Genetic Variation For Traits Research Articles

Genetic variation of traits measured in several environments. II. Inference on between-environment homogeneity of intra-class correlations

Variation genetique de caracteres mesures dans plusieurs milieux. II. Inference relative a des correlations intra-classe constantes entre milieux. Cet article decrit une approche permettant d'estimer les composantes de variance-covariance entre milieux dans le cas de correlation intra-classe homogenes entre milieux, sans faire d'hypothese sur les correlations genetiques entre milieux pris 2 a 2. Un algorithme iteratif d'esperance-maximisation (EM), comparable a celui decrit par Foulley et Quaas (1994), est propose pour calculer les estimations du maximum de vraisemblance restreinte (REML) des composantes residuelles et familiales de variance covariance. Trois parametrisations differentes (coordonnees cartesiennes, polaires et spheriques) sont proposees pour calculer les estimateurs EM-REML sous le modele reduit (les correlations intra-classe sont supposees toutes egales a une meme constante). Cette procedure est illustree par l'analyse de donnees simulees.

Marker assisted selection ‐ an overview

Abstract The main force driving gene mapping in domestic animals, is the potential for using gene maps as a means of identifying and mapping the genetic loci responsible for genetic variation in traits of economic importance. The ultimate objective is utilizing this information for marker‐assisted selection (MAS) using DNA level polymorphisms. This overview considers: (1) The need for MAS, (2) The relationship of gene mapping to MAS, (3) Implementing MAS. Examples illustrating the potential contribution of MAS to animal genetic improvement are presented, including (I) Preselection of candidate bulls for progeny testing in dairy cattle improvement, (2) Introgression of trypanotolerance from N'Dama to other cattle breeds, and (3) Improvement of a successful layer cross.

Variation in performance on two grape cultivars within and among populations of grape Phylloxera from wild and cultivated habitats

AbstractWhen an indigenous insect becomes a pest, comparisons of performance of pest and non‐pest populations on crop plants and of genetic variation in that performance may provide insight into the evolution of pest populations. To measure such genetic variation, 8–15 clones of the grape phylloxera (Daktulosphaira vitifoliae Fitch) were collected from wild grapevines in each of 3 geographically isolated sites (populations) and from commercial vineyards in northern California. A complete life table was made for clonal replicates from populations collected from wild grapevines on each of two commercial grape cultivars, the susceptible Vitis vinifera (L.) cultivar Cabernet Sauvignon, and the phylloxera‐resistant rootstock ‘AxR# 1’. Variation in mean performance on these two hosts was partitioned among clones within collection sites and among sites. Performance measures included an individual analog to the intrinsic rate of increase (r), age at first oviposition, fecundity in the first ten days of reproduction, total fecundity, and longevity. The overall performance of phylloxera from the wild grapevines on the resistant cultivar AxR# 1 was greater than or equal to that on the susceptible cultivar Cabernet Sauvignon. There was significant variation among clones within populations from wild grapes in the rate of increase on ‘AxR# 1’ and marginally significant clonal variation in some of the component parameters. There was no significant variation among clones within populations on ‘Cabernet Sauvignon’ and no significant differences between populations on either crop in any trait.In a second experiment we compared the relative performance of 15–17 clones from wild grapevines and from commercial vineyards when reared on ‘Cabernet Sauvignon’ and ‘AxR# 1’. Phylloxera from commercial vineyards had much higher overall performance on ‘Cabernet Sauvignon’ than did phylloxera from the wild grapevines. Phylloxera from the commercial vineyard also had higher performance on ‘Cabernet Sauvignon’ than on ‘AxR’ l' but the performance of the phylloxera from wild and commercial grapes did not differ on ‘AxR# 1’.Our results show that there is genetic variation in traits related to performance on a resistant root‐stock within these indigenous non‐pest populations of phylloxera, but not among them. The pattern of performance of pest and non‐pest populations on two commercial cultivars suggests that current levels of phylloxera performance on crop cultivars are the result of adaptation to those cultivars which has occurred while phylloxera has been associated with viticulture. Implications of these results for understanding the recent adaptation of phylloxera to ‘AxR# 1’ in California are also discussed.

Genetic and ontogenetic variation in behaviour: its possible role in the maintenance of genetic variation in the wing dimorphism of Gryllus firmus

Genetic variation may be preserved in populations by several different modes of behaviour. In this paper we examine the consequences of behaviour on genetic variation in traits that are determined by genetic factors and by environmental conditions experienced during ontogeny. The particular trait considered is wing dimorphism in the sand cricket Gryllus firmus. In this species, as is typical of wing dimorphic insects, the adult wing morph (macropterous or micropterous) is determined by both genetic constitution and the temperature experienced during a specific period of nymphal development. Wing morph may thus be controlled, in part, by the thermal preference of nymphs. The effective heritability of wing morphology will be increased if nymphs with a genetic disposition to a particular wing morph select the temperature that causes that morph to be expressed. By contrast, effective heritability will be decreased if nymphs show no preference, or nymphs select temperatures that reduce phenotypic variation among individuals. During the period of ontogeny when future wing morph is sensitive to temperature, nymphal crickets that are genetically disposed to become macropterous select lower temperatures than crickets that have the opposite genetic disposition. Likewise, nymphs that are being raised under conditions promoting macroptery select lower temperatures than nymphs being raised under conditions favouring microptery. The consequence of this behaviour is that genetic variation for wing morph may be masked, and hence preserved.

Pharmacokinetic considerations in abuse liability evaluation

The behavioral effects of a drug are related to three factors: its intrinsic pharmacological activity, its physicochemical properties, and its pharmacokinetic parameters. In many cases differences in absorption, distribution, metabolism, and elimination may explain the different abuse liability profiles of drugs from within the same pharmacological class. Rapid absorption rate and high lipid solubility are the most important factors contributing to early drug concentrations in the brain. Differences in drug metabolism may be related to dose-dependent kinetics, first-pass metabolism, and variations in genetic traits (e.g. poor or extensive metabolizers). Metabolic pathways may produce active metabolites with similar or greater pharmacological activity than the parent substance. Drugs with a rapid elimination rate have been associated with greater self-administration and with early emergence of withdrawal symptoms. More pharmacokinetic studies are needed in human drug abuse liability evaluations. Knowledge of the plasma concentrations of drugs and their pharmacokinetic parameters can be essential to interpret differences among similar drugs in human abuse liability assessments.

Sufficient Conditions for Multiple Niche Polymorphism

Sufficient Conditions for Multiple Niche Polymorphism