Effect of homologous recombination on rate of mutation in myeloma cells. (A) ARP myeloma cells were either transfected every 2 weeks with control siRNAs for 90 days (lane 1), exposed to nickel chloride (0.3 mg/mL) for 5 days (lane 2), or transfected every 2 weeks with siRNAs targeting HsRAD51 for 90 days (lane 3). Genomic DNA was isolated and evaluated with huSNP arrays (Affymetrix) as described. A representative figure showing all chromosomes (i) and an enlarged version of chromosome 20 (ii) is shown as an example. Dark lines indicate new LOH loci. (B,C) Summary of change in LOH over all chromosomes; error bars indicate standard error of the mean of triplicate assays. (B) Induction of LOH in ARP cells after exposure to nickel chloride as a percentage of control cell values. (C) Reduction in LOH in ARP cells after suppression of HR by HsRAD51 directed siRNA as a percentage of control cell values.