The collaborative cross stems from an 8-way interstrain cross. Eight carefully selected inbred strains are crossed to produce four F1 hybrids. These hybrids are then crossed together; one thousand independent inbreds are derived after 20 additional generations of brother × sister mating. In the end, this cross will be materialized by a resource of about one thousand different inbred strains (actually recombinant inbred strains, RIS) whose genome will be a “patchwork” with a roughly equivalent contribution of the original inbred strains. For each strain the “patchwork” will be unique. Altogether, the resource of 1000 strains will represent 135,000 recombination events in the mouse genome and will segregate for a large quantity of polymorphisms. (Redrawn with permission from Nature © 2004, The Complex Trait Consortium, 2004.
