Genetic Correlation between Growth Rate and Feed Per Unit Gain in Mice

Abstract

The additive genetic covariance and genetic correlation of postweaning gain and feed per unit gain were estimated for a genetically variable population of mice during a 17-generation span in which selection for postweaning gain was practiced. Estimates indicated a high (nearly perfect) negative genetic correlation. The total response in gain to direct selection practiced was estimated to be about 4.6 gm. or 43% of the original population mean. In the case of feed per unit gain adjusted for average test weight of mice the correlated response to selection for gain was estimated to be slightly over −.10 per generation or a total of −1.84 for 17 generations (from about 6.50 to 4.66). This was only 59% of the response predicted using the standard prediction formula. However, response in gain itself was only 70% of prediction. The authors incline to the view that additive genetic covariance between the variables is approximately as great as estimated, that negative genetic correlation between the variables was large (though certainly not perfect) through the entire period studied, and that the discrepancy between observed and predicted correlated response was largely due to less response than predicted in postweaning gain itself.