1. The total cumulative number of the Medaka embryos examined at the end of this project reached 488, 890. This number of embryos corresponds to a total of 1, 198, 2-79 loci.
2. The wild type male Medaka were exposed to gamma-rays, fission neutron or ethylnitrosourea. These treated males were allowed to mate with non-treated female tester Medaka which are homozygous recessive at the 3 loci, i. e. b/b ; gu/gu ; lf/lf.
3. The gamma-irradiations were done using a 111-TBq ^<137>Cs gamma source located in the Research Center for Nuclear Science and Engineering, The University of Tokyo. The dose-rate used was 0.95 Gy/min.
4. The irradiations with fission neutron were performed in the UTR-Kinki reactor (Atomic Energy Research Institute, Kinki University, in collaboration with Prof. S. Kondo and Dr. T. Ito) operated at 1 Watt with the following conditions : dDn/dt=16.9 cGy/hr, dDg/dt=24.8 cGy/hr.
5. The treatments of the Medaka with ethylnitrosourea (ENU) were done by allowing the male Medaka to s
wim in 1 mM aqueous solution of ENU (pH=5.8) at 27ﾟC for 2 hours, following by extensive rinse with tap water.
6. The spontaneous total mutation 5 rate was 4.2x10^<-5>/locus, while the spontaneous viable mutation rate was 5.5x10^<-6>/locus, a value vdry close to that of the mouse (8.1x10^<-6>/locus, Ressell & Kelly (1982)).
7. The induced rates of viable mutation per unit dose (rad) of gamma-rays for the Medaka sperm, spegmatids and spermatogonia were found to be respectively 176, 51 and 7.5 (x10^<-8>/locus).
8. Based on the above-obtained values, the doubling gamma-ray dose for the induction of viable mutation was estimated to be 3.2, 12 and 98 rad (cGy) for sperm, spermatids and spermatogonia, respectively.
9. Wg have established a method to obtain cell lines from individual Medaka embryos with malformation of various severities which is expected to result in dominant lethal mutation. Surprisingly, cell lines from moribund malformed : embryos tended to grow over a year more actively than those from the normal' controls without malformation.
10. We also established an AP-PCR method to examine induced DNA damages in male getm cells, which is expected to give more direct clue to study the mechanisms of embryonic selection during development. Less