Gene mapping for complex or quantitative traits remains a challenging task. This is primarily because complex trait variation is caused by numerous quantitative trait loci (QTL), each of relatively small effect size that traditional genetic approaches struggle to isolate. Complex traits are particularly relevant for evolutionary adaptations, since most of them are based on quantitative characters that are likely to involve many genes. Hence, understanding the genetics of complex traits is also a prerogative for understanding the genetics of evolutionary processes.
Bodyweight is an archetypal complex trait in mice. A plethora of resources including mapping crosses, recombinant inbred lines, and long-term selection lines have helped identify many bodyweight QTLs. But despite decades of intensive study, a fine-grained understanding of the genes underlying growth and/or bodyweight remains elusive. Increased bodyweight in house mice has been observed repeatedly and independently, both under long-term artificial selection in the laboratory, and in natural populations in the wild. Since most of these mice are primarily derived from the Western house mouse M. m. domesticus and share recent genetic ancestry, some part of the response to selection is likely to have a shared allelic basis. We applied “parallel selection mapping” to identify this component of shared loci underlying parallel increase in bodyweight across multiple long-term artificial selection experiments in mice.