Divergent selection for pentobarbital-induced sedation times in mice

Divergent selection for pentobarbital sedation-time response was practiced in mice for 9 generations. At the end of 9 generations of selection, the long-sedation-time line (LST) slept an average of 433 min; the short sedation time line (SST) slept an average of 29 min. The control line (C) slept an average of 71 min. These differences represent an almost 15-fold increase in sedation time for the LST compared to the SST line and a 6-fold increase compared to the C line. The SST line slept about 40% less than the C line after 9 generations of selection (measured in tenth generation progeny). Analysis of selection differentials and realized heritabilities indicated that selection response did not diminish after 9 generations of selection. Realized heritabilities for sedation time ranged from 0.43 to 0.83 for the LST line and from 0.55 to 0.81 for the SST line. Realized heritabilities did not decrease in magnitude due to selection progress, indicating that more progress can still be achieved. Comparing corrected (for environmental factors) to uncorrected heritabilities showed the importance of including a control line in selection experiments. Crossing of lines to study gene action responsible for this trait revealed that this trait was controlled by a number of genes with additive gene action without dominance, overdominance, epistasis, or maternal effects.