Partial additivity of the mitotic delays induced by separate γ-irradiation of sea-urchin eggs and sperm

Eggs and sperm of the sea-urchin, (Arbacia punctulate), were exposed to the same dose of gamma radiation in the dose range 0 to 20 KR. Normal or irradiated eggs were fertilized with normal or irradiated sperm. Mitosis was delayed to the same extent when either eggs or sperm exposed to the same dose were combined with a normal gamete. When irradiated eggs were fertilized with sperm previously exposed to the same dose, the mean mitotic delay was larger than when only one gamete was irradiated, yet there was very little overlap between the division times of zygotes containing one irradiated gamete and those with both gametes irradiated. The mitotic delay resulting from separate irradiation of sperm and eggs with a particular dose was the same as that resulting from irradiation of sperm alone with twice that dose. The division times of eggs exposed to a given dose and fertilized with sperm exposed to twice that dose did not overlap the division times of irradiated eggs fertilized with normal sperm, and there was only partial overlap of division times between populations derived from control and irradiated eggs both fertilized with sperm exposed to twice the dose of the eggs. It ismore » argued that this would not have been the case if there had been no additivity of the effects of damage to the separate gametes. (UK)« less