Showing papers in "Genetics in 1943"

Mutations of bacteria from virus sensitivity to virus resistance

Abstract: This article reported Luria and Delbruck's breakthrough study in which they established that viruses do not induce mutations in bacteria, but that virus-resisting mutations are spontaneous. Their "fluctuation test" theory demonstrated that bacteria were ideal subjects for genetic research.

The Genetic Basis for Constructing Selection Indexes

Abstract: "The key is man9s power of accumulative selection: nature gives successive variations; man adds them up in certain directions useful to him"—Darwin, p 35, sixth edition of The Origin of Species 1920

Inheritance and Physiology of Efficiency in Iron Utilization in Soybeans.

Abstract: TRIKING differences in chlorosis typical of iron deficiency were noted in s I938 among a considerable number of soybean varieties when tested on calcareous soils for the first time since their introduction into the United States from Manchuria. Because these strains were not greatly different morphologically, it was thought that such wide differences in chlorosis would lend themselves especially well to a study of the inheritance and physiology of iron availability in plants. Reported casks \"1 significant differential responses of diverse plant genotypes within the same species to varying nutrient levels are not numerous. The more important to date have been reviewed recently by BURKHOLDER and MCVEIGH (1940) and will not be discussed here. They largely concern differential response of inbred lines and hybrids of corn to varying increments or sources of the major growth elements. No previous report has been found of intraspecific heritable differences in the hydrogen-ion concentration of vegetable plant tissues. Genetically controlled differences in the acidity of flower petal sap of Primula sinensis and other species have been reported by SCOTT-MONCRIEFF (1936, 1939). Macerated petal tissue of plants homozygous for the single c,37----%e gene causing low acidity showed a pH of approximately 6.0 while the dominant allele resulted in a flower petal pH of approximately 5.3. Although numerous investigations have been conducted on the availability of iron to plants, the problem is still unsolved in several aspects. Chlorosis due to iron deficiency has frequently been reported when plants were grown in either soils containing an excess of lime or nutrient solutions with high pH. Most early investigators assumed that the low hydrogen-ion concentration in either case caused iron to be precipitated in the medium, thereby rendering it non-available to plants. Discoveries that in many cases chlorotic tissues contained as much or more iron than normal tissues have altered the concepts of iron availability. Since iron may occur in abundance in tissues of chlorotic plants, it would seem that much or all of this iron is in non-available form, suggesting that some internal factors may be involved in its availability to chlorophyll-containing cells.

Chromosome Length in Relation to Transmission Frequency of Maize Trisomes.

Abstract: RISOMIC inheritance was first reported in maize by MCCLINTOCK (1929) T in a study of segregating progenies derived from a spontaneous triploid (RANDOLPH and MCCLINTOCK 1926). Later MCCLINTOCK and HILL (1931) identified the primary trisome of chromosome IO, the shortest member of the maize chromosome complement which carries the r-g linkage group, and certain general observations on the known primary trisomic types of maize were made by RHOADES and MCCLINTOCK (1935). The present study was undertaken to compare the breeding behavior of the eight available primary trisomic types in maize.

Tests for Recombination Amongst Three Lethal Mutations in the House Mouse.

Abstract: N T H E mouse a peculiar relation exists amongst three lethal mutations I which produce similar effects on development. Animals which inherit two doses of the same lethal die as early embryos, while those which inherit one dose each of two different lethals of this group may be viable. This is the result to be expected when the lethals involved occupy different loci, but in the present case the different lethals have shown no recombination with each other and may therefore be considered either as unilocal or as occupying different loci amongst which crossing over is prevented. If the first alternative were proved to be correct, there would be revealed a type of complementary interaction amongst alleles which could not be reconciled readily with theories which regard changes a t the same locus as purely quantitative in character. It is a fact, however, that the mutations in question have certain other effects in common and thus resemble other series of multiple alleles, the members of which appear to differ in quantity of effect. The first step in resolving this contradictory situation is to determine whether or not the mutations involved are unilocal. In the present paper the question will be examined as to whether or not any recombination occurs in animals heterozygous for different members of this group of lethals.

On the Cytology of Tityus Bahiensis with Special Reference to Meiotic Prophase.

Abstract: of chromosomes from related species described by other authors, as first stated by PIZA (1939a). Somatic divisions show six irregularly curved chromosomes: in the meiosis of spermatocytes three tetrads are easily distinguished, all chromatids being rod shaped, without showing signs of chiasmas, of constrictions, or any specific attachment region. The most interesting feature so far reported is the parallel movement of the chromosomes or chromatid pairs during the first anaphase. This parallel movement in Tityus seems to be the same as described first by SCHRADER (1935) for some Hemiptera (see GEITLER 1938 for further references). PIZA (1939b) has formulated far reaching speculations on this subject with which we cannot agree. The description of meiotic prophase as given by PIZA (1939a) is very incomplete. He describes very briefly leptotene, zygotene, and early pachytene stages, without corresponding illustrations. I n the description of pachynema PIZA (1939”~ p. 256) writes that “the nucleus seems to be occupied by extensive filaments of very clear chromomeric structure which describe many and large spirals, strongly accentuated in the point of separation of the respective segments.” It is not clear to what structure the term “segment” refers. Later prophase stages were not observed in the three males studied by PIZA. He assumes that in late pachynema the tetrads condense and become regular in outline, passing thus into metaphase (fig. 3, Z.C.). Finally PIZA declares categorically that “nothing exists which could be compared to a true chiasma” (Z.C., p. 2 5 7 ) . Here again we encounter some difficulty in interpreting the statement without a clear definition of what the author calls a “true chiasma” (quiasma verdadeiro). Figures d and f (plate I , Z.c,), which show photomicrographs of a chromosome arrangement in metaphase with a reciprocal translocation, are described as “chiasmas between two bivalents caused by reciprocal translocations.” We could not find any further observations on the prophase in the later papers (PIZA 1939b, 1940, 1941). The first difficulty in our study of this animal consisted in the relatively small number of males to be encountered. In several localities no male was found a t all among several hundreds of females, and it has not yet been possible to decide about the method of reproduction in these cases. In other localities, all in the vicinity of the same town, males were found, though always in smaller number than females. Small individuals have generally very few cells in meiotic T Sgo Paulo, Brazil, differs considerably with regard to form and number

Inheritance of the X Chromosome in Exceptional Males of Sciara Ocellaris (Diptera).

Abstract: HE present paper represents an attempt to throw further light on the T subject of sex determination and the sex chromosome mechanism in Sciara. Earlier work in this field has been reviewed by METZ (1938), and a brief review here will suffice. In some species of Sciara and in some strains of other species, females produce progenies, or families, which are all or nearly all of one sex. In such a progeny the few individuals of the other sex which may occur are called exceptional males (in female progenies) or exceptional females (in male progenies). It was found by METZ that males normally get their somatic X chromosome from the female parent. CROUSE and SMITHSTOCKING (1938) state that there are many cases of irregularity in the inheritance of the X chromosome in males when the yellow mutant strain of S. ocellaris is crossed with wild type. The irregularity does not appear to be causually associated with the mutant gene. A sex-linked mutant gene is necessary as a marker in order to detect the irregularity, which is presumably occurring also when a marker is not present. The evidence given below indicates that the inheritance of the X chromosome is irregular only in exceptional males and, to some extent, in males of “bisexual” progenies which are predominantly female, and further that exceptional males which retain the paternal X chromosome are sterile. I n S. coprophiEa female-producing females differ from male-producing females by the possession of a modified X chromsome, designated X’ (X prime). Female producers are heterozygous (X’X), while male producers are homozygous for the normal X chromosome (XX). All females which receive the X’ chromosome are female producers. The two types of females are apparently produced in a I: I ratio. I n S. ocellaris, on the other hand, the ratio of males to females within a progeny varies greatly. Some strains behave much like S. coprophila and give “unisexual” progenies. Others give both sexes in varying proportions. It has been found in studies as yet unpublished that some females from a “bisexual” strain may give “unisexual” progenies while their sisters yield progenies of various proportions of males and females all‘the way to a ratio of I : I. Generally in such cases the “unisexual” progenies of sisters are of the same sex and the “bisexual” progenies of their sisters tend to have more individuals of this sex than of the other sex. I n other cases the progenies of sisters may be predominantly about the I : I ratio, or the mode may apparently be around any arbitrary ratio, or the distribution may be bi-modal. I n both “unisexual” and “bisexual” strains of S. ocellaris male producers and female producers frequently are not produced in a I: I ratio. Tests for the X’ chromosome in S. ocellaris show that it does not exist sharply distinguishable

Interrelationships of the Cellular Characters of Several Species of Columba.

Abstract: MMUNOLOGICAL methods have so often been employed as a means of I differentiating species, particularly in animals but also in plants, that it is almost a truism to state that antigenic differences are one of the more important criteria by which qualitative differences between species may be assayed. In animal species, the serum antigens have been somewhat more widely used in such comparisons than have the antigens of the tissues or blood cells. LANDSTEINER and MILLER (1925”) suggested that this was due to the presumption that the species specificities of the precipitins and of the hemagglutinins are of the same order and that species specificity means protein specificity, whereas there is definite evidence that the antigens which engender antibodies against red blood cells do not consist simply of proteins. Various reports from this laboratory (IRWIN and COLE 1936a, 1940; IRWIN, COLE, and GORDON 1936; IRWIN 1939) have shown that, following a comparison of the relationships of the cellular characters of several pairs of species of pigeons and doves, certain general statements may be made. First, each species possessed antigenic components in common with the other and, secondly, in addition to the common substances, each species possessed cellular constituents peculiar to itself (that is, species-specific characters). The hybrids between any two species studied invariably contained all the common components of the two parental species and all or nearly all the species-specific properties of both parents. Furthermore, segregation of the species-specific characters has been observed, by virtue of successive backcrosses of the species hybrid and selected backcross hybrids to one or both parental species. Thus, in thiee different species crosses-Pearlneck (Streptopelia chinensis) X Ring dove (St. risoria), Pearlneck X Senegal (St. senPgalensis), and Columba guinea XC. livia domeslica, respectively-at least certain of the cellular characters peculiar to Pearlneck in the first two crosses and to guinea in the third have been obtained in unit form-that is, no further separation of these characters has been observed following the appropriate backcrosses. It has also been shown, first by immunological procedures and then verified by genetical findings, that some of the cellular characters which distinguish one species (Pearlneck) from another (Ring dove) may be shared with still a third species (Senegal) (IRWIN and COLE 1940). Also, a t least one, and probably two, of the antigenic substances which differentiate C. guinea from C. livia