Dw Fulker

Combined Linkage and Association Sib-Pair Analysis for Quantitative Traits

An extension to current maximum-likelihood variance-components procedures for mapping quantitative-trait loci in sib pairs that allows a simultaneous test of allelic association is proposed. The method involves modeling of the allelic means for a test of association, with simultaneous modeling of the sib-pair covariance structure for a test of linkage. By partitioning of the mean effect of a locus into between- and within-sibship components, the method controls for spurious associations due to population stratification and admixture. The power and efficacy of the method are illustrated through simulation of various models of both real and spurious association.

Fitting genetic models with LISREL: hypothesis testing.

A brief introduction to the mathematical theory involved in model fitting is provided. The properties of maximum-likelihood estimates are described, and their advantages in fitting structural models are given. Identification of models is considered. Standard errors of parameter estimates are compared with the use of likelihood-ratio (L-R) statistics. For structural modeling, L-R tests are invariant to parameter transformation and give robust tests of significance. Some guidelines for fitting models to data collected from twins are given, with discussion of the relative merits of parsimony and data description.

Adoption results for self-reported personality

Twin studies consistently indicate moderate genetic influence on individual differences in personality as assessed using self-report questionnaires, with heritability estimates typically about 40%. In this first analysis of self-report personality data from the longitudinal Colorado Adoption Project, little evidence is found for additive genetic influence in parent-offspring and sibling adoption analyses based on a foundation sample of 245 adoptive families and 245 nonadoptive families with adopted and nonadopted children assessed yearly from 9 to 16 years. Although several factors might contribute to the discrepancy between twin and adoption results, we suggest that nonadditive genetic influence, which can be detected by twin studies but not by adoption studies, is a likely culprit. These findings have important implications for attempts to identify specific genes responsible for genetic influence on personality.

A Developmental-Genetic Analysis of Continuity and Change in the Bayley Mental Development Index from 14 to 24 Months: The MacArthur Longitudinal Twin Study

A developmental-genetic model was fitted to Bayley Mental Development Index (MDI) data to address questions concerning the origins of individual differences in MDI performance and the origins of change and continuity during infancy More than 350 pairs of identical and same-sex fraternal twins were studied longitudinally at 14, 20, and 24 months of age There was substantial genetic continuity of general cognitive ability from 14 to 24 months, but significant new genetic variation also appeared at 24 months Shared family environmental influences were global across all three ages and not time-specific Finally, nonshared environmental influences did not contribute to the observed continuity of general cognitive ability, only to change

Genetics of escape-avoidance conditioning in laboratory and wild populations of rats: A biometrical approach

The interest of biometrical geneticists in the genetic architecture of behavior is explained with reference to the additive, dominance, and epistatic components of variation and their relation to evolutionary pressures. For one phenotype, escape-avoidance conditioning inRattus norvegicus, a fairly complete description of its genetic architecture has been gradually built and the major conclusions from four studies of this phenotype are reported: a selection study initially demonstrated the presence of large amounts of additive genetic variation and produced phenotypically extreme lines needed for later work; a diallel cross provided the opportunity for detailed examination of the dominance effects; a triple test cross permitted a similar examination of epistatic effects; and finally, another triple test cross using wild rats provided a confirmatory first attempt to test the assumption that a wild populations genetic architecture did not differ markedly from that found in laboratory populations. In relating the genetic findings to the evolutionary significance of behaviors in the escape-avoidance paradigm, it is argued that interspecific comparisons might play a major role.

Longitudinal stability of cognitive ability from infancy to early childhood: Genetic and environmental etiologies.

A path model of genetic and shared family environmental transmission was fitted to general cognitive ability data from 1-, 2-, 3-, and 4-year-old adopted and nonadopted children and their parents in order to assess the etiology of longitudinal stability from infancy to early childhood. Stability across years is moderate and is due mainly to influences not predicted by parental IQ. Results of the present study, in conjunction with those of previous twin studies, suggest substantial genetic stability from infancy and early childhood to adulthood.

Using the triple test cross to investigate the genetics of behavior in wild populations. II. Escape-avoidance conditioning inRattus norvegicus

The detailed results of a triple test cross using wild rats crossed to partially inbred sublines of the Roman High and Low Avoidance selection strains clearly indicated considerable amounts of additive genetic variation in the wild population for avoidance performance while there is a general absence of nonadditive variation, with the exception of some dominance variation together with duplicate type epistasis. Where present, directional dominance for this phenotype is toward high performance only for later trials, and the effects of any epistasis reinforce this trend. The overall conformity of these results to the predictions from previous laboratory rat studies suggests no reason to reject the representativeness assumption necessary for arguments from genetic architecture in laboratory populations to adaptive significance in contemporary wild populations.

Using the triple test cross to investigate the genetics of behavior in wild populations I. Methodological considerations

The rationale for using the triple test cross breeding design to investigate the genetics of behavior in wild populations is outlined. The breeding design, biometrical models, and methods of analysis are specified and the limitations on the interpretation of studies are discussed, especially in relation to the need for adequate tester lines.

Using the triple test cross to investigate the genetics of behavior in wild populations. III. Activity and reactivity

A wild x laboratory rat triple test-cross study of open-field defecation, open-field ambulation, and a measure of rearing-up activity in a non-stressful environment revealed three different patterns of results. For open-field defecation, where the tester lines were expected to be inadequate to detect nonadditive variation, only putative additive effects were detected and a minimum broad heritability of 20% in the wild population was revealed. For open-field ambulation an architecture including ambidirectional dominance was in line with laboratory rat studies, while for rearing behavior epistatic effects were indicated. The implications of these results for domestication and for past and future evolution are discussed.

Multivariate Familial Analysis of Cognitive Measures in the Colorado Family Reading Study.

Multivariate path analysis is employed to examine the etiologies of variation and covariation of three composite cognitive measures in the Colorado Family Reading Study: reading ability, symbol-processing speed, and spatial/reasoning. Measures of phenotypic assortative and cross-assortative mating are incorporated in a multivariate analysis of familial resemblance within nuclear families. Phenotypic variances and covariances are partitioned into components due to familial (genetic and/or family environmental) influences and to specific, nontransmissible environmental influences in families with a reading-disabled child as well as families with children of normal reading ability. Comparable moderate familial influences are found across family type for all three composites and the phenotypic correlations between traits are largely due to familial influences.