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Title: Genetic analysis of long-term selection experiments
Author: Beniwal, Baldev K.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1991
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A long-term selection experiment with mice for 38 generations was analysed. Genetic parameters were estimated for lean mass, body weight, litter size and other associated traits using univariate and multivariate REML analyses with an animal model fitting litters as an additional random effect. Different combinations of selected and control lines were analysed. The change in genetic parameters during the course of selection and infinitesimal model assumptions were examined. Three replicates, each having high and low selected lines for lean mass at 10 weeks of age were maintained for 20 generations with unselected controls (P-Lines). This resulted in a divergence of 7 phenotypic standard deviation units (igmap) between the high and low lean mass lines. After 20 generations replicates were crossed and the selection criterion was changed to 10 week body weight (P6-Lines) without maintaining the controls. At generation 38 the selected lines diverged by 23.2g (8.7 igmap) for 10 week body weight. The estimates of heritability (h2) and c2 (common litter variance/phenotypic variance ratio) for lean mass were 0.5 and 0.2 from the univariate REML analyses of both control lines alone and of pooled data of control+ high+ low lines. Estimates of c2 were higher in the high lines and lower in the low lines, controls being intermediate. The estimates of genetic paramters for body weight were similar to the lean mass in the P-lines. Analysis of the selected lines indicated a steady decline in their additive genetic variance (va) during the course of selection for both lean mass and body weight, even though allowance was made in the infinitesimal model for reductions in Va due to inbreeding and linkage disequilibrium. The multivariate REML estimates of h2 and c2 for lean mass and body weight were similar to those from the univariate analyses. The genetic (rg) and phenotypic correlations (rp) between lean mass and body weight were very high (> 0.9) and positive. Lean mass also showed positive correlations (rg and rp) with gonadal fat pad weight, but when gonadal fat pad weight was expressed as a proportion of body weight it showed small negative correlations with lean mass.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available