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. T hus. the character was considered to be inherited by the autosomal recessiv e mode. We found two groups that differed according to the time of onset am ong the backcross and F-2 progeny: an early-onset group (EOG), in which cat aracts developed by about 4 months after birth, and a late-onset group (LOG ). in which cataracts developed 8 months or more after birth, Linkage analy sis 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 o ne gene. The gene on Chr 8 was named Catil, and that on Chr 15, Cati2. Cati 1 was involved in the occurrence of cataract, and the conditions required f or cataract to develop were Cati1(i)/ Cati1(i) or Cati1(i)/Cati1(w). Howeve r, in the cataract rats with Cati1(i)/ Cati1(w), the allele of Cati2 was al ways Cati2(i)/Cati2(i). Cati2 was involved in the timing of onset of the ca taract, and the precondition for early onset was Cati2(i)/Cati2(i).