These transgenic mice carry the Brainbow 1.0 cassette, incorporating dTomato, mCerulean, and EYFP, driven by the broadly-expressed CAG (CMV-chicken beta actin) promoter. These fluorescent markers are useful in tracing cell lineage. This strain, line 3, carries 3 copies of the transgene. dTomato red fluorescent protein is expressed strongly in a variety of tissues and developmental stages. Exposure of the transgene to Cre recombinase stochastically alters individual copies of the transgenes such that either EYFP (enhanced yellow fluorescent protein) or mCerulean (blue fluorescent protein) become expressed, resulting in labeling of cells with distinct colors. As many as 10 distinct color combinations have been observed in this line. Expression is reportedly seen in E3.5, 4.5, and E13.5 embryos. These alterations are genetic and heritable by the progeny of the cells. Attempts to breed this line to homozygosity were not successful in the donating lab. Hemizygotes are viable and fertile.