Mapping quantitative trait loci for murine growth: a closer look at genetic architecture

Over 20 years ago, D. S. Falconer and others launched an important avenue o f research into the quantitative of body size growth in mice. This study co ntinues in that tradition by locating quantitative trait loci (QTLs) respon sible for murine growth, such as age-specific weights and growth periods, a nd examining the genetic architecture for body weight. We identified a larg e number of potential QTLs in an earlier F2 intercross (Intercross I) of th e SM/J and LG/J inbred mouse strains. Many of these QTLs are replicated in a second F2 intercross (Intercross II) between the same two strains. These replicated regions provide candidate regions for future fine-mapping studie s. We also examined body size and growth QTLs using the combined data set f rom these two intercrosses, resulting in 96 microsatellite markers being sc ored for 1045 individuals. An examination of the genetic architecture for a ge-specific weight and growth periods resulted in locating 20 separate QTLs , which were mainly additive in nature, although dominance was found to aff ect early growth and body size. QTLs affecting early and late growth were g enerally distinct, mapping to separate chromosome locations. This QTL patte rn indicates largely separate genetic and physiological systems for early a nd later murine growth, as Falconer suggested. We also found sex-specific Q TLs for body size with implications for the evolution of sexual dimorphism.