Showing papers in "Genetics in 1968"

Genetics of the left arm of the chromosome of bacteriophage lambda

Abstract: HE chromosome of temperate bacteriophage lambda consists of three functionally distinct regions of approximately equal size. The right arm contains the genes for regulation (EISEN et al. 1966), DNA synthesis (JOYNER et al. 1966) and cell lysis (HARRIS (et al. 1967). The central portion of the h DNA molecule is concerned with the processes of prophage integration (KELLENBERGER, ZICHICHI and WEIGLE 1961 ; ZISSLER 1967) and vegetative recombination (FRANKLIN 1967). Neither of these latter functions is essential for vegetative growth and the DNA in this region can be deleted with no loss of viability (FRANKLIN 1967; HUSKEY 1968). The left arm of the lambda chromosome is comprised of genes controlling DNA maturation (DOVE 1966; SALZMAN and WEISSBACH 1967) and genes which code for the structural components of the lambda phage particle ( WEIGLE 1966). Although many studies have been devoted to the right and central portions of the lambda chromosome, the little that we know about the left arm is mostly of a qualitative nature. CAMPBELL (1961 ) isolated suppressor-sensitive (sus) nonsense mutants of h and defined 13 complementation classes in the left arm on the basis of complementation spot tests. He also ordered these 13 classes with respect to one another by deletion mapping with hdg transducing phage. The present study was prompted by this lack of quantitative genetic information concerning the left arm of the lambda chromosome. Many of the sus mutants of CAMPBELL cannot be used to analyze the left arm in a quantitative manner. This is due to the fact that CAMPBELL’S mutants give small burst sizes under permissive conditions, suggesting that the mutant phenotype is not fully suppressed in the permissive host. To obtain reproducible recombination values in order to establish the size and spatial arrangement of genes in the left arm of the h genome, the burst size of sus mutants under permissive growth conditions should approach that of lambda wild type. Therefore, new conditions for performing crosses have been devised and new sus mutants have been isolated which appear to be fully suppressed in the permissive host. The complementation between genes in the left arm has been studied by measuring the total phage yield of non-permissive cells which have been infected with two different sus mutants. Evidence is presented that the left arm of the lambda

Compatibility reactions on solid medium and interstrain inhibition in Ustilago maydis.

Abstract: HE fungus Ustilago m q d i s is the cause of boil smut disease of corn. Although Tthe complete sexual cycle of the fungus requires the host, rapid vegetative growth on artificial medium is easily obtained. With the work of PERKINS (1 949) and the extensive investigations of HOLLIDAY (1961a) U. may& has been established as a useful tool for genetical research. Since it is also a plant pathogen it may aid in the investigation of the genetics of pathogenicity. The symptoms of the corn smut disease, gall formation and brandspore formation, are the result of the mating of two haploid strains within the host. Mating is under the control of two gene loci, a and b. There are only two a alleles but perhaps as many as 25 b alleles. Only strains with different alleles at both loci will mate; such combinations are termed “compatible”, and the a and b loci are called incompatibility loci. As early as 1932, SLEUMER and later BOWMAN (1946) and ROWELL (1955) described what they consider a mating reaction on artificial medium. They observed fusion of compatible haploid cells under a microscope; the resultant fusion product, however, developed no further. Also in 1932, BAUCH described a macroscopic indication of mating. Two compatible strains, when spotted one upon the other on malt agar, became covered with a heavy mycelial growth. Incompatible combinations and individual haploids remained yeast-like, the usual growth pattern on artificial medium. In the present paper the reaction BAUCH described is called plate mating. Some of the internal and external restrictions on plate mating are defined. A second interaction on agar called interstrain inhibition is also described; the inheritance of this inhibition is considered in detail. It is the first reported instance of extrachromosomal inheritance in U. maydis. Both plate mating and interstrain inhibition provide information on the development of the fungus in corn.

Synthetic Lethality and Semi-Lethality among Functionally Related Mutants of DROSOPHILA MELANOGASTER

Abstract: sex-linked mutant deep orange (dor) of Drosophila melanogaster is Tzonsible for a peculiar type of female sterility: mutant females produce no progeny when crossed to mutant males but yield some offspring (heterozygous daughters) when mated to wild-type males (MERRELL 1947). The effects of this mutant on embryonic development have been extensively studied by COUNCE (1956a) and more recently by HILDRETH and LUCCHESI (1967). In addition to the sterility phene, dor alters the pigmentation of the eyes (which are orange in color) and confers an abnormal spectrum of relative pteridine concentrations. An unusual characteristic of dor is that isoxanthopterin appears to be accumulated by mutant females (COUNCE 1957). During the course of preliminary investigations into the biochemical basis of dor female-sterility, art attempt was made to prevent the accumulation of isoxanthopterin in mutant females by genetic means. This resulted in the discovery of a highly specific synthetic lethal system involving dor and a non-allelic third chromosome mutant, rosy (ry) . The dor-ry system is similar to three other synthetic lethal systems, previously described in D. melanogaster: purpleoid (pd) and Purpleoider (Pdr) (BRIDGES 1922; as cited in BRIDGES and BREHME 1944) ; prune (pn) and Prune-killer (K-pn) ( STURTEVANT 1956) ; and Henna-recessiue-3 (Hnr3) and rosy (ry6) (TAIRA 1960; GOLDBERG, SCHALET and CHOVNICK 1962). A search was undertaken for the purpose of uncovering additional interactions among some of the mutants mentioned above. Since six of the latter affect eye color and/or pteridine levels, a number of other eye color mutants were tested. In addition, the female sterile mutant fused (fu) , similar in many respects to dor (although allowing lethal embryos to develop further than dor embryos (COUNCE 195613) ). was used in

The effects of inbreeding at loci with heterozygote advantage

Abstract: INCE the early studies of FISHER and WRIGHT the theory of selection within populations of finite size has received much attention. KIMURA (1964) has reviewed the part of the theory that is based on continuous models in which it is usually assumed that individuals mate at random within small closed sub-populations or lines. In such a situation we are concerned with the distribution of the frequency of individual genes over many replicate lines, or, equivalently, the distribution of the frequency of identical genes within the same line. In this report we study selection favouring heterozygous individuals with random mating within lines and no selection or crossing occurring between lines. The model for inbreeding which we discuss must be distinguished from an alternative situation, perhaps more common in plants, in which inbreeding occurs within an infinitely large population as a result of non-random mating, for example by selfing or mixed selfing and outcrossing. In the latter type of model, selection also may occur between sublines and recurrent mutation is not required for equilibria of gene frequency to occur without fixation, whereas it is in our model. These equilibrium situations have been analysed recently in some detail by ALLARD and co-workers. Many of their results for single loci are reviewed by JAIN and WORKMAN (1967) and analysis of a two locus model is given by JAIN and ALLARD (1966). The effect of selection for heterozygous individuals in small lines when there is no between-line selection has been studied by REEVE (1955) using transition probability matrices for mating types in lines of only a few individuals, and by ROBERTSON (1962). The latter considered two situations-firstly when there is a balance between mutation and fixation and secondly when, in the absence of mutation, the amount of heterozygosis is declining at a steady rate. In both, the critical factor proved to be the equilibrium gene frequency, which depends on the relative fitness of the two homozygotes. If the equilibrium frequency lies outside the range 0.2 to 0.8 then selection may have an effect opposite to that usually expected and increase the rate of fixation. In the present paper we shall be concerned with the intermediate stages of selection for the heterozygote in small lines with a known initial gene frequency. Selection may alter the mean gene frequency and the proportion of heterozygotes

Characterization of two bacterial mutants with temperature-sensitive synthesis of DNA.

Abstract: DESPITE considerable interest in recent years, the replication of bacterial DNA and the mechanism of its regulation are still poorly understood, as can be seen in recent reviews of the subject (LARK 1966; MAALBE and KJELDGAARD 1966). One approach to the study of essential cellular syntheses is through the study of temperature-sensitive mutants (APIRION 1966; EPSTEIN et al., 1963; NEIDHARDT 1966). Already several papers have appeared describing bacterial mutants impaired in synthesis of DNA at higher temperature ( BONHOEFFER 1966; KOHIYAMA et al. 1966; MENDELSON and GROSS 1967). The present report describes a procedure for the isolation of bacterial mutants with tcmperaturesensitive synthesis of DNA and the characterization of two mutants representative of the types which were most frequently encountered. The mutants studied resemble the two classes found previously (KOHIYAMA et al. 1966); but from the experiments presented here, it is evident that at least one of them represents a new kind of block in DNA synthesis. A preliminary report of these mutants has been presented ( FANGMAN 1966).

Genetic control of synaptonemal complexes in drosophila melanogaster

Abstract: AN ovary of an adult female Drosophila melanogaster consists of a parallel cluster of ovarioles, each of which is differentiated into an anterior germarium and a posterior vitellarium (see KOCH, SMITH, and KING 1967, their Figure 1 ) , The vitellarium is composed of a series of interconnected egg chambers which lie in single file. Each chamber is in a more advanced developmental stage than the one anterior to it, and each contains an oocyte and 15 nurse cells surrounded by a monolayer of follicle cells (ibid., Figure 2). The egg and its fifteen nurse cells are fourth generation descendants of a single germarial cell called a cystoblast. The cells formed by the mitotic activity of a cystoblast are called cystocytes, and it is within region 1 of the germarium that such mitoses occur (ibid., Figure 2). The cystocytes generated from a single germarial cystoblast form a branching chain of cells. The 16 cells are connected by 15 canals, each surrounded by a ring rich in protein (ibi:d., Figure 6). The cystocytes can be characterized by the number of ring canals each contains. Two cystocytes (designated l e and 2e) are interconnected and each possesses four ring canals; two cells (3e and 4e) contain three canals each, four cells (5-8e) contain two ring canals each, and eight cells (9-16e) have but one canal each (ibid., Figure 7). Cells l e and 2e undergo a different type of nuclear differentiation from cells 3-16e. Since only these two cells enter meiotic prophase, they have been named pro-oocytes, while the remaining fourteen are called pro-nurse cells. The production of fourth generation cystocytes and their differentiation into pro-oocytes and pro-nurse cells begins during the pupal stage, and continues throughout adult life (KING, AGGARWAL and AGGARWAL 1968:l. In each 16-cell cluster, however, one of the two prooocytes eventually switches to the nurse cell developmental pathway ( BROWN and KING 1964). Pro-oocytes may be readily differentiated from pro-nurse cells at the electron microscopic level by their nuclear morphology (KOCH, SMITH and KING 1967). Ribbon-like synaptonemal complexes are seen only in pro-oocyte nuclei (KING, AGGARWAL and AGGARWAL, their Figure 13). In the nucleus of the pro-oocyte

Regulation of methionine synthesis in Salmonella typhimurium: mutants resistant to inhibition by analogues of methionine

Abstract: BIOCHEMICAL and genetical experiments with methionine auxothrophs of Salmonella typhimurium (SMITH 1961 ; SMITH and CHILDS 1966; CHILDS and SMITH unpublished) have resulted in the recognition of six structural genes ( m t A , B, C, E, F and H ) concerned with well defined sequential steps in the biosynthesis of methionine (Figure 1) . Mutants of another gene (metG) do not have a specific enzyme deficiency: they are leaky due to a low level of activity of all the methimine enzymes. Methionine inhibits the activity of homoserine O-transsuccinylase (metA) and represses the synthesis of all the enzymes of the pathway (ROWBURY 1964). Two pairs of genes (metA and H and metB and F ) are linked closely enough to be co-transducible whereas the mete, E and G genes are each located in well separated regions of the circular bacterial genome (Figure 3). On the basis of this partial clustering of genes concerned with related functions, it seemed likely that the mode of regulation of methionine synthesis in this organism would be sufficiently different from that of the control of lactose (BECKWITH 1967) and arabinose fermentation (ENGLESBERG et al. 1965) in EScherichia coli, histidine (AMES et al. 1967) and leucine (BURNS et al. 1966) synthesis in S. typhimurium and tryptophan synthesis in both organisms (BLUME and BALBINDER 1966; YANOFSKY and LENNOX 1959) to justify further investigation. Mutants of bacteria resistant to inhibition by analogues of metabolic end products have often been shown to be abnormal in regulation of the biosynthesis of the normal end product ( COHEN and JACOB 1959) and to be readily amenable to both biochemical and genetic analyses. The methionine analogues a-DL-methyl methionine, DL-ethionine and DL-norleucine were found to be inhibitory and this paper is concerned with the isolation, phenotypic characterisation, enzymic abnormalities and mapping of mutants resistant to these analogues. Preliminary results (SMITH and LAWRENCE 1966) suggested that the regulation of methionine synthesis in S . typhimurium possesses some unique features.

The Effect of the Mating-Type Alleles on Intragenic Recombination in Yeast

Abstract: alleles a and CY govern the mating reaction in Saccharomyces cereuisiae T y E ~ ~ ~ ~ ~ ~ ~ and LINDEGREN 1943). High-frequency mating is obtained when haploid a or diploid a a cells are mixed with CY or 01 CY cells (ROMAN, PHILLIPS, and SANDS 1955). Matiings of cells of like mating type are rare and have been observed, in fact, only between CY cells. The mating type alleles also govern spomlation. Cells that have at least one a and one CY allele can be induced to sporulate, whereas a a and 01 CY celjls do not sporulate under any of the conditions that have been tried. Intragenic recombination occurs spontaneously in a O( diploids and its frequency can be increased substantially with ultraviolet light (ROMAN and JACOB 1957). Thus there is reason to believe that chromosomal pairing can occur during mitosis in cells of this type (see also WILKIE and LEWIS 1963; HURST and FOGEL 1964). The fact that a a and 01 ,T cells do not sporulate suggests the possibility that such cells are defective in the meiotic process. Mitotic intragenic recombination should not be affected if the lesion does not interfere with chromosomal pairing and exchange. If the lesion prevents or inhibits pairing and exchange, a reduction in intragenic recombination would be expected. The experiments described below were designed to test these alternatives.

Transferrin Groups of Tunas

Abstract: RANSFERRIN pol.ymorphism has been demonstrated by gel electrophoresis Tin many vertebrates. These include men (SMITHIES and HILLER 1959), monkeys (GOODMAN and POULIK 1961), cattle (ASHTON 1958; SMITHIES and HICKMAN 1958), sheep and goats (ASHTON and FERGUSON 1963; EFREMOV and BRAEND 1964), horses (BRAEND and STORMONT 1964), burros (NIECE and KRACHT 1967), pigs (ASHTON 1960a), mice (ASHTON and BRADEN 196l), antelopes (ASHTON and CARR 1965), harp seals (NAEVDAL 1965), doves (MUELLER 1961), chickens ( OGDEN, MORTON, GILMOUR and MCDERMID 1962), and gadoid fishes ( MBLLER and NAEVDAL 1966; M ~ L L E R 1966). BARRETT and TSUYUKI (1967) have found polymorphisms of transferrin in several scombroid fishes-yellowfin tuna, skipjack tuna, albacore, and bonito. The animals most thoroughly studied have been domestic cattle. Transferrin phenotypes have been shown to be associated with differences in fertility and fetal mortality (ASHTON 1959), and maternal-fetal incompatibility (ASHTON 1965). Transferrin phenotypes have also been associated with differences in the production of milk and butterfat (ASHTON 1960b; ASHTON, FALLON and SUTHERLAND 1964). This paper (1 ) describes transferrin polymorphisms in skipjack tuna (Katsuwonus pelamis), southern bluefin tuna (Thunnus naccoyi) , and yellowfin tuna ( T . albacares) from the Atlantic and Pacific Oceans; (2) presents evidence of differential adaptive vallues of phenotypes in skipjack tuna; and (3) discusses possible mechanisms of maintaining transferrin polymorphism in a randomly mating population.

A map of distances along the DNA molecule of phage T4.

Abstract: HE comparison of genetic map distances with distances along the DNA Tmolecule requires measurements which do not depend on frequencies of recombination between genetic markers. Several investigators have used various methods to estimate the amount of DNA in certain segments of bacteriophage genomes ( MESELSON and WEIGJX 1961 ; KAISER 1962; STAHL et al. 1964; JORDAN and MESELSON 1965; HOGNESS et al. 1966; GOLDBERG 1966; MOSIG 1966). This paper describes non-recombination distance measurements which depend on the probability of cutting DNA fragments between marker pairs of bacteriophage T4 during maturation. These measurements have led to the construction of a map of physical distances between genetic markers of this phage which is a complete circle. Populations of bacteriophage T 4 include small fractions of non-viable particles of lower than average buoyant density (“light” particles), each containing a single DNA fragment of fixed length which can be measured. Although these light particles are not viable in single infection, in mixed infection with normal particles they transmit their genetic information to viable progeny. Since the fragments represent continuous random segments of the circular genome, the “light” particles can be used to measure distances between genetic markers ( MOSIG 1966). Previous experiments using this approach had provided preliminary measurements of distances between an rZZ reference marker and 22 amber ( a m ) mutations in other genes (which are located within one third of the map on either side of the rZZ reference marker (MOSIG 1966). However, some inconsistencies among these data were not yet understood at that time (MOSIG 1966, Table 2). The light particles used in some of the previous experiments had not been examined for the length of their DNA molecules. Apparently this led to the inconsistencies. More thorough investigations revealed two additional classes of nonviable light T4 particles, in addition to those described by MOSIG (1963). These particles contain DNA fragments which are 0.77 or 0.9 of the normal molecular length. This paper reports an extension of the previous distance measurements, using only light particles whose DNA molecule had been measured, and also using more a m mutations and rZ and rZZZ mutations as additional reference markers. The results of these experiments can be summarized in three fractional maps, each of which represents the distances of certain am mutations from one of the reference markers. When the three fractional maps are combined, they yield a self-consistent circular T4 map.

Selection for litter size in mice in the presence and absence of gonadotropin treatment.

Abstract: HE extent to which reproductive characteristics can be modified by selection Tis of interest in understanding the nature of genetic variation in characteristics closely correlated with fitness. It is also relevant to the question of effecting genetic improvement in an important trait in species producing protein for human food. Different species and races within species have acquired widely different reproductive rates in the course of their evolution, but there is extensive evidence that intrapopulation genetic variability, or at least the component of it providing the basis for response to mass selection, is low. Such evidence has been reported, for example, for Drosophila (ROBERTSON 1957; KOJIMA and KELLEHER 19863) ; mice (FALCONER 1960b; DALTON and BYWATER 1963) ; swine (BOYLAN, REMPEL and COMSTOCK 1960) and sheep (REEVE and ROBERTSON 1953). This low heritability is commonly attributed to the association of reproductive rate with fitness, i.e., to the fact that natural selection has acted directionally with respect to reproductive capacity, and hence most of the additive genetic variation has been fixed (KOJIMA and KELLEHE,R 1963). The experiments to be reported here are part of a series designed to compare the effectiveness of alternative methods of selection for reproductive capacity, using the laboratory mouse as the experimental animal. This paper presents the results of selection for number born in untreated and superovulated lines. Superovulation treatment has been reported ( FALCONER et al. 1961 ) to increase phenotypic variability in litter size; selection following such treatment was carried out to determine if this is an effective means of exposing latent genetic variability.

Fine structure mapping of the tryptophan genes in Pseudomonas putida.

Abstract: ave used the tryptophan pathway to develop a gene transfer system via wta:sducing bacteriophage in Pseudomonas putida ( CHAKRAEARTY, GUNSALUS and GUNSALUS 1967). The tryptophan pathway itself has proved interesting in the number and nature of its enzymes, their mode of regulation, and the organization of the genes in the bacterial chromosome. Enzymatic analysis of extracts of prototrophic and auxotrophic strains grown on limiting and excess tryptophan levels has demonstrated six enzymatic activities under three types of regulation (CRAWFORD and GUNSALUS 1966). The reactions and gene designations are shown in Figure 1. Assignation of letters for the individual genes follows the suggestion of DEMEREC, et al., (1966). Three early enzymes, anthranilate synthase (AS) , phosphoribosyl transferase (PRT) , and the condensing enzyme for indole ring closure, indole-glycerol phosphate synthase (InGPS), are under repression control; they are produced in increased amounts on exhaustion of tryptophan, though not necessarily in a coordinate manner. The AS is feedback inhibited by tryptophan (QUEENER and GUNSALUS 1968). The genes controlling the synthesis of these enzymes (trpA (AS), trpB (PRT), and trpD (InGPS), are closely linked by transduction (CHAKRABARTY, GUNSALUS and GUNSALUS 1967, 1968). A first estimate of the size of the catalytically active proteins was obtained by molecular sieve filtration on Sephadex G-1 00 ( ENATSU and CRAWFORD 1968). The PRT and InGPS activities were recovered in better than 80% yield with retention volumes indicating respective molecular weights of 64,000 and 32,000. The recovery of AS activity rarely exceeds 20% and has subsequently been shown to require two protein fractions, separable from the other tryptophan enzymatic activities, with molecular sizes of about 17,000 and 80,000 estimated from a Sephadex G-100 column (QUEENER and GUNSALUS 1968). Of ten AS mutants examined, all lacked activity for the larger component. There is evidence for an intermediate between chorismate and anthranilate, based in part on the activity of the two enzyme components when separated by a dialysis membrane. SOMERVILLE and ELFORD (1967) have also presented evidence for several

The mechanism of modulator transposition in maize

Abstract: CCLINTOCK (1956) suggested that a transposable element in maize moves Mfrom the donor site to a different recipient site on the chromosome during the mitotic reduplication process. GREENBLATT and BRINK (1962, 1963) and GREENBLATT (1966) were able to offer experimental support for this idea, and further, developed a working hypothesis of a mechanism of the element's movement. Since the evidence collected by GREENBLATT and BRINK (1962,1963) was based solely on their analysis of red-light variegated twin mutations occurring in medium variegated pericarp, it was not clear at that time whether the model accounted for the way in which all transpositions occur. In fact, it was believed that there might be two or more ways in which an element might transpose. It is the purpose of this report to present a new hypothesis of the mechanism of transposition and show that it is the only mechanism that explains all of the transposition data concerning the autonomous controlling element, Modulator, moving away from the P locus to other chromosomal sites. Since Modulator (Mp) does not produce a direct effect on the maize phenotype, it has been studied by analyzing its interaction with the red pericarp allele on chromosome 1. The listing which follows serves to summarize the pertinent points that are known of this transposable element (Mp)-gene ( P ) interaction. P: This allele is of conventional chromosomal specificity on chromosome 1 conditioning a dominant red pigment in the pericarp, cob, and husk tissues (ANDERSON 1924). Mp: Modulator is a transposable element which has no direct control of any recognizable plant phenotype, but is capable of moving autonomously from one chromosomal site to another during development of the plant. PrMp: When Mp is located at the P locus the PT gene does not come to expression. However, in some cell lineages Mp leaves the P locus during the course of pericarp development, and in these pericarp cells where Mp is absent from PT, the chromosomal gene does come to expression and the red pigment develops. The resultant phenotype is known as medium variegated, and is characterized by a high frequency of red stripes on a colorless background (BRINK and NILAN 1952). P r M p -ttr-Mp: When a transposed Modulator (tr-Mp) is included in a cell lineage which contains the P\"Mp complex, the resultant pericarp phenotype ex-