Biomedical subjects

P Narain

Publications and source records attributed to P Narain.

11 recordsLinked to original sources

PubMed2003

Accuracy of marker-assisted selection with auxiliary traits.

Genetic information on molecular markers is increasingly being used in plant and animal improvement programmes particularly as indirect means to improve a metric trait by selection either on an individual basis or on the basis of an index incorporating such information. This paper examines the utility of an index of selection that not only combines phenotypic and molecular information on the trait under improvement but also combines similar information on one or more auxiliary traits. The accuracy of such a selection procedure has been theoretically studied for sufficiently large populations so that the effects of detected quantitative trait loci can be perfectly estimated. The theory is illustrated numerically by considering one auxiliary trait. It is shown that the use of an auxiliary trait improves the selection accuracy; and, hence, the relative efficiency of index selection compared to individual selection which is based on the same intensity of selection. This is particularly so for higher magnitudes of residual genetic correlation and environmental correlation having opposite signs, lower values of the proportion of genetic variation in the main trait associated with the markers, negligible proportion of genetic variation in the auxiliary trait associated with the markers, and lower values of the heritability of the main trait but higher values of the heritability of the auxiliary trait.

Animals↗

PubMed1988

Predictors of immediate and 6-month outcomes in hospitalized elderly patients. The importance of functional status.

This article presents results of a prospective multivariate study of hospitalized elderly patients at an acute-care Veterans Administration (VA) hospital to identify factors on hospital admission predictive of several short- and long-term outcomes: in-hospital and 6-month mortality, immediate and delayed nursing home admission, length of hospital stay, and 6-month rehospitalization. All patients aged 70 years and over admitted to acute-care beds on the medical service wards during a 1-year period were included in the study (N = 396). Factors most predictive of 6-month mortality (using logistic regression) were decreased functional status, admitting diagnosis, and decreased mental status. Factors most predictive of nursing home admission were decreased functional status, living location, and decreased mental status. Functional status was a stronger predictor of length of stay, mortality, and nursing home placement than was principal admitting diagnosis--of relevance to the current emphasis on diagnosis-related groups (DRGs). These data may be helpful in improving discharge planning, in resource allocation, and in targeting patients for different specialized geriatric programs.

Activities of Daily Living↗

PubMed1987

Genetic differentiation of quantitative characters between populations or species. II: Optimal selection in infinite populations.

Using a new and more general genetic model called the discrete-allelic state model and assuming discrete-time process, the evolutionary changes of genetic variation of quantitative characters, controlled by a few loci, within and between populations during the process of genetic differentiation of populations or species, are studied under the effects of mutation and centripetal selection in infinitely large populations. While in a finite population and ignoring selection, the rate of change of additive genetic variance depends on mutation and effective population size, traits under optimal selection in infinitely large populations go through the dynamics of a rather complicated form depending on the relative intensities of selection and mutation. When a population, which has reached steady-state by mutation-selection balance, splits into two, in one of which the same optimum genotype holds but in the other the optimum shifts a few standard deviations away from the original optimum, the corresponding daughter population starts differentiating from its sister population by favouring certain class of mutant alleles and discarding others which were originally favoured. During this process of turn over of genes, both the intra- and inter-populational variances undergo a complicated change, and the ratio of the former to the latter is a non-linear function of time of divergence. This pattern is qualitatively very different from the case when selection is absent. The intra-population distribution of genotypic values, during this transition, is shown to deviate considerably from normality. The presence of linkage seems to retard the accumulation of intra-populational genetic variance. The implications of these results are discussed in comparison with the earlier findings of evolutionary models of quantitative traits.

Alleles↗

PubMed1985

Progeny testing with auxiliary traits.

The problem of determining the breeding worth of a male on the basis of the phenotypic values of his female progeny is discussed. The use of one or more auxiliary traits in conjunction with the main trait for progeny testing seems to have an edge over the conventional method in which no auxiliary traits are used. A general expression for the accuracy of selection based on the progeny test is derived and a generalised sire index is proposed. Detailed numerical investigation with one auxiliary trait reveals that the accuracy of the progeny test in such a case is always increased. The maximum gain in accuracy is found when the phenotypic and additive genetic correlations between the main and the auxiliary traits are of opposite signs. The number of progeny required to attain a pre-assigned value of accuracy is determined for several cases. It is found that the use of auxiliary trait reduces this number resulting in decreased cost of the progeny testing programme. The effect of the number of auxiliary traits on the gain in accuracy is also studied under some simplified situations.

Animals↗

PubMed1983