Fine-mapping of fearfulness

Geneticists cut their teeth on conditions controlled by single loci. The harder task is to find the many loci that work together to control a single trait. In the 7 November Proceedings of the National Academy of Sciences Mott et al. demonstrate a new method for mapping these quantitative trait loci (QTL; Proc Natl Acad Sci USA 2000, published online before print). Previous methods all have their limits: family-based studies tend to be small and so can only do coarse mapping; population-based association studies give greater numbers (and thus potentially greater resolution) but are complicated by variable and unknown inheritance histories; and breeding studies in mice are plagued by a possible lack of segregating loci when two inbred mouse populations are used as founders. Mott et al. get around this last problem by using the progeny from an eight-way cross that was started 30 years ago and is...