The relation of radiation sensitivity to pronuclear chromosome structure. II. Differences in radiation sensitivty between two stocks of Phryne cincta characterized by low or high crossing-over frequency.

After treatment of spermatozoa of Phryne cincta from a Berlin population (bs) with low crossing-over and from an Alpine population (as) with high crossing-over frequency, egg mortality was ascertained and chromosomal mutation rate determined by examination of the polytene chromosomes of the F1 progeny. - The as stock exhibits a 1.33 times greater radiation sensitivity than the bs stock, both in chromosomal mutation and in egg mortality rates. There is no evidence that factors other than structural ones account for the differences in radiation sensitivity. From inversion length measurements, it was proposed that a reduction of the spiral diameter of the paternal pronucleus chromosomes is responsible for a higher site number and thereby for a greater radiation sensitivity.