[1] Natl Inst Radiol Sci, Inage Ku, Chiba, Chiba 2638555, Japan
[2] Chiba Univ, Grad Sch Sci & Technol, Inage Ku, Chiba, Chiba 2638522, Japan
[3] Hokkaido Univ, Grad Sch Environm Earth Sci, Div Biosci, Lab Cytogenet,Kita Ku, Sapporo, Hokkaido 0600810, Japan
[4] Hokkaido Univ, Fac Sci, Chromosome Res Unit, Kita Ku, Sapporo, Hokkaido 0600810, Japan