The next set of slides provide a very short interlude on QTL mapping. You will need to do some independent reading on this topic if this is your first exposure to QTL mapping. The recombinant inbred strains that we are using in WebQTL and in this particular demo were generated about 25 years ago by Dr. Ben Taylor at The Jackson Laboratory. He crossed a female C57BL/6J mouse with a male DBA/2J mice. At the bottom of this slide we have schematized one chromosome pair from three out of 80 BXD RI strains.  The dashed vertical lines that lead to the final BXD RI lines involve 20 full sib matings (about 6 years of breeding). Some lines die  out during inbreeding. For example, there is no extant BXD3 or BXD4 strain.