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 F 1 animals, but it developed in both male and female animals of backcross and F 2 . The occurrence rate of cataract was 48.5% in the backcross progeny and 19.4% in the F 2 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 F 2 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 Cati1 , and that on Chr 15, Cati2 . Cati1 was involved in the occurrence of cataract, and the conditions required for cataract to develop were Cati1 i / Cati1 i or Cati1 i / Cati1 w . However, in the cataract rats with Cati1 i / Cati1 w , the allele of Cati2 was always Cati2 i / Cati2 i . Cati2 was involved in the timing of onset of the cataract, and the precondition for early onset was Cati2 i / Cati2 i .