tws¹⁹⁶/Df(3R)by62, tws¹⁹⁶/tws^j11C8 and tws¹⁹⁶/tws⁴³⁰ third instar larval brains exhibit high frequencies of cells with chromosome aberrations (CABs, metaphases displaying from one to five CABs and metaphases with more than five CABs often showing an extensive chromosome fragmentation) compared to controls. Specifically they exhibit: chromatid and isochromatid deletions and exchanges of chromatid and chromosome type. Most aberrations and exchanges are complete, namely they contain all the elements that give rise to the CAB.

Under normal conditions tws¹⁹⁶/Df(3R)by62 and tws¹⁹⁶/tws^j11C8 third instar larval brains exhibit an increase in the average frequency of nuclei with γ-H2Av foci (indicative of double strand breaks) compared to controls. After 5 Gy X-ray treatment, in mutant and control brains, the frequency of nuclei with γ-H2Av-positive foci peaks at 5 minutes post irradiation (PIR) and remains high at 30 minutes PIR to progressively decrease at 1 and 2 hr PIR. At 4 and 6 hr PIR, the frequencies of nuclei with foci remain high in mutant brains while they drop in controls.