Genetic background separately regulates polyQ aggregation and toxicity. (a) Introgression of Q40 locus from Bristol to DR1350 background. The Q40 transgene is integrated on chromosome X. (b) Early onset of aggregation in DR1350 relative to Bristol background. Late L2 larvae were scored, 10 animals each. (c) Comparison of number of polyQ aggregates per L4 animal in different backgrounds. Each symbol represents an individual animal, at least 16 animals per genotype. (d) Distribution of polyQ aggregates in muscle cells in young adult (1) Q40Bristol and (2) Q40DR1350 animals. Lower panels show magnification of the selected regions, arrow indicates head muscles. (e,f) PolyQ-induced decrease in muscle function. Swimming motions (bends per minute) were scored for (e) day 2 or (f) day 3 adult animals of the indicated genotypes, 30 to 45 animals for each genotype. (c,e,f) Data were analyzed by ANOVA followed by Bonferroni’s multiple comparison test, α = 0.01, ***P<0.001. (b) Data were analyzed by unpaired t-test, two-tailed, with Welch’s correction, P<0.0001.