Comparisons between different age groups showed that mutant frequencies in pachytene
spermatocytes in 15-month-old or 26-month-old mice 15 days post IR were significantly
increased compared to the same IR treatment sub-group in 4-month-old mice (Table 1).
Round spermatids in 26-month-old 49 days after IR displayed significantly higher mutant
frequency than that in the 4-month-old same IR treatment sub-group. No significant
differences in mutant frequency between pachytene spermatocytes and round spermatids
were found at the same IR-treatment sub-groups regardless of age (Table 1).