Exposure to ionizing radiation results in persistent perturbations of mammary gland gene expression. A) Total number of transcripts perturbed 2-month after exposure to 2 Gy of whole body γ radiation. About 67% of the transcriptomes were upregulated and 33% remained downregulated. B) Transcripts significantly modulated relative to control (p<0.05 and more than 2-fold change) were plotted showing fold change distribution. Most of the upregulated genes were between 1 and 3 fold and the downregulated genes were clustered mostly between -1 and -2 fold.