Biomedical subjects

D A Sorensen

Publications and source records attributed to D A Sorensen.

5 recordsLinked to original sources

PubMed1992

Estimation of direct and correlated responses to selection using univariate animal models.

Analytic results obtained using simple models show that estimates of selection response of univariate experiments using animal models are completely dependent on the heritability used as prior when fixed effects are nested within generations, and both on the prior and on the true heritability parameter when fixed effects overlap across generations. Univariate animal model estimators of correlated changes of a trait not selected directly are usually biased. The absolute value of the estimate of the correlated response is smaller than the true value when the traits are only genetically correlated and larger than the expected value of zero when they are only environmentally correlated. The validity of the results derived from the analysis of simple models is confirmed using computer simulations, which illustrate the magnitude of the bias. It is emphasized that use of univariate animal models to estimate response in breeding programs whose breeding objectives include several correlated traits may lead to erroneous conclusions.

Analysis of Variance↗

PubMed1989

A computer-assisted management information system for nutrition services.

A computer-assisted management information system was created to facilitate effective management of clinical nutrition services and labor resources in a 330-bed teaching and research hospital. Standards were developed for the quality and quantity of nutrition care, time required to provide nutrition care, and utilization of dietitians' time. Computer software was developed to report the volume of services provided, the need for services, and the utilization of labor hours. Data were evaluated to determine whether services were consistent with standards and to calculate a recommended number of clinical dietitian full-time equivalents for the hospital. Furthermore, the management information system was instrumental in developing a fee-for-service structure, for evenly distributing work loads among dietitians, and for monitoring adherence to standards of care.

Dietetics↗

PubMed1986

Analysis of selection experiments using mixed model methodology.

Use of mixed model techniques to estimate genetic variance and selection response is illustrated by simple examples. A minimum variance quadratic unbiased estimator (MIVQUE) of genetic variance using a reduced animal model is derived. Properties of the mixed model estimator of response are discussed and illustrated with results from Monte Carlo simulation. The mixed model estimator of response requires knowledge of the base population heritability. When the latter is not known, simulation results suggest that using a MIVQUE estimate obtained from the data yields estimates of response in good agreement with the true response. If a number of conditions are satisfied, the mixed model estimator of response partitions the phenotypic trend into its genetic and environmental components, without need for a control population. These conditions are unlikely to hold in long-term selection experiments. More work is needed to understand the implications of finite numbers of loci or the presence of unaccounted natural selection opposing artificial selection, for example, on the properties of the mixed model estimator of response.

Animals↗

PubMed1985

Relationships between herd type and genetic and environmental variances in Holsteins.

Type classification data from the Holstein Association of Canada on 354,308 daughters of 13,694 sires were subdivided into 20 groups of approximately equal size according to herd average final score. Genetic and environmental variances were estimated for each group by Henderson's new method. Traits considered and their heritabilities averaged over groups were: final score .13; final class .11; dairy character .17; capacity .24; rump .16; feet and legs .10; mammary system .12; fore udder .12; rear udder .12; size .31. Regressions of genetic variances on group number ordered according to herd final score indicated significant trends only for rump and feet and legs for which higher genetic variances were found for higher type scores. Regressions of environmental variances on group number were significant for all traits. Higher environmental variances were found for lower final scores, final class, dairy character, and capacity, but the opposite was observed for size. The distribution of environmental variances across groups was U-shaped for rump, feet and legs, for udder, and rear udder; lowest variances were associated with intermediate scores for overall type.

Animals↗

PubMed1982

Effect of short term directional selection on genetic variability: experiments with Drosophila melanogaster.

Experimental checks on theoretical predictions of the build up of negative linkage disequilibrium with directional selection were made using abdominal bristle number in Drosophila melanogaster. Selection was practised for three generations before relaxation. Realized heritabilities and thus genotype variances were estimated by divergent selection. In one replicate, little change of variance occurred but in the other it increased substantially on relaxation. This result is compatible with a model of one or more genes of large effect at extreme frequencies in the base population. This is illustrated with Monte Carlo simulations. Interpretations of results was aided by considering the build up of negative disequilibrium.

Animals↗