Geneticists state that a true chimera is extremely rare. Virginia Papaioannou, a Professor of Genetics and Development at Columbia University, explains that a chimera results from the combination of cells from two distinct embryos. When these cells fuse together early enough, they form a single organism with its genetic material coming from two separate individuals. In contrast, mosaic cats have different genetic components in their cells but are still considered a single individual. Although cats like Quimera and Venus are stunning examples of calico cats, Papaioannou considers them to be chimeras.