Analysis of response to 20 generations of selection for body composition in mice: fit to infinitesimal model assumptions.

摘要

Data were analysed from a divergent selection experiment for an indicator of body composition in the mouse, the ratio of gonadal fat pad to body weight (GFPR). Lines were selected for 20 generations for fat or lean or were unselected, with 3 replicates of each. Selection was within full-sib families, 16 families per replicate for the first 7 generations, 8 subsequently. At generation 20, GFPR in the fat lines was twice that of controls and in the lean lines it was half that of the controls. A log transformation removed both asymmetry of response and heterogeneity of variance among lines and was used throughout. Estimates of genetic variance and heritability (approximately 50%) obtained using restricted maximum likelihood (REML) with an animal model were very similar, whether estimated from the first few generations of selection, or from all 20 generations, or from late generations with a fitted pedigree. The estimates were similar when estimated from selected or control lines. Estimates from REMLagreed with estimates of realized heritability. The results all accord with expectations under the infinitesimal model, despite the 4-fold changes in mean. Relaxed selection lines, derived from generation 20, showed little regression in fatness after 40generations without selection.