STUDIES ON THE KARYOTYPE DIFFERENTIATION OF THE NORWAY RAT, IV. SEGREGATION AND FERTILITY OF THE NORWAY RATS WITH INVERSION PAIR NO. 1

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A female LEW (Lewis) strain rat with the chromosome mosaic consisting of two types was originally obtained; from this rat offspring with the normal and the inversion pair no. 1 (+/i) were obtained. By use of the latter rats, the segregation of the inversion pair no. 1 was examined by the following combination of matings; inversion heterozygous females and normal males (+/i_??_×+/+_??_), its reciprocal (+/+_??_×+/i_??_), and female and male inversion heterozygotes (+/i_??_× +/i_??_). Inversion heterozygotes and homozygotes were segregated in their offspring as we expected, but the number of inversion homozygotes was slightly smaller than the expected one, although there is no significant difference. Based on the litter size in the offspring, the fertility of the inversion heterozygotes and homozygotes were examined. The litter size from the inversion heterozygotes was slightly smaller than the control, but that from the inversion homozygotes was not different from the control one. This means that the fertility of the Norway rat with inversion pair no. 1 was normal.