Genetic Basis of Response to 50 Generations of Selection on Body Weight in Inbred Mice

Corresponding author: Peter D. Keightley, Institute of Cell, Animal and Population Biology, University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, Scotland, p.keightley{at}edinburgh.ac.uk (E-mail).

Communicating editor: Z-B. ZENG

A long-established inbred strain of mice was divergently selected for body weight for 50 generations. Selection of new mutations affecting the trait eventually led to a divergence of approximately three phenotypic standard deviations between the high and low lines. Heritability for body weight increased at a rate between 0.23% and 0.57% per generation from new mutations, depending on the genetic model assumed. About two-thirds of the selection response was in the upward direction. The response was episodic, suggesting a substantial contribution from the selection of mutations with large effects on the trait. A maximum likelihood procedure was used to estimate the number of factors contributing to the response using data from line crosses, with models of n equivalent gene effects (i.e., to estimate the Wright-Castle index), or n genes with variable effects. The results of the analysis of data from a cross between the selected high line and an unselected control line indicated that two major factors were involved, with the suggestion of an additional minor factor.

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