Quantitative trait locus mapping in laboratory mice derived from a replicated selection experiment for open-field activity

Bidirectional selection in rodents has been used to derive animal models of human behavior. An important question is whether selection for behavior op erates on a limited number of QTL or whether the number and individual cont ribution of QTL varies between selection experiments. To address this quest ion, we mapped QTL in two large F-2 intercrosses (N = 815 and 821) from the four lines derived from a replicated selection experiment for open-field a ctivity, an animal model for susceptibility to anxiety. Our analyses indica te that selection operated on the same relatively small number of loci in b oth crosses. Haplotype information and the direction of effect of each QTL allele were used to confirm that the QTL mapped in the two crosses lie in t he same chromosomal regions, although we were unable to determine whether Q TL in the two crosses represent the same genes. We conclude that the geneti c architecture of the selected strains is similar and relatively simple.