Figure 1.

DREs of low LET radiation upon HPRT mutations (×10⁸). + and 1, mouse L5178Y cells, per cGy (refs. 5 and 7–10, and reviewed in refs. 1, 4, and 5). Points E1 and E2 are Evans and coworkers' data (13). □ and 2, Chinese hamster V-79, subline 85 cells, per 4 cGy (6). × and ▵, Human TK6 lymphoblastoid cells, per cGy. ×, refs. 3 and 12. Points K1, K2, and K3 are König's and Kiefer's data (18). Points G1–G5 are from Grosovsky and Little (14). Points ▵ G2–G5 resulted from irradiation at multiple acute doses (see text). Curves 1 and 2 are of the parabolic form, y = ax² + bx + c.