bluuebunny/crossref_metadata_2025 huggingface dataset:
A MEIOTIC UV-SENSITIVE MUTANT THAT CAUSES DELETION OF DUPLICATIONS IN NEUROSPORA
Authors: Newmeyer Dorothy , Galeazzi Donna R
Published: April 2021

The meiotic-3 (mei-3) mutant of Neurospora crassa has several effects: (1) When homozygous, it almost completely blocks meiosis and ascospore formation, (2) it is sensitive to UV, (3) its growth is inhibited by histidine and, (4) it increases the instability of nontandem duplications. This was shown for duplications produced by five different rearrangements and was demonstrated by two different criteria. The effects on meiosis and duplication instability are expressed strongly at 25°; the effects on sensitivity to UV and to histidine are expressed strongly at 38.5° but only slightly at 25°. Nevertheless, all four effects were shown to be due to a single gene. mei-3 is not allelic with previously reported UV-sensitive mutants.—Two other results were obtained that are not necessarily due to mei-3: (1) A cross involving mei-3 produced a new unlinked meiotic mutant, mei-4, which is not sensitive to UV or histidine, and (2) a burst of several new mutants occurred in a different mei-3 stock, including a partial revertant of mei-3.—mei-3 has previously been shown to cause frequent complete loss of a terminal duplicate segment, beginning exactly at the original rearrangement breakpoint. Possible mechanisms are discussed by which a UV-sensitive mutant could cause such precise deletions.
INDIRECT SUPPRESSION IN CAENORHABDITIS ELEGANS
Authors: Riddle Donald L , Brenner S
Published: April 2021

Two cases of indirect suppression have been characterized. One case involves suppressors compensating for defects in muscle structure. Nine independent suppressor mutations were judged to lie in a single suppressor gene, sup-3. Suppression is dominant, but dose dependent, and results in improved locomotion, as well as in an increase in the ability of mutant animals to lay eggs. Mutations in six genes known to affect muscle structure were tested for suppression by representative sup-3 mutations. Alleles of three of the six genes are suppressed, two of which are known to code for thick filament proteins. One suppressor allele was identified as a deletion by genetic criteria. A second case of indirect suppression is not associated with muscle defects, but involves two mutant genes producing uncoordinated phenotypes very similar to one another. As in the first case, suppression is dominant but dose dependent and is not allele specific.
RANK-ORDER SELECTION IS CAPABLE OF MAINTAINING ALL GENETIC POLYMORPHISMS
Authors: Wills Christopher
Published: April 2021

The fitness of organisms may be due chiefly to a fitness curve imposed on their ranking in the population with respect to heterozygosity. If this is so, then the number of polymorphisms that can be retained at a particular selective equilibrium increases as the square of the population size. All of the genetic variation that we currently observe and infer to exist can probably be maintained by selection in a population of about 105 individuals. Selection acting in this way is so strong that these polymorphisms can be expected to behave very differently from neutral ones.
EXPERIMENTAL EVOLUTION OF A NEW ENZYMATIC FUNCTION. II. EVOLUTION OF MULTIPLE FUNCTIONS FOR EBG ENZYME IN E. COLI
Authors: Hall Barry G
Published: April 2021

The evolution of ebgo enzyme of Escherichia coli, an enzyme which is unable to hydrolyze lactose, lactulose, lactobionate, or galactose-arabinoside effectively, has been directed in successive steps so that the evolved enzyme is able to hydrolyze these galactosides effectively. I show that in order for a strain of E. coli with a lacZ deletion to evolve the ability to use lactobionate as a carbon source, a series of mutations must occur in the ebg genes, and that these mutations must be selected in a particular order. The ordered series of mutations constitutes an obligatory evolutionary pathway for the acquisition of a new function for ebgo enzyme. A comparison of newly evolved strains with parental strains shows that when ebg enzyme acquires a new function, its old functions often suffer; but that in several cases old functions are either unaffected or are improved. I conclude that divergence of functions catalyzed by an enzyme need not require gene duplication.
GENETICS OF HEMOGLOBIN IN THE DEER MOUSE, PEROMYSCUS MANICULATUS. II. MULTIPLE ALLELES AT REGULATORY LOCI
Authors: Snyder Lee R G
Published: April 2021

Deer mice are polymorphic for electrophoretic hemoglobin phenotypes showing one, two, or three bands. Within the multibanded phenotypes, there is considerable variation in the hemoglobin partitioning, defined as the fraction of total hemoglobin made up by the secondary and tertiary bands. In subspecies sonoriensis, for example, hemoglobin partitionings range from 0.03 to 0.38. The inheritance of partitioning values is under remarkably strict genetic control. The genetic variation is additive and the narrow heritability is close to 1.0. The inheritance data can be modeled in precise detail by postulating multiple-allele polymorphisms at globin regulatory loci. Comparison of simulated versus actual inheritance data demonstrates that the so-called null structural alleles actually produce functional globins.—The genetic controls in Peromyscus may be analogous to those in primates. Unfortunately, the molecular mechanisms effecting the regulation are unknown. Different subspecies of P. maniculatus show strikingly different arrays of partitioning values, but the role of natural selection in maintaining the quantitative polymorphisms remains obscure
EXACT INBREEDING COEFFICIENTS IN POPULATIONS WITH OVERLAPPING GENERATIONS
Authors: Choy S C , Weir B S
Published: April 2021

A theory is given that allows inbreeding coefficients to be calculated exactly for populations with overlapping generations. Emphasis is placed on providing equations well suited for computer iteration. Both monoecious and dioecious populations are considered and family size is not restricted to being Poisson. One-locus and two-locus inbreeding coefficients are evaluated, although the reader may omit the two-locus sections. The exact treatment is shown to be preferable to approximate treatments in that it applies to both early and late generations for all populations sizes. Inbreeding effective numbers found by the exact treatment are compared to various approximate numbers, and the approximate values are found to be generally very good.
ANALYSIS OF GYNANDROMORPH SURVIVALS IN DROSOPHILA MELANOGASTER INFECTED WITH THE MALE-KILLING SR ORGANISMS
Authors: Tsuchiyama Sumi , Sakaguchi Bungo , Oishi Kugao
Published: April 2021

The effects of SRO (Sex-ratio organism; previously called SR spirochetes) infection on the viability of gynandromorphs of D. melanogaster were examined. A fraction of gynadromorphs, most of them with small areas of XO tissue, survived, but the majority were not viable when XO nuclei or cells are affected by the infecting SRO. Apparently the replacement of lethal XO nuclei or cells by adjacent XX ones does not take place. Some possibilities are discussed as to the time and the primary site of the lethal action of SRO.
ISOLATION OF A GLYCEROL-UTILIZING MUTANT OF NICOTIANA TABACUM
Authors: Chaleff R S , Parsons M F
Published: April 2021

Although normal tobacco cell cultures cannot grow on glycerol as the sole carbon source, a spontaneous mutant cell line capable of utilizing glycerol has been isolated. Plants have been regenerated from this mutant cell line, and the results of preliminary genetic analyses are reported. The mutation appears to be specific for glycerol in that it does not alter the capability for callus growth on several other sugars tested.
RESPONSE TO SELECTION FOR MATING SPEED AND CHANGES IN GENE ARRANGEMENT FREQUENCIES IN DESCENDANTS FROM A SINGLE POPULATION OF DROSOPHILA PSEUDOOBSCURA
Authors: Spuhler Karen P , Crumpacker David W , Williams James S , Bradley Brian P
Published: April 2021

Heritability estimates, based on 19 generations of selection for fast and slow mating speed, were not significantly different from zero at the 0.05 level in any replicate of selected lines in a population of flies descended from the Mather population in California. Only the combined heritability estimate of approximately 2% was significant. This indicated that very little additive genetic variance was present in the base population and that strong directional selection for rapid mating may have occurred in the previous history of the local population at Mather and/or during its many generations of laboratory propagation. Frequencies of third chromosome gene arrangements were monitored during the course of selection. Balancing selection, unrelated to that imposed for mating speed, and genetic drift appeared to be the major factors causing changes in chromosome frequencies. Present differences in adaptive value of third chromosome variants in nature may be associated with nonadditive effects on mating speed, as well as effects on other components of fitness.
ULTRAVIOLET-INDUCED REVERSION OF cyc1 ALLELES IN RADIATION SENSITIVE STRAINS OF YEAST. II. rev2 MUTANT STRAINS
Authors: Lawrence Christopher W , Christensen Roshan B
Published: April 2021

The range of specificity of the rev2-1 mutation, an allele that reduces the frequency of ochre revertants induced by UV in Saccharomyces cerevisiae (Lemontt 1971a), has been investigated by examining its influence on the reversion of eleven well-defined and contrasting cyc1 mutations. We have shown, in support of a suggestion of Lemontt (1971a), that the REV2 gene product is concerned only with the reversion of ochre alleles; it plays virtually no role in the reversion of amber, missense or frameshift mutations. We have also shown that its effect is specific and confined to only some highly revertible ochre alleles. The REV2 gene product appears to enhance reversion at these sites by facilitating the conversion of two otherwise nonmutagenic photo-products into a single premutational lesion. UV-induced killing of rev2-1 strains was found to be significantly greater on fermentable rather than on nonfermentable media.
ORGANIZATION OF THE CHORION GENES OF BOMBYX MORI, A MULTIGENE FAMILY. I. EVIDENCE FOR LINKAGE TO CHROMOSOME 2
Authors: Goldsmith Marian R , Basehoar Gayle
Published: April 2021

The chorion genes of silkmoths comprise a multigene family that codes for 50 or more highly specialized structural proteins found in the eggshell. A detailed study of the chromosomal organization of these genes was initiated, using inbred stocks of Bombyx mori as a source of electrophoretic variants for genetic markers. Chorion protein patterns were screened on thin-slab polyacrylamide isoelectric focusing gels. A wide range of polymorphism was observed between stocks. However, isoelectric focusing patterns obtained within a stock were nearly homogeneous, indicating that inbreeding has produced a high degree of homozygosis. Testcrosses were carried out to examine the linkage relationships between electrophoretic markers in four inbred stocks. One race (C108) was selected as a standard against which to compare the inheritance of the variants found in the other three stocks. Chorion markers behaved like codominant Mendelian traits in F1 crosses. A total of 15 out of 16 C108 markers cosegregated in subsequent testcrosses, indicating that they are linked. These genes were mapped to the second chromosome, using markers Gr and Y.
WITH SELECTION FOR FECUNDITY THE MEAN FITNESS DOES NOT NECESSARILY INCREASE
Authors: Pollak Edward
Published: April 2021

A population with two alleles at one locus is considered. It is assumed that there is random mating of adults and that matings in which a particular pair of genotypes is involved may have a different mean number of offspring, or fecundity, than other types of matings. There is assumed to be no other selection. It is shown that the genotypic frequencies that maximize the mean fecundity of the population are not necessarily the same as the stable equilibrium frequencies. Thus, examples can be found for which the mean fecundity decreases from one generation to the next, and one such example is presented. An example in which there is no stable equilibrium, and the mean fecundity oscillates, is also given.
ISOLATION AND GENETIC CHARACTERIZATION OF A MUTATION AFFECTING RIBOSOMAL RESISTANCE TO CYCLOHEXIMIDE IN TETRAHYMENA
Authors: Ares Manuel , Bruns Peter J
Published: April 2021

A dominant mutation at a new locus affecting resistance to cycloheximide has been isolated by exploiting a synergistic relationship with a previously known mutation for cycloheximide resistance in Tetrahymena. The new mutation (ChxB) was induced in a line homozygous for ChxA and was recovered from that background by a new technique termed interrupted genomic exclusion. Segregation data from the interrupted genomic exclusion suggest that ChxA and ChxB are separate, linked loci showing 30% recombination. Minimal lethal doses of cycloheximide for the four possible combinations of the wild-type and mutant alleles of these two genes are: wild type 6 µg/ml, ChxA 125 µg/ml, ChxB 10 µg/ml, ChxA-ChxB 175 µg/ml.
REGULATION OF MOUSE MAJOR URINARY PROTEIN PRODUCTION BY THE MUP-A GENE
Authors: Szoka P R , Paigen K
Published: April 2021

A method was developed to quantitate the daily excretion of the three major urinary proteins (mups) to test which parameters of the mup phenotype are controlled by the the Mup-a gene. Electrophoretic separation of the mup proteins, followed by staining and spectrophotometric scanning was used to characterize the phenotypes of various inbred strains. The mup phenotype of a strain proved to have two components: the absolute levels and the relative proportions of the mups present in the urine. Testosterone treatment alters both components of the mup phenotype, increasing mup excretion and altering their relative proportions. The induced proteins are the same as the basal proteins as judged by electrophoretic mobility, molecular weight, and reactivity with antibody. All strains excrete all three mups when induced. The Mup-a gene appears to be a single, codominantly expressed regulatory locus that controls the induced proportions of the three proteins. However, other genes in addition to Mup-a participate in controlling the basal mup proportions, as well as individual and total mup levels before and after testosterone treatment.
THE EFFECT OF RECOMBINATION-DEFECTIVE MEIOTIC MUTANTS ON FOURTH-CHROMOSOME CROSSING OVER IN DROSOPHILA MELANOGASTER
Authors: Sandler L , Szauter Paul
Published: April 2021

Crossing over was measured on the normally achiasmate fourth chromosome in females homozygous for one of our different recombination-defective meiotic mutants. Under the influence of those meiotic mutants that affect the major chromosomes by altering the spatial distribution of exchanges, meiotic fourth-chromosome recombinants were recovered irrespective of whether or not the meiotic mutant decreases crossing over on the other chromosomes. No crossing over, on the other hand, was detected on chromosome 4 in either wild type or in the presence of a meiotic mutant that decreases the frequency, but that does not affect the spatial distribution, of exchange on the major chromosomes. It is concluded from these observations that (a) in wild type there are regional constraints on exchange that can be attenuated or eliminated by the defects caused by recombination-defective meiotic mutants; (b) these very constraints account for the absence of recombination on chromosome 4 in wild type; and (c) despite being normally achiasmate, chromosome 4 responds to recombination-defective meiotic mutants in the same way as do the other chromosomes.
INTERACTION AMONG C, R AND Vp IN THE CONTROL OF THE Bz GLUCOSYLTRANSFERASE DURING ENDOSPERM DEVELOPMENT IN MAIZE
Authors: Dooner Hugo K , Nelson Oliver E
Published: April 2021

The enzyme UPD glucose: flavonoid 3-0-glucosyltransferase (UFGT), involved in anthocyanin biosynthesis, is controlled by at least four genes (Bz, C, R and Vp) in the maize endosperm. Bz is the structural gene for the enzyme. Early in endosperm development, the enzyme is present in an uninduced low level that is independent of C, R and Vp, and dependent solely on Bz. Beginning at about the fourth week of development, C, R and Vp interact with each other to induce high levels of UFGT. The enzyme accumulates thereafter in normal endosperms, reaching its highest level at maturity. The nature of the developmental signal (s) controlled by C, R and Vp is discussed.
ABERRATIONS INDUCED IN CHROMOSOMES OF SOMATIC CELLS OF DROSOPHILA MELANOGASTER IRRADIATED IN C-METAPHASE
Authors: De Marco Antonio , Belloni Maria Pia , Cozzi Renata , Febbo Dario , Ricordy Ruggero
Published: April 2021

Experiments conducted on the X irradiation of neural ganglia of Drosophila melanogaster are described. The ganglia were placed in saline containing colchicine. After two hours; they were irradiated and then samples were fixed at 5,15,25,35 minutes from the beginning of irradiation. The results obtained show that the aberration level increases with time subsequent to fixing. This increase takes place first for chromatid deletions and then for isochromatid deletions and chromatid exchanges. Gaps and subchromatid exchanges do not, on the contrary, show any increase with time. We did not observe a difference in radiosensitivity between the sexes. Some hypotheses are put forth in an attempt to explain these results.
CHIASMA FREQUENCY AND DISTRIBUTION IN A MAIZE FAMILY SEGREGATING FOR K10 AND TRISOMY 10
Authors: Ward E J
Published: April 2021

Chiasma frequency was determined from total chiasma counts, and the distribution of these exchanges was determined by the ratio of proximal to distal chiasmata. No effect of trisomy 10 could be demonstrated. Confirmation was obtained of earlier work showing more proximal and fewer distal chiasmata in K10 plants than in controls. However, diakinesis data failed to confirm the ability of K1O to increase total chiasmata as suggested from metaphase I results.
PARTIAL SELFING AND LINKAGE: THE EFFECT OF A HETEROTIC LOCUS ON A NEUTRAL LOCUS
Authors: Strobeck Curtis
Published: April 2021

Equilibria are determined for the two-locus model in a partially selfing population when one locus is neutral and the other locus is heterotic. At an equilibrium point, the frequency of heterozygotes at the neutral locus is greater than that expected from one-locus theory, even if the heterotic locus is on a different chromosome. Thus, the neutral locus also appears to be heterotic. The magnitude of this effect is determined for several different proportions of selfing and amounts of recombination.
REGULATORY MUTANTS AT THE his1 LOCUS OF YEAST
Authors: Lax Carol , Fogel Seymour , Cramer Carole
Published: April 2021

The hisl gene in Saccharomyces cereuisiae codes for phosphoribosyl transferase, an allosteric enzyme that catalyzes the initial step in histidine biosynthesis. Mutants that specifically alter the feedback regulatory function were isolated by selecting hisl prototrophic revertants that overproduce and excrete histidine. The prototrophs were obtained from diploids homoallelic for his1-7 and heterozygous for the flanking markers thr3 and arg6. Among six independently derived mutant isolates, three distinct levels of histidine excretion were detected. The mutants were shown to be second-site alterations mapping at the his1 locus by recovery of the original auoxtrophic parental alleles. The double mutants, HIS1-7e, are dominant with respect to catalytic function but recessive in regulatory function. When removed from this hisl-7 background, the mutant regulatory site (HIS1-e) still confers prototrophy but not histidine excretion. To yield the excretion phenotype, the primary and altered secondary sites are required in cis array. Differences in histidine excretion levels correlate with resistance to the histidine analogue, triazoalanine.
THE EFFECT OF TEMPERATURE AND PARENTAL AGE ON RECOMBINATION AND NONDISJUNCTION IN CAENORHABDITIS ELEGANS
Authors: Rose A M , Baillie D L
Published: April 2021

The effect of temperature and parental age on recombination frequency in C. elegans was studied between pairs of closely linked markers on linkage groups I and V. In the regions studied, recombination frequency vaned three-fold over the temperature range 13.5° to 26°. Temperature-shift experiments indicated that a temperature-sensitive recombination event occurs approximately 50 oocytes prior to fertilization. Recombination frequency was observed to decrease with maternal age. The greatest decrease was observed in the first 24 hours of egg production. The frequency of male progeny, a measure of X-chromosome nondisjunction was also studied. This frequency increased with elevated temperature and age of the parent.
ANALYSIS OF THE CUT LOCUS OF DROSOPHILA MELANOGASTER
Authors: Johnson T K , Judd B H
Published: April 2021

Mutants of the cut (ct) locus can be divided into two classes: viable and lethal. Most of the viable alleles are characterized by varying degrees of scalloping and notching of the wings. One mutant, kinked femur, exhibits kinking of the femurs and failure of wing expansion, but no other changes in wing structure. In heterozygous combination with the other viable alleles, it exhibits complete complementation, but it fails to complement with lethal ct alleles with respect to its viable phenotype. Similarly, all of the other viable ct alleles express a mutant wing phenotype when heterozygous with lethal ct alleles.—Mapping experiments indicate that the lethal alleles, which comprise the majority of all ct mutations recovered, are confined to a small region at the right end of the locus. That this restriction is real and not an artifact imposed by the limited number of lethal mutations mapped in the locus is supported by an examination of the mutant ctJC20, a presumptive deficiency for the left-most third of the locus. Despite its behavior as a deletion, ctJC20 is viable, though mutant, in combination with the lethal alleles. The restriction of the noncomplementary lethals to a small part of the locus, distinct from the other ct mutants, suggests a polarity that may define a segment that functions only in cis within the complex.—Based on the comparison of the data with the prediction of several models, we suggest that the left portion of the locus, which contains the viable alleles, defines a regulatory region controlling the expression of the locus, while the segment encoding a polypeptide product is at the right end and only it is capable of mutating to a lethal state.
SYNAPTONEMAL COMPLEX AND RECOMBINATION NODULES IN WILD-TYPE DROSOPHILA MELANOGASTER FEMALES
Authors: Carpenter Adelaide T C
Published: April 2021

Electron microscope serial section reconstruction analysis of all zygotene-pachytene nuclei of meiotic cells from three wild-type germaria (a subunit of the ovary containing the early meiotic stages arrayed in temporal developmental sequence) of Drosophila melanogaster females corroborates and extends earlier observations (CARPENTER 1975a) on the nature and sequence of ultrastructural events occurring during the time of meiotic recombination. Emphasis has been placed on (1) the time of appearance and disappearance of the synaptonemal complex (SC) and the changes in its dimensions that accompany a cell's progression through pachytene, and (2) the appearance, disappearance, number and chromosomal locations of recombination nodules (CARPENTER 1975b). For both the SC and the recombination nodule the availability of several developmental series has provided an estimate of the biological variability in the properties of these recombination-associated structures. The much more extensive data presented here substantiate the earlier hypothesis that recombination nodules occur at sites where reciprocal meiotic recombination will occur, has occurred, or is occurring. A second morphological type of recombination nodule is reported; it is suggested that the presence of the latter type of nodule may correlate with sites of gene conversion. The hypothesis that there may be two types of meiotic recombination processes is discussed.
A NEW METHOD TO DISTINGUISH BETWEEN MEIOTIC AND PREMEIOTIC RECOMBINATIONAL EVENTS IN DROSOPHILA MELANOGASTER
Authors: Hiraizumi Yuichiro
Published: April 2021

A new method is proposed to distinguish between meiotic and premeiotic exchange events in Drosophila melanogaster males associated with male recombination activities. The method was applied to data that have accumulated in this laboratory during the past five years, and it was concluded that a large fraction, perhaps the overwhelming majority, of the male recombinants were due to exchange events that took place before meiosis.
POPULATION GENETICS OF DROSOPHILA AMYLASE. I. GENETIC CONTROL OF TISSUE-SPECIFIC EXPRESSION IN D. PSEUDOOBSCURA
Authors: Powell Jeffrey R , Lichtenfels Jenifer M
Published: April 2021

Drosophila pseudoobscura is polymorphic for tissue-specific expression of α-amylase in adult midguts. This enzyme is encoded by a single locus, Amy, on the third chroniosome. In this paper we show: (1) Up to about 12 days post-eclosion, the midgut activity patterns remain stable; after 12 days areas not showing activity previously begin to show activity. ThuS the genes controlling the expression of Amy are temporally acting. (2) Diet affects the quantitative, but not the qualitative, expression of Amy. (3) The expression of Amy in adult midguts is under genetic control. Selection for different frequencies of patterns is possible; realized heritabilities are 0.20 to 0.50. Partial linkage with third chromosome inversions has been demonstrated; the genes or elements controlling Amy expression are not, howevr, confined to the third chromosome. (4) The genetic elements controlling tissue-specific expression of amylase do not coordinately control the expression of five other "digestive-type" enzymes that were studied.—This polymophism appears to be analogous to that studied by ABRAHAM and DOANE (1978) in D. melanogaster, wherein they have mapped regulatory genes.
MATING-TYPE EFFECT ON CIS MUTATIONS LEADING TO CONSTITUTIVITY OF ORNITHINE TRANSAMINASE IN DIPLOID CELLS OF SACCHAROMYCES CEREVISIAE
Authors: Deschamps Jacqueline , Wiame Jean-Marie
Published: April 2021

Cis-acting regulatory mutations have been isolated that affect L-ornithine transaminase (OTAse), an enzyme catalyzing the second step of arginine breakdown in yeast. These mutations lead to constitutive synthesis of OTAse at various levels. Two different types of mutations have been recovered, both of which are tightly linked to the structural gene (cargB) for this enzyme. One type behaves as a classical operator-constitutive mutation similar to the cargB+O-—l mutation previously described (DUBOIS et al. 1978) .—The second type is peculiar in two respects : the higher level of constitutive OTAse synthesis and the expression of constitutivity in diploid cells. These mutations are designated curgB+Oh. They behave as usual operator-constitutive mutations in diploid strains homozygous for mating type (a/a or α/α), but the constitutivity is strongly reduced in a/α diploid cells.
MAPPING CHROMOSOMAL GENES OF SACCHAROMYCES CEREVISIAE USING AN IMPROVED GENETIC MAPPING METHOD
Authors: Wickner Reed B
Published: April 2021

A triploid (3n) strain of Saccharomyces cereuisiae was constructed carrying a standard marker on each of chromosomes I through XVII in the ——/+J+ configuration. This is called a "supertriploid." Meiotic spores from this strain (n + ∼ n/2) were mated with a haploid (n) carrying an unmapped mutation. Meiotic analysis of each zygote clone (2n + ∼ n/2) produced in this way resulted in elimination of an average of 4.2 chromosomes as the possible location of the unmapped marker. The distribution of extra chromosomes in the 2n + ∼ n/2) strains was nearly random. Meiotic segregrants of these crosses carrying the unmapped mutation in the -/+ configuration were then crossed with multiply marked haploid strains to further narrow the possible location of the unmapped mutation to a single chromosome. Scoring of markers by complemention tests was simplified by mating spore clones with mixtures of a and α strains, each pair carrying the same set of markers. Using this new, more rapid method ("supertriploid mapping"), eight genes required for the maintenance of the killer plasmid were located on the genetic map of S. cerevisiae.
GENETIC VARIATION IN AMOUNT OF SALIVARY AMYLASE IN THE BANK VOLE, CLETHRIONOMYS GLAREOLA
Authors: Hjorth J Peter , Meisler Miriam , Nielsen J TØnnes
Published: April 2021

Several investigated bank vole populations are polymorphic for the number of salivary amylase loci, and individual chromosomes may carry one, two or three linked amylase structural genes. In the present study, we have used bank vole stocks homozygous for different chromosomes to investigate the relationship between amylase production and gene number. By measuring the amylase activity in parotid glands and the percentage of amylase protein in saliva, we have been able to demonstrate that the amount of salivary amylase is directly proportional to the proposed gene number. The paper also describes the allele, Amysu, which codes for a heat-labile salivary amylase. The relative amounts of the heat-labile isozyme have been determined in different hetero-zygotes containing this allele, and these results also support the multiple locus model. Finally, a stock devoid of salivary amylase activity was established. Animils from this strain have, however, a protein in the parotid glands and in saliva that is very similar to amylase in molecular weight, amino acid composition and in its binding to glycogen and cyclohepta-amylose. In genetic crosses, the protein segregates as an amylase allele. Therefore, this protein, encoded by the functionally null alleleAmyN, may represent an incorrectly processed amylase precursor.
ENZYME POLYMORPHISM AND CYCLIC PARTHENOGENESIS IN DAPHNIA MAGNA. II. HETEROSIS FOLLOWING SEXUAL REPRODUCTION
Authors: Young J P W
Published: April 2021

Cyclical parthenogenesis exaggerates the force of selection relative to recombination and will therefore enhance interlocus effects. Observations of electrophoretic variation in a natural population of Daphnia magna Straus (Crustacea: Cladocera) are interpreted in this light. Sexual reproduction led to Hardy-Weinberg equilibrium, but heterozygote excesses rapidly developed at each of three observed loci during subsequent parthenogenesis. Homozygote fecundity was often lower than that of heterozygotes; this may have been the cause of some of the observed frequency changes. The superior fitness of the enzyme heterozygotes does not imply that selection was necessarily acting on the enzyme loci themselves, since apparent heterosis is the expected result of linkage disequilibrium.
A STUDY OF LINKAGE DISEQUILIBRIUM IN BRITISH POPULATIONS OF DROSOPHILA SUBOBSCURA
Authors: Charlesworth B , Charlesworth D , Loukas M
Published: April 2021

Data have been obtained concerning the genetic content of samples of O chromosomes from three British populations, and J chromosomes from one population, of Drosophila subobscura. Some improvements to the genetic map of the O and J chromosomes have been made. Allele frequencies at the loci studied do not show much geographical variation, except where associations with geographically varying gene arrangements distort the picture. Striking nonrandom associations between alleles at three enzyme loci and closely linked O chromosome gene arrangements are present. Some historical explanation for these associations cannot at present be ruled out, but it is clear that a very high degree of genetic differentiation must exist between different gene arrangements in this species. There is no convincing direct evidence for linkage disequilibrium between pairs of enzyme loci, although there is a significant association between close linkage and a high value of the linkage disequilibrium measure. This suggests that there may be disequilibria between closely linked enzyme loci that are too small to be individually detectable. These results are in broad agreement with those reported by workers on other Drosophila species. At present there appears to be no evidence to support the concept that selection is sufficiently strong at individual enzyme loci to produce a high degree of nonrandom associations. (FRANKLIN and LEWONTIN 1970).
MUTANTS OF TETRAHYMENA THERMOPHILA WITH TEMPERATURE-SENSITIVE FOOD VACUOLE FORMATION. I. ISOLATION AND GENETIC CHARACTERIZATION
Authors: Suhr-Jessen Peter B , Orias Eduardo
Published: April 2021

Germ-line mutants have been isolated in Tetrahymena thermophila that have recessive, temperature-sensitive defects in phagocytosis. Nitrosoguanidine-mutagenized cells were induced to undergo cytogamy, and clones were isolated that were unable to form food vacuoles after two days of growth at 39°. Most of the mutants belong to a single complementation group, designated vacA. They have defects in oral development—not in phagocytosis per se—that are undetectable under light microscopy. One fertile mutant, phenotypically indistinguishable from the vacA group, has its vac mutation(s) restricted to the macronucleus, and it is a heterokaryon for two other markers. This clone probably resulted from a failure of the two gametic nuclei to fuse after nor,mal exchange. Two additional mutants were studied, but their sterility prevented a full genetic analysis. One of these clones has a rudimentary oral apparatus and defective contractile vacuole pores; both defects may be determined by the same mutation. The other clone has a structurally normal oral apparatus and may be defective in phagocytosis per se.——The induction and characterization of germ-line mutations that affect oral development open the way for the genetic dissection of the morphogenesis of a complex eukaryotic organelle, and make available additional useful mutants for the study of nutrition and transmembrane active transport.
HYBRID DYSGENESIS IN DROSOPHILA MELANOGASTER: MORPHOLOGICAL AND CYTOLOGICAL STUDIES OF OVARIAN DYSGENESIS
Authors: Schaefer Ruth E , Kidwell Margaret G , Fausto-Sterling Anne
Published: April 2021

A type of intraspecific hybrid sterility, between two strains of Drosophila melanogaster, referred to as GD (gonadal dysgenesis) sterility, is observed when females from a type of strain called M are crossed with males from a second type called P. Absence of egg-laying is characteristic of female GD sterility and its manifestation is conditional on high developmental temperatures. Morphological and cytological studies of GD sterile females are described. These individuals were normal in body size and external appearance. No defects in sperm storage were observed. Both adult and larval ovaries were drastically reduced in size in comparison with control ovaries. This ovarian dysgenesis was sometimes unilateral, but more frequently it was bilateral, particularly in females developing at the highest test temperature. The ovarioles of dysgenic ovaries contained no vitellaria; the germaria lacked any cells resembling the cystocyte clusters of normal ovaries. I t is concluded that sterility results from an early blockage in ovarian development, rather than from atrophy of previously developed structures. Possible mechanisms for this developmental arrest are discussed.
CHROMOSOMAL LOCATION OF TWO MITOCHONDRIAL MALATE DEHYDROGENASE STRUCTURAL GENES IN ZEA MAYS USING TRISOMICS AND B-A TRANSLOCATIONS
Authors: McMillin David E , Roupakias D G , Scandalios John G
Published: April 2021

Maize mitochondrial malate dehydrogenase is coded by four genetic loci, Mdhl, Mdh.2, Mdh3 and Mdh4. Two of the four loci have been located on the long arm of chromosome 6, using trisomic analysis and B-A translocations.
EVOLUTIONARY CONSERVATION OF EQUINE Gc ALLELES AND OF MAMMALIAN Gc/ALBUMIN LINKAGE
Authors: Weitkamp Lowell R , Allen Peter Z
Published: April 2021

Ancient origin of the equine vitamin D binding protein (Gc) polymorphism is suggested by the finding of two alleles, GcF and Gcs, in each of three equine subgenera, Equus, Asinus and Hippotigris. The equine Gc and albumin loci are closely linked (lod score = 6). Although no recombinants were observed, the data are not inconsistent with a map distance similar to the 2 centimorgans reported for the human albumin/Gc linkage relationship. Gametic association between the GcF and AlbF alleles appears probable in the American Standardbred horse, perhaps as a result of population structure. Since Gc and albumin are both polymorphic in rodents and possibly other orders, this linkage group will be useful for studies of the evolution of mammalian linkage groups, as well as for a comparison of meiotic recombination frequencies and linkage disequilibria in different species.
DELETIONS GENERATED BY THE TRANSPOSON Tn10 IN THE srl recA REGION OF THE ESCHERICHIA COLI K-12 CHROMOSOME
Authors: Csonka LÁszlÓ N , Clark Alvin J
Published: April 2021

A negative regulatory gene for the srl operon (srlR) was recognized by the characteristics of an insertion mutation generated by the transposon TnlO determining tetracycline resistance. This finding is discussed in light of previous hypotheses on the regulation of the srl genes, which mediate metabolism of glucitol (i.e, sorbitol). Mapping showed that the order of genes in this region is: srlR srlD srlC recA alaS. Using two different methods, five mutations of both srl and recA were detected. The phenotype conferred by these mutations, UV sensitivity and extreme recombination deficiency, is characteristic of standard recA point mutants. Three of the mutations were deletions that also removed the genes for tetracycline resistance of the nearby transposon. A fourth mutation ended at a distance from Tn10 sufficient to allow separation of the two by recombination following P1 transduction; our tests did not allow US to conclude whether this mutation was an inversion or a deletion. The fifth mutation was a deletion that seemed to end immediately adjacent to the boundary of Tn10. proximal to recA. Mechanisms for the generaticn of these srl recA mutations are discussed.
GENETIC ANALYSIS OF GAMMA-RAY MUTAGENESIS IN YEAST. II. ALLELE-SPECIFIC CONTROL OF MUTAGENESIS
Authors: McKee Richard H , Lawrence Christopher W
Published: April 2021

We find that partially different sets of gene functions are required for the production of different kinds of mutations induced by 6OCo γ rays in Saccharomyces cereuisiae. This observation is very similar to others made previously with respect to UV mutagenesis (LAWRENCE and CHRISTENSEN 1978a,b, 1979) and confirms the conclusion that such distinctive patterns of genetic control reflect properties of the test alleles and their genetic locations, rather than the kinds of lesions required to revert them. The data also support the model of mutagenic repair outlined in the first paper of this series (MCKEE and LAWRENCE 1979), in which partially different sets of gene functions are required for the production of different kinds of mutations, the formation of mutations at different genetic sites and the induction of mutations by different mutagens.
SITE-SPECIFIC INSTABILITY IN DROSOPHILA MELANOGASTER: THE ORIGIN OF THE MUTATION AND CYTOGENETIC EVIDENCE FOR SITE SPECIFICITY
Authors: Lim J K
Published: April 2021

During a study of delayed mutations, an unstable X chromosome (UC) was detected. Spontaneous X-linked recessive lethal mutations were detected in 34 of 993 sperm sampled from 50 males carrying this chromosome. All but three of the 34 lethals originated as clusters in three of the 50 males Cytogenetic and complementation analyses revealed 14 intrachromosomal rearrangements: ten inversions, two reverse repeats, one deficiency and one transposition. Eight of the 14 rearrangements have one break in the 6F1-2 doublet and two rearrangements have a break in 6F1-5 of the X chromosome. The remaining four rearrangements have in addition to the aberrations a lethal point mutation between 6F1 and 6F5. Though each of the lethal lines was established from a single lethal-bearing female, chromosome polymorphism is evident in 17 of the 18 lines having rearrangements, with certain aberrations recurring in several lines. The lethal mutations revert frequently to the nonlethal state, and cytological evidence indicates that more than one mutational event may occur at the unstable locus of the chromosome during one generation. Two lethal lines had more than one type of chromosome rearrangement sharing a common breakpoint. These observations are consistent with the view that the instability in the Uc lines is caused by a transposable element capable of site-specific chromosome breaks and perpetual generation of mutations. The mutagenic and genetic properties of transposable elements can be related to the two-mutation theory of KNUDSON (1971) for cancer initiation.
TOWARDS A GENETIC THEORY FOR THE EVOLUTION OF THE SEX RATIO
Authors: Uyenoyama Marcy K , Bengtsson Bengt Olle
Published: April 2021

Present address: Department of Zoology, University of Texas, Austin, Texas 78712.—Permanent address: Institute 0f Genetics, University of Lund, S-223 62 Lund, Sweden.
HERITABILITY OF POLYCHOTOMOUS CHARACTERS
Authors: Gianola Daniel
Published: April 2021

Characters with phenotypic expression consisting of a response in one of several mutually exclusive and exhaustive categories are considered. Formulae relating heritability in the discrete, outward scale to heritability in underlying normal and exponential scales are presented. For the normal case with two response categories, results reduce to the well-known formula for heritability of binary traits.
A SUPPRESSOR OF MATING-TYPE LOCUS MUTATIONS IN SACCHAROMYCES CEREVISIAE: EVIDENCE FOR AND IDENTIFICATION OF CRYPTIC MATING-TYPE LOCI
Authors: Rine Jasper , Strathern Jeffrey N , Hicks James B , Herskowitz Ira
Published: April 2021

A mutation has been identified that suppresses the mating and sporulation defects of all mutations in the mating-type loci of S. cereuisiae. This suppressor, sir1-1, restores mating ability to matαl and matα2 mutants and restores sporulation ability to matα2 and mata1 mutants. MATa sir1-1 strains exhibit a polar budding pattern and have reduced sensitivity to α-factor, both properties of a/α diploids. Furthermore, sir1-1 allows MATa/MATa, matα1/matα1, and MATα/MATα strains to sporulate efficiently. All actions of sir1-1 are recessive to SIR1. The ability of sir1-1 to supply all functions necessary for mating and sporulation and its effects in a cells are explained by proposing that sir1-1 allows expression of mating type loci which are ordinarily not expressed. The ability of sir1-1 to suppress the matαl-5 mutation is dependent on the HMa gene, previously identified as required for switching of mating types from a to α. Thus, as predicted by the cassette model, HMa is functionally equivalent to MATα since it supplies functions of MATα. We propose that sir1-1 is defective in a function, Sir ("Silent-information regulator"), whose role may be to regulate expression of HMa and HMα.
RARE-CELL FUSION EVENTS BETWEEN DIPLOID AND HAPLOID STRAINS OF THE SEXUALLY AGGLUTINATIVE YEAST HANSENULA WINGEI
Authors: Crandall Marjorie , Caulton Joan H
Published: April 2021

Diploids of the yeast Hansenula wingei are nonagglutinative and do not form zygotes in mixed cultures with either sexually agglutinative haploid mating type. However, a low frequency of diploid x haploid cell fusions (about 10-3) is detectable by prototrophic selection. This frequency of rare diploid x haploid matings is not increased after the diploid culture is induced for sexual agglutination. Therefore, we conclude that genes that repress mating are different from those that repress sexual agglutination.——Six prototrophs isolated from one diploid x haploid cross had an average DNA value (¼g DNA per 108 cells) of 6.19, compared to 2.53 and 4.35 for the haploid and diploid swains, respectively. Four prototrophs were clearly cell-fusion products because they contained genes from both the diploid and the haploid partners. However, genetic analysis of the prototrophs yielded results inconsistent with triploid meiosis; all six isolates yielded a 2:2 segregation for the mating-type alleles and linked genes.——Mitotic segregation of monosomic (2n-1) cells lacking one homolog of the chromosome carrying the mating-type locus is proposed to explain the rare production of sexually active cells in the diploid cultures. Fusion between such monosomic cells and normal haploids is thought to have produced 3n-1 cells, disomic for the chromosome carrying the mating-type locus. We conclude that in the diploid strain we studied, the physiological mechanisms repressing sexual agglutination and conjugation function efficiently, but events occurring during mitosis lead to a low frequency of genetically altered cells in the population.
POLYMORPHISMS, LINKAGE AND MAPPING OF FOUR ENZYME LOCI IN THE FISH GENUS XIPHOPHORUS (POECILIIDAE)
Authors: Morizot Donald C , Siciliano Michael J
Published: April 2021

Electrophoretic variants at four additional enzyme loci—two esterases (Est-2, Est-3), retinal lactate dehydrogenase (LDH-1) and mannose phosphate isomerase (MPI)-among three species and four subspecies of fish of the genus Xiphophorus were observed. Electrophoretic patterns in F1 hybrid heterozygotes confirmed the monomeric structures of MPI and the esterases and the tetrametric structure of LDH in these fishes. Variant alleles of all four loci displayed normal Mendelian segregation in backcross and F2 hybrids. Recombination data from backcross hybrids mapped with Haldane's mapping function indicate the four loci to be linked as Est-2—0.43—Est-3—0.26—LDH-1—O.19—MPI. Significant interference was detected and apparently concentrated in the Est-3 to MPI region. No significant sex-specific differences in recombination were observed. This group (designated linkage group 11) was shown to assort independently from the three loci of linkage group I (adenosine deaminase, glucose-6phosphate dehydrogenase, and 6-phospho-gluconate dehydrogenase) and from glyceraldehyde-3-phosphate dehydrogenase and two isocitrate dehydrogenase loci. Evidence for conservation of the linkage group, at least in part, in other vertebrate species is presented.
ADULT TRIPLOIDS IN A RAINBOW TROUT FAMILY
Authors: Thorgaard Gary H , Gall Graham A E
Published: April 2021

Six triploid individuals were found in a full-sib family of 11 adult rainbow trout (Salmo gairdneri) from a domesticated hatchery stock. The triploid individuals were normal in size and external appearance, had underdeveloped gonads, and showed no evidence of 3n/2n chimerism or mosaicism. XXY triploids were males, suggesting that the Y chromosome is male determining in trout. Because they may avoid production losses associated with sexual maturation in normal fish, triploid trout and salmon could potentially be useful in fish culture.
THE GENETIC STRUCTURE OF NATURAL POPULATIONS OF DROSOPHILA MELANOGASTER. XIV. EFFECTS OF THE INCOMPLETE DOMINANCE OF THE IN(2LR)SM1 (Cy) CHROMOSOME ON THE ESTIMATES OF VARIOUS GENETIC PARAMETERS
Authors: Mukai Terumi
Published: April 2021

Recent reports (MUKAI et al. 1974; KATZand CARDELLINO1978; COCKER-HAM and MUEAI 1978) have indicated that the Cy chromosome is not always dominant over its homologous chromosome with respect to viability. Thus,the genetic parameters previously estimated using viabilities determined by the Cy method are biased. In the present paper, the biases of the estimates for the polygenic mutation rate, the degree of dominance and the homozygous load are examined. The results indicate that the biases for the mutation rate and the degree ofdominance are small and that the estimate of the homozygous load relative to the average viability of the population is not biased.