Table 1. Metaphase cells with one or more abnormal chromosomes.

Animal status and age	Total number of abnormal chromosomes (abnormal cells/total cells in metaphase)	Types of aberrations
Eight-week-old control	15 (2/13)	Small marker chromosomes
Eight-week-old irradiation	27 (4/15)	Chromatid break; trisomy 8; trisomy 18; + marker chromosomes
26-month-old control*	0 (0/5)
26-month-old radiation*	30 (3/10)	+ small markers; chromatin unraveling

The asterisk indicates that a set of 26-month-old animals has been added from a separate but same procedure X-ray study to increase the total number of cells examined for post X-ray chromosomal abnormalities. The first number indicates the total number of abnormal chromosomes found. The numbers inside the parentheses indicate the fraction of abnormal cells (some with several abnormal chromosomes) over the total cells that were present in a complete metaphase spread condition.