The introduction of genetic material from inferior into superior strains

1. A series of experiments have been carried out withDrosophila melanogasterin order to improve further a population, highly selected for a quantitative character, by introducing genetic material from an inferior population. The effects of selecting the latter before crossing to the selected line, of waiting after crossing before restarting selection and of varying the intensity of selection after crossing have been studied. The inferior population used was the large random breeding population from which the selected line had been produced by selecting downwards for sternopleural bristles.

2. There proved to be some incompatibility between the conditions necessary to achieve the two criteria of success—the time to surpass the selected line and the extent by which it was eventually exceeded. The lines which surpassed it soonest had not been selected before crossing and had been selected intensely immediately afterwards. Those which surpassed it most had had the greatest amount of selection before crossing followed by the most intense selection afterwards.

3. Crossing-over did not appear to be a limiting factor after crossing. Neither a period of relaxation after crossing nor a lower intensity of selection after crossing increased the chance of success.

4. Genetic analyses were made of several lines which had exceeded the original selected line. In separate lines, second, third and fourth chromosomes were found which were superior to the chromosomes of the selected line. This and other evidence shows that the limits in such lines with a small number of parents are not in any way absolute but artefacts of the selection programme. The extreme third and fourth chromosomes were both recessive to that of the selected line in the effect on bristle score.

5. A theoretical discussion of such selection programmes is given, assuming that the character is controlled by independently segregating loci. It is shown that, if two alleles at different loci have an equal but small chance of fixation in the initial selection, one because it is rare and the other because, though frequent, it has little effect on the character, such a programme will tend to pick up the former rather than the latter. Of two such rare alleles with an equal initial chance of fixation, the one additive and the other recessive, the chance of fixation of the latter will be greater in a crossing programme.

Linkage disequilibrium in finite populations

A theoretical investigation has been made of the influence of population size (N) and recombination fraction (c) on linkage disequilibrium (D) between a pair of loci. Two situations were studied: (i) where both loci had no effect on fitness and (ii) where they showed heterozygote superiority, but no epistacy.If the populations are initially in linkage equilibrium, then the mean value ofD remains zero with inbreeding, but the mean ofD (2) increases to a maximum value and decreases until fixation is reached at both loci. The tighter the linkage and the greater the selection, then the later is the maximum in the mean ofD (2) reached, and the larger its value. The correlation of gene frequencies,r, in the population of gametes within segregating lines was also studied. It was found that, for a range of selection intensities and initial gene frequencies, the mean value ofr (2) was determined almost entirely byN c and time, measured proportional toN.The implication of these results on observations of linkage disequilibrium in natural populations is discussed.

Human placental lipid metabolism. III. Synthesis and hydrolysis of phospholipids

Both diacyl GPC (glycerylphosphorylcholine) and diacyl GPE (glycerylphosphorylethanolamine) are synthesized in human placental tissue from their respective monoacyl precursors. The origin of the monacyl phosphatides is apparently not the result of placental phosphatide acyl-hydrolase activity. The most likely source is maternal serum. The declining level of 1-acyl GPC in maternal serum is not attributable to lysophosphatide acylhydrolase activity and is probably explained by placental utilization for the synthesis of diacyl GPC.

Some observations on the diagnosis and epidemiology of leptospirosis in swine

The results of combined epidemiological, clinical, serological, bacteriological and histopathological studies following an outbreak of disease caused by L. pomona on a farm stocked with cattle, sheep, pigs, goats and horses maintained for experimental purposes, are reported.The incidence of infection was high in horses, cattle and pigs. A few low titres were seen in sheep. The goats were not infected. Apart from a single bovine abortion all the clinical symptoms observed occurred in pregnant sows. Seven of these aborted or gave birth to stillborn pigs within a six week period. Fifteen species of wildlife were trapped or shot on the farm during the year following the outbreak. L. pomona was isolated from four skunks and a porcupine. Epidemiological studies indicated that wildlife reservoir hosts were the primary source of infection for the domestic livestock. Leptospiruria and the serological response were studied in a group of eight infected sows. Microscopic agglutination titres of 10(2) or less could not be associated with leptospiruria and the duration of leptospiruria was found to range from a few weeks to over two years in individual sows. Direct dark-field examination of urine proved superior to guinea-pig inoculation as a method of detecting leptospiruria and it is suggested that the former technique could be adopted with advantage as a routine aid to diagnosis.

Artificial selection in plants and animals

shall be dealing in this paper with the results of selection experiments in plant said animal populations, partly from the point of view of the effectiveness of the selection in actually producing improvement, but rather more in terms of the formation that these experiments give us about the architecture of quantitative genetic variation in different kinds of characters. I shall be dealing almost entirely vith outbreeding species. As I know very little about plants I shall have to restrict myself to those plant species which behave like animals. A theory of the short-term effects of selection has existed for almost thirty years. Fundamental to this is the concept of a basic random outbreeding population; and the theory, in giving a static statistical description of the population at present, allows an immediate prediction of the response of the population to selection pressure. Strictly speaking this prediction is valid only for a single generation and its usefulness over several generations will vary from population to population. In essence this is because the prediction of changes of mean in the population are in |terms of the genetic and phenotypic variance at the time of selection, but the theory cannot predict the change of the variances though these must be expected to change as well as the mean as selection proceeds. Experimental examination of the validity of this theory rests almost entirely on experiments with laboratory animals. I would name particularly the experiments of Mather on Drosophila and of various workers in Edinburgh on both Drosophila and mice. It is a rather odd fact that the group of workers, mostly in the United States, concerned with the development of the theory were in fact primarily concerned experimentally with inbreeding and crossing experiments on animals, and as a result there are very few critical selection experiments in larger animals which were started more than about ten years ago. The notable exception to this is Lerner’s well-documented selection experiment for egg production in poultry. There were of course many statistical analyses of the genetic variation in populations of plants and animals and results of these suggested that the response to selection in many characteristics of economic importance should be fairly rapid. Recent selection experiments have confirmed this and show that the wide extent of potential genetic variation that we know to exist in our laboratory populations and also in wild populations of animals is also found in populations of domestic plants and animals.

Some observations on asymmetrical correlated responses to selection

The pattern of changes of the genetic covariance between two characters on selection was examined in an effort to explain the asymmetry of correlated responses in two traits, or of the same trait in two environments, frequently observed in experimental results.

The algebraic conclusions were further examined by model selection experiments using a computer. The computer was programmed to calculate the change in gene frequency from generation to generation and to calculate from it the expected changes in genetic variances and covariance as selection proceeded. This procedure was carried out with several models of gene effects and gene frequencies.

Asymmetry of the genetic covariance, and consequently of the correlated responses, resulted when the relative change in gene frequency at the loci contributing positively and negatively to the covariance depended on the trait selected. The conditions necessary for the development of asymmetry were examined and the results suggest that any symmetry found in an experiment is perhaps more surprising than asymmetry. Probably the most frequent contribution to asymmetry in practice will be from loci contributing negatively to the covariance and having frequencies other than 0·5.

Accurate prediction of correlated response over many generations is therefore not possible without prior knowledge of the composition of the genetic covariance, as well as its magnitude. The validity of existing theory for the prediction of correlated responses is likely to be much poorer than for the prediction of direct responses. Predictions would then have to be based on the genetic parameters estimated in each generation.

Hog cholera. V. Demonstration of the antigen in swine tissues by the fluorescent antibody technique

The fluorescent antibody technique was employed to detect hog cholera virus in tissue sections of various organs from experimentally infected swine. The method proved to be highly sensitive and infection could be detected in these animals as early as three days after inoculation with the virus. Best results were obtained when tissues were collected from young animals in advanced disease rather than from sows or from pigs in the early febrile phase. Tonsil, spleen and lymph node were the tissues of choice and were most satisfactory when removed from freshly killed animals rather than from those that had died.

A study of Toxoplasma infection in chickens and cats on a family farm

Presumptive evidence of toxoplasmosis was obtained following histological and serological studies of tissues from chickens and cats kept on a family farm. This was confirmed by transmission of the infection to experimental laboratory animals and back to chickens. The significance of the low grade serological reaction in one of the persons living on the farm was not clear.

Symptoms and pathology produced by toxic Microcystis aeruginosa NRC-1 in laboratory and domestic animals

Toxicity tests with lyophilized M. aeruginosa NRC-1 cells have been conducted using mice, guinea pigs, rabbits, chickens, ducks, two calves and one lamb as the test animals. The symptoms and pathological changes are described. On an equivalent weight basis it required three to five times the oral dosage to kill the large animals and birds as it did to kill the laboratory animals. The symptoms were less pronounced and the survival times were longer in the more resistant animals. Enlargement and congestion of the liver with necrosis of the hepatic cells were constant and pathognomonic. These findings are in general agreement with the observations of other workers who have examined the toxicity of naturally occurring Microcystis waterblooms. The toxicities and structures of microcystin and of six other biologically active cyclic polypeptides are summarized. The pathological effects produced by microcystin in laboratory and domestic animals resemble those produced in man but differ from those produced in animals by the toxic peptides of Amanita phalloides.

Hog cholera IV. Detection of the virus in tissue culture preparations by the fluorescent antibody technique

The fluorescent-antibody technique was employed for detection of hog cholera virus in tissue cultures inoculated with spleens of infected animals. As controls, cultures were also inoculated with material from normal swine and from those infected with other agents. In the first series 71 of 73 infected spleens, or 97 per cent, were detected. There were no false positive reactions among the controls. Results obtained with the second series of pigs showed that spleens collected during advanced stages of the disease were more satisfactory specimens than those collected earlier during the high temperature phase of infection. Findings with the third series of older swine indicated that their spleens were less satisfactory as a source of virus than those from young pigs. Tissues from freshly killed animals provided better specimen material than those from animals which had died.

A Note on the Rectal Instillation of Rabies Material into Syrian Hamsters

Sixty-nine hamsters ranging in age from 18 to 33 days were exposed to rabies-positive suspensions by rectal instillation. None of the animals became infected during the 60-day observation period.Les auteurs ont instillé par la voie rectale des suspensions de cerveaux rabiques à 69 hamsters dont l'âge variait de 18 à 33 jours. Aucun de ces animaux n'a succombé à l'infection au cours d'une période d'observation de 60 jours.

Isolation and Identification of a Leptospire of The Hebdomadis Serogroup (L. Hardjo) From Cattle in Canada

During the summer of 1961 an outbreak of atypical mastitis in a small herd of dairy cattle was investigated. The clinical findings, which included a single abortion, were suggestive of leptospirosis and serological studies indicated that a serotype other than the usual L. pomona was the causative agent. A fastidious leptospire recovered from the urine of one cow has been identified as L. hardjo, a member of the hebdomadis group. The difficulties encountered in isolation, adaptation to standard media and serotyping are described.

Toxoplasmosis III. Studies Using the Complement-Fixation Test and Fluorescence-Inhibition Test with Sera of Experimentally Exposed Birds

The direct, modified direct and indirect complement-fixation tests and the fluorescence-inhibition test were investigated using sera from pigeons, chickens and turkeys which had been exposed to Toxoplasma gondii. The direct CF test was suitable for use with pigeon sera. The indirect CF method effectively demonstrated antibodies in chicken and turkey sera. FI tests were less sensitive than the CF methods.

Toxoplasmosis II. Studies of Animal Sera Using Complement-Fixation Tests

Serological studies were performed in guinea pigs, a sheep, calf, goat and two pigs experimentally infected with toxoplasmosis. The direct complement-fixation method was effective in detecting antibodies in guinea-pig, goat and sheep sera. The modified complement-fixation technique supplementing complement with normal bovine serum fraction, was required when testing bovine serum. With swine sera best reactions occurred in the indirect complement-fixation test and definite but low grade reactions were produced in the direct test after pro-complementary activity was removed by pH treatment of the sera. Allergic skin reactions were produced in the experimental animals but improvement in the antigen is necessary before the test could be used generally in the field as a diagnostic method for animal toxoplasmosis.

Comparison of the Complement-Fixation Test and the Microscopic-Agglutination Test (Agglutination-Lysis) for the Detection of Leptospiral Serogroup Antibodies

The MA and CF tests using alcohol extracted antigens have been compared with sera from infected rabbits and calves. The MA test was highly serotype specific with serum from both animal species. The CF test was broadly reactive with serum from rabbits infected with various serotypes. However, when bovine serum was used cross reactivity was reduced and it was necessary to use pooled antigens to detect heterologous serotypes.

Immunological Activity of Leptospira Pomona Bacterins

Seven commercially available leptospiral bacterins were compared in guinea pigs and on that basis two of them, the best and the poorest, were further compared in calves. A wide variation was observed in their antigenicity and in their ability to provide protection. Guinea pigs appeared to be satisfactory test animals for evaluation of bacterins prepared for use in cattle.

Toxoplasmosis I. Studies by the Fluorescein-labelled Antibody Technique

The fluorescein-labelled antibody technique was investigated for the diagnosis of toxoplasmosis. The direct method, the inhibition and indirect modifications are suitable for the demonstration of Toxoplasma gondii in fluid and tissue-impression slides from animals in the acute phase of infection. The method was not applicable with the frozen tissue sections. The fluorescein-labelled antibody inhibition technique detected antibodies in immune sera from various species of animal. However the titres obtained were lower than with the complement-fixation test.

Fluorescein-Labelled Antibody Technique for the Demonstration of Leptospira Pomona

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The Effect of Prolonged Injection of Ethionine on Rabbits and Guinea Pigs on a High Cholesterol Diet

The complement titers, protein and lipid values of the serum, and the pathologic findings were compared in ethionine-injected and untreated rabbits and guinea pigs on cholesterol-supplemented or stock diets. All of the ethionine-injected rabbits when sacrificed after 7–24 week's treatment showed some degree of pathologic change in the liver and kidney or both; in some, other organs as well were affected. Atheromatous lesions in the aorta and vessels of the heart were found in all rabbits that had been on the high-cholesterol diet for periods of 14–24 weeks, their location and extent was similar in the ethionine-treated and control animals. No such lesions were observed in any of the guinea pigs on the cholesterol-supplemented diet, although there was a marked accumulation of lipid in the liver, pancreas and other organs.

The complement titers and total protein content of the serum of the untreated rabbits on the high cholesterol diet tended to be higher than those of the untreated controls on the stock diet; this difference was not observed in the corresponding groups of guinea pigs. Complement titers fell and remained low in both dietary groups of rabbits and guinea pigs during the period of ethionine treatment; in rabbits the total serum protein values were depressed initially but later rose to normal levels; prolonged ethionine treatment had no apparent effect upon the hyperlipemia developing in cholesterol-fed rabbits, but in guinea pigs on the same diet an initial rise in serum lipids was followed by a decline during ensuing months of ethionine injection.

The basic mechanisms underlying these changes observed in ethionine-injected animals are discussed briefly from the physiologic and immunologic standpoint.

The Value of Laboratory Reports on Stools in Cases of Suspected Amœbic Dysentery, and their Interpretation by the Clinician; with a Special Note on the Diagnostic Significance of Charcot-Leyden Crystals

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