Master of Science / Department of Statistics / Gary L. Gadbury / QTL (quantitative-trait locus) analysis aims to locate and estimate the effects of genes that are responsible for quantitative traits, such as grain protein content and yield, by means of statistical methods that evaluate the association of genetic variation with trait (phenotypic) variation. Quantitative traits are typically polygenic, i.e., controlled by multiple genes, with varying degrees of in uence on the phenotype. Several methods have been developed to increase the accuracy of QTL location and effect estimates. One of them, multiple interval mapping (MIM) (Kao et al. 1999), has been shown to be more accurate than conventional methods such as composite interval mapping (CIM) (Zeng 1994). Other QTL analysis methods have been developed to perform additional analyses that might be useful for breeders, such as of pleiotropy and QTL-by-environment (QxE) interaction. It has been shown (Jiang and Zeng 1995) that these analyses can be carried out with a multivariate extension of CIM (MT-CIM) that exploits the correlation structure in a set of traits. In doing so, this method also improves the accuracy of QTL location detection. This thesis describes the multivariate extension of MIM (MT-MIM) using ideas from MT-CIM. The development of additional multivariate tests, such as of pleiotropy and QxE interaction, and several methods pertinent to the development of MT-MIM are also described. A small simulation study shows that MT-MIM is more accurate than MT-CIM and univariate MIM. Results for real data show that MT-MIM is able to provide a more accurate and precise estimate of QTL location.

Les herbivores invertébrés sont présents dans presque tous les habitats de la planète et peuvent grandement affecter la performance des plantes en nature. Que ce soit en communautés naturelles ou artificielles, une grande variation des taux d'herbivorie entre différentes espèces de plante [i.e. plantes] peut être observée. Ceci s'explique par le fait que les caractéristiques fonctionnelles des plantes, aussi appelées « traits », affectent les préférences des herbivores. Une espèce de plante, de par ces traits physiologiques, morphologiques ou phénologiques, peut donc décourager et/ou éviter l'herbivorie. La compréhension des relations entre les herbivores invertébrés et les traits des plantes est donc indispensable à la compréhension de l'assemblage des communautés herbivores-plantes. Cependant, les connaissances sur les liens entre les différents traits des plantes et la préférence des herbivores sont diffuses et incomplètes. Ce mémoire vise donc à quantifier et caractériser les effets de plusieurs traits fonctionnels de plantes herbacées sur la quantité de dommage foliaire faite par des herbivores invertébrés et à comparer ces effets entre monocultures et polycultures. Pour ce faire, j'ai participé au projet du Jena Experiment , une prairie expérimentale située en Allemagne visant à étudier la biodiversité. Cette prairie est exposée aux herbivores invertébrés naturels se trouvant sur le site de l'étude. Pour réaliser mon projet, les degrés d'herbivorie causés par les invertébrés ainsi que les valeurs de plusieurs traits fonctionnels des plantes ont été mesurés pour chacune de 51 espèces de plante [i.e. plantes] se trouvant sur le site d'étude. Travaillant d'abord avec des monocultures, sept traits sur 42 mesurés ont été sélectionnés dans une régression multiple en tant que prédicteurs importants de l'herbivorie. Le modèle est robuste et explique 63% de la variation en dommage subi par les espèces à l'étude. Parmi ces sept traits, deux sont physiologiques (concentration de lignine et d' azote dans les feuilles), deux sont morphologiques (architecture des racines et érection de la tige), un est phénologique (durée de vie du feuillage) et deux sont reliés aux herbivores (nombre d'espèces de coléoptère et d'hémiptère pouvant potentiellement prédater les plantes). Dans une seconde étape, à partir de l'herbivorie mesurée en monoculture et des sept traits sélectionnés dans le premier volet, trois modèles ont été développés pour prédire l'herbivorie dans des communautés formant un gradient de biodiversité de une à 60 espèces de plantes. Pour les trois différents modèles, le pouvoir de prédiction était faible; de 6 à 32% de variance en dommage foliaire expliquée. De plus, la déviation entre valeurs observées et valeurs prédites de l'herbivorie augmentait significativement avec l'augmentation du niveau de biodiversité dans les communautés. Les résultats de ce mémoire suggèrent que des patrons complexes de corrélation entre les différents traits des plantes existent et qu'il est donc nécessaire de travailler avec le plus de traits possibles pour identifier ceux qui contrôlent vraiment l'herbivorie. De plus, des interactions entre les différentes espèces de plante [i.e. plantes] d'une communauté semblent affecter de façon importante, directement ou pas, les dommages foliaires infligés par les herbivores invertébrés.Les conclusions de ce mémoire remettent en question l'importance relative des traits agrégés pour prédire des processus écologiques à facteur biotique tel que l'herbivorie et soulignent la complexité des relations entre deux niveaux trophiques.

Whitefish (Coregonus lavaretus) populations diverge into morphs that differ in body size along a benthic-limnetic axis and throughout the depth of the water column. This process is assumedly initiated by the presence of northern pike (Esox lucius) and is followed by morphological adaptations to available food resources. In this study eight populations of whitefish was studied with the purpose of increasing the knowledge about adaptive trait utility in the feeding apparatus of whitefish. This was done by analyzing the mean and absolute maximum and minimum prey size ingested by fish along four morphological trait gradients. The morphological traits was body size, gill raker number and density, and gape size. The results show clear evidence of morphological adaptations in both the benthic and limnetic habitat, furthermore, when comparing the two prey size responses (mean and absolute values) it becomes clear that none of the studied whitefish is physically constrained in terms of the largest prey they can ingest. However, large fish seem to be limited in eating small prey sizes. Interestingly, I also found strong indicators for filter feeding adaptation for one of the studied populations.

Thesis (MA)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The present study focuses on the salutogenic properties of families and attempted to identify factors that promote resilience in post-divorce families. McCubbin and Patterson's (1983) double ABCX model explains how families adapt to crises (divorce), and takes into account other life events that also impact on the family's resources. A cross-sectional research design was chosen to identify factors related to family resilience. The 98 participating families were identified on the grounds of the nature of the crisis and the developmental phase of the family. Self-report questionnaires were completed by the parent and a child acting as representatives of the family. These questionnaires consisted of a biographical questionnaire, the Relative and Friend Support Index, the Social Support Index, Family Crises Oriented Personal Evaluation Scales, Family Sense of Coherence Scale, and the Family Hardiness Index. Intra-family support, support of the extended family, support of friends, religion, open communication amongst family members, and work- and financial security were identified as factors promoting resilience in these post-divorce families. / AFRIKAANSE OPSOMMING: Hierdie studie fokus op salutogenetiese eienskappe van gesinne en poog am faktore wat verband hou met veerkragtigheid in enkelouergesinne te identifiseer. McCubbin en Patterson (1983) se dubbele ABCX-model verduidelik gesinne se aanpassing na 'n krisis (egskeiding) en neem oak ander lewensgebeure in ag wat terselfdertyd op die gesin se hulpbranne begin staatmaak. 'n Dwarssnit navorsingsontwerp is gebruik am faktore te identifiseer en te beskryf wat met gesinsveerkragtigheid verband hou. Die 98 gesinne wat aan hierdie ondersoek deelgeneem het, is ge"ldentifiseer op grand van die aard van die krisis en ontwikkelingstadium van die gesinne. Selfrapporteringsvraelyste is deur die ouer en In kind, as verteenwoordigers van die gesin, voltooi. Die vraelyste het bestaan uit 'n biografiese vraelys (wat oak 'n oopend vraag ingesluit het), Relative and Friend Support Index, Social Support Index; Family Crises Oriented Personal Evaluation Scales, Family Sense of Coherence Scale, en die Family Hardiness Index. Intra- gesinsondersteuning, ondersteuning deur die uitgebreide familie, ondersteuning van vriende, geloof, oop kommunikasie onder gesinslede, positiewe gesindheid rakend hulle toekoms, en finansiele- en werksekuritiet, is ge"ldentifiseer as faktore wat bydra tot veerkragtigheid in enkelouergesinne.

Thesis (MA)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The death of a parent calls on the family to utilize all its resources in order to adapt successfully and maintain normal family functioning. Within the mental health field a paradigm-shift from pathology-based to health-oriented is underway. Integral to this health-oriented paradigm is resilience, the ability to rebound after being stressed or challenged, as well as being able to rise above adversity and to survive stress. Family resilience theory emphasizes the role that family characteristics, behaviour patterns and capabilities play in cushioning the impact of stressful life events and in assisting the family in recovering from crises (McCubbin, Thompson, & McCubbin, 1996). Using a crosssectional survey research design, the present study aimed to explore and explicate those resiliency factors which enable families to adjust and adapt successfully after the loss of a parent. Families in which the death of a parent took place 1 to 3 years ago, and in which the eldest child was between 12 and 19 years old were approached to take part in this study. Thirty nine families completed questionnaires, as well as an open-ended question in which they were asked to report the most important factors or strengths which they felt helped their family through the stressful period. Results indicate that intrafamilial support such as emotional and practical support amongst family members, and family hardiness characteristics such as the internal strengths and durability of the family unit, contribute to resilience within the family. Individual characteristics, such as positive personality characteristics like optimism, are as important. Support from extended family and friends, as well as support obtained from religious and spiritual beliefs and activities, were reported as facilitating successful adjustment to the loss. / AFRIKAANSE OPSOMMING: Die dood van 'n ouer vereis dat 'n gesin alle bronne moet benut ten einde suksesvolle aanpassing en gewone gesinsfunksionering te handhaaf. Binne die geestesgesondheidsveld is daar 'n paradigma-verskuiwing vanaf patologie-gebaseerd na gesondheidsgeoriënteerd. Integraal tot hierdie gesondheidsgeoriënteerde paradigma is veerkragtigheid, die vermoë om terug te bons, uit te styg, en te oorleef nadat teëspoed ervaar is. Gesinsveerkragtigheidsteorieë beklemtoon die rol wat gesinseienskappe, gedragspatrone en bekwaamhede speel met betrekking tot die versagting van die impak van stresvolle lewenservaringe, asook die gesin se herstel na die krisis (McCubbin, Thompson, & McCubbin, 1996). 'n Dwarssnit opname-navorsingsontwerp is gebruik om die veerkragtigheidsfaktore te identifiseer en te beskryf wat gesinne help om suksesvol na die dood van 'n ouer aan te pas. Gesinne waar 'n ouer tussen een en drie jaar vantevore gesterf het, en die oudste kind tussen 12 en 19 jaar oud is, is genader vir deelname aan hierdie ondersoek. Nege-en-dertig gesinne het vraelyste sowel as 'n oop-end vraag voltooi waarin hulle gevra is om die belangrikste faktore te beskryf wat hul gesin deur die stresvolle periode gehelp het. Resultate dui daarop dat intragesinsondersteuning soos emosionele en praktiese ondersteuning, en gesinsgehardheid met kenmerke van interne sterkte en die volhoubaarheid van die gesin as eenheid, bygedra het tot gesinsveerkragtigheid. Individuele eienskappe soos optimisme het net so 'n essensiële rol gespeel. Ondersteuning van familie en vriende, asook ondersteuning as gevolg van godsdienstige en spirituele oortuigings en aktiwiteite, was fasiliterend in die suksesvolle aanpassing na die dood van 'n ouer.

Children's thinking has been described by Piaget and others in general terms, which suggest that there are major developmental changes that affect children's thinking at various stages of their development. Some criticisms of Piaget's theory have related to his approach to describing children's thinking as a context free phenomenon. In relation to this point, arguments have been put forward for the need to investigate the development of children's thinking, within particular content areas, and the investigations reported in this thesis have concentrated on the development of religious thinking of children aged from ~6 to 11 years. A review of previous investigations into this area of children's thought development reveals major shortcomings, both in the experimental approaches used and in the theories that have been constructed. In particular it is argued that there has been a tendency for investigators to propose stage development theories on the basis of inadequate results. It is argued that there is a need for investigations which approach this problem from new directions. As a first step, a series of investigations, which employ a variety of approaches and which investigate various cognitive and semantic factors that may influence the development of religious thinking in children, are presented. The investigations that are reported involved individual interviews with 440 children, in the age range from 6 to 11 years. A variety of experimental techniques were employed, including those investigating the children's understanding of various biblical parables, their understanding of the meaning of words used in religious discourse, their conception of historical time and ability to sequentially order events in time, and the way that these factors affected their understanding of religious ideas. The results of the investigations are discussed in terms of the variety of aspects, which they reveal, relating to the development of religious thinking in children. It is argued that this evidence does not support the idea of the development of religious thinking being a unidimensional stage related process; however, the evidence collected from these studies is insufficient to form the basis of an alternative model. It is argued that future studies that follow this approach will be necessary if a satisfactory theory is to be constructed. The educational implications of these findings are discussed and it is argued that certain curriculum changes in the area of religious education may have been made on the basis of insufficient evidence and inadequate theories.

No description available.

The relationship between psychological hardiness and individuals' coping with two life events, involuntary job loss and post-parental launching of adolescent children, was investigated in a sample of 146 adults, 83 of which had experienced job loss and 61 of which had experienced the empty nest. Volunteers completed questionnaires which measured hardiness, distress, coping strategies, neuroticism, and extraversion. Multivariate analyses were performed, both with and without covariates, for overall hardiness as well as the hardiness subscales of control, commitment, and challenge. Significant hardiness by life event interactions on escape-avoidance coping were found in both sets of analyses. Main effects for hardiness, however, disappeared when controls for neuroticism and extraversion were utilized. Findings underscore the necessity of employing neuroticism controls in future hardiness research.

The study investigated five factors which can affect the equating of scores from two tests onto a common score scale. The five factors studied were: (a) distribution type (i.e., normal versus uniform); (b) standard deviation of itemdifficulties (i.e., .68, .95, .99); (c) test length or number of test items (i.e., 50,100, 200); (d) number of common items (i.e., 10,20,30); and (e) sample size (i.e., 100, 300, 500). The significant two-way interaction effects were for common item length and test length, standard deviation of item difficulties and distribution type, and standard deviation of item difficulties and sample size.

Thèse diffusée initialement dans le cadre d'un projet pilote des Presses de l'Université de Montréal/Centre d'édition numérique UdeM (1997-2008) avec l'autorisation de l'auteur.