The Cat^b (catalase 1 null) mutation was identified in a screen for low catalase activity by Feinstein et al. (1964, 1966) at Argonne National Laboratory of offpring of (C3H x 101) male mice irradiated at Oak Ridge National Laboratory (600 R in fractionated exposures), then crossed to females of the Oak Ridge "multiple recessive testing stock" derived from a cross of NB mice (aabbc^ch p/c^ch p d se/d se) and mice of a non-inbred stock homozygous for three of the same recessive mutations, as well as for s, from which mice homozygous for all seven mutations were bred and maintained afterward by random breeding (Russell 1951). Putative heterozygotes for catalase deficiency were crossed to normal mice (not clearly identified, but presumably unirradiated progeny of (101 x C3H)F1 X ORNL testing stock), and offspring exhibiting low catalase activity were backcrossed to the heterozygous parent (Feinstein et al. 1966).Cat^b was subsequently transferred by backcrossing for eight generations onto C3H/HeAnl, a line carrying mouse mammary tumor virus (MMTV) and another line (C3Hf) free of the virus (Feinstein et al. 1978). The Jackson Laboratory received C3HfB/Ga-Cat^b, now C3Ga.Cg-Cat^b/J (stock #001906), from Allen H. Gates, then at the University of Rochester, in 1982.

Although all C3H strains carry the rd1 (retinal degeneration 1) mutation at Pde6b, the gene encoding the beta subunit of phosphodiesterase 1, retinas of these mice exhibited a peculiar, granular appearance distinct from the usual Pde6b^rd1 phenotype. F2 progeny of a cross of C3HfB/Ga-Cat^b and C57BL/6J mice exhibited three retinal phenotypes: 1) normal; 2) patches of pigment deposition and large, diffuse pigmented regions typical Pde6b^rd1 homozygotes; and 3) small, discrete, light-colored dots throughout the fundus. Mice exhibiting the last phenotype were intercrossed among themselves to produce a stock homozygous for Mfrp^rd6 and for the wild-type allele at Pde6b. During this process, a separate mutation with a distinct map position was identified and characterized as Crb1^rd8. STOCK Crb1^rd8 Mfrp^rd6/J (stock #004299) is homozygous for both Mfrp^rd6 and Crb1^rd8 on this mixed genetic background that derived in part from C57BL/6J, C3H, 101, and a linkage testing stock derived from non-inbred stocks. In order to isolate Mfrp^rd6 and Crb1^rd8 this strain was backcrossed to C57BL/6J, and selection for either Mfrp^rd6 or Crb1^rd8 yielded B6.C3Ga-Mfrp^rd6/J (stock #003684) and STOCK Crb1^rd8/J (stock #003392) respectively.

• 000664 C57BL/6J

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