the laboratory mouse (mus musculus) is a species widely used as a model organism in diverse areas of biology. this species is considered an almost perfect model system because of its short generation interval, simple breeding strategies and high biotic potential; these, as well as other characteristics, make the mouse an almost unique resource in experimental genetics. the instituto de genética experimental, facultad de ciencias médicas, universidad nacional de rosario developed several lines of mice in long-term divergent selection experiments on body conformation. due to the joint effects of selective breeding for more than 100 generations, a correlated response to selection, non-directional effects of inbreeding and genetic drift, and the appearance of new mutations, each line fixed different allelic combinations. morphometric studies of the hemimandible and the femur corroborated the feature of singular genotype attributed to each line. this is why the lines of this colony became an attractive murine model to study complex genetic traits such as growth, development and body composition, muscle contractile properties, resistance to parasitosis, susceptibility to mammary spontaneous carcinogenesis as well as the influence of the host on the growth of a transplantable mammary adenocarcinoma. the results obtained demonstrate that these lines are a source of significant genetic variance in all the characters analyzed.