Studies on the karyotype differentiation of the Norway rat, 17

Acute dose of 700 R of γ-ray (Cs137) was irradiated to the hindquater of 6 F-344 strain male rats, and then they were mated to other non-irradiated 7 females. Among them 3 females produced 27 offspring, one male of which showed the 9;14 translocation. The short arm from one of the metacentric no. 14 was broken near the centromeric region, and the broken end was translocated to the centromeric region of one of the acrocentric no. 9. Thus, one of the no. 14 was changed into a small acrocentric, but one of the no. 9 into the submetacentric type. The translocation heterozygous males (9;14) were mated to the normal females of the same F-344 strain, and 35 offspring (female 20: male 15) were obtained. They segregated into 17 normal (female 10: male 7) and 18 translocation heterozygotes (female 10: male 8). The segregation ratio of these two types was almost 1:1. By the reciprocal mating, 6 offspring from one litter were obtained. They also segregated into the normal (2) and the heterozygotes (4). In all the 41 offspring they segregated into the normals (19) and the translocation heterozygotes (22). The segregation ratio was not significantly different from the expected one (chi2 = 0.22, p = 0.7-0.5). In the 9;14 translocation of the F-344, the litter size in the F1 and F2 type matings was slightly smaller than the normal one (6.5-7.0). In the F1 type matings (normal x hetero. or its reciprocal), the average litter size was 4.1 and in the F2 type matings(hetero. x hetero.), it was only 2.7. (Namekawa, K.)