficiency mapping is consistent with the notion that each band encodes a single genetic function. We have also screened for mutations at the 87A7 heat shock locus, using a chromosome that has only one copy of the gene encoding the 70,000 dalton heat-shock protein (hsp70). No lethal or visible mutations at 87A7 were identified from 10,719 mutagenized chromosomes, and no female-sterile mutations at 87A7 were recovered from the 1,520 chromosomes whose progeny were tested for female fertility. We found no evidence that a functional hsp70 gene is required for development under laboratory conditions.
NULL ALLELE FREQUENCIES AT ALLOZYME LOCI IN NATURAL POPULATIONS OF DROSOPHILA MELANOGASTER
Authors: Langley Charles H , Voelker Robert A , Brown Andrew J Leigh , Ohnishi Seido , Dickson Barbara , Montgomery Elizabeth
Published: April 2021

We have sampled a London population of Drosophila melanogaster for null alleles at twenty-five allozyme loci. The same loci and biochemical techniques were used as in our previous survey of a North Carolina population (Voelker et al. 1980). This second survey is completely concordant with the first. No nulls were detected among the five X-linked loci. The mean frequency of nulls at the twenty autosomal loci was 0.0023. Although there is significant interlocus heterogeneity, the two populations appear to have the same frequencies at each locus. This suggests that null alleles at these allozyme loci are in mutation-selection balance, and we estimate the average heterozygous effect of an allozyme null to be 0.0015. Consideration of allozyme null-allele frequencies, the effects of allozyme null alleles on viability and fertility and the generally greater amount of genetic variability at allozyme loci determined by electrophoresis lead us to doubt the validity of generalizing from allozyme data to the whole genome.
THE ACTION OF THE NOTCH LOCUS IN DROSOPHILA MELANOGASTER. II. BIOCHEMICAL EFFECTS OF RECESSIVE LETHALS ON MITOCHONDRIAL ENZYMES
Authors: Thörig George E W , Heinstra Pieter W H , Scharloo Willem
Published: April 2021

We show that six mapped recessive lethal point mutations of the Notch locus affect mitochondrial enzyme activities: NADH oxidase, NADH dehydrogenase, succinate dehydrogenase and α-glycerophosphate dehydrogenase. The mutant N264-40, which has the same morphological and embryological effects as the Notch8 deletion, demonstrates the same biochemical effects and dosage relations as Notch8. The other five mapped recessive lethals also affect four enzymic activities. They show specific patterns of activity that depend in several cases on the wild-type chromosome in the heterozygous females. That effect occurs with mutants located in the extreme right part of the Notch locus where some mutations, according to other authors, show temperature-sensitive expression.
TECHNIQUES FOR MANIPULATING CHROMOSOMAL REARRANGEMENTS AND THEIR APPLICATION TO DROSOPHILA MELANOGASTER. I. PERICENTRIC INVERSIONS
Authors: Craymer Loring
Published: April 2021

Techniques have been developed for manipulating pericentric inversions in Drosophila that are based on the lethality of grossly aneuploid zygotes and the existence of recombinationally interconvertible genotypes for any heterozygous inversion complex: males of some of these genotypes will produce only aneuploid sperm, which can be used to rescue complementary aneuploid ova and selectively recover recombinational derivatives of inversions. Markers can be recombined into inversions through a sequence of selected single exchanges, and a novel type of duplication can be synthesized from overlapping inversions that has the characteristics of both insertional and tandem duplications; there are also applications to half-tetrad analyses.——Two cytogenetic screens are developed: (1) the dominant lethality of a large insertional-tandem duplication can be reverted by deletional events that give rise to net deficiencies or duplications, and (2) deficiencies and tandem duplications in proximal regions can be selectively recovered as the results of unequal exchanges within an inversion loop. Recombinants have been recovered between breakpoints separated by distances of as little as fifty bands, arguing against the existence of some small number of sites necessary for the initiation of recombinational pairing. In several instances, hyperploids for four to six numbered divisions were observed to be fertile in both sexes.
CORRELATED RESPONSES IN MALE REPRODUCTIVE TRAITS IN MICE SELECTED FOR LITTER SIZE AND BODY WEIGHT
Authors: Eisen E J , Johnson B H
Published: April 2021

Correlated responses in male reproductive traits were determined at 4, 6 and 8 weeks of age in lines of mice selected for large litter size (L+), large 6-week body weight (W+), large litter size and small body weight (L+W-) and small litter size and large body weight (L-W+), and in an unselected control (K). Concentration of serum testosterone and weights of testes, seminal vesicles, epididymides and adrenal glands increased with age. Line differences in testosterone concentration were not detected. L+ and W+ males exhibited positive correlated responses in testes, epididymides and seminal vesicle weights. Testis weight adjusted for body weight was significantly larger for L+ than controls and approached significance for Wf . Realized genetic correlation betestis weight and litter size was 0.60± 0.04, and the realized partial genetic correlation holding body weight constant was 0.42. Therefore, pleiotropic loci, acting viathe hypothalamic-pituitary axis, affect testis weight and litter size independently of body weight. Additionally, genes influencing overall growth have a pleiotropic effect on testis weight and litter size in mice; the realized genetic correlations of body weight with testis weight and with litter size were 0.60 ± 0.03 and 0.52 ± 0.10. Testis weight increased in both L+W- and L-W+ males. The positive correlated response in L+W- may have resulted from changes in frequency of genes controlling reproductive processes; whereas, in L-W+ it could have been the result of changes in the frequency of genes associated with body weight.