Druckrey 1937 from a yellow, pink-eyed strain. Inbred and reduced to one pair after World War II. Crosses with Wistar stock and subsequent inbreeding led to the development of BDII. According to Druckrey (1971), strains BDIII-BDX were then developed from a cross of a single BDI x BDII mating pair, with subsequent selection for coat colour alleles. However, the strains have four different RT1 haplotypes (d, v, l and e) rather than the two that would be expected from such a cross (Stark and Zeiss 1970). The strains can _not_ be regarded as a set of recombinant inbred strains as defined by Bailey (1971), although their definition by coat colour alleles makes the set easily identifiable , and should help (but not guarantee!) to ensure authenticity. According to Druckrey (1971), all strains have a low tumour incidence, with a median life-span of 700-950 days, depending on strain.