The chromosomal break frequency in the 75C1-2 region is significantly increased in a 2x SuUR^+t4.9 background.

Homozygotes show a increased frequency of heterochromatization in the distal parts of the X chromosome of the T(1;2)dor^var7 rearrangement compared to animals which are wild-type for SuUR. Homozygotes show a increased frequency of heterochromatization in the distal parts of the X chromosome of the Dp(1;1)pn2 rearrangement compared to animals which are wild-type for SuUR.

Animals containing four or more doses of SuUR⁺ (increasing numbers of copies of SuUR^+t4.9 in a SuUR⁺ background) results in a change in the morphology of female salivary gland chromosomes; there are an increased number of ectopic contacts and weak points. Additional copies of SuUR⁺ increase the frequency of breaks in regions of the polytene chromosomes that already contain weak points in the control strain. In addition, females containing extra copies of SuUR⁺ have breaks in the polytene chromosomes at numerous new sites where breaks are not seen in the wild type. The total number of weak points increases from 58 in the control strain containing two doses of SuUR⁺ to 161 in females carrying from four to eight doses of SuUR⁺. Weak points are absent (with very rare exceptions) in wild-type male X chromosomes, but in males carrying four doses of SuUR⁺, weak points appear at 17 sites with frequencies between 3% and 50%. The number of sites and frequency of breaks in these males is about half that found in corresponding transgenic females (carrying four doses of SuUR⁺).