On the use of animal models in the analysis of selection experiments

The use of an animal model in the analysis of selection experiments offers the theoretical advantage of accounting for changes occurring in the genetic parameters in the course of the experiments. Explicit estimators of realized heritability (h2r)(see attached document)are derived in this paper for balanced one-generation selection designs. Expressions are given for the expectations and variances of the estimators in relation to the true heritability and for the sensitivity of the estimators to the prior value of heritability. Sensitivity is generally high, except for high values of the true heritability and/or extremely large family sizes. The uncertainty on heritability may, however, be taken into account in a context of Bayesian inference, which allows a simultaneous estimation of the initial heritability and of the response. On the other hand, animal model estimators, being dependent on the genetic model assumed, may not provide adequate measures of the actual responses. They also tend to overestimate the accuracy of genetic trend evaluations, since genetic drift is not properly accounted for. Animal models, however, provide a way of evaluating the effects of selection and limited population size in long-term selection experiments, and thus permit a check on the validity of the underlying infinitesimal additive genetic model. Some examples based on published results of long-term selection experiments on mice are discussed.L’application du modèle animal à l’analyse des expériences de sélection permet en théorie une prise en compte de l’évolution des paramètres génétiques au cours de l’expérience. Des estimateurs explicites de l’héritabilité réalisée h2r (document ci-joint) sont présentés dans cet article pour le cas d’expériences de sélection sur une génération en dispositif équilibré. Des expressions sont données des espérances et des variances des estimateurs en fonction de l’héritabilité vraie, ainsi qu’une expression de la sensibilité des estimateurs à la valeur initiale de l’héritabilité. Cette sensibilité est généralement élevée, sauf pour des valeurs élevées de l’héritabilité vraie et/ou des tailles de famille très grandes. Cependant une méthode bayésienne d’inférence permet de s’affranchir de cette difficulté, en estimant simultanément la valeur initiale de l’héritabilité et la réponse. Par ailleurs, les estimateurs du modèle animal, parce que dépendants du modèle génétique supposé, ne fournissent pas toujours des mesures adéquates des réponses à la sélection. Ils tendent aussi à surestimer la précision des évolutions génétiques tracées, puisque la dérive génétique n’est pas bien prise en compte. Le modèle animal, en contrepartie, constitue une méthode d’évaluation des effets de la sélection et de la taille limitée des lignées dans les expériences de longue durée, et permet ainsi de tester la validité du modèle génétique additif infinitésimal sous-jacent. Quelques exemples basés sur des résultats de la littérature relatifs à des expériences de longue durée chez la souris sont discutés

Synchrony, Amalgam and Communion: Erico Verissimo\u27s O Tempo E O Vento as Symbolic Complex

Erico Verissimo\u27s O Tempo e o Vento has long been considered his masterpiece more, it would seem, by dint of its quantity than its quality, since relatively little research has been done on this novel. The attitudes reflected in O Tempo e o Vento concerning the relationship of time and space and man\u27s affiliation thereto have been previously ignored and only through a structuralist analysis of this novel have these determinations been discovered. The structuralist approach comprises certain inherent assumptions of an a priori system of knowledge. One assumption is reflected in the structure of language which presupposes for all mankind a common system of perceiving reality. Another assumption is the unconscious or collective mentality as explicated by Carl Gustav Jung. Finally, the acausal relationship of time and space and man\u27s compatibility with these realms are taken into consideration

An overview of the Weitzman approach to diversity

The diversity of a set of breeds or species is defined in the Weitzman approach by a recursion formula using the pairwise genetic distances between the elements of the set. The algorithm for computing the diversity function of Weitzman is described. It also provides a taxonomy of the set which is interpreted as the maximum likelihood phylogeny. The theory is illustrated by an application to 19 European cattle breeds. The possible uses of the method for defining optimal conservation strategies are briefly discussed.Un aperçu sur l’approche de la diversité selon Weitzman. La diversité d’un ensemble d’espèces, ou de races, est définie par Weitzman de façon récursive ; les données de départ sont les distances génétiques entre les éléments de l’ensemble pris deux à deux. L’algorithme de calcul de la diversité fournit, comme résultat intermédiaire, un arbre de classement des espèces en présence, qui est interprété comme une phylogénie du maximum de vraisemblance. La théorie est illustrée par un exemple d’application à 19 races bovines européennes, et les utilisations possibles de la méthode pour définir des stratégies optimales de conservation sont discutées brièvement

Selection for litter size in pigs. II. Efficiency of closed and open selection lines*

A selection experiment on litter size in the pig was carried on for seventeen generations in an Inra experimental herd. The founder population was made up of 10 males and 120 females from the Large White breed. Selection was first performed for ten generations in a closed line, compared to a control line derived from the same founder population. Selection was carried on within sire family on the total number of piglets born in the first two litters of the dam (TB1 + TB2). After ten generations, the selection criterion became dam TB1 only. The control line was then discontinued and a panel of frozen semen from the 11th generation boars was created for later comparisons. The selected line was opened to gilt daughters of hyperprolific boars and sows, at a rate of 1/8 per generation, and the same selection procedure was applied irrespective of the origin of the gilt. During the whole experiment, the number of ova shed (OS) and the number of live embryos (LE) at 30 days in the 3rd pregnancy were recorded. These two parts of the experiment were analysed using REML estimation of genetic parameters and a BLUP-Animal Model in order to estimate the responses to selection. Significant heritabilities for TB1, TB2, OS and LE were obtained, i.e. 0.10, 0.05, 0.43 and 0.19, respectively. Significant common environment variances and covariances were estimated for nearly all traits. Significantly positive BLUP responses per generation were observed from G0 to G17 for TB1 (+0.086), TB2 (+0.078), OS (+0.197) and LE (+0.157). However, the responses were 3- to 4-fold higher in the G12–G17 interval compared to G0–G11, and they were also in fair agreement with previous estimates based on standard least-squares procedures, using the control line and the control frozen semen panel. Since G11, the selection intensity was increased by nearly 80 p. cent compared to the previous generations, and the proportion of hyperprolific ancestry increased up to 65 p. cent in the sows of the last generation. The total genetic gain of about 1.4 piglets at birth per litter could be shared between a gain due to immigration, of about 0.8 piglets per litter, and a within-line selection gain of about 0.6 piglets. Thus by combining selection and immigration in the second part of the experiment, advantage could be taken from both the genetic superiority of the immigrants and the higher internal selection intensity made possible by immigration

Mesophilic and thermophilic methane fermentation of Euphorbia tirucallis

La méthanisation d'#Euphorbia tirucalli$ a été réalisée en conditions mésophile et modérément thermophile. Trois différents pré-traitements de cette plante ont été testés : simple fragmentation, broyat, séchage puis broyage. Les digesteurs ont été alimentés avec 5 % de matière sèche en batch. Lors d'une expérimentation de 35 jours, le meilleur rendement (0,78 1/1/j) a été obtenu avec les fragments de plante en condition thermophile modérée. (Résumé d'auteur

Homolytic Reduction of Onium Salts

Onium salts have proved to be efficient sources of carbon-centered radicals. They can undergo homolytic reduction by single electron transfer (SET) and participate in subsequent synthetic transformations. This review aims to provide an overview on the behavior of onium salts including diazonium, sulfonium, selenonium, telluronium, phosphonium and iodonium cations toward various reductive methods such as radiolysis, electrolysis, photolysis or the use of SET reagents. Mechanistic and synthetic aspects are presented. Applications in polymers and materials science are not covered