Performance of QDs vs Organic Fluorophores. Parallel hybridizations on the hemyzygous rat model using the same chromosomal preparation and the same biotin-labeled transgenic probe (A and B) show fluorescent signals comparable in size and brightness after indirect detection with either FITC (green) or QD585 (red) conjugated streptavidin. With both QD detection and organic fluorophore detection, it is also possible to estimate whether the insertion site is likely to contain one or multiple copies of the transgene (C and D). In this specific model, the relative size of two different insertions within the same karyotype suggests one of the two insertion sites (arrowhead) to contain multiple copies of the transgene. The inset shows a single copy transgene integration on a different chromosome.