Showing papers in "Genetics in 1971"

Mutants of yeast defective in mutation induced by ultraviolet light.

Abstract: NDUCED mutations are thought to arise as a result of enzymatic processes uti‘lizing DNA damage as a substrate (BRIDGES 1969). Although the molecular mechanism is not known, evidence reviewed by WITKIN (1969) suggests that in E. coli mutations are produced during postreplication repair of lethal damage induced by ultraviolet light (UV) and controlled by r e d and ezrf (or lexf) genes. Strains carrying rec or ezr, although normal in excision repair, exhibit reduced or no UV mutability compared to wild type. In addition, such strains are UV sensitive, X-ray sensitive, and recombination deficient in varying degrees ( WITKIN 1969). In previous studies of UV-induced mutation in fungi, UV-sensitive strains have been selected on the assumption that UV mutagenesis might be related to dark repair of lethal damage. In some of these UV-sensitive strains, the frequencies of UV mutation are reduced compared to wild type at equal UV doses (CHANG, LENNOX and TUVESON 1968; NASIM 1968; WOHLRAB and TUVESON 1969). whereas in others these frequencies are enhanced (AVERBECK et al. 1970; RESNICK 1969; ZAKHAROV, KOZINA and FEDOROVA, 1970). To identify new genes controlling UV-induced mutation, it is desirable to select strains directly for defective mutation induction, thereby avoiding the prior condition that all such mutants be UV-sensitive. Mutants of Saccharomyces cereuisiae were selected ( LEMONTT and MORTIMER 1970) for reduced ability to undergo UV-induced locus reversion of the ochresuppressible (GILMORE 1967; HAWTHORNE 1969) argl-17 allele. This paper describes the isolation and some characteristics of these “reversionless” mutants, The results are discussed in relation to current ideas about induced mutagenesis.

Inbreeding and variance effective numbers in populations with overlapping generations.

Abstract: HE concept of effective population number originated with SEWALL WRIGHT (1931,1938). He and others have calculated effective population numbers for a variety of models of population reproduction. In particular, KIMURA and CROW (1963) have calculated the variance effective number for a population of constant size in which there are overlapping generations and age-dependent birth and death rates. NEI has presented (NEI and IMAIZUMI 1966) a different formula as a correction to KIMURA and CROW. In this paper, I will argue that the KIMURA & CROW formula is incorrect and the NEI formula is not precisely defined. I will derive equations for both inbreeding and variance effective numbers in models of population reproduction in which birth and death rates are age specific.

Polarity and enzyme functions in mutants of the first three genes of the tryptophan operon of Escherichia coli.

Abstract: N operons which are believed to be transcribed into polycistronic messenger I RNA molecules, some revertible mutations result in a lowered rate of synthesis of enzymes specified by genes operator-distal to the mutated gene. This phenomenon, termed polarity (FRANKLIN and LURIA 1961 ; JACOB and MONOD 1961 ) , has been studied in several organisms and a variety of explanations have been proposed for the observed effect on enzyme levels. Mutational changes which cause polarity are now known to have in common the introduction of a polypeptide chain-termination codon within a structural gene of an operon (NEWTON et al. 1965; WHITFIELD, MARTIN and AMES 1966; YANOFSKY and ITO 1966). Mutations of the missense type, resulting in amino acid substitutions, do not cause polarity. In the present study mutants of the first three genes of the tryptophan operon of Escherichia coli were characterized. The properties of the mutants and their respective altered proteins or protein fragments revealed interesting features of the corresponding wild-type proteins. Many of the mutants exhibited polarity and were employed in determinations of the shape of the polarity gradient for their respective genes. Additionally, antipolarity ( ITO and CRAWFORD 1965; YANOFSKY and ITO 1967), an effect on expression of the gene immediately preceding a gene with a chain termination mutation, was examined in strong polar mutants of several genes of the operon.

Genic mutants with altered system of excitation in Paramecium aurelia. II. Mutagenesis, screening and genetic analysis of the mutants.

Abstract: HE development of behavioral genetics in Paramecium aurelia reported here Tis part of an attempt to dissect the system of behavioral control centering on the excitable membrane. Molecular lesions can be produced in cells by mutagenesis. Mutants can then be screened for behavioral deviations which indicate lesions in the excitable system. By studying the phenotypic expression behaviorally and electrophysiologically, one can try to understand the relation between the mutated molecular entities and the normal function of the system. It may also be possible to identify the mutated molecules using available immunological and biochemical techniques. While the rationale behind this work is the same as BENZER’S (1967), the level of study is quite different from the genetic dissection of the nervous system. The pellicular fibrils in ciliates have apparently no function in coordinating ciliary beats (OKAJIMA and KINOSITA 1966; NAITOH and ECKERT 196913) as had been previously suggested (TAYLOR 1920), and are thus a poor analog of the central nervous system of multicellular forms. On the other hand, these eukaryotes can be viewed as excitable cells capable of generating receptor potentials and action potentials (KINOSITA, DRYL and NAITOH 1964a, 1964b; NAITOH and ECKERT 1968a, 1968b, 1969a) upon proper electrical, mechanical and chemical stimulations. Protozoa are thus comparable to excitable cells such as neurons, muscle fibers and hair cells in metazoa. Paramecium as an experimental material for such study offers the following advantages: 1. Paramecium behaves relatively stereotypically (JENNINGS 1906). The locomotor behavior of the organism reflects the electrical behavior of the membrane. Ciliary reversal (hence, backward swimming) is correlated with membrane depolarization, whereas augmented ciliary beat in the normal direction (rapid forward swimming) is correlated with hyperpolarization (KINOSITA, DRYL and NAITOH 1964a, 196413). Changes in membrane (and other structural components involved in movement) by mutation will appear as changes in behavior. Thus,

The Relation between Fitness Components and Population Prediction in Drosophila. II: Population Prediction.

Abstract: HIS is the second of two articles (PROUT 1971) describing an experimental Tsystem for estimating fitness components in Drosophila. The system is principally concerned with the fitness components operating in the adult phase of the life cycle where fertility and mating effects can generate complications in the pattern of selection. The objective is the estimation of a sufficient set of adult components for the purpose of predicting genotype frequencies in a poplation. In the first article the experimental system is described in detail and then applied to certain fourth chromosome mutants of Drosophila melanogaster. In this article the estimates of fitness components are incorporated into recurrence equations which are then used to predict the behavior of experimental populations segregating for these same mutants. MATERIALS AND METHODS Drosophila melanogaster fourth chromosome recessive mutants eyeless (eyt) and shaven (sun) in repulsion linkage constitute the genetic system used to test the method. Because of the negligible recombination within fourth chromosomes, the two mutants are treated as segregating alleles which complement to produce a wild-type heterozygote. The three genotypes will be denoted ee. e/s, ss, for eyeless, heterozygote, and shaven, respectively. Five populations were started with e/s flies. Each population was maintained in a half-pint culture bottle containing medium. The eggs laid were allowed to develop at 25°C for two weeks, at the end of which time the adult flies were transferred to a new bottle for 24 hr of egg laying, after which the adult flies were removed, and a sample d 100 (ignoring sex) was classified and counted. The eggs resulting from the 24 hr of egg laying constituted the beginning of the next generation. The five populations, designated A through E, were maintained for 25 generations. As will be shown presently, all populations quickly established a polymorphic equilibrium. In order to provide data for testing the theory, artificial perturbations of the equilibrium were introduced twice during the history of the populations, at generation 9 and at generation 21. A perturbation was accomplished in the following way: For a given population at the end of the 2-week period, instead of transferring the flies as usual, the entire population was etherized and all flies were discarded except the females of one of the homozygous phenotypes (eyeless or shaven). Then only these females, most of whom had previously mated, were used as founders of the next generation by the usual 24 hr of egg laying. The next and subsequent generations were treated routinely. At generation 9, populations A and B were selected for shaven (against eyeless), D and E were selected in favor of eyeless (against shaven), while population C was left unperturbed. At generation 21, A and B were selected for eyeless, D and E were selected for shaven, and C was left unperturbed.

Analysis of chromosome 4 in Drosophila melanogaster. II. Ethyl methanesulfonate induced lethals.

Abstract: O U T S I D E the realm of the prokaryotes, it may appear unlikely that a complete inventory of the genetic material contained in the individual vehicles of hereditary transmission, the chromosomes, can be obtained. The chromosomes of higher plants and animals are either too large or the methods required for such an analysis are lacking. However, an approach to the problem is possible with the smallest autosome (number 4 ) in Drosophila melanogaster. In this genetically best-known diploid organism appropriate methods are available and the size of chromosome 4 (0.2-0.3 p at oogonial metaphase) suggests that the number of loci might be a relatively small, workable figure. An attempt is being made to uncover all of the major loci on chromosome 4, i.e., those loci capable of mutating to either a recessive lethal, semilethal, sterile, or visible state. In the first paper of this series (HOCHMAN, GLOOR and GREEN 1964), we reported that a study of some 50 spontaneous and X-ray-induced lethals had revealed a minimum of 22 vital loci on the fourth chromosome. Subsequently, two brief communications (HOCHMAN 1967a,b) noted that the use of chemical mutagens had substantially increased the number of lethal chromosomes recovered and raised the number of loci detected. This paper contains an account of approximately 100 chromosome 4 mutations induced by chemical means (primarily recessive lethals which occurred following treatments with ethyl methanesulfonate) . Analyses of the interactions of these mutations inter se and with the older spontaneous and radiation-induced factors have elevated the number of vital loci disclosed to 33 and strengthened our earlier estimate that the total number of essential loci on this microchromosome is less than 40. Evidence of the existence of the first complex locus on chromosome 4 will be presented here, as will an attempt to reconcile the disparity between our postulated number of microchromosomal genes and that derived from this autosome’s DNA content as estimated from the work of others.

Mating Types in Saccharomyces: Their Convertibility and Homothallism

Abstract: GENETIC systems controlling homothallism uersus heterothallism in Saccharomyces yeasts have been reported by several authors ( WINGE and ROBERTS 1949; TAKAHASHI 1958; HERMAN and ROMAN 1966; TAKANO and OSHIMA 1967). Allelism tests indicated that all the homothallism gene systems in S. cereuisiae and its related species are the same (TAKANO and OSHIMA 1970a). The controlling system in these strains consists of two unlinked genes, HO, and HM. The HO, gene acts as a specific mutator for the 01 mating-type allele and changes 01 to a shortly after spore germination (TAKANO and OSHIMA 1970b). A cell converted from 01 to a can make a zygote with its neighboring 01 cell. An a allele converted from 01, designated a’, is as stable as normal a, and responds like a normal a to HO,. Thus the 01 HO, hm clone is homothallic, and after meiosis it segregates 2 homothallic : 2a in every ascus (TAKANO and OSHIMA l967,1970a, 1970b). The HM gene has no effect alone, but when combined with HO,, it converts a to homothallism (TAKANO and OSHIMA 1967). This paper presents data demonstrating that the combination of two complementary genes, HO, and HM, brings about the conversion of an a allele to a. An 01 mating-type allele, 01’) derived from the a or d allele is stable and cannot be distinguished from normal O( either in its ability to form zygotes with a cells or in its response to HO,.

Prevention of congenital otolith defect in pallid mutant mice by manganese supplementation.

Abstract: HERE are numerous genetic loci in mice which affect primarily pigmenta‘tion; SEARLE (1968) lists 44 loci with nearly 100 mutations. Eighteen (40%) of these loci possess mutant alleles with known pleiotropic effects. In some cases the pleiotropic effect has been traced to a biochemical, morphological, or developmental phenomenon, but no direct relationship has been demonstrated between the mutation’s effect on pigmentation and the associated defect. The investigations presented in this paper suggest that some of these pleiotropic effects may involve subtle relationships between pigmentation and trace-element requirements. The gene used in these studies is pallid (symbolized by pa) which was discovered in a wild population of mice (ROBERTS 1931). I t was first identified as pink-eyed-2 because it was similar to but phenotypically and genetically distinct from pink-eyed dilution. In addition to the effect of pa on pigmentation, CASTLE (1941) observed that the viability of pa mice was considerably reduced under crowded conditions, and that they “tended to be nervous and jumpy.” LYON ( 195 1 ) showed that specific behavioral anomalies of these mice were associated with otolith defects within the inner ear. As a result of these studies and of LYON’S (1953, I954,1955a, 1955b) more detailed examination of pa, it can be described as a color mutation with pleiotropic effects on behavior, growth, and viability. The effect on pigmentation (including the absence of pigment from the membranous labyrinth) is fully penetrant in the homozygote recessive (pa/pa) whereas the effect on otolith formation is highly variable. Although the mass of otolith crystals (otoconia) may be reduced in or absent from any of the four otoliths, there is considerable asymmetry between left and right ears and between the utricle and saccule of the same ear. LYON (1954) elegantly demonstrated a significant effect of litter size on the penetrance of the otolith defect. She therefore postulated that the otolith defect “may be due to competition [in utero] for food substances, either general o r particular, o r for oxygen, space, etc.”

A Study of Frequency-Dependent Selection Observed in the Esterase-6 Locus of DROSOPHILA MELANOGASTER Using a Conditioned Media Method.

Abstract: an earlier paper, KOJIMA and YARBROUGH (1967) reported that the relative ':abilities between the fertilized egg stage and the adult stage were not constant for the three genotypes of esterase-6, when the gene frequency was deviating from its equilibrium frequency in a laboratory population of Drosophila melanogaster. which had not changed genotype frequencies at several loci for more than 45 generations. Furthermore, the intensity of selection appeared to depend upon the degree of deviation from the equilibrium gene frequency. The greater the deviation, the more intense was the selection pressure toward the equilibrium frequency. A similar but more carefully designed experiment, using Drosophila melanogaster's alcohol dehydrogenase (ADH) locus with two alleles, showed a similar result for viability as those of the Est-6 experiment cited above (KOJIMA and TOBARI 1969a). This mode of selection was called frequency-dependent selection by these authors. In this paper, alleles esterase-6F and -6s are abbreviated as F and S, respectively. YARBROUGH and KOJIMA (1967) also carried out a separate study by setting up a series of cage populations using the same Est-6 lines, in which the frequency of the F allele was approximately 90% in four cages, and approximately 10% in another four cages at the initial generation. The F frequency converged rapidly to the 0.40-0.50 range in the cages with the high initial F frequency, and to the 0.30-0.35 range in the cages with the low initial frequency. Thereafter, it approached very slowly to the original equilibrium value of the F frequency. From this information, they also concluded that the fitness values of the three genotypes (FF, FS, SS) were frequency dependent. The major objective of this paper is to propose a possible mechanism which explains the observed results reported by the papers mentioned above, by examining a major component of fitness associated with this small region of chromosome (interval about 2.5 % recombination long) marked by the esterase-6 locus. MATERIALS AND METHODS

Measurement of fitness at the esterase-5 locus in drosophila pseudoobscura

Abstract: KNOWLEDGE of the amount of genic variation in natural populations is the first step towards understanding how such variation is maintained. The first systematic studies of the amount of genic variation in natural populations of Drosophila pseudoobscura were reported by HUBBY, LEWONTIN, and co-workers (HUBBY and LEWONTIN 1966; LEWONTIN and HUBBY 1966; PRAKASH, LEWONTIN and HUBBY 1969) who estimated that 40% of the loci are polymorphic and that on the average 12% of loci per individual are heterozygous in North American populations of the species. Similar estimates of heterozygosity have now been made for several organisms, including mice (SELANDER and YANG 1969) and humans (HARRIS 1969; LEWONTIN 1967). All these estimates indicate that the proportion of polymorphic loci in natural populations may be much greater than was previously supposed. Were these polymorphisms maintained primarily by heterosis operating independently at each locus, populations probably would not be able to tolerate the huge genetic load involved (see LEWONTIN and HUBBY 1966). SVED, REED and BODMER (1967) have attempted to solve this dilemma by postulating that there is a limit to maximum fitness because of gene interaction. Owing to the rarity of the maximally fit genotypes, the amount of reduction in the selective advantage of heterozygote over homozygote at individual loci is extremely small. KING (1967) proposed a different threshold model in which he assumed that a certain proportion of the population with the “worst combination of genes, environment, and luck” will be eliminated by natural selection. The effect of KING’S model is similar to that of SVED, REED and BODMER (1967) both in the sense that maximal fitness is approached asymptotically as heterozygosity increases, and that there are thousands of different genotypes with essentially the same fitness. According to these models a large number of polymorphic loci can be maintained without increasing genetic load to an excess. However, both hypotheses fail to explain the relatively small loss of fitness found when natural populations are inbred. The hypothesis of neutrality or very small selection coefficients of allozymes as proposed by KIMURA (1968) may be adequate to explain the maintenance of large amounts of polymorphism by assuming a rather high mutation rate, migration rate, and population size, but it does not appear to be an adequate explanation of

Growth and reproduction in mice selected for rapid body weight gain.

Abstract: EVERAL investigators have reported the results of selecting for measures of growth rate or body size in mice (GOODALE 1938; MACARTHUR 1944, 1949; FALCONER 1953; RAHNEFELD et al. 1963; ROBERTS 1967). Direct response to selection has been substantial in each of these cases. Litter size has been shown to increase in several of the lines, the increase in the experiment reported by RAHNEFELD et al. (1966) being nearly three mice per litter. This suggested the possibility that litter size might be increased more rapidly by indirect selection, for body weight gain, than by direct selection, particularly since results of selection for litter size have indicated quite low heritability for this trait (FALCONER 1960; DALTON and BYWATER 1963). A line selected for rapid post-weaning gain was therefore included in an experiment in which the effects of selecting for litter size and its components were being studied. This permitted a direct comparison of the effects of these two kinds of selection, using the same base population and selecting contemporarily within the same laboratory. Results from this project of selecting for litter size and for its components have been reported (BRADFORD 1968, 1969). The present paper reports the direct and correlated responses to selection in the rapid gain line and lines derived from it. The results suggest a complex relationship between body size and reproduction in the mouse, and provide additional evidence on the nature of the genetic control of litter size. MATERIALS AND METHODS The base population was a cross of four inbred lines (C57BL/6JJ, AKR/J, C3H/J, DBA/2J). Details of the formation of the stock and of the management of the colony are given in an earlier paper (BRADFORD 1968). The diet used was commercially prepared “White Diet” with specified minimum protein and fat contents of 24% and 7% respectively. The strain selected for rapid post-weaning gain was designated line G. Eighteen males were each mated to two females each generation. Litters were counted the day of birth, and sexed at two days of age when litters of more than 10 were reduced to 10; there was no augmentation of litters with fewer than 10. Young were weaned, weighed, and ear notched at 21 days and caged, by sex, 4 to 7 per cage to 42 days of age when they were reweighed. Those individuals with the greatest weight increase between the two weighings were selected, regardless of litter, litter size or coat color genotype. Normally more than the necessary 18 males and 36 females were kept at six weeks, but only those numbers were mated except in the latest generations when numbers were increased slightly. Matings were made at approximately nine weeks of age, thus producing four generations per year. Males remained with the females for 7-10 days in the early part of

Localization of tRNA genes in the salivary chromosomes of Drosophila by RNA:DNA hybridization.

Abstract: HE methods for in situ molecular hybridization to nuclei and chromosomes Thave been developed due primarily to the efforts of GALL and PARDUE (1969), PARDUE et al. (1970) and JOHN, BIRNSTIEL and JONES (1969). In theory the procedure permits the use of any fraction of labeled RNA or DNA to locate the site of specific binding in a genome, provided there is enough radioactivity for detection by autoradiography. During o w recent successful hybridization study locating the genes coding for 5s RNA at region 56EF on chromosome 2 (R) in Drosophila melanogaster ( WIMBER and STEFFENSEN 1970), it became apparent that numerous other sites on the salivary chromosomes were labeled due to the binding of [3H]tRNA which was present in the 5s RNA fraction. The present experiments exploit these observations and provide evidence of cytological location of the genes which code for the transfer RNA molecules in Drosophila melanogaster. The analysis of the location of the [\"]tRNA:DNA hybrids has been done for the X chromosome and most of chromosome 2, including the entire right arm (2R) and the distal half of the left arm (2L).