Genetic analysis of cataract in Ihara epileptic rat

We analyzed the mode of inheritance of cataract in the Ihara epileptic rat (IER) by crossing experiments, and mapped cataract-related genes by linkage analysis. Cataract did not develop in the F1 animals, but it developed in both male and female animals of backcross and F2. The occurrence rate of cataract was 48.5% in the backcross progeny and 19.4% in the F2 progeny. Thus, the character was considered to be inherited by the autosomal recessive mode. We found two groups that differed according to the time of onset among the backcross and F2 progeny: an early-onset group (EOG), in which cataracts developed by about 4 months after birth, and a late-onset group (LOG), in which cataracts developed 8 months or more after birth. Linkage analysis indicated the presence of one cataract gene each on Chromosome (Chr) 8 and Chr 15, and the cataract was demonstrated to be governed by more than one gene. The gene on Chr 8 was named Catil, and that on Chr 15. Cati2. Catil was involved in the occurrence of cataract, and the conditions required for cataract to develop were Cati1i/Cati1i or Cati1i/Cati1w. However, in the cataract rats with Cati1i/ Cati1w, the allele of Cati2 was always Cati2i/Cati2i. Cati2 was involved in the timing of onset of the cataract, and the precondition for early onset was Cati2i/Cati2i.