Barcode analysis of primary bone marrow cell cultures. (A) Tracking the clonal complexity of a primary BM culture over time. Subclone sequencing shows 54 unique barcodes of 78 sequencing trials after 1 week of culture, and only 11 of 50 after 5 weeks of culture. White bars represent barcodes that were identified at 1 time point only, and colored bars represent barcodes that were found at both time points. (B) Distribution plots showing the observed and expected barcode frequencies for the 2 time points. Binomial distribution modeling predicts that the barcode complexity in the culture markedly decreased over time. Note that the model for week 5 excludes the outlier that was found 36 times and is therefore calculated for 14 trials only. (C) Inverse PCR identifies the integration site and the corresponding barcode for 2 monoclonal cultures initiated with single transduced BM progenitor cells. LTR, long terminal repeat.