04/24/2025
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Chimerism occurs when an individual animal has cells that contain two distinct sets of DNA (or two distinct genomes). This condition can result from the fusion of two embryos (twins) early in pregnancy. Chimerism is not always obvious just by looking at an individual. However, in some cases, it can cause a rare physical appearance.
Here we share a confirmed case from 2012 of chimerism in dogs: "Tiger", a purebred Labrador Retriever born with an unusual black and yellow patterned coat. Scientists discovered that she was a chimera by testing the hairs in different colored patches: the black hairs had a different genotype than that of the yellow hairs! Most likely, Tiger is the result of twin embryos fusing together, where one embryo would have given rise to a yellow lab and the other to a black lab. Combined, they created this fascinating pattern.
Image description: The top left image shows Tiger as a newborn with her black and yellow patterned coat. The top right image also shows Tiger but at six months of age. The bottom image is of the newborn litter with Tiger and her solid-colored siblings. Source: Dreger and Schmutz, 2012 https://doi.org/10.1016/j.mcp.2012.03.004
