1. Chromosomal rearrangements from exposure to radiation.

The analyses of chromosomal rearrangements resulting from the exposure of corn seeds to the bomb explosion at Bikini and the control X‑ray treatments have been completed.

Among all of the chromosome aberrations analyzed in connection with these studies, 1176 were in translocations, 57 were inversions, 24 were deletions, and a few were trisomic pieces. Except for the deletions, an effort is being made by Dr. Anderson and his associates to maintain all in suitable standard stocks.

The breaks produced by the various dosages and sources of radiation are not distributed at random, among the 10 chromosomes, the 20 chromosome arms, or the different sections of the chromosome arms.

The non‑random distribution of the Bikini‑treated material was different from that of the X‑ray treated controls.

Chromosome arms with mixed heavily and lightly staining areas have more than the expected number of breaks regardless of the radiation treatment.

Chromosome arms with a heavily staining distal area have less than the expected number of breaks following all types of radiation exposures.

Chromosome arms staining heavily adjacent to the fibre attachment had more breaks than expected when treated with X‑ray, and fewer breaks than expected when exposed to the Bikini radiations.

Chromosome arms staining lightly throughout their length had fewer breaks than expected when treated with X‑ray and more than expected when exposed to the Bikini radiations.

The distribution of breaks along the chromosomes that have mixed heavily and slightly staining areas differs distinctly from that of chromosomes with a heavily staining distal region. X‑rays produced more breaks in the middle sections of the chromosomes and less in the distal sections than were produced by the Bikini exposure.

In general, the Bikini exposure produced more breaks in the lighter staining distal sections of the chromosome arms than the higher X‑ray exposures.

Among the whole population of translocations there is a tendency for breaks the same distance from the fibre attachment to be associated more frequently than expected.

A. E. Longley