a) Images of interphase cells with γH2AX-negative Y chromosome or γH2AX-positive Y chromosomes within an MN body after 4d DOX/IAA treatment. Scale bar, 5 μm. b) Frequency of γH2AX-positive Y chromosomes. Data were pooled from (left to right): 549, 353, 429, and 293 cells. c) Images of interphase cells with 53BP1-negative or 53BP1-positive Y chromosomes after 4-day DOX/IAA treatment. Scale bar, 5 μm. d) Frequency of 53BP1-positive Y chromosomes. Data were pooled from (left to right): 567, 543, 634, and 592 cells. e) Images of metaphase spreads with an intact or fragmented Y chromosome after 4d DOX/IAA treatment. Scale bar, 10 μm. f) Frequency of Y chromosome fragmentation. Data pooled from (left to right): 329, 291, 347, and 373 metaphase spreads. Bar graphs in (b), (d), and (f) represent the mean ± SEM of n = 3 independent experiments. Statistical analyses were calculated by unpaired Student’s t-test.